HLA-A*2416: a new allele of the HLA-A19 lineage

We here report on a new HLA-A19 allele (A*2416) found in a German kidney recipient. Serological class I typing revealed HLA-A11,19 without clear definition of the A19 split antigen. As with serology, polymerase chain reaction (PCR)-based typing also revealed inconclusive results. We therefore sequenced the gene from the 5' flanking region through the 3'-end of exon 4 of this allele after haplotype-specific PCR amplification. The sequence analysis revealed a new HLA-A allele which is identical to A*3101 with the exception of the 3' half of exon 2 which is identical to the common A9 alleles. The phylogenetic analysis constructed with the nearest-neighbor algorithm and based on exons 1-4 or introns 1-3 clearly indicated, that A*2416 belongs unequivocally to the A19 lineage.

CP-154,526: a potent and selective nonpeptide antagonist of corticotropin releasing factor receptors

Here we describe the properties of CP-154,526, a potent and selective nonpeptide antagonist of corticotropin (ACTH) releasing factor (CRF) receptors. CP-154,526 binds with high affinity to CRF receptors (Ki < 10 nM) and blocks CRF-stimulated adenylate cyclase activity in membranes prepared from rat cortex and pituitary. Systemically administered CP-154,526 antagonizes the stimulatory effects of exogenous CRF on plasma ACTH, locus coeruleus neuronal firing and startle response amplitude. Potential anxiolytic activity of CP-154,526 was revealed in a fearpotentiated startle paradigm. These data are presented in the context of clinical findings, which suggest that CRF is hypersecreted in certain pathological states. We propose that a CRF antagonist such as CP-154,526 could affirm the role of CRF in certain psychiatric diseases and may be of significant value in the treatment of these disorders.

Characterization of CP-122,721; a nonpeptide antagonist of the neurokinin NK1 receptor

CP-122,721 [(+)-(2S,3S)-3-(2-methoxy-5-trifluoromethoxybenzyl)amino-2 -phenylpiperidine] interacts with high affinity (pIC50 = 9.8) at the human NK1 receptor expressed in IM-9 cells. In the presence of CP-122,721, there was a reduction in Bmax of [125I]BH-SP binding with no change in affinity suggesting that CP-122,721 does not interact with the NK1 receptor in competitive manner. In an in vitro functional assay. CP-122,721 blocked SP-induced excitation of locus ceruleus cells in guinea pig brain slices with a IC50 value of 7 nM. In vivo, CP-122,721 potently blocked plasma extravasation in guinea pig lung elicited by aerosolized capsaicin (1 mM) with an ID50 = 0.01 mg/kg, p.o. Orally administered CP-122,721 antagonized Sar9, Met (O2)11-SP-induced locomotor activity in guinea pigs with an ID50 = 0.2 mg/kg suggesting good entry into the central nervous system. In addition, consistent with insurmountable blockade observed in vitro, CP-122,721 (0.01, 0.03 0.3 mg/kg, p.o.) produced a rightward shift in the dose response curve for SP-induced hypotension in the awake dog that was accompanied by a decrease in the maximal response. Thus, in vitro and in vivo CP-122,721 appears to behave functionally as a non-competitive antagonist producing an insurmountable blockade of the actions of SP.

Comparison of the effects of sertraline and its metabolite desmethylsertraline on blockade of central 5-HT reuptake in vivo

N-demethylation of the selective serotonin reuptake inhibitor sertraline to desmethylsertraline yields a compound with 10- to 20-fold less potency at blocking serotonin (5-HT) reuptake as measured in vitro. In the present study desmethylsertraline (DMS) was examined in two in vivo models of reuptake inhibition--elevation of extracellular 5-HT in the corpus striatum as measured by microdialysis and inhibition of firing of serotonin-containing dorsal raphe neurons. Whereas sertraline (1, 3.2, and 10 mg/kg s.c.) produced a dose-dependent increase in extracellular 5-HT and a decrease in 5-HIAA in rat striatum, desmethylsertraline was without effect on either parameter. In similar fashion, desmethylsertraline had no effect on dorsal raphe cell firing at a dose (1,000 micrograms/kg i.v.) nearly 20-fold the ED50 for sertraline (52 micrograms/kg). Taken together, these data suggest that DMS does not contribute to the blockade of central 5-HT reuptake produced by sertraline in vivo and therefore would be expected to play a negligible role in its clinical activity.

