Latent inhibition in an insect: the role of aminergic signaling.

Latent inhibition (LI) is a decrement in learning performance that results from the nonreinforced pre-exposure of the to-be-conditioned stimulus, in both vertebrates and invertebrates. In vertebrates, LI development involves dopamine and serotonin; in invertebrates there is yet no information. We studied differential olfactory conditioning of the proboscis extension response in the honeybee Apis mellifera, and we compared LI in individuals treated with antagonists of biogenic amines (dopamine, octopamine, and serotonin). An antagonist of octopamine receptors and two antagonists of serotonin receptors showed LI disruption. We thus provide evidence that serotonin would participate in the regulation of LI in honeybees.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. 4. Opioid receptor binding properties of 8-[N-(4'-phenyl)-phenethyl)carboxamido] analogues of cyclazocine and ethylketocycalzocine.

The synthesis and evaluation of a series of aryl-containing N-monosubstituted analogues of the lead compound 8-carboxamidocyclazocine were performed to probe a putative hydrophobic binding pocket of opioid receptors. High binding affinity to mu, kappa, and delta opioid receptors was observed for the 8-[N-(4'-phenyl)-phenethyl)carboxamido] analogue.

Differential neuropharmacological effects of mu, kappa and sigma opioid agonists on cortical EEG power spectra in the rat. Stereospecificity and naloxone antagonism.

The study was designed to determine and compare the acute effects of the enantiomers of mu, kappa and sigma opioid agonists on the cortical EEG with the spectral analysis technique. The relative ability of naloxone to antagonize such effects was also assessed. Adult female Sprague-Dawley rats were implanted with chronic cortical EEG and temporalis muscle EMG recording electrodes, and with permanent indwelling external jugular cannulae. (-)-Methadone(mu agonist) produced increases in spectral power over the zero to 10Hz range, while (-)-ketocyclazocine (kappa agonist) produced increases in the 5-8 Hz band as a predominant peak. The(+) enantiomers of methadone and ketocyclazocine were inactive. The drug (+)-SK-10,047 (sigma agonist), produced a predominant spectral peak in the 7-9 HZ band that was associated with behavior that suggested psychotomimetic effects. The effects of morphine (mu agonist) on EEG and EEG power spectra were more sensitive to antagonism by naloxone than those produced by ketocyclazocine. The effects of (+/-)-SKF-10,047 and (+)-SKF-10,047 were not antagonized by 10 mg/kg of naloxone, while the effects of (-)-SKF-10,047 were partially antagonized by 10 mg/kg of naloxone. These findings further delineate the specificity of the differential effects of mu, kappa and sigma opioid agonists on the EEG and EEg power spectra in the rat.

Similar anticonvulsant, but unique, behavioural effects of opioid agonists in the seizure-sensitive Mongolian gerbil.

Opioid agonists were used to investigate the modulation of seizures mediated by mu, kappa and delta opiate receptors in the seizure-sensitive Mongolian gerbil. Morphine (1.0-25 mg/kg, s.c.) were used as prototypic agonists for mu, kappa and delta opiate receptors. Each opioid decreased the incidence and severity of the seizure as compared to control values. The anticonvulsant effects of morphine (10 mg/kg, s.c.) and ketocyclazocine (0.5 mg/kg, s.c.) were reversed by naloxone (1.0 mg/kg, s.c.), while the anticonvulsant effects of N-allylnormetazocine (2 mg/kg, s.c.) were not significantly changed by naloxone. Additionally, abnormal behavior was observed following administration of the opioids. Morphine (10 mg/kg, s.c.) produced excitation and hyperresponsiveness with intermittent cataleptic-like states. Ketocyclazocine (10 mg/kg, s.c.) predominantly produced a stuporous, immobile state, accompanied by some loss of posture. N-allylnormetazocine (10 mg/kg, s.c.) produced ataxia and stereotypic side-to-side head nodding . Naloxone was able to reverse the behavioral effects produced by morphine and ketocyclazocine but not those produced by N-allylnormetazocine. The data presented are consistent with earlier studies which demonstrated the anticonvulsant effects of beta-endorphin in the gerbil. This study further suggests that opioids have a protective role against seizure activity in the gerbil and the opioid anticonvulsant effect is not specific to one type of opioid agonist.

Synthesis and opioid receptor affinity of morphinan and benzomorphan derivatives: mixed kappa agonists and mu agonists/antagonists as potential pharmacotherapeutics for cocaine dependence.

