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Behavioural consequences of selective activation of 5-HT receptor subtypes Berendsen, Hermanus Henricus Gerardus

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Publication date: 1991

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Citation for published version (APA): Berendsen, H. H. G. (1991). Behavioural consequences of selective activation of 5-HT receptor subtypes: Possible implications for the mode of action of . s.n.

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Download date: 02-10-2021 Chapter 4 Antagonism of 8-OH-DPAT-induced behaviour in rats

European Journal of Pharmacology (1990) 187,97 - 103 SUMMARY Selective activation of the 5-HTIAreceptor induces lower lip retraction (LLR) in rats. 8-Hydroxy-dipropylaminotetralin (8-OH-DPAT) -induced LLR could not be antagonised by the 5-HT antagonists , or . In fact, some 5-HT antagonists induced LLR. However, 8-OH-DPAT-induced LLR could be antagonised by , , spiroxatrine and NAN-190, but not by the 01- adrenoceptor antagonist metoprolol, the PZadrenoceptor antagonist butoxamine or the antagonist . This antagonism was competitive as the dose- response curve of 8-OH-DPAT was shifted to the right. Pindolol, spiperone, spiroxatrine and NAN-190 all have a high affinity for the 5-HTIA receptor. This indicates that blockade of 8-OH-DPAT-induced LLR is only possible by selective blockade of 5-HTIA receptors. A possible mechanism of action is discussed. The increased defecation induced by 8-OH-DPAT could be antagonised by pindolol and NAN-190. The effect of spiroxatrine and haloperidol on the 8-OH-DPAT- induced increase in defecation was bimodal: an increase after a low and a decrease after a high dose of 8-OH-DPAT. Metoprolol and butoxamine had no effect on 8-OH-DPAT- induced increase in defecation, thereby excluding an influence of P-adrenoceptors.

4.1 INTRODUCTION Activation of 5-HTIA receptors with the selective 5-HTIA agonist 8-hydroxy- dipropylaminotetralin (8-OH-DPAT) induces in rats a behavioural response consisting of hyperlocomotion, head weaving, flat body posture and reciprocal forepaw treading (Arvidsson et al., 1981; Tricklebank et al. 1984; Hjorth et al., 1982). Recently, we observed that 8-OH-DPAT affects the musculature of the lower lip of rats in such a way that the lower incisors of the rats become completely visible. We termed this lower lip retraction (LLR) (Berendsen et a]., 1989a). LLR could also be induced by , and Ru 24969 (5-methoxy(tetra hydro-4-piridinyl) indole). These compounds all have high affinity for the 5-HTIA receptor (Gozlan et al., 1983; Peroutka, 1985; Hoyer, 1988). 5-Methoxy-N,N-dimethyltryptamine (5-MeODMT) which binds to 5- HTIA, 5-HT,,, 5-HT,c and 5-HT2 receptors (Gozlan et al., 1983; Sills et al., 1984; Peroutka, 1985; Engel et al., 1986) only induced LLR when given in combination with , or metergoline. This is probably due to blockade of the 5- HTlc and 5-HT2 receptors, thereby leaving the more selective stimulation of 5-HT,, receptors by 5-MeODMT (Berendsen et al., 1989a). Antagonism of 8-OH-DPAT-induced behaviour, however, seems to be problematic. The 8-OH-DPAT-induced forepaw treading can only be antagonised by , pindolol and compounds with dopamine antagonistic properties such as haloperidol, , methiothepin and spiperone. Methysergide, , metergoline and cyproheptadine are ineffective (Tricklebank et al., 1984; Berendsen et al., unpublished observations). 8-OH-DPAT-induced hyperphagia can be antagonised by spiperone and haloperidol but not by metergoline (Fletcher and Davies, 1990). The 5-HT antagonists metergoline and methysergide are similarly inactive in antagonising 8-OH-DPAT-induced LLR. The dopamine antagonists haloperidol and mesulergine are also inactive; the latter compound also has strong 5-HT antagonistic properties. In fact, metergoline, cyproheptadine and ritanserin induce slight LLR (Berendsen et al., 1989a) and hyperphagia (Fletcher, 1988). Metergoline and methysergide act as agonists on forskolin- stimulated adenylate cyclase activity in the calf hippocampus, whereas methiothepin and spiperone behave as antagonists (Schoeffter and Hoyer, 1988). It is apparently difficult to find antagonists for 5-FITlA-mediatedeffects. We now report that 8-OH-DPAT-induced LLR can be antagonised by ligands that have selectivity for the 5-HTIA receptor, such as spiperone, spiroxatrine, pindolol and the recently synthetised 5-HTIA antagonist NAN-190 (2-methoxy- phenyl-phtalimidobutyl ; Glennon et al., 1989).