Synthesis, in vitro binding profile, and autoradiographic analysis of [3H]-cis-3-[(2-methoxybenzyl)amino]-2-phenylpiperidine, a highly potent and selective nonpeptide substance P receptor antagonist radioligand

The synthesis of a highly potent and selective NK1 receptor antagonist radioligand, [3H]-cis-3-[(2-methoxybenzyl)amino]-2-phenylpiperidine (6a) is described. The in vitro binding pharmacology and autoradiographic distribution of 6a in guinea pig brain following peripheral administration are also reported.

The substance P receptor antagonist CP-96,345 interacts with Ca2+ channels

The nonpeptide substance P receptor antagonist CP-96,345 was found to displace binding to Ca2+ channel binding sites labelled with either [3H]desmethoxyverapamil or [3H]diltiazem and to enhance [3H]nitrendipine binding. Unlike the substance P receptor antagonist activity of CP-96,345, these effects on Ca2+ channel binding sites were neither stereoselective nor species-dependent. It is concluded that CP-96,345 may act as an antagonist of L-type Ca2+ channels in addition to being a potent NK1 receptor (substance P) antagonist.

Activity and distribution of binding sites in brain of a nonpeptide substance P (NK1) receptor antagonist

CP-96,345, a nonpeptide substance P antagonist, is selective for the tachykinin NK1 receptor. The compound binds to a single population of sites in guinea pig brain and potently inhibits substance P-induced excitation of locus ceruleus neurons. CP-96,345 should be a useful tool for studying the action of substance P in the central nervous system.

Thiazole as a carbonyl bioisostere. A novel class of highly potent and selective 5-HT3 receptor antagonists

A novel structural class of highly potent and selective 5-HT3 receptor antagonists is described. The compounds in this new series contain a thiazole moiety linking an aromatic group and a nitrogen-containing basic region; the thiazole group appears to be acting as a carbonyl bioisostere in this system. An optimized member of this series, 4-(2-methoxyphenyl)-2-[[4(5)-methyl-5(4)-imidazolyl]methyl]thiazole (5), exhibits oral activity in the Bezold-Jarisch reflex paradigm comparable to or better than the standard agents ondansetron (1) and ICS-205-930 (2). Several of the structure-activity relationships are rationalized in terms of a computer pharmacophore model for 5-HT3 receptor binding.

Pharmacology of sertraline: a review

Sertraline is a member of a new class of psychotherapeutic agents that selectively inhibit serotonin reuptake in the brain. Animal studies have demonstrated that inhibition of serotonin reuptake leads to enhanced serotonergic neurotransmission and indirectly results in a down-regulation of beta-adrenoceptors. The preclinical pharmacology of sertraline predicts antidepressant activity without accompanying anticholinergic, cardiotonic, or sedative side effects. Recent laboratory and clinical observations pertaining to body weight and obsessive compulsive disorder suggest the possibility of broader clinical indications for selective serotonin reuptake blockers such as sertraline.

Some behavioral effects of hallucinogens are mediated by a postsynaptic serotonergic action: evidence from single unit studies in freely moving cats

Although central serotonergic systems appear to be linked importantly to the mechanism of action of a variety of hallucinogenic drugs, the nature of this interaction has remained unclear. In the present study, the question of whether the critical link is presynaptic or postsynaptic was examined in cats. Behaviorally inactive doses (1.0 mg/kg) of the serotonin receptor antagonists mianserin, ketanserin or metergoline effectively blocked behavior, as measured by the cat limb flick response, elicited by either LSD (50 micrograms/kg) or DOM (250 micrograms/kg) but not that resulting either from lisuride (50 micrograms/kg) or a high dose of apomorphine (4 mg/kg). Pretreatment with 1.0 mg/kg of mianserin, which completely attenuated LSD's behavioral effect, failed to alter LSD-induced depression of mesencephalic serotonergic neuron discharge. These results demonstrate that at least some of the behavioral effects of LSD can be blocked by pharmacological antagonism of postsynaptic serotonin receptors which leaves LSD's presynaptic effect unaffected. Thus, the behavioral, and possibly psychoactive, effects of hallucinogens appear to be attributable to an action at 5HT2 receptors, presumably located postsynaptically.

