Origin of 5-hydroxyindoleacetic acid in the spinl fluid.

5-Hydroxyindoleacetic acid applied intracisternally in cats does not appear in spinal fluid. Changes of 5-hydroxyindoleacetic acid concentration in the spinal cord are clearly reflected in the perfusate of the spinal subarachnoid space. Thus, 5-hydroxyindoleacetic acid in the spinal fluid originates from the spinal cord and reflects metabolic changes of 5-hydroxytryptamine in the spinal tissue, but not those in the brain.

Circadian ovulatory rhythms in Japanese quail: role of ocular and extraocular pacemakers.

Previous studies have shown that the circadian system of Japanese quail is composed of multiple photic inputs and multiple oscillators. Among these are extraretinal photoreceptors that mediate both circadian and photoperiodic responses and circadian pacemakers in the eyes that, via neural and hormonal outputs, help to maintain rhythmicity of central circadian clocks (presumably located in the suprachiasmatic area of the hypothalamus). Furthermore, a component of the central circadian system is influenced by reproductive hormones. Under certain conditions, the circadian system of female quail can be induced to split into two circadian components: one driven by ocular pacemakers and one driven by feedback from reproductive hormones. Importantly, ovulation is either inhibited or permitted as these two oscillators (or sets of oscillators) constantly change internal phase relationships with each other, suggesting an "internal coincidence" mechanism in the control of ovulation. The oviposition patterns of quail in light-dark (LD) cycles also support an internal coincidence mechanism. The authors tested the hypothesis that the ocular pacemakers are an important component of an internal coincidence mechanism controlling ovulation by examinig the effects of blinding by complete eye removal (EX), and the effects of eye-patching, on the body temperature and oviposition patterns of quail exposed to 24-h LD cycles. They also examined the effects of EX on quail exposed to continuous light (LL) and to continuous darkness (DD). Neither EX nor eye-patching affected the oviposition patterns of birds in LD. Furthermore, robust body temperature and oviposition rhythms continued in EX birds in LL, but body temperature became arrhythmic in DD with the cessation of ovulation. The results do not show a role for ocular pacemakers in the control of ovulation, but they do support the hypotheses that (1) entrainment of the central oscillators by extraretinally perceived light is sufficient to preserve a normal ovulatory pattern in LD in the absence of the ocular pacemakers, and (2) in LL, feedback of reproductive hormones onto the central oscillators is sufficient to organize the circadian system even in the absence of the ocular pacemakers. Whether or not the ocular pacemakers are normally involved in the control of ovulation is still an open question.

Formal properties of the circadian and photoperiodic systems of Japanese quail: phase response curve and effects of T-cycles.

A role for the circadian system in photoperiodic time measurement in Japanese quail is controversial. The authors undertook studies of the circadian and photoperiodic system of Japanese quail to try to identify a role for the circadian system in photoperiodic time measurement. The circadian studies showed that the circadian system acts like a low-amplitude oscillator: It is readily reset by light without significant transients, has a Type 0 phase response curve (PRC), and has a large range of entrainment. In fact, a cycle length that is often used in resonance protocols (LD 6:30) is within the range of entrainment. The authors employed T-cycle experiments; that is, LD cycles with 6- and 14-h photoperiods and period lengths ranging from 18 to 36 h to test for circadian involvement in photoperiodic time measurement. The results did not give evidence for circadian involvement in photoperiodic time measurement: T-cycles utilizing 6-h photoperiods were uniformly noninductive (that is, did not stimulate the reproductive system), whereas T-cycles utilizing 14-h photoperiods were inductive (stimulatory). A good match was observed between the phase-angles exhibited on the T-cycles employing 6-h photoperiods and the predicted phase-angles calculated from a PRC generated from 6-h light pulses.

Stereological analysis of alpha and beta zones of syncytiotrophoblast in human term placenta.

