New methoxy-chroman derivatives, 4[N-(5-methoxy-chroman-3-yl)N- propylamino]butyl-8-azaspiro-(4,5)-decane-7,9-dione [(+/-)-S 20244] and its enantiomers, (+)-S 20499 and (-)-S 20500, with potent agonist properties at central 5-hydroxytryptamine1A receptors

The potential interaction of the new methoxy-chroman derivatives: (+/-)-S 20244 (4-[N-(5-methoxy-chroman-3-yl)N-propylamino]butyl-8-azaspiro- (4,5)-decane-7,9-dione) and its enantiomers (+)-S 20499 and (-)-S 20500 with central 5-hydroxytryptamine1A (5-HT1A) receptors was assessed using biochemical and electrophysiological tests in the rat. In vitro binding assays revealed that these drugs bound with high affinity to 5-HT1A sites in hippocampal membranes (Ki: 0.19 nM for (+)-S 20499, 0.95 nM for (-)-S 20500 and 0.35 nM for the racemate (+/-) S 20244). As seen with the prototypical 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin, (+/-)-S 20244, (+)-S 20499 and (-)-S 20500 inhibited forskolin-activated adenylate cyclase in hippocampal homogenates with potencies corresponding to their respective affinities for 5-HT1A sites. The maximal inhibitory effect of the chroman derivatives was not additive with that of 8-hydroxy-2-(di-n- propylamino)tetralin and could be competitively reduced by 5-HT1A antagonists such as (-)-propranolol and (+/-)-tertatolol. Electrophysiological recordings within the dorsal raphe nucleus both in vitro (in brain-stem slices) and in vivo (in chloral hydrate anesthetized rats) showed that (+)-S 20499, (+/-)-S 20244 and (-)-S 20500 induced, in that order of (decreasing) potency, a dose-dependent reduction in the spontaneous firing of serotoninergic neurons. In vitro, as well as in vivo, the inhibitory influence of the chroman derivatives on the discharge frequency of serotoninergic neurons could be competitively antagonized by (+/-)-tertatolol. Finally, oral administration of increasing doses of the most potent enantiomer, (+)-S 20499, induced a marked reduction in the rate of 5-HT turnover, without affecting that of dopamine, in various brain areas. All these biochemical and electrophysiological data indicate that (+)-S 20499 is a highly potent agonist at both presynaptic (i.e., somatodendritic) and postsynaptic 5-HT1A receptors in the rat brain

(−)Tertatolol is a potent antagonist at pre- and postsynaptic serotonin 5-HT1A receptors in the rat brain

The potential 5-HT1A antagonist properties of the ß-antagonist tertatolol were assessed using biochemical and electrophysiological assays in the rat. (±) Tertatolol bound with high affinity (Ki = 38 nM) to 5-HT1A sites labelled by [3H]8-OH-DPAT in hippocampal membranes. The (–)stereoisomer (Ki = 18 nM) was about 50-fold more potent than the (+)stereoisomer (Ki = 864 nM) to inhibit the specific binding of [3H]-8-OHDPAT. As expected of a 5-HT1A antagonist, (–)tertatolol prevented in a concentration-dependent manner (Ki = 24 nM) the inhibitory effect of 8-OH-DPAT on forskolin-stimulated adenylate cyclase activity in rat hippocampal homogenates. Furthermore in vivo pretreatment with (–)tertatolol (5 mg/kg s.c.) significantly reduced the inhibitory influence of 8-OH-DPAT (0.3 mg/ kg s.c.) on the accumulation of 5-hydroxytryptophan in various brain areas after the blockade of aromatic L-amino acid decarboxylase by NSD-1015 (100 mg/kg i.p.). In vitro (in brainstem slices; Ki 50 nM) and in vivo (in chloral hydrate anaesthetized rats; ID50 0.40 mg/kg i.v.), (–)tertatolol prevented the inhibitory effects of the 5-HT1A receptor agonists 8-OH-DPAT, ipsapirone and lesopitron on the firing rate of serotoninergic neurones within the dorsal raphe nucleus. In about 25% of these neurones, the basal firing rate was significantly increased by (–)tertatolol (up to +47% in vitro, and +30% in vivo). These data indicate that (-)tertatolol is a potent competitive antagonist at both pre (in the dorsal raphe nucleus) - and post (in the hippocampus) - synaptic 5-HT1A receptors in the rat brain

Central Pre- and Postsynaptic 5-HTIA Receptors in Rats Treated Chronically With a Novel Antidepressant, Cericlamine

Biochemical and electrophysiological approaches were used to assess the possible changes in 5-hydroxytryptamine (serotonin) 5-HT1A receptors in the rat brain after a long-term treatment with cericlamine [2-(3,4-dichlorobenzyl)-2-dimethylamino-1-propanol], a novel serotonin reuptake inhibitor with antidepressant properties. Possible changes in other serotonin receptor binding sites (5-HT2A, 5-HT2C and 5-HT3) were also investigated after this treatment. Cericlamine was injected for 2 weeks at a dose (16 mg/kg i.p., twice daily) that ensured complete prevention of 4-methyl-alpha-ethyl-meta-tyramine-induced depletion of brain serotonin. In vitro binding and quantitative autoradiographic studies showed that neither 5-HT1A, 5-HT2A, 5-HT2C nor 5-HT3 receptor binding sites in various brain areas were affected by the 14-day treatment with cericlamine. Although forskolin-stimulated adenylate cyclase activity was significantly increased in hippocampal homogenates from cericlamine-treated rats, the reduction in this enzymatic activity due to 5-HT1A receptor stimulation by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) was unchanged in these animals as compared with controls. In contrast, in vitro and in vivo electrophysiological recordings of serotoninergic neurons in the dorsal raphe nucleus revealed a clearcut functional desensitization of somatodendritic 5-HT1A autoreceptors. Thus the potency of 8-OH-DPAT and ipsapirone to depress the firing rate of these neurons in brain stem slices was significantly reduced after the 2-week treatment with cericlamine. In vivo, the potency of an injection of cericlamine to inhibit the discharge of serotoninergic neurons was also markedly less in rats that had been pretreated for 2 weeks with this drug as compared with controls. However, the inhibitory effects of systemically injected 8-OH-DPAT and ipsapirone on the electrical activity of serotoninergic neurons were as pronounced in cericlamine-treated rats as in controls. In addition, the reduction in serotonin synthesis due to an acute treatment with 8-OH-DPAT (0.1 or 0.3 mg/kg s.c.) was not significantly different in both groups of rats. These data support the idea that postsynaptic (in the hippocampus) and somatodendritic (in the dorsal raphe nucleus) 5-HT1A receptors are differently regulated in the rat brain, because only the latter receptors desensitized after a long-term blockade of serotonin reuptake by cericlamine. They also suggest that the inhibitory influence of systemically administered direct 5-HT1A agonists such as 8-OH-DPAT and ipsapirone on the electrical and metabolic activity of serotoninergic neurons does not result solely from the stimulation of somatodendritic 5-HT1A autoreceptors