Activity of serotonin-containing neurons in nucleus centralis superior of freely moving cats

Serotonergic neurons were recorded in the nucleus centralis superior (NCS) in freely moving cats and were initially identified on-line by their slow and regular spontaneous activity (mean 2.55 +/- 0.21 spikes/s). Discharge rates of NCS serotonergic neurons were highest during active waking (AW) (mean 2.94 +/- 0.28 spikes/s), decreased during slow-wave sleep (middle of SWS: mean 1.38 +/- 0.18 spikes/s), and were lowest during REM sleep (mean 0.46 +/- 0.13 spikes/s). The activity of serotonergic NCS neurons did not significantly increase during transient elevations of the EMG during AW but did significantly decrease immediately preceding, and during the occurrence of, SWS spindles. These neurons were responsive to phasic auditory and visual stimuli, with most neurons showing excitatory responses. In response to a small dose of the serotonin-specific agonist 5-methoxy-N,N-dimethyltryptamine (50 micrograms/kg, i.m.), NCS serotonergic neurons responded with a mean decrease in unit activity of 43.9 +/- 6.1%. Among the NCS serotonergic neurons a subpopulation differed from the remaining serotonergic neurons in that they showed a much smaller decrease in unit activity across the sleep-wake cycle and responded with an inhibition of activity to phasic auditory and visual stimuli. The results of this study are compared with those previously reported for serotonergic neurons in the dorsal raphe nucleus, nucleus raphe pallidus, and nucleus raphe magnus of freely moving cats.

Chloral hydrate anesthesia alters the responsiveness of central serotonergic neurons in the cat

The influence of chloral hydrate anesthesia on the spontaneous activity and responsiveness of serotonergic neurons was examined by administering chloral hydrate (300 mg/kg, i.p.) to freely moving cats from which serotonergic unit activity in the dorsal raphe nucleus (DRN) was being recorded. Although chloral hydrate administration produced a surgical level of anesthesia within 15 min following injection, it produced only a small decrease (approximately 20%) in the spontaneous activity of DRN serotonergic neurons. In contrast, the responsiveness of these same neurons was greatly altered by chloral hydrate administration. By examining the same neuron before and after chloral hydrate injection, it was found that chloral hydrate anesthesia completely abolished the excitatory responses of DRN serotonergic neurons to auditory and visual stimuli, as well as their excitatory response to electrical stimulation of the gigantocellular tegmental field (FTG) in the pontine reticular formation. On the other hand, the inhibition of serotonergic neuron firing resulting from systemic administration of WB 4101 (1.0 mg/kg, i.p.), a selective alpha 1 adrenergic receptor antagonist, was greatly potentiated by chloral hydrate anesthesia. Therefore, these data indicate that chloral hydrate anesthesia produces profound changes in the physiological and pharmacological responses of central serotonergic neurons which are not predictable by examination of spontaneous activity alone. Furthermore, as discussed, it it not clear to what extent these confounding influences might generalize to other anesthetized or immobilized preparations. Thus, beyond the obvious advantage which allows for the study of relationships between neuronal activity and behavior, single unit studies conducted in awake, freely moving animals also may be of greater value for basic physiological and pharmacological studies.

Raphe unit activity in freely moving cats is altered by manipulations of central but not peripheral motor systems

Single unit activity of serotonergic neurons in the dorsal raphe nucleus of freely moving cats was recorded in experiments which manipulated central or peripheral motor systems. Unilateral microinjections of the cholinomimetic agent, carbachol, into the pontine tegmentum, produced muscle atonia. During these periods of drug-induced atonia, the activity of serotonergic neurons was reduced 97% below pre-drug baseline rates. In experiments where microinjections of carbachol did not produce muscle atonia, no significant change occurred in serotonergic unit discharge rate. Muscle tonus was also altered by systemic injections of mephenesin, a centrally acting muscle relaxant. A low dose of mephenesin (50 mg/kg) produced mild atonia which was correlated with a 16% reduction in serotonergic neuron discharge rate relative to pre-drug baseline. A higher dose of mephenesin (150 mg/kg) produced complete atonia, during which serotonergic unit activity was reduced by 68% below baseline firing rate. To distinguish between centrally and peripherally induced atonia, we injected either succinylcholine or dantrolene, systemically. These are both drugs whose muscle relaxant properties are known to be mediated by peripheral mechanisms. In neither case was a change in serotonergic unit discharge rate seen following drug-induced atonia. These data demonstrate that manipulation of central, but not peripheral, motor systems can profoundly affect the activity of serotonergic neurons of the dorsal raphe nucleus. Alternate hypotheses are also discussed.