This report concerns the synthesis and preliminary pharmacological evaluation of a novel series of kappa agonists related to the morphinan (-)-cyclorphan (3a) and the benzomorphan (-)-cyclazocine (2) as potential agents for the pharmacotherapy of cocaine abuse. Recent evidence suggests that agonists acting at kappa opioid receptors may modulate the activity of dopaminergic neurons and alter the neurochemical and behavioral effects of cocaine. We describe the synthesis and chemical characterization of a series of morphinans 3a-c, structural analogues of cyclorphan [(-)-3-hydroxy-N-cyclopropylmethylmorphinan S(+)-mandelate, 3a], the 10-ketomorphinans 4a,b, and the 8-ketobenzomorphan 1b. Binding experiments demonstrated that the cyclobutyl analogue 3b [(-)-3-hydroxy-N-cyclobutylmethylmorphinan S(+)-mandelate, 3b, MCL-101] of cyclorphan (3a) had a high affinity for mu, delta, and kappa opioid receptors in guinea pig brain membranes. Both 3a,b were approximately 2-fold more selective for the kappa receptor than for the mu receptor. However 3b (the cyclobutyl analogue) was 18-fold more selective for the kappa receptor in comparison to the delta receptor, while cyclorphan (3a) had only 4-fold greater affinity for the kappa receptor in comparison to the delta receptor. These findings were confirmed in the antinociceptive tests (tail-flick and acetic acid writhing) in mice, which demonstrated that cyclorphan (3a) produced antinociception that was mediated by the delta receptor while 3b did not produce agonist or antagonist effects at the delta receptor. Both 3a,b had comparable kappa agonist properties. 3a,b had opposing effects at the mu receptor: 3b was a mu agonist whereas 3a was a mu antagonist.

Opiates and medial hypothalamic knife cuts cause hyperphagia through different mechanisms.

Several experiments were performed to determine whether the hyperphagia caused by medial hypothalamic knife cuts and that induced by opiate agonists are mediated by a common mechanism. In the first set of experiments, male Sprague-Dawley rats were given bilateral parasagittal medial hypothalamic knife cuts or a sham procedure and fed a high-fat Crisco-chow diet. Knife-cut and sham-operated rats were approximately equally sensitive to the suppressive effects of naloxone on food intake. The kappa opiate receptor agonist ketocyclazocine generally increased daytime food intake in sham-operated rats; in contrast, the normal hyperphagia of knife-cut rats was in most cases either unchanged or decreased by ketocyclazocine. In a second set of experiments, neither diet composition nor hypothalamic knife cuts significantly affected the feeding responses to naloxone or the stimulatory effects of the kappa agonist butorphanol tartrate. It was hypothesized that the differential effects of ketocyclazocine in knife-cut and sham-operated rats are a consequence of the sedative effects of the drug combined with the elevated baseline of the knife-cut subjects. This hypothesis was supported by a third experiment, in which ketocyclazocine also reduced nocturnal intake in unoperated rats and butorphanol increased intake. That feeding responses to naloxone and butorphanol were essentially unchanged by hypothalamic knife cuts suggests that the opioid feeding system is independent of the longitudinal feeding inhibitory pathway believed to be involved in knife-cut-induced hyperphagia.

Interactions between narcotic agonists, partial agonists andd antagonists evaluated by punished an unpunished behavior in the rat.

The effects of morphine, ketocyclazocine, cyclazocine, and SKF-10,047 were tested alone and in conjunction with naltrexone or naloxone, in rats responding under a multiple fixed-interval 3-min schedule of food presentation. Under this paradigm, electric shock was delivered on a fixed-ratio schedule for responses occurring during alternate schedule components. All of the drugs (except naltrexone and naloxone) decreased average rates of responding maintained by the unpunished component in a dose-dependent manner. The rate-decreasing effects of morphine and ketocyclazocine were antagonized by naltrexone. The rate-decreasing effects of cyclazocine were only slightly reversed by the antagonists, while those effects of SKF-10,047 were not affected by naltrexone. In some animals, certain doses of SKF-10,047 increased unpunished responding. This rate-increasing effect was antagonized by naltrexone. Morphine, ketocyclazocine, cyclazocine, and SKF-10,047 increased responding that was suppressed by electric shock, and these increases were antagonized by naltrexone and naloxone. Thus, the antagonism of opiate effects by narcotic antagonists depends in part on the behavior being evaluated.

Stimulation of food intake following opiate agonists in rats but not hamsters.

The proposed mu and kappa opiate receptor agonists morphine and ketocyclazocine, as well as meperidine, were compared for their ability to stimulate feeding and drinking by male rats and hamsters that were not deprived of food or water. Morphine (8.0 mg/kg) and ketocyclazocine (0.5-4.0 mg/kg), but not meperidine (0.5-64.0 mg/kg), increased 3-h food intake by rats. By 6 h the hyperphagic responses were less pronounced. However, 6-h water intake was increased by all three agonists. In contrast to rats, hamsters failed to increased food or water intake over an 8-h period following morphine (6.25-800 mg/kg), ketocyclazocine (0.25-16.0 mg/kg), or meperidine (1.0-128 mg/kg) administration. Thus, kappa or mu opiate receptors may mediate the observed hyperphagic effect of opiate agonists on rat food intake. In addition, these results are consistent with our earlier suggestion that hamsters lack an opiate-sensitive feeding system.

Kappa opioid receptor-mediated analgesia in the developing rat.

The prototypic kappa opiate ketocyclazocine produced robust analgesia in 10-day-old rats in the tail-flick nociceptive test. The kappa-opiate behavioral response coincided with the onset of a rapid rise to adult levels in brain kappa receptor site density. In contrast, morphine (prototypic mu opiate) was without marked effect until 14 days of age. The period of rapid mu receptor increase did not take place until days 14-16, which was after kappa receptor levels had already plateaued. Further, there was no or incomplete cross-tolerance between ketocyclazocine and morphine