4.2 MATERIALS AND METHODS

4.2.1 Animals

Naive male Wistar rats (Cpb;WU, Harlan Spraque Dawley, Zeist, The Netherlands) weighing 200 - 350 g were used in these studies. The animals were housed in white PVC cages (40 x 40 x 18 cm) with a wire mesh lid, five animals per cage, under controlled 12 h light - dark cycle, with lights on at 06:OO a.m. The rats were allowed free access to standard food pellets and tap water. The animals were used for an experiment up to 3 times with at least one drug free week between two experiments. All animals within an experiment had the same drug history.

4.2.2 Procedure

The experiments were performed between 9:30 and 14:00 h. A maximum of 20 animals were scored at the same time and at least 10 animals were used for each dose treatment. The animals were treated in a random sequence. The antagonists were injected 30 min before 8-OH-DPAT was injected. Immediately after treatment with 8-OH-DPAT, the rats were placed individually in clear macrolon cages (23 x 17 x 15 cm) with a grid floor. Lower lip retraction was measured after 15, 30 and 45 min as described before (Berendsen et al., 1989a) : 0 = lower incisors not or hardly visible (not different from placebo treated animals), 0.5 = partly visible, 1 = completely visible. After completion of a test block (45 min) the number of fecal boli produced by the animals in this 45 min period was counted. LLR score LLR score

LLR score LLR score

0.5 - 0.5-

. 1 1 1 I I I I I I 0.1 0.22 0.46 1.O 2.2 0.1 0.22 0.46 1.O 8-OH-DPAT (rnglkg) 8-OH-DPAT (mglkg)

Figure 1: Dose response curves of 8-OH-DPAT after pretreatment with placebo .- and (A) pindolo14.6 mag A--- A or 10 rnglkg o --- o; (B) spiperone 1 mglkg; (C) spiroxatrine 0.46 mgkg and (D) NAN-190 3 mglkg. The vertical bars represent the S.E.M. The antagonists were injected s.c. 30 min before 8-OH-DPAT. At least 10 animals were used for each point. * Pc0.05; ** Pc0.01; *** Pc0.001 when compared to the corresponding control group. 4.2.3 Drugs and solutions

The following drugs were used: butoxamine HC1 (Burroughs Wellcome); haloperidol (HaldolR; Janssen Pharmaceuticals); 8-hydroxy -2-(di-n-propylamino) tetralin HBr (8-OH-DPAT; RBI); metoprolol tartrate (Hassle); (+) pindolol and spiperone Sigma); spiroxatrine (RBI); 1-(2-methoxypheny1)- 1- { [C(Zphtalimido) butyl] piperazine} (NAN-190) was synthetised by Dr. M. Combourieu, Laboratoires Lyocentre, Aurillac, France. Spiperone and spiroxatrine were dissolved in an aqueous solution of 0.5 mglml of tartaric acid and adjusted to pH 4.0 - 4.5 with NaOH. Haloperidol was diluted from 5 mgtml HaldolR ampoules to the required concentrations using sterile saline solution. NAN-190 was suspended in a solution of 5% mulgofen (EL 719R, GAF Corp.) in saline. The other compounds were dissolved in sterile saline solution. All drug solutions were freshly prepared and injected S.C.into the loose skin at the back of the neck. A dose volume of 5 mVkg body weight was used. Control animals received an equivalent volume of vehicle. When drug solutions were made up from the salt of the compound, the doses refer to the weight of the salt.