Response of dopaminergic neurons in cat to auditory stimuli presented across the sleep-waking cycle

The response of dopaminergic neurons of the substantia nigra pars compacta to auditory clicks continuously presented across the sleep-wake cycle was studied in cats. The initial excitatory followed by inhibitory response to the click which occurred during quiet waking diminished as the cat progressed into slow-wave sleep and was absent during REM sleep. Upon awakening from REM sleep, dopamine neurons once again displayed an excitatory/inhibitory response to the clicks, implying that the decrease across the sleep-wake cycle was not attributable to long-term habituation.

Raphe neurons: firing rate correlates with size of drug response

Significant negative correlations were obtained between the spontaneous discharge rate during waking and the neural response to systemic injections of either 5-MeODMT or LSD for serotonergic neurons in the dorsal raphe nucleus, nucleus centralis superior, and nucleus raphe pallidus of unanesthetized and unrestrained cats. These data are discussed in terms of an hypothesis which accounts for both the rate of spontaneous activity of serotonergic neurons and the magnitude of their response to serotonin agonist drugs in terms of autoreceptor density on individual neurons.

Behavioral correlates of dopaminergic unit activity in freely moving cats

Single unit activity of dopaminergic neurons in the substantia nigra was recorded in freely moving cats under a variety of conditions. These neurons displayed their highest discharge rate during active waking (3.68 +/- 0.30 spikes/s), which was 20% greater than their discharge rate during quiet waking (3.07 +/- 0.20). Although these cells fired somewhat faster during active waking, their activity displayed no correlation with phasic EMG changes, and, in general, their activity showed little relationship to overt behavioral changes. As the cat progressed from quiet waking through slow-wave sleep and REM sleep there was no significant change in either the rate or pattern of firing of dopaminergic neurons. In addition, no correlation was observed between the activity of these neurons and either sleep spindles or PGO waves. These neurons did respond, however, to the repeated presentation of a click or light flash with excitation followed by inhibition, with no evidence of habituation. One of the most impressive changes in dopaminergic unit activity was a large decrease in association with orienting responses. This was seen in over 50% of the cells in which this relationship was examined. As the behavioral orientation habituated with repeated stimulus presentation, so did the associated dopaminergic unit suppression. In conclusion, dopaminergic neurons maintain a remarkably constant rate and pattern of firing across a variety of behaviors and states. However, this stability can be dramatically altered under special circumstances, such as during and following orienting responses.

Activity of serotonin-containing neurons in the nucleus raphe pallidus of freely moving cats

Serotonergic neurons within nucleus raphe pallidus (NRP) of freely moving cats initially were distinguished by their slow (less than 8 Hz), regular discharge and long duration (mean = 2.3 ms) action potentials. The activity of serotonergic NRP neurons was highest during active waking (mean = 4.85 +/- 0.37 spikes/s) and gradually slowed, with little change in firing pattern, during the transition from waking through slow wave sleep (middle of SWS: mean = 3.76 +/- 0.36 spikes/s). In REM sleep there was a precipitous decrease in firing rate (mean = 0.92 +/- 0.23 spikes/s) and loss of discharge regularity. Although there was no significant difference in firing rate between active and quiet waking, discharge rates were significantly increased during transient elevations of the EMG, but these rate increases usually were associated with specific motor behaviors only. The activity of serotonergic NRP neurons during SWS was not related to the occurrence of either sleep spindles in the cortical EEG or PGO waves recorded from the lateral geniculate nucleus. These neurons also were relatively unresponsive to phasic auditory or visual stimuli, with most of the neurons examined showing weak excitatory responses. Activity of all serotonergic NRP neurons tested was suppressed (mean = -81.3 +/- 4.3%) by the serotonergic agonist 5-methoxy-N,N-dimethyltryptamine (250 micrograms/kg, i.m.). The results of this study are compared with those previously reported for serotonergic neurons in the dorsal raphe nucleus of freely moving cats and the issue of homogeneity in central serotonergic systems is discussed.