The investigations were carried out to attempt to define and analyze various quantitative structural parameters of syncytiotrophoblast in human term placenta, especially of its functionally active parts, that is alpha and beta zones. The results demonstrated the following: The arrangement of alpha and beta zones in the placenta as a whole is even and regionally independent. Beta zones prevail quantitatively. Alpha zones make up only 8% of the total volume, 18% of the total surface and 39% of the thickness of beta zones. Sexual dimorphism is shown by a significantly higher volume density (VVa)(P less than 0.002), total volume (Va)(P less than 0.05) and surface density (SVa) (P less than 0.025) of alpha zones in placentas of female newborns. The fetoplacental index is higher in male newborns. During the tenth lunar month the structure of syncytiotrophoblast is changed. Between the 38th and 39th week the volume and surface densities of alpha zones are significantly higher (P less than 0.01), and in the 40th week the volume density and total volume of beta zones prevail significantly (P less than 0.01).

Recent developments in the behavioral pharmacology of benzodiazepine (omega) receptors: evidence for the functional significance of receptor subtypes.

Recent research in molecular biology has demonstrated the complexity of GABAA receptors and shown that benzodiazepine (BZ-omega) receptor subtypes have a structural reality. It is therefore appropriate to ask whether the different pharmacological effects produced by benzodiazepines (anticonvulsant activity, anxiety reduction, motor incoordination, learning deficits, characteristic discriminative stimulus effects, tolerance and dependence) are associated with activity at different receptor subtypes. The present paper reviews the literature dealing with the behavioral effects of novel BZ (omega) receptor ligands relevant to the question of the functional significance of the BZ1 (omega 1) and BZ2 (omega 2) receptor subtypes. The only drugs currently available with a considerable degree of selectivity are alpidem and zolpidem. These compounds have relatively high affinity for GABAA receptors containing the alpha 1 subunit (corresponding to the BZ1 (omega 1) subtype) and very low affinity for receptors with the alpha 5 subunit (corresponding to one type of BZ2 (omega 2) receptor). Pharmacological effects observed with these, and other, less selective compounds allow several tentative conclusions to be drawn: (a) Little is known of the role of subtype selectivity in anxiolytic or amnestic effects but compounds with low intrinsic activity may reduce anxiety without giving rise to sedation or motor incoordination and BZ1 (omega 1) selective drugs appear to disrupt memory only at sedative doses; (b) Selectivity for BZ1 (omega 1) receptors may be associated with sleep-inducing activity but not with motor incoordination, suggesting that BZ2 (omega 2) receptors may be of particular importance in mechanisms of muscle relaxation; (c) The discriminative stimulus effects of different BZ (omega) receptor ligands are not identical and differences may be related to receptor selectivity; (d) Compounds with BZ1 (omega 1) selectivity and compounds with low intrinsic activity produce little or no tolerance and dependence. A wider range of selective compounds will be necessary to investigate these factors in detail and many different pharmacological profiles can be expected from drugs with selectivity and different levels of intrinsic activity.

Concentrations of putative neurovascular transmitters in major cerebral arteries and small pial vessels of various species.

The levels of noradrenaline, neuropeptide Y, 5-hydroxytryptamine, and substance P were measured and compared between the large arteries of the circle of Willis and the small cerebral vessels of the pia mater in the rat, rabbit, cat, and monkey. In all species, noradrenaline and neuropeptide Y concentrations were greater in the larger arteries than in small pial vessels. Noradrenaline concentrations were dramatically reduced following cervical sympathectomy, with the extent of diminution differing greatly in the various species; the effects of cervical ganglionectomy on neuropeptide Y concentrations were less pronounced. 5-Hydroxytryptamine concentrations in rats, cats, and rabbits were significantly greater in the small pial vessels, although measurable concentrations existed in the circle of Willis. In cats and monkeys, substance P was found in major arteries, but was not detectable at the level of the small pial vessels. The differences in the regional distribution of the various neurotransmitter candidates in the cerebrovascular bed may reflect their physiological significance.

Differential development of tolerance to the depressant effects of benzodiazepine and non-benzodiazepine agonists at the omega (BZ) modulatory sites of GABAA receptors.

