CZ20004079A3 - Novel use - Google Patents

Abstract

This solution relates to pharmaceutical compositions comprising a nicotinic agonist positive modulator receptors, wherein said positive modulator has the ability increase the efficacy of said nicotinic agonist receptors.

Description

New use

Technical field

The present invention relates to novel compositions comprising a nicotinic receptor agonist positive modulator, wherein said positive modulator has the ability to enhance the efficacy of said nicotinic receptor agonist.

BACKGROUND OF THE INVENTION

Cholinergic receptors normally bind the endogenous neurotransmitter acetylcholine (ACh), triggering the opening of ion channels. Acetylcholine receptors in the mammalian ventral nervous system can be divided according to muscarinic or nicotinic agonist activity into a muscarinic (nAChR) and nicotinic (nAChR) subgroup. Nicotinic acetylcholine receptors are ligand-controlled ion channels containing five subunits (for review see Colquhon et al., Advances in Pharmacology 39, 191-220 (1997); Williams et al., Drug News & Perspectives 7, 205-223 (1994); Doherty et al., Annual Reports in Medicinal Chemistry 30, 41-50 (1995)). Members of the nAChR gene family are divided into two groups depending on their sequences; β subunits are considered to be members of one group, while the other is referred to as β subunits and (for review, see Karlin & Akabas, Neuron 15: 1231-1244 (1995); Sargent, Annu. Rev. Neurosci. 16: 403-443 (1993)). )). Three of the α, α7, α8 and cc9 subunits form a functional receptor when expressed alone and therefore appear to form homooligomeric receptors.

The nAChR allosteric transfer status model includes:

at least a rest phase, an activated phase, and a desensitized closed channel condition (see Williams et al., Karlin & Akabas supra). Different nAChR ligands can therefore differently stabilize the conformation state to which they preferentially bind. For example, the acetylcholine (ACh) and (-) - nicotine agonist stabilize the active and desensitized state.

Changes in the activity of the nicotinic receptors have been demonstrated in a number of diseases. Some of these, such as myasthenia gravis and ADNFLE (autosomal dominant frontal lobe epilepsy night) (Kuryatov et al., J. Neurosci. 17 (23), 9035-9047 (1997)), are associated with a reduction in nicotine transmission activity, either due to decreased number of receptors or increased desensitization, with the process by which the receptors become insensitive to agonists. Reduction of nicotinic receptors is also thought to mediate cognitive deficits in diseases such as Alzheimer's disease and schizophrenia (see Williams et al., Supra). Also, the effects of nicotine from tobacco are mediated by nicotine receptors. Increased nicotinic receptor activity may reduce tobacco demand.

Use of compounds that bind to nicotinic acetylcholine receptors in the treatment of a variety of diseases including reduced cholinergic function such as Alzheimer's disease, cognitive or attention deficit, attention deficit, hyperactive disorders, anxiety, depression, smoking cessation, neuroprotection, schizophrenia, analgesia, syndrome Gilles de Tourette and Parkinson. the disease discussed by McDonnald et al. in Nicotinic Acetylcholine Receptors: Molecular Biology, Chemistry and Pharmacology ', Chapter 5 of the Annual Reports in Medicinal Chemistry, Vol.

30, pp. 41-50, Academic Press Inc., San Diego

φ φ ·

California; and in Williams et al., Neuronal Nicotinic Receptors, Drug News & Perspectives, 205-223 (1994).

Although treatment with nicotinic receptor agonists that act at the same site as acetylcholine (ACh) is problematic, acetylcholine (ACh) not only activates but also blocks receptor activity by a process involving desensitization (for review, see Ochoa et al., Cellular and Molecular Neurobiology 9, 141-178 (1989)) and non-competitive blockade (open channel block) (Forman and Miller, Biophysical Journal 54 (1), 149-158 (1988)). Furthermore, prolonged activation appears to induce long-lasting inactivation. Therefore, acetylcholine agonists (ACh) can be expected to reduce as well as enhance activity. At nicotinic receptors in general and particularly at the nicotinic receptors, desensitization limits the duration of flow during agonist administration.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1

An agonist-induced electric current traces model representing determining the increase in agonist efficiency by determining the amplitude of the electric current. Lines indicate the duration of application of the compounds.