Locomotor activity and ingestive behavior after damage to ascending serotonergic systems

The effects of electrolytic midbrain raphe lesions on ingestive behavior and locomotor activity of rats were compared to those produced by intracerebral injections of 5,7 dihydroxytryptamine (5,7 DHT) at various points along the ascending serotonergic pathways. Only electrolytic lesions of the median and/or dorsal raphe nuclei produced significant changes in food intake, water intake, body weight gain, and wheel running activity. Intracerebral injections of 5,7 DHT, a selective serotonergic neurotoxin, had no effect on any of these variables. However, 5,7 DHT induced lesions produced decreases in forebrain synaptosomal uptake of serotonin which were equivalent to, or greater than, those resulting from electrolytic lesions of the midbrain raphe nuclei. Failure of 5,7 DHT injections to replicate the behavioral changes resulting from electrolytic lesions of the midbrain raphe nuclei suggests that loss of ascending serotonergic projections was not responsible for the behavioral effects that followed the electrolytic lesions.

Medullary serotonergic neurons are insensitive to 5-MeoDMT and LSD

A comparison was made of the effects of 5-MeoDMT or LSD on serotonergic unit activity in the dorsal raphe nucleus (DRN) and nucleus raphe pallidus (NRP) of freely moving cats. NRP neurons were substantially less responsive than DRN neurons to both drugs. NRP neurons were unresponsive to behaviorally effective low doses of these drugs whereas the activity of DRN neurons was strongly depressed. These data are discussed in terms of autoregulatory control of serotonergic neurons.

Serotonergic innervation of the lateral hypothalamus: evidence from synaptosomal uptake studies

Uptake of tritiated serotonin by synaptosomes prepared from rat lateral hypothalamus was examined. Uptake of serotonin into lateral hypothalamic synaptosomes occurred by both saturable and non-saturable processes. The saturable process was a high affinity transport with kinetic parameters that agree closely with those previously reported for serotonin uptake into synaptosomes prepared from other brain regions. Fluoxetine, a selective inhibitor of uptake into serotonergic neurons, was a potent inhibitor of serotonin uptake into lateral hypothalamic synaptosomes. Desipramine and benztropine, noradrenergic and dopaminergic uptake inhibitors respectively, were much less effective. Damage to the ascending serotonergic system, by either electrolytic lesion of the dorsal or median raphe nucleus, or by 5,7 dihydroxytryptamine injections into the midbrain serotonergic pathways, significantly reduced the uptake of serotonin by lateral hypothalamic synaptosomes. Taken together, these data provide further evidence for a serotonergic terminal field within the lateral hypothalamus.

Raphe unit activity in freely moving cats: effects of phasic auditory and visual stimuli

The effects of phasic auditory or visual stimuli upon the single unit activity of serotonergic neurons within the dorsal raphe nucleus (DRN) were studied in freely moving cats. The predominant response to auditory stimulation (86% of the cells) was excitation, with a mean latency of 40 +/- 3 ms (S.E.M.) and a mean duration of 64 +/- 4 ms. This was typically followed by a longer period (206 +/- 32 ms) with unit activity below the baseline level. This did not appear to be a stimulus-induced inhibition of unit activity, however, since its duration closely corresponded to the normal interspike interval for that particular neuron. The response to repetitive auditory stimulation showed no evidence of habituation and was even present during sleep. A similar response, although generally of lesser magnitude, was evoked by a phasic visual stimulation in 64% of the cells tested. The mean latency for the response to visual stimulation was 53 +/- 4 ms, the mean duration of excitation was 76 +/- 7 ms, and the mean duration of the subsequent suppressed period was 239 +/- 37 ms. The response to the visual stimulus also showed no evidence of habituation. These data indicate that serotonergic neurons of the DRN are driven, with similar temporal characteristics, by stimuli in two different sensory modalities. We hypothesize that these similar effects are attributable to a common excitatory input.