Table 1. Lower lip retraction (LLR) score of rats pretreated with haloperidol (2.2 mg/kg), metropolol (10 mglkg) or butoxarnine (10 mg/kg). At least LO animals per treatment group were used. Antagonists were given 30 min before 8-OH-DPAT (maximal score =3).

Pretreatment 8-OH-DPAT LLR score % change (dose) (mg/kg s.c.) mean k S.E.M.

Placebo

Haloperidol (2.2 mg/kg)

Metoprolol (10 mg/kg)

Butoxamine ( 10 mg/kg)

------?<0.05 when compared to the corresponding control group. 4.2.4 Statistics

Lower lip retraction was scored three times (at 15, 30 and 45 min after treatment) and the scores were summed for each rat. In this way a total maximal score of 3 could be reached for each animal. The final results are expressed as the mean score per group * S.E.M. The statistical significance of the drug effects was determined by comparing the results of each group to the results of the relevant control group using the non- parametric rank sum test on scores (Lehman, 1974). The number of fecal boli was expressed as the mean number per group f S.E.M. and the statistical significance was determined with the non-parametric rank sum test on scores.

4.3 RESULTS

4.3.1 Lower lip retraction

Injection of 8-OH-DPAT (0.046 - 1.0 mgkg) to placebo-treated rats resulted in a strong LLR response. The dose response curves of 8-OH-DPAT were shifted to the right by pindolol(4.6 and 10 mgkg, fig. lA), spiperone (1 mgkg, fig. lB), spiroxatrine (0.46 mg/kg, fig. 1C) and NAN-190 (3 mglkg, fig. 1D) but not by butoxarnine (10 mgkg) or metoprolol (10 mgkg, table 1). Haloperidol (2.2 mgkg) had only a small effect on 8-OH-DPAT (0.22 mgkg)-induced LLR. The shift of the dose-response curve after pindolol was dose-dependent: 10 mgkg causing a larger shift than 4.6 mgkg. Treatment with spiperone, spiroxatrine and haloperidol also induced strong sedation and catalepsy. The animals lay flat, with their belly and head on the grid floor of the cage. Other symptoms that were seen after 8-OH-DPAT treatment were flat body posture, hindlimb abduction, forepaw treading and increased defecation. Forepaw treading was inhibited by pindolol, spiperone, spiroxatrine, NAN-190 and haloperidol, but not by metoprolol or butoxamine.

4.3.2 Defecation

8-OH-DPAT caused a marked increase in defecation which was maximal after 0.1 or 0.22 mgkg and varied between 5.1 f 0.9 and 8.8 f 0.8. The mean number of fecal boli of placebo-treated rats placed in the same situation during the same period was less than 1. The mean number of fecal boli after treatment with spiroxatrine (0.46 mgkg), spiperone (1.0 mgkg) and haloperidol (2.2 mglkg) were 1.1 + 0.5; 3.1 f 0.3 and 3.4 f 0.7 respectively, whereas these numbers were 0.8 f 0.5 and 2.8 f 0.7 after pindolol (10 mgkg) and NAN-190 (3 mgkg) treatment, respectively. The increase in defecation induced by 8-OH-DPAT was strongly antagonised by pindolol and NAN-190 (Table 2). A dose of 0.46 mgkg pindolol almost completely blocked the increased defecation elicited by 8-OH-DPAT (0.1 mgkg). This antagonism seems to be competitive since pindolol antagonised increased defecation elicited by higher doses of 8-OH-DPAT less effectively than the response elicited by 0.1 mgkg of 8-OH-DPAT. The effects of spiroxatrine and haloperidol were more complicated. After a low dose of 8-OH-DPAT (0.046 mgkg), these compounds potentiated the increase in defecation whereas after a high dose of 8-OH-DPAT (0.46 mgkg) these compounds significantly inhibited the defecation. After treatment with spiperone the level of defecation after 8-OH-DPAT was reduced but this reduction was not statistically significant. Metoprolol and butoxamine had no effect on 8-OH-DPAT-induced increase in defecation.