Figure 2

An agonist-induced electric current traces model representing the determination of agonist potency by determining the area under the curve. The arrows indicate the overlap of the current ACh and the current ACh + modulator. Lines indicate the duration of application of the compounds.

Figure 3

Effect of 5-hydroxyindole on acetylcolin (ACh) activity at the α7-nicotinic receptor. The 100% electric current value is extrapolated from the ACh curve.

(·) ACh ()) ACh + 0.5 mM 5-hydroxyindole

Figure 4

Effect of 5-hydroxyindole on acetylcholine (ACh) activity at α7-nicotinic receptor (human, rat and chicken) expressed on Xenopus oocytes.

Figure 5

Effect of 5-hydroxyindole on acetylcholine (ACh) (Staples) activity and (-) - spiro [lazabicyclo [2.2.2] octane-3,5 * -oxazolidine] -2 * -none (full) channels of the α7-nicotinic receptor expressed on Xenopus oocytes.

Figure 6

Effect of nAChR α7 on agonist activity measured by Ca ²⁺ flux through nAChR α 7 expressed on HEK-293 cells. The agonist is represented by (-) - spiro [1-azabicyclo [2.2.2] octane-3,5 * -oxazolidine] -2 * -non.

• ···

SUMMARY OF THE INVENTION

It has surprisingly been found that some compounds, such as 5-hydroxyindole (5-OH 1), may potentiate the efficacy of agonists at nicotinic receptors. This efficiency gain may be greater than twice. Compounds with this type of activity (hereinafter referred to as positive modulators) are believed to be particularly useful in the treatment of conditions associated with the reduction of nicotine transmission. At therapeutic doses, such compounds could restore normal interneuronal communication without affecting the time profile of activation. In addition, they would not cause long-term inactivation as may be caused by prolonged administration of agonists.

The existence of this activity-enhancing activity has not previously been anticipated in the art. Albuquerque et al. have reported another allosteric site at nicotinic receptors, which they call a non-competitive agonist site. Compounds acting at this site are also called allosterically activating ligands (APL). Compounds that appear to act at this site include several cholinesterase inhibitors, codeine and serotonin (5-HT). It was reported that activity through this non-competitive agonist site did not affect the level of maximal response to acetylcholine (ACh); shifts the dose-response curve to the left (Maelicke and Albuquerque, DDT 1, 53-59, 1996).

Another difference between APL and the present invention is the effect that modulators have on total electrical current (measured as area under the curve) in the presence of a saturating concentration of agonist. APLs have nAChR α7 expressed on • ·· · • · ·

oocytes had little or no effect on the area under the curve, an 8 to 10% increase in area under the curve was observed after a 1 second agonist administration. In contrast, 5-hydroxyindole (5OHi) causes a large increase in area under the curve (increase of ~ 400%) under the same conditions (see Figure 4, upper footprint).

The specificity of action on the nicotinic receptor family is yet another distinguishing feature between APL and the invention. APL exerts its positive modulating effect at all nicotinic receptors tested, including muscle receptors of the αβββ type.

At some non-nicotinic receptors, compounds have been found that may reduce desensitization of the receptors. At excitatory amino acid receptors of AMPA type, cyclothiazide, some lectins such as wheat germ agglutinin, piracetam-like nootropics, and AMPAkins have been shown to reduce desensitization (Partin et al., Neuron 11, 1069-1082 (1993)). Glycine has been reported to reduce desensitization of NMDA-type excitatory amino acid receptors (Mayer et al., Nature 338, 425-427 (1989)). Although compounds have been found that reduce desensitization of one receptor family, they generally do not have the same effect on other receptor families. For example, cyclothiazide has little or no effect on the NMDA or KA subtypes of glutamate receptors (Partin et al., Neuron 11, 1069-1082 (1993)); in addition, cyclothiazide was found to block 5-HT 3 receptors (Gurley, unpublished results). Glyci has no effect on 5-HT3 receptors (Gurley and Lanthorn, (in press) Neurosci. Lett.).