In a previous study, it was found that both the benzodiazepine hypnotic, midazolam, and the imidazopyridine hypnotic, zolpidem, which has selective affinity for a sub-population of omega (benzodiazepine, BZ) modulatory sites of GABA(A) receptors, produced similar decreases in rates of food-reinforced lever pressing in rats. However, during 10 days of repeated administration, marked tolerance developed to the depressant effect of midazolam but little tolerance developed with zolpidem. It was found in the present study that, with a within-subject design similar to that used previously, tolerance developed to the response rate-decreasing activity of the benzodiazepine, triazolam and the cyclopyrrolone, zopiclone but not to that of the triazolopyridazine, CL 218,872. In another experiment, using a between-groups design, tolerance developed to the effect of midazolam, even if the injections were not associated with daily test sessions, providing no evidence for a drug-environment interaction. The lack of tolerance to zolpidem was confirmed in two experiments. There was little indication of tolerance to the depressant effect of zolpidem, even after 19 days administration of daily doses, up to 30 mg/kg, a dose 10 times greater than that which completely suppressed responding. These results showed that the extent to which tolerance develops to the effects of drugs with affinity for omega (BZ) modulatory sites can show wide variations which may be related to differences in mechanisms of action.

Discriminative stimulus properties of chlordiazepoxide and zolpidem. Agonist and antagonist effects of CGS 9896 and ZK 91296.

In previous studies the effects of CGS 9896, a pyrazoloquinoline ligand at benzodiazepine receptors, in rats trained to discriminate benzodiazepines from vehicle, have been variable. The present experiment confirmed that this compound produced responding on the drug-lever in rats trained to discriminate 5 mg/kg of chlordiazepoxide from saline, and showed that CGS 9896 did not antagonise the effect of chlordiazepoxide in this test. In contrast, CGS 9896 antagonised the stimulus properties of zolpidem (2 mg/kg), a non-benzodiazepine hypnotic, which displaces benzodiazepines from their binding sites. The drug CGS 9896 also antagonised responding on the drug-lever produced by chlordiazepoxide in rats trained with zolpidem. The beta-carboline, ZK 91296, produced effects similar to those of CGS 9896, giving rise to responding on the drug-lever in rats trained with chlordiazepoxide and antagonising the zolpidem cue. These results demonstrate the mixed agonist-antagonist effects of CGS 9896 and ZK 91296 and suggest that the stimulus properties of chlordiazepoxide and zolpidem may be mediated by different sub-types of benzodiazepine receptors.

Investigation of the development of tolerance to the actions of zolpidem and midazolam.

It is well established that tolerance can develop very rapidly to the behaviour-suppressing effects of benzodiazepines. In previous studies, however, the depressant action of zolpidem, a novel hypnotic acting at the benzodiazepine receptor, on operant behaviour in rats was maintained after many injections. An experiment was carried out, therefore, to compare the effects of acute and chronic administration of zolpidem and midazolam. Rats were trained to press a lever in standard operant test chambers to obtain 45 mg food pellets on an FR 10 schedule. Dose-response curves were then established, before, immediately after and 4 weeks after the daily administration of midazolam (3.0 mg/kg s.c.) or zolpidem (1.0 mg/kg) for 10 days. In confirmation of previous work, marked tolerance developed to the response-rate-decreasing effect of midazolam, the dose-response curve being shifted to the right by a factor of 6 and also flattened. No significant dissipation of this tolerance occurred during a period of 4-6 weeks. In contrast, repeated administration of zolpidem produced only a small degree of tolerance, the dose-response curve being shifted by a factor of two. There was little evidence for cross tolerance between the two drugs, zolpidem-treated rats being sensitive to a dose of midazolam and midazolam-treated rats sensitive to a dose of zolpidem. Although the explanation for the development of tolerance to midazolam is unknown, these results suggest that the mechanisms of action of midazolam and zolpidem in reducing response rates are different.

Further behavioural evidence for the selective sedative action of zolpidem.