4.4 DISCUSSION The dose-response curve of 8-OH-DPAT-induced LLR can be shifted to the right by pindolol, spiperone, spiroxatrine and NAN-190, indicating competitive antagonism of 8-OH-DPAT-induced LLR by these compounds. These compounds all have a high affinity for the 5-HTIAreceptor. Some variation in LLR response to 8-OH-DPAT was seen. A similar variation is seen in the increased fecal excretions elicited by 8-OH- DPAT. A possible explanation for this variability might be that the animals were used for similar experiments before (see Methods). Within an experiment, however, all animals had the same drug history. Pindolol is a P-adrenoceptor blocking compound with high affinity for the 5-HTIAand 5-HTIBreceptors (Nahorski and Willcocks 1983; Hoyer, 1988). An effect of P-adrenoceptor blocking properties on LLR could be excluded by the lack of effect of the PI-selective antagonist metoprolol (Ablad et al, 1973), which does not have 5-HT antagonistic activity (Hjorth and Carlsson, 1985) and the ineffectivity of the p2-selective antagonist butoxamine (Leclerc et al., 1981). Thus the 5-HTlA/5-HTlB antagonistic activity of pindolol must be responsible for inhibition of 8-OH-DPAT-induced LLR. The dopamine antagonists spiperone and spiroxatrine have high affinity for the 5-HTIA receptors (Leysen et al., 1981; 1986; Hoyer 1988; Nelson and Taylor, 1986; Nelson et al., 1987a). It is unlikely that their effect on 8-OH- DPAT- induced LLR was mediated by blockade of dopamine receptors since the haloperidol had no effect on 8-OH-DPAT-induced lower lip retraction (Berendsen et al., 1989a; table 1). In these LLR experiments spiroxatrine behaved as an antagonist whereas in an isolated organ preparation it does not block 8- OH-DPAT (Leysen et al., 1986) and it acts as an agonist on forskolin - stimulated adenylate cyclase activity in rat hippocampus (Nelson et al., 1987b). Hemck-Davis and Titeler (1988) concluded that spiroxatrine has "agonist-like" binding properties in its interaction with the 5-HTIAreceptor. NAN-190 was designed as a 5-HTIA antagonist (Glennon et al., 1989). In drug discrimination tests this compound antagonises the stimulus effects of 8-OH-DPAT and does not produce TFMPP-like effects or antagonism of the TFMPP stimulus (Glennon et al, 1989). This indicates that the compound lacks the 5-HTlc and 5-HT2 properties of TFMPP (Hoyer, 1988). In our experiments, the compound antagonised 8-OH-DPAT- Table 2. Mean number of fecal boli + S.E.M. produced in the 45 min of the test by the rats treated with 8-OH-DPAT after pretreatment with the different antagonists. Antagonists were given 30 min before 8-OH-DPAT.

Number of fecal boli 8-OH-DPAT Mean f S.E.M. Mean f S.E.M. % change (mg/kg LC.) after: after: Placebo Pindolo14.6 mg/kg 0.1 5.1 f 0.9 0.3 f 0.2 - 94C 0.22 5.1 f 0.5 0.9 f 0.4 - 82' 0.46 6.1 f 1.2 1.5 f 0.5 - 75= 1.O 5.2 f 0.8 4.1 f 0.9 - 21 Pindolol 10 mg/kg 0.1 0.3 f 0.2 - 94C 0.22 0.4 f 0.2 - 92' 0.46 0.5 f 0.3 - 92' 1.0 0.9 f 0.5 - 83b 2.2 2.7 f 0.6 Placebo Spiroxatrine 0.46 mg/kg 0.046 2.1 f 0.8 3.9 f 0.6 + 86 0.1 6.0 + 0.6 3.2 f 0.6 - 47a 0.22 6.9 * 0.7 3.7 f 0.9 - 46' 0.46 5.9 i 0.7 2.0 f 0.5 - 66b Placebo Spiperone 1 mg/kg