The site was found using compound (5-OH 1), known to reduce desensitization to 5-HT 3 receptors

(Kooyman A.R. et al., British Journal of Pharmacology 108, 287-289 (1993)). In contrast, only one other compound that produces or increases activity at the 5-HT 3 receptor, 5-HT alone, has been reported to increase activity at the nicotinic receptors (Schrattenholz et al., Molecular Pharmacology 49, 1-6 (1996)), although this activity has never been reported on Xenopus oocytes. Most agonists have no activity at the 5-HT 3 receptor or are antagonists at the nicotinic receptors (unpublished results). Moreover, the present inventors have not been able to reproduce the finding that 5-HT increases the activity at the nicotinic receptor. Therefore, the enhancing effect of the 5-OH 1 antagonist at nicotinic receptors could not be predicted.

Accordingly, in a first aspect, the present invention provides a pharmaceutical composition comprising a nicotinic receptor agonist positive modulator together with a pharmaceutically acceptable carrier, wherein said positive modulator has the ability to enhance the efficacy of said receptor agonist. For the purposes of this invention, a positive modulator or positive modulator of a nicotinic receptor agonist is to be understood as meaning a compound which has the ability to increase the maximum efficacy of a nicotinic receptor agonist.

It is to be understood that the invention encompasses compositions comprising either a positive modulator as the only active agent that modulates the activity of endogenous nicotinic receptor agonists or a positive modulator in combination with a nicotinic receptor agonist. Accordingly, said pharmaceutical compositions comprising a positive nicotinic receptor agonist modulator may additionally comprise nicotinic receptor agonists.

In a preferred embodiment of the invention said positive modulator is 5-hydroxyindole.

In another preferred embodiment of the invention said nicotinic receptor agonist is an α7-nicotinic receptor agonist. An example of an α7-nicotinic receptor agonist is (-) - spiro [1-azabicyclo [2.2.2] octane-3,5 * -oxazolidine] -2 * -non. Several α7-nicotinic receptor agonists are known in the art, for example from WO 96/06098, WO 97/30998 and WO 99/03859.

In another aspect, the invention provides a method of treating conditions associated with reduced nicotine transmission, by administering a therapeutically effective amount of a positive nicotinic receptor agonist modulator to a patient in need thereof, wherein said positive modulator has the ability to increase the efficacy of said nicotinic receptor agonist.

It is understood that the method of treatment of the invention comprises either a positive modulator as the only active agent that modulates the activity of endogenous nicotinic receptor agonists or a positive modulator administered with a nicotinic receptor agonist.

In a preferred embodiment of the invention said method of treatment comprises a positive modulator which is 5-hydroxyindole.

In another preferred embodiment of the invention said method of treatment comprises nicotinic receptor agonists which are α7-nicotinic receptor agonists. An example of such an α7-nicotinic receptor agonist is (-) - spiro [19 ··]

-azabicyclo [2.2.2] octane-3,5 * -oxazolidin-2 * -one. Several α7-nicotinic receptor agonists are known in the art, for example from WO 96/06098, WO 97/30998 and WO 99/03859.

Another aspect of the invention is the use of a pharmaceutical composition of the invention for the manufacture of a medicament for the treatment or prophylaxis of conditions associated with reduced nicotine transmission or conditions associated with reduced density of nicotinic receptors which may fall under the following diseases and conditions comprising administering a therapeutically effective amount of a compound of of the invention to a patient.

It is understood that the use includes compositions comprising either a positive modulator as the only active agent that modulates the activity of endogenous nicotinic receptor agonists or a positive modulator in combination with a nicotinic receptor agonist. Therefore, said pharmaceutical compositions comprising a positive nicotinic receptor agonist modulator may additionally comprise nicotinic receptor agonists.

In a preferred embodiment of the invention the use comprises a positive modulator which is 5-hydroxyindole.

In another preferred embodiment of the invention, the use of said nicotinic receptor agonist is represented by an α7-nicotinic receptor agonist. An example of such an α7-nicotinic receptor agonist is (-) - spiro [1-azabicyclo [2.2.2] octane-3,5'-oxazolidin] -2'-one. Several α7-nicotinic receptor agonists are known in the art, for example from WO 96/06098, WO 97/30998 and WO 99/03859.

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Examples of diseases or conditions include schizophrenia, mania and manic depression, anxiety, Alzheimer's disease, learning deficit, cognitive deficit, attention deficit, memory loss, attention deficit hyperactivity disorder, Parkinson's disease, Huntington's disease, Gilles de Tourette syndrome, jet lag and dependence nicotine (including the consequences of exposure to nicotine containing products).