Small doses of benzodiazepines stimulate behavioural output in experimental animals in a variety of situations. Zolpidem, which displaces benzodiazepines from their binding sites, however, has been shown to exert preferential sedative activity. In order to investigate whether small doses of zolpidem would also have stimulant effects, the actions of zolpidem and chlordiazepoxide were compared in three procedures which are sensitive to the behavioural-facilitating effects of benzodiazepines in rats. A small dose of chlordiazepoxide (3.0 mg/kg) increased locomotion in an open field whereas a large dose (30 mg/kg) suppressed this behaviour. Zolpidem (0.3-3.0 mg/kg) only decreased locomotion. The effects of both chlordiazepoxide and zolpidem were antagonised by flumazenil. Chlordiazepoxide (2.5-10 mg/kg) increased the intake of food in rats habituated to a daily feeding schedule but similar doses of zolpidem neither increased nor decreased the intake of food. Rates of punished operant responding were increased by chlordiazepoxide (3.0-30 mg/kg) but zolpidem (1.0-4.0 mg/kg) produced no such anti-punishment effect and suppressed responding at the large dose. These results show that zolpidem does not increase behavioural output in situations which are sensitive to the stimulant effects of benzodiazepines and further emphasize the selective sedative activity of this drug.

Repeated treatment with alpidem, a new anxiolytic, does not induce tolerance or physical dependence.

Alpidem is a new anxiolytic of imidazopyridine structure which has a high affinity for the omega 1 (BZ1) modulatory site of the GABAA receptor. The present study investigated whether tolerance and physical dependence develop after repeated treatment with alpidem, as is observed with benzodiazepines. Mice were given alpidem (100 mg/kg, p.o.) or diazepam (5 mg/kg, p.o.) twice daily for 10 consecutive days. Tolerance was assessed by measuring antagonism of pentylenetetrazole- and isoniazid-induced convulsions and bicuculline-provoked mortality, following repeated drug treatment. Decreases in the latency to isoniazid-induced convulsions and in the minimal convulsant dose of pentylenetetrazole were taken as an index of physical dependence and were evaluated at different times (3, 6, 14, 42, 67, 96 hr) after drug withdrawal or after flumazenil administration. In addition, changes in sensitivity to the convulsant effect of a beta-carboline (beta-CCM) were measured. Repeated treatment with diazepam produced tolerance to its anticonvulsant activities as indicated by shifts of the dose-response curves by a factor of 3-5. After discontinuation of diazepam treatment, spontaneous withdrawal occurred within 24 hr and lasted 67 hr as indicated by decreases in the threshold for convulsions induced by isoniazid and pentylenetetrazole. Flumazenil-induced withdrawal was observed in both isoniazid and pentylenetetrazole-induced convulsion models. Hypersensitivity of mice to the convulsant effect of beta-CCM also occurred. In contrast, repeated treatment with alpidem did not produce tolerance to its anticonvulsant effects and neither spontaneous nor flumazenil-induced withdrawal was observed in the pentylenetetrazole and isoniazid models. Moreover, withdrawal of alpidem did not induce any change in the convulsant activity of beta-CCM. These differences between alpidem and diazepam may be related to the low level of receptor occupancy during repeated treatment with alpidem because of its selectivity for omega 1 (BZ1) sites and to its moderate intrinsic activity.

Discriminative stimulus effects of alpidem, a new imidazopyridine anxiolytic.

Alpidem in an imidazopyridine derivative which binds selectively to the omega 1 (BZ1) receptor subtype. It is active in some, but not all, behavioural tests sensitive to benzodiazepine anxiolytics and has clinical anti-anxiety effects. However, in a previous study, it was shown that alpidem did not substitute for chlordiazepoxide in rats trained to discriminate this benzodiazepine. The present experiments were carried out to investigate the discriminative stimulus properties of alpidem in greater detail. In the first experiment rats learned to discriminate a dose of 10 mg/kg alpidem from saline. Acquisition of the discrimination was long and performance unstable. Chlordiazepoxide, clorazepate and zolpidem substituted only partially for alpidem but the effects of the training dose of alpidem were blocked by 10 mg/kg flumazenil. The second experiment established stimulus control more rapidly to a dose of 30 mg/kg alpidem. Alpidem induced dose-related stimulus control, and dose-related and complete substitution for alpidem was produced by zolpidem, abecarnil, CL 218,872, triazolam and suriclone. Partial substitution occurred with chlordiazepoxide, clorazepate and pentobarbital. In most cases, high levels of substitution were produced only by doses which greatly reduced response rates even though the training dose of alpidem produced only modest decreases in rates. Ethanol, buspirone and bretazenil produced very little substitution for alpidem and both flumazenil and bretazenil antagonised the effects of alpidem. In two further experiments alpidem was found to substitute for the stimulus produced by zolpidem (2 mg/kg) but not for that produced by ethanol (1.5 g/kg).(ABSTRACT TRUNCATED AT 250 WORDS)