Effects of adrenergic drugs on raphe unit activity in freely moving cats

Previous work has suggested that central noradrenergic neurons may have an important influence on the activity of serotonergic neurons located in the dorsal raphe nucleus. Pharmacological studies have indicated that an alpha -adrenergic input is necessary to maintain the activity of these raphe cells. This issue was examined in freely moving cats by studying the effects of adrenergic drugs on raphe unit activity. Systemic administration of the selective alpha 1-antagonists WB4101 (0.5 and 1.0 mg/kg) or prazosin (10 mg/kg), or the non-competitive antagonist phenoxybenzamine (10 mg/kg), produced strong behavioral effects but had little effect on raphe unit activity. A low dose of the alpha -agonist clonidine (0.05 mg/kg), which decreases adrenergic transmission, produced similar results. These same drugs also had negligible effects on the evoked responses of raphe units to auditory or visual stimulation. Administration of d-amphetamine, a catecholamine releaser, produced behavioral stereotypy but had no significant effect on the discharge of raphe units. These data suggest that the adrenergic influence on serotonergic raphe neurons is very small in the freely moving cat. This is in contrast to the reported complete suppression of unit activity produced by alpha -adrenergic blockade in the chloral hydrate anesthetized rat.

Dissociations between the effects of hallucinogenic drugs on behavior and raphe unit activity in freely moving cats

The hypothesis that the action of hallucinogenic drugs is mediated by a depression of the activity of brain serotonergic (raphe) neurons was tested by examining the behavioral effects of several hallucinogenic drugs while concurrently monitoring the activity of raphe neurons in freely moving cats. LSD produced a dose-dependent decrease in raphe unit activity and a dose-dependent increase in certain behaviors (e.g. limb flick and abortive groom), and the peak of the behavioral and unit changes were temporally correlated. However, there were three important dissociations between the behavioral and electrophysiological effects of LSD. Firstly, low doses of LSD produced only small decreases in raphe unit activity but significant behavioral changes. Secondly, the duration of LSD-induced behavioral changes significantly outlasted the depression of raphe unit activity. And thirdly, raphe neurons were at least as responsive to LSD during tolerance as they were in the nontolerant condition. Psilocin produced a dose-dependent decrease in raphe unit activity, while the behavioral changes were not dose-related. However, the peak behavioral changes corresponded to the maximal depression of raphe unit activity. The phenylethylamine hallucinogens, DOM and mescaline, both produced large behavioral changes but no overall effect on raphe neurons. Following administration of DOM or mescaline, some raphe units showed a significant increase, while some showed a significant decrease, and others showed no change in activity. Therefore, the phenylethylamine hallucinogens may exert a depressant effect upon a subset of serotonin-containing neurons, and an amphetamine-like excitatory effect upon another subset of these neurons. Consistent with previous studies, all hallucinogens produced a high concentration of slow waves in the cortical EEG. Following administration of LSD or psilocin, the appearance of slow waves in the EEG was often associated with a transitory decrease in unit activity, while this was not observed for the phenylethylamine hallucinogens. The present data, in conjunction with recent data from other laboratories, suggest that the serotonin hypothesis of hallucinogenic drug action should be re-evaluated.

Cats develop tolerance to d-amphetamine's effects upon locomotion and stereotyped behaviors

Administration of d-amphetamine sulfate (7.5 mg/kg i.p.) twice daily to cats produces an initial large increase in both locomotion and behavioral stereotypy. As this regimen continues beyond three days, however, both measures show large significant decreases. We hypothesize that this tolerance to the behavioral effects of amphetamine is attributable to the concomitant decrease (approx. 70%) in presynaptic stores of dopamine and norepinephrine.

Effects of damage to median raphe nucleus on ingestive behavior and wheel running activity

The effects of damage to the median raphe nucleus on the ingestive behavior and wheel running activity of rats were studied. This nucleus was damaged by the placement of either electrolytic or chemical (5,7-dihydroxytryptamine) lesions. After the placement of either type of lesion, wheel running activity was significantly decreased for the duration of the 8 week post-operative period. Although there were transient decreases in both food and water intakes after damage to the median raphe nucleus, these decreases did not appear to result from impairments in neuro-regulatory mechanisms. Rather, the decrease in food intake seemed to be related to the decrease in locomotor activity, and the decrease in water intake appeared to be linked to the decrease in food intake. In some rats with electrolytic lesions in the median raphe nucleus, the decrease in water intake was followed by a transient period of hyperdipsia.