It is understood that said positive modulator can be administered either to act on endogenous nicotinic receptor agonists or in combination with an exogenous nicotinic receptor agonist.

Another aspect of the invention relates to a pharmaceutical composition for the treatment or prevention of conditions or diseases, as exemplified above, which arise from dysfunction of nicotinic acetylcholine receptor neutransmission in mammals, preferably humans, wherein the composition comprises either a positive modulator as the only activity modulating activity. endogenous nicotinic receptor agonists, or a positive modulator in combination with a nicotinic receptor agonist. Thus, the use of a pharmaceutical composition comprising a positive nicotinic receptor agonist modulator may further comprise nicotinic receptor agonists effective in treating or preventing such diseases or conditions and an inert pharmaceutically acceptable carrier.

For the above uses, the dosage administered will, of course, vary with the composition employed, the mode of administration and the treatment desired. However, satisfactory results will generally be obtained when the active components are administered in a daily dose of from about 0.1 mg to about 20 mg per kilogram of body weight of the mammal, preferably administered in divided doses. 4 times a day or in a sustained release form. In humans, the total daily dose will range from 5 mg to 1400 mg, more preferably from 10 mg to 100 mg, and unit dosage forms suitable for oral administration will contain from 2 mg to 1400 mg of active ingredients mixed with a liquid or solid pharmaceutical carrier or diluent.

The above compositions may be used alone or in the form of a suitable pharmaceutical formulation for enteral, parenteral, oral, rectal or nasal administration.

Examples of suitable diluents and carriers are:

- for tablets and dragees: lactose, starch, talc, stearic acid; for capsules: tartaric acid or lactose;

- for injectable solutions: water, alcohols, glycerin, vegetable oils; for suppositories: natural or hardened oils or waxes.

Also provided is a process for the preparation of such pharmaceutical compositions which comprises simultaneous or sequential mixing of the components.

In another aspect, the invention provides a method for identifying a positive modulator of nicotinic receptor agonists. Compounds are considered to be positive modulators when, in the presence of a saturating concentration of nAChR α7 acetylcholine agonist, an electric current that exceeds 200% of the control electric current (100% potentiation) is induced when measured from baseline to peak (see experimental methods). Checklist • ···· ·· · ··

9 9 9 99

999,999 9 9

9 9 9 9 9

9 9 9 9 9

999 999 99 999 99 electrical current is defined as the agonist-induced electrical current in the absence of a modulator. The acetylcholine saturation concentration (ACh) is defined as ten times the EC50 for the specific type of nAChR α7 used. The EC50 is defined as the concentration that elicits half the maximal response. EC 50 values for nAChR α7 subtypes typically range from 100 to 300 µΜ (Bertrand et al., Neuroscience Letters 146, 87-90 (1992); Peng et al., Molecular Pharmacology 45, 546-554 (1994)). Furthermore, compounds are considered to be positive modulators if, in the presence of a saturating concentration of the agonist, the total electrical current through the receptor (current) exceeds 200% of the control electrical current. One measure of total electrical current is the area under the curve (trace of electrical current) during agonist administration.

Accordingly, the method of the invention for identifying a positive nicotinic receptor agonist modulator may comprise the step of a) expressing nicotinic receptor on the surface of cells; b) contacting said nicotinic receptor with a compound known as a nicotinic receptor agonist and testing the compound for positive modulatory activity; c) determining whether the test compound exhibits a positive modulation of the effect of said nicotinic receptor agonist resulting in an amplitude of the current (measured from baseline to peak) or total current (measured as the area under the curve of the electric current) greater than 200% of control ). The cell could be a Xenopus oocyte, a HEK-293 cell or a cultured neuron. The nicotinic receptor can be either human, rat, chicken, mouse or bovine nicotinic receptor.

In another aspect, the invention relates to a method for identifying a positive modulator of a nicotinic receptor agonist, wherein the nicotinic receptor is an α7-nicotinic receptor.