Placebo NAN-190 3 mg/kg

Placebo Haloperidol 2.2 mg/kg

Metoprolol 10 mg/kg

Butoxamine 10 mg/kg

a P < 0.05; P < 0.01; P < 0.001 when compared to the corresponding control group. induced LLR. These experiments show that only selective 5-HTIA antagonists inhibit 8-OH-DPAT-induced LLR. This is in contrast with 8-OH-DPAT-induced forepaw treading and hyperphagia, the symptoms of which can also be inhibited by dopamine antagonists (Tricklebank et al., 1984; Muscat et al., 1989). In previous experiments we showed that 8-OH-DPAT-induced LLR could be inhibited by agonists for 5-HTlc andlor 5-HT2 receptors, such as mCPP and DOI. These 5-HTICand 5-HT2 agonists thus act as functional antagonists for the receptor (Berendsen et al., 1989a,b). It was also shown that 8-OH-DPAT-induced LLR could not be antagonised by metergoline and methysergide; in fact, these compounds induced slight LLR. In 8-OH-DPAT-induced feeding experiments, metergoline was unable to reduce 8-OH-DPAT-induced hyperphagia; in fact, it induced hyperphagia by itself (Fletcher and Davies 1990; Fletcher, 1988). Metergoline and methysergide have a higher affinity for 5-HTlc and 5-HT2 than for 5-HTIAreceptors (Hoyer, 1988). A possible explanation is that all three 5-HT receptor subtypes (5-HTIA, 5-HTIC and 5-HT2) are tonically activated. In a steady state situation there is no net predominance of activation of one receptor subtype. If, after giving an antagonist, more 5-HTlc and 5-HT2 than 5-HTIA receptors are blocked, and thus the tonus on the 5-HTlc and 5-HT2 receptors is more reduced than the tonus on the 5-HTIA receptors, the net result will be the appearance of 5-HTIA- related behaviour. One might call this functional agonism. In this way it is clear that antagonism of 5-HTIA related behaviour is difficult to achieve with non-selective antagonists. These non-selective antagonists not only reduce access to 5-HTIAreceptors but reduce access to 5-HTlc andlor 5-HT2 receptors to a greater extend; the net result will appear as if there is partial activation of 5-HTIAreceptors. It was seen in these and former experiments (Berendsen et al., 1989a) that 8-OH-DPAT causes, besides LLR, excessive defecation. This is probably a centrally mediated effect since this increase in defecation was not found in anesthetized rats and the motility of guinea pig intestines was not changed after 1 mgkg of 8-OH-DPAT given i.v. (Berendsen and Hobbelen, unpublised observations). The increased defecation after 8-OH-DPAT was antagonised by pindolol and NAN-190, with the high dose of pindolol being more effective than the low dose. The strong effects of these compounds might even suggest that the increased defecation observed after 8-OH-DPAT is easier to inhibit than LLR. This antagonism could be overcome by a high dose of 8-OH-DPAT, indicating that the antagonism of pindolol and NAN-190 is competitive. Interpretation of the effects of spiperone, spiroxatrine and haloperidol is complicated by the fact that high (cataleptogenic) doses of dopamine antagonists induce an increase in defecation themselves (Russell et al., 1987; Sanberg et al., 1989). In our studies, increase in defecation induced by a low dose (0.046 mgtkg) of 8-OH-DPAT was potentiated by haloperidol and spiroxatrine whereas the increased defecation elicited by a high dose (0.46 mgkg) of 8-OH-DPAT was antagonised by these compounds. The defecation results thus do not consistently parallel the LLR results. The interpretation of these results is further complicated by and interactions. In this study, we have shown that antagonism of 8-OH-DPAT-induced LLR requires selectivity for the 5-HTIAreceptor. Other &OH-DPAT induced behaviours, such as forepaw treading, hyperphagia and excessive defecation, however, can be attenuated by compounds that possess dopamine antagonistic properties. An estimation of the potencies of the compounds that antagonize LLR indicates that these compounds show the same order of potency in blocking LLR as they show for their affinity for the 5-HTIAreceptor as determined in binding studies: NAN-190 > spiroxatrine > spiperone > pindolol (Hoyer, 1988; John, personal communications). These compounds, however, also bind to non-serotonergic sites. Spiroxatrine and spiperone bind strongly to dopamine receptors, pindolol binds to P-adrenoceptors and NAN-190 binds to a-adrenoceptors and doparnine receptors. The choice of which compound to use in other studies will depend on the role these receptors play in the tissue to be studied.