The discriminative stimulus properties of zolpidem, a novel imidazopyridine hypnotic.

Zolpidem is a non-benzodiazepine hypnotic drug which displaces benzodiazepines from their binding sites in different brain structures. Previous work has demonstrated several differences between zolpidem and benzodiazepines, including differences between the stimulus properties of zolpidem and chlordiazepoxide. In the present study the discriminative stimulus properties of zolpidem were analysed by training rats to discriminate between this drug and saline. It was found that stimulus control developed readily with 2 mg/kg but not with 1 mg/kg zolpidem. The effect was dose-related, had a short duration of action and was antagonised by Ro 15-1788. Furthermore, stimulus control produced by zolpidem was associated with marked reductions in rates of responding. Injections of chlordiazepoxide, triazolam, lorazepam, zopiclone, CL 218,872 and pentobarbital produced dose-related responding on the zolpidem-associated lever but haloperidol did not. However, in general, the doses of those drugs which produced drug-lever responding also reduced response rates. It is possible that the above mentioned differences between the discriminative stimulus produced by zolpidem in rats and those produced by other sedatives may be due to a selective action of zolpidem on a sub-type of benzodiazepine binding site.

Effects of zolpidem, a new imidazopyridine hypnotic, on the acquisition of conditioned fear in mice. Comparison with triazolam and CL 218,872.

Benzodiazepines and other compounds which act at benzodiazepine binding sites have been shown previously to attenuate the acquisition of conditioned fear in rodents when administered before the acquisition session, an effect which may parallel the disruption of human memory produced by anxiolytics and sedatives. Such an action is usually, but not invariably, produced by doses which have direct behavioural depressant effects. The present study was carried out to extend previous work by investigating the effects of the hypnotic benzodiazepine triazolam and the nonbenzodiazepines zolpidem and CL 218,872 on the acquisition of learned fear in mice. All these drugs reduced locomotor activity shortly after injection. They also produced disruptions of the acquisition of learned fear. Triazolam exerted behavioural effects similar to those found previously with other benzodiazepines, the does which disrupted the acquisition of conditioned fear being similar to, or lower than, the doses which depressed locomotion. In contrast, the results indicated that zolpidem was more potent at reducing locomotion than at interfering with fear conditioning, a result which may reflect the preferential sedative action of zolpidem.

Circadian organization and the role of the pineal in birds.

All organisms exhibit significant daily rhythms in a myriad of functions from molecular levels to the level of the whole organism. Significantly, most of these rhythms will persist under constant conditions, showing that they are driven by an internal circadian clock. In birds the circadian system is composed of several interacting sites, each of which may contain a circadian clock. These sites include the pineal organ, the suprachiasmatic nucleus (SCN) of the hypothalamus, and, in some species, the eyes. Light is the most powerful entraining stimulus for circadian rhythms and, in birds, light can affect the system via three different pathways: the eyes, the pineal, and extraretinal photoreceptors located in the deep brain. Circadian pacemakers in the pineal and in the eyes of some avian species communicate with the hypothalamic pacemakers via the rhythmic synthesis and release of the hormone melatonin. Often the hypothalamic pacemakers are unable to sustain persistent rhythmicity in constant conditions in the absence of periodic melatonin input from the pineal (or eyes). It has also been proposed that pineal pacemakers may be unable to sustain rhythmicity in constant conditions without periodic neural input from the SCN. Significant variation can occur among birds in the relative roles that the pineal, the SCN, and the eyes play within the circadian system; for example, in the house sparrow pacemakers in the pineal play the predominant role, in the pigeon circadian pacemakers in both the pineal and eyes play a significant role, and in Japanese quail ocular pacemakers play the predominant role.