In yet another aspect, the invention provides a method for identifying a compound that is a nicotinic receptor agonist, said method comprising the step of a) expressing nicotinic receptors on the surface of cells; b) contacting said nicotinic receptor with a compound tested for nicotinic receptor agonist activity in the presence of a positive nicotinic receptor agonist modulator;

and c) determining whether the test compound exhibits nicotinic receptor agonist activity. The cell could be a Xenopus oocyte, a HEK-293 cell or a cultured neuron. The nicotinic receptor may be either human, rat, sheep, mouse or bovine nicotinic receptor. One of skill in the art will appreciate that nicotinic receptor agonist activity can be determined in a manner known in the art, such as those described in the experimental section below.

In another aspect, the invention relates to a method for identifying a compound that is a nicotinic receptor agonist, wherein the nicotinic receptor is the α7-nicotinic receptor.

Experimental methods

(a) Recording of electric current on Xenopus oocyte

The Xenop oocyte provides a significant means of evaluating the functions of proteins considered to be ligand-opened ion channel subunits. Injections of RNA transcribed from cDNA clones encoding appropriate receptor receptors

a subunit or injection of a cDNA in which the coding sequence is located downstream of the promoter leads to the detection of ligand-opened ion channels on the oocyte surface (see, for example, Boulter et al., Proc. Natl. Sci. U.S.A. 84, 7763-7767 (1987)).

At the same time, one convenient technique for evaluating nicotinic potency enhancement is the two-electrode voltage recording of Xenopus oocytes expressing α7-nicotinic receptors from cDNA.

Xenopus laevis frogs (Xenopus I, Kalamazoo, Michigan) are anesthetized using 0.15% tricain. The oocyte is removed into OR2 solution (82 mM sodium chloride, 2.5 mM potassium chloride, 5 mM HEPES, 1.5 mM sodium dihydrogen phosphate, 1 mM magnesium chloride, 0.1 mM EDTA; pH 7.4). Oocytes are defoliated by incubation in 25 ml OR2 containing 0.2% collagenase 1A (Sigma) twice for 60 min on a plate vibrating at 1 Hz and stored in Leibovitz L-15 medium (50 gg / ml gentomycin, 10 units / ml penicillin and 10 gg / ml streptomycin). The next day approximately 50 ng of cRNA is injected into each oocyte. cRNA was synthesized from cDNA using a Message instrument (purchased from Abion).

The external recording solution consists of 90 mM sodium chloride, 1 mM potassium chloride, 1 mM magnesium chloride, 1 mM barium chloride, 5 mM HEPES, pH 7.4). A two-electrode voltage recording at the terminals was obtained using an Oocyte Clamp amplifier (OC 725C; Warner Instrument, Hamden, Connecticut). The cells are pierced with electrodes with a tip resistance of 1 to 2 ΜΩ after filling with 3M potassium chloride. Records are started until the membrane potential stabilizes at -20 mV negative (residual membrane potentials are less negative when barium cations are replaced by calcium cations in the wash solution. The membrane potential is measured to -80 mV. Acetylcholine (ACh) is purchased from Sigma Oocytes are continuously washed (5 ml / min) with recording solution with or without acetyleholin (ACh).

The amplitude of the electric current is measured from baseline to peak. EC 50 values, peak effect, and slope of the curve are estimated by comparing the data to the logistic equation using GraphPad Prism (GraphPad Software, Inc., San Diego, California).

The increase in agonist effect induced by a positive modulator can be calculated in two ways:

1) As a percentage of the amplitude of the electric current amplitude, which is defined as 100 (I _{m-1 c} ) / I _c , where I _m is the amplitude of the electric current in the presence of a modulator and I _c is the electric current in the absence of a modulator (Figure 1).

2) As a percentage of potentiation of the area under the agonist trace. The area under the curve is commonly represented by the total ion flow through the channel (Figure 2). In the example shown in Figure 2, although the amplitude of the electric current is not increased, the area under the curve is potentiated by about 100% over the control over the agonist administration.

b) Display of calcium cation flow

Another way to evaluate modulator activity is to display calcium cation flow through the nAChR <x7 receptors temporarily expressed on the cell line.