4.5 REFERENCES Ablad, B., D. Carlsson and L. Ek, 1973, Pharmacological studies of two new cardioselective @-receptoragonist, Life Sci. 12, 107.

Arvidsson, L.E., U. Hacksell, J. Lars, G. Nilson, S. Hjorth, A. Carlsson, P. Lindberg, D. Sanchez and H. Wikstrvm, 1981, 8-Hydroxy-2-(di-n-propylamino)tetralin, a new centrally acting, 5-hydroxytryptamine receptor agonist, J. Med. Chem. 24,921.

Berendsen, H.H.G., F. Jenck and C.L.E. Broekkamp, 1989a, Selective activation of 5-HTIA-receptorsinduces lower lip retraction in the rat. Pharmacol. Biochem. Behav. 33, 821.

Berendsen, H.H.G., R.J.M. Smets and C.L.E. Broekkamp, 1989b, Functional interplay of (5-HT)-receptor subtypes, In: The behavioural pharmacology of 5-HT. eds. P. Bevan, A.R. Cools and T. Archer (Lawrens Erlbaum Assoc. Inc., New York) p. 83.

Engel, G., M. Gothert , D. Hoyer, E. Schlicker and K. Hillebrands, 1986, Identity of inhibitory presynaptic 5-hydroxytryptamine (5-HT) autoreceptors in the rat brain cortex with 5-HTIBbinding sites. Naunyn-Schmiedeberg's Arch. Pharmacol. 332: 1.

Fletcher, P.J., 1988, Increased food intake in satiated rats induced by the 5-HT antagonists methysergide, metergoline and ritanserin, Psychopharmacology 96, 237.

Fletcher, P.J. and M. Davies, 1990, A pharmacological analysis of the eating response induced by 8-OH-DPAT injected into the dorsal raphe nucleus reveals the involvement of a dopaminergic mechanism, Psychopharmacology 100, 188.

Glennon, R.A., N.A. Naiman, M.E. Pierson, M. Titeler, R.A. Lyon, J.L. Herndon and B. Misenheimer, 1989, Stimulus properties of arylpiperazines: NAN- 190, a potential 5-HTIAserotonin antagonist, Drug Dev. Res. 16, 335. Gozlan, H., S. El Mestikawy, L. Pichat, J. Glowinski and M. Manon, 1983, Identification of presynaptic serotonin autoreceptors using a new ligand: 3H-PAT, Nature 305, 140.

Herrick-Davis, K. and M. Titeler, 1988, [3H] Spiroxatrine: a 5-HTIAradioligand with agonist binding properties, J. Neurochem. 50,528.

Hjorth, S. and A. Carlsson, 1985, (-) Pindolol stereo- specifically inhibits rat brain serotonin (5-HT) synthesis, Neuropharmacology 24, 1143.