Selective antagonists of dopamine receptor subtypes differentially affect substance P levels in the striatum and substantia nigra.

Repeated administration to rats of SCH 23390, a specific antagonist of the D-1 dopamine receptor, produced an increase in the substance P immunoreactivity in the striatum but not in the substantia nigra, whereas similar treatment with sulpiride, a specific D-2 dopamine receptor antagonist, reduced the nigral but not the striatal content of the peptide. When the two antagonists were given together, the SCH 23390-induced increase in striatal substance P was significantly reduced. The SCH 23390-induced increase in striatal substance P was curtailed by concomitant administration of progabide, a selective gamma-aminobutyric acid (GABA) receptor agonist. These results suggest the existence in the nigro-striatal complex of two different substance P-containing neurons which are differentially regulated by the dopamine receptor subtypes and indicate a role of GABA in the action of SCH 23390.

[3H]Haloperidol labels brain dopamine receptors after its injection into the internal carotid artery of the rat.

Pulse injection of [3H]haloperidol (0.2 microCi; 0.003 microgram) into the internal carotid artery of the rat specifically labelled dopamine receptors in striatum and olfactory tubercle, as indicated by the kinetics of, and the effects of neuroleptic drugs on, the ligand disposition. The described method may prove useful for labelling brain receptors with ligands which readily cross the blood-brain barrier but which do not selectively mark their receptors if injected systemically.

Involvement of the D-2 dopamine receptor in the neuroleptic-induced decrease in nigral substance P.

Repeated treatment with, but not single administration of drugs which impair dopaminergic transmission produced a consistent reduction in substance P immunoreactivity in the rat substantia nigra. This effect appears to be related to the D-2 dopamine receptor function as the blockade of this receptor subtype by selective antagonists produced effects qualitatively similar to those produced by drugs lacking selectivity for different subclasses of dopamine receptors.

Progabide reverses the nigral substance P reduction induced by chronic impairment of dopaminergic transmission.

Repeated treatment with haloperidol or lesion of nigrostriatal dopaminergic neurons with 6-hydroxydopamine produced a reduction in substance P immunoreactivity in the rat substantia nigra. This reduction was reversed by the repeated administration of progabide, a selective GABA receptor agonist. As GABA inhibits substance P release, these results suggest that the reduction in nigral substance P levels was due to an increased liberation of the peptide probably related to deficient GABAergic function induced by impairment of striatal dopaminergic transmission.

The interaction between zolpidem and beta-CMC: a clue to the identification of receptor sites involved in the sedative effect of zolpidem.

The interaction of beta-CMC, an amino beta-carboline recently described as a selective antagonist of the sedative effect of diazepam, with zolpidem, an imidazopyridine hypnotic, which like beta-CMC binds preferentially to the omega 1 (BZ-1) site of the GABA benzodiazepine chloride channel receptor complex, was investigated. In mice, beta-CMC antagonized the effect of zolpidem against isoniazid-induced convulsions without affecting its activity against convulsions induced by pentylenetetrazole or electroshock. beta-CMC also antagonized the decrease in locomotor activity and the impairment in muscle strength provoked by zolpidem. In rats trained to discriminate zolpidem, beta-CMC antagonized both the interoceptive stimulus and the decrease in the rate of lever pressing produced by zolpidem. This selective antagonism, inhibition of effects of zolpidem exerted by low doses (locomotor activity and isoniazid-induced convulsions) as well as effects produced by high doses (muscle strength) but not those provoked by intermediate doses (pentylenetetrazole and electroshock-induced convulsions), could not be explained by a receptor occupancy hypothesis. These results suggest that the anticonvulsant and sedative effects of zolpidem do not involve the same receptor subtype and that the hypnoselective properties of zolpidem may be linked to its selectivity for the omega 1 (BZ-1) site of the GABAA receptor.