Cells expressing α 7 receptors (e.g., HEK-293 cells or cell culture neurons) are grown to confluency on 96-well plates and treated with fluo-3, a fluorescent calcium identifier. To test α7 modulating activity, a 96-well plate is placed in a fluorescence imaging reader (FLIPR) and test compounds are added to all wells together with an α7 agonist. Activation of the receptors is measured by the penetration of calcium into the cells, which is quantified by increasing the fluorescence intensity of each well, recorded simultaneously by FLIPR. The modulating effect is determined by increasing fluorescence over the agonist alone. Similarly, to test nAChR α7 agonist activity, test compounds are co-administered with all α1 modulators in all wells. Activation of the receptors is measured by the penetration of calcium into the cells, which is quantified by increasing the fluorescence intensity of each well, recorded simultaneously by FLIPR. The agonist effect is determined by increasing fluorescence over the modulator itself.

Cell culture neurons are prepared as follows: 11-day-old fetuses of Sprague-Dawley rats (E-18) are aseptically removed from pregnant females, sacrificed, frontal cortex removed, diaper peeled, and cleaned cortex placed in cold HBSS . If a hippocampus is desired, the hippocampus is removed from the cortex and placed in cold HBSS. Tissues are mechanically pulverized, washed once in HBSS (200 g for 30 min at 4 ° C), resuspended in a modification of Sat's medium enriched with glutamine, antibiotics, potassium chloride, insulin, transferrin, selenium and 5% heat inactivated fetal bovine serum (FBS) endotoxin-free) and placed in each of the 24 wells of the plate (coated with poly-L-lysine).

The wells may comprise a glass lid also coated with poly-L-lysine. The plates are incubated at 37 ° C in a carbon dioxide incubator. After 24 hours, the medium is removed, fresh medium is added, and the cells are allowed to grow for at least an additional 11 days, fed if necessary.

DETAILED DESCRIPTION OF THE INVENTION

Example 1

Changes in nicotinic agonist potency are evaluated by measuring the combined effects of the nicotinic agonist with the test compounds. The procedure generally consists of pretreatment with the test compound and concomitant administration of the agonist and test compound. 5-Hydroxyindole is tested at a concentration of 500 μΜ against a series of concentrations of acetylcholine (ACh). Acetylcholine (ACh) is first tested alone so that the EC50 and maximal response can be determined. Then the same concentration of acetylcholine (ACh) is applied together with 5-hydroxy-indole. The results (Figure 3) show that the maximum response to acetylcholine (ACh) is increased (maximum amplitude increased 2-fold).

The effect of 0.5 mM 5-hydroxyindole (5-OH 1) on the area under the curve for agonist saturation concentration (3 mM acetylcholine (ACh)) was determined. 5-Hydroxyindole (5-OHi) causes a large increase in area under the curve (~ 400% increase) (Figure

4).

Applied alone does not induce 5-hydroxyindole electrical current in injected cocytes for α 7 nicotinic receptors.

Example 2

The effect of 5-hydroxyindole on various nicotinic agonists is tested. An increase in potency due to 5-hydroxyindole is observed for all nicotinic agonists tested, for example, for (-) - spiro [1-azabicyclo [2.2.2] octane-3,5 * -oxazolidin] -2 * -one (Figure 5) . The empty boxes represent the electrical current induced by acetylcholine (ACh) (3 mM) with a modulator (+) and without a modulator (-). The solid boxes represent the electrical current generated by the nicotinic agonist referred to as AR-R 17779 (100 μΜ) with and without modulator (-). The modulator in this example is 1 mM 5-hydroxyindole (5-OH 1).

Compounds tested with similar results include (-) - nicotine and choline (data not shown). Therefore, the effect appears to be general for any cholinergic agonist.

Example 3

The increase in effect achieved by 5-hydroxyindole has not been observed at any other nicotinic receptors, such as mouse muscle-type nicotinic receptors.

Example 4

A series of compounds were tested for positive modulation of acetylcholine (ACh) activity. Only a few compounds retained activity enhancing activity. In particular, serotonin (5-HT) does not increase efficacy. This preliminary analysis of the tight analogues indicates a considerable relationship in structural activity indicating a selective site of action.

Example 5

The effect of nAChR α7 modulator on agonist activity is measured by the calcium cation flow through nAChR α1 expressed on HEK-293 cells. The nicotinic (-) - spiro [1-azabicyclo [2.2.2] octane-3,5'-oxazolidin] -2'-one agonist is used. The results are shown in Figure 1

In the presence of the agonist alone (without a modulator), a discernible signal cannot be obtained. In the presence of an agonist together with a modulator, an increase in modulator activity is observed.

Claims (28)

PATENT CLAIMS What is claimed is: 1. A pharmaceutical composition comprising a positive nicotinic receptor agonist modulator together with a pharmaceutically acceptable carrier, wherein said positive modulator has the ability to enhance the efficacy of said nicotinic receptor agonist. The pharmaceutical composition of claim 1, further comprising a nicotinic receptor agonist. Pharmaceutical composition according to claim 1 or 2, characterized in that said positive modulator is 5-hydroxyindole. The pharmaceutical composition of any one of claims 1 to 3, wherein said nicotinic receptor agonist is an α7-nicotinic receptor agonist. 5. A method of treating conditions associated with reduced nicotinic transmission comprising administering a therapeutically effective amount of a positive nicotinic receptor agonist modulator to a patient in need thereof, wherein said positive modulator has the ability to enhance the efficacy of said nicotinic receptor agonist. The method of claim 5, wherein said positive modulator is co-administered with a nicotinic receptor agonist. 7. The method of claim 5 or 6, wherein said positive modulator is 5-hydroxyindole. The method of any one of claims 5 to 7, wherein said nicotinic receptor agonist is an α7-nicotinic receptor agonist. The method of any one of claims 5 to 8, wherein the treatment is treatment of Alzheimer's disease, attention deficit hyperactive disorder, schizophrenia, anxiety or nicotine dependence. The method of any one of claims 5 to 8, wherein the treatment is treatment of Alzheimer's disease. Method according to any one of claims 5 to 8, characterized in that the treatment is the treatment of attention deficit hyperactive disorder. 12. The method of any one of claims 5 to 8, wherein the treatment is treatment of schizophrenia. The method of any one of claims 5 to 8, wherein the treatment is nicotine dependence treatment. 14. A method for identifying a positive nicotinic receptor agonist modulator, comprising the steps of a) expressing nicotinic receptor on the surface of cells; b) contacting said nicotinic receptor with a compound known as a nicotinic receptor agonist and testing the compound for positive modulatory activity; c) determining whether the test compound exhibits a positive modulation of the effect of said nicotinic receptor agonist. 15. A method for identifying a nicotinic receptor agonist compound comprising the steps of a) expressing nicotinic receptors on the surface of cells; b) contacting said nicotinic receptor with a compound tested for nicotinic receptor agonist activity in the presence of a positive nicotinic receptor agonist modulator; and c) determining whether the test compound exhibits nicotinic receptor agonist activity. 16. The method of claim 14 or 15, wherein the cell is a Xenopus oocyte, a HEK-293 cell or a neuron grown in the cell. 17. The method of claim 14 or 15, wherein said nicotinic receptor is an α7-nicotinic receptor. 18. The method of claim 14 or 15, wherein the nicotinic receptor is either a human, rat, chicken, mouse or bovine nicotinic receptor. A compound which is identifiable by a method according to any one of claims 10 to 18. Use of a positive nicotinic receptor agonist modulator for the manufacture of a medicament for the treatment or prophylaxis of conditions associated with reduced nicotine transmission. Use of a positive nicotinic receptor agonist modulator together with a nicotinic receptor agonist for the manufacture of a medicament for the treatment of conditions associated with reduced nicotinic transmission. Use according to claim 20 or 21, wherein the modulator is 5-hydroxyindole. The use of claim 20 or 21, wherein the nicotinic receptor agonist is an α7-nicotinic receptor agonist. Use according to any one of claims 20 to 23 for the manufacture of a medicament for the treatment of Alzheimer's disease, attention deficit hyperactive disorder, schizophrenia, anxiety or nicotine dependence. Use according to any one of claims 20 to 23 for the manufacture of a medicament for the treatment of Alzheimer's disease. Use according to any one of claims 20 to 23 for the manufacture of a medicament for the treatment of an attention deficit hyperactive disorder. Use according to any one of claims 20 to 23 for the manufacture of a medicament for the treatment of schizophrenia. Use according to any one of claims 20 to 23 for the manufacture of a medicament for the treatment of nicotine dependence.