Hjorth S.A., A. Carlsson, P. Lindberg, D. Sanchez, H. Wikstrom, L-E. Arvidsson, U. Hacksell and J.L.G. Nilsson, 1982, 8-hydroxy-2-(di-n-propylamino)tetralin, 8-OH- DPAT, a potent and selective simplified ergot congener with central 5-HT-receptor stimulating activity. J. Neural Trans. 55, 169.

Hoyer, D., 1988, Functional correlates of serotonin 5-HT1 recognition sites, J. Rec. Res. 8, 59.

Leclerc, G., B. Raout, J. Velly and J. Schwartz, 1981, P-adrenergic subtypes, Trends Pharmacol. Sci. 17, 18.

Lehman, E.L., 1974, Nonparametrics: Statistical Methods based on Ranks (McGraw Hill, London).

Leysen, J.E., F. Awouters, L. Kennis, P.M. Laduron, J. Vandenberk and P.A.J. Janssen, 1981, Receptor binding profile of R 41468, a novel antagonist at 5-HT2 receptors. Life. Sci. 28, 1015.

Leysen, J.E., F.C. Colpaert, W. Janssens, C.J..E. Niemegeers, J.M. van Nueten and P.A.J. Janssen, 1986, Spiroxatrine derivatives with high affinity and selective binding to 5-HTIAsites apparently lack pharmacological activity, Soc. Neurosci. Abstr. 12, 362.

Muscat, R., A.M.J. Montgomery and P. Willner, 1989, Blockade of 8-OH-DPAT induced feeding by dopamine antagonists. Psychopharmacology 99,402.

Nahorski, S.R. and A.R. Willcocks, 1983, Interactions of p-adrenoceptor antagonists with 5-hydroxytryptamine receptor binding in rat cerebral cortex, Brit. J. Pharmacol. 78, 107.

Nelson, D.L., A.L. Killam, P.J. Monroe, S.S. Nikam and A.R. Martin, 1987b, Use of spiroxatrine in the characterization of serotonin receptor subtypes, Pharmacologist 29, 111. Nelson, D.L., P.J. Monroe, G. Larnbert and H.I. Yamamura, 1987a, [3H] spiroxatrine labels a serotoninlA-like site in the rat hippocampus, Life Sci. 41, 1567.

Nelson, D.L. and E.W. Taylor, 1986, Spiroxatrine: A selective serotoniniA , European J. Pharmacol. 124,207.

Peroutka S.J., 1985, Selective labelling of 5-HTIA and 5-HTIB binding sites in bovine brain, Brain Res. 344, 167.

Russell, K.H., S.H. Hagenmeyer-Houser and P.R. Sanberg, 1987, Haloperidol- induced emotional defecation: A possible model for neuroleptic anxiety syndrome. Psychopharmacology 9 1,45.

Sanberg, P.R., K.H. Russell, S.H. Hagenmeyer-Houser, M. Giordano, E.M. Zubrycki and D.L. Garver, 1989, Neuroleptic-induced emotional defecation: effects of scopolamine and haloperidol. Psychopharmacology 99,60.

Schoeffter, P. and D. Hoyer, 1988, Centrally acting hypotensive agents with affinity for 5-HTIAbinding sites inhibit forskolin-stimulated adenylate cyclase activity in calf hippocampus, Brit. J. Pharmacol. 95,975.

Segal, M. and M. Weinstock, 1983, Differential effects of 5-hydroxytryptamine antagonists on behaviours resulting from activation of different pathways arising from the raphe nuclei, Psychopharmacology 79, 72.

Sills, M.A., B.B. Wolfe and A. Frazer, 1984, Determination of selective and non selective compounds for the 5-HTIA and STlBreceptor subtypes in rat frontal cortex, J. Pharmacol. Exp. Ther. 231,480.

Tricklebank, M.D., C. Forler and J.R. Fozard, 1984, The involvement of subtypes of the 5-HT, receptor and the systems in the behavioural response to 8-hydroxy-2-(di-n-propy1amino)tetralin in the rat. European. J. Pharmacol. 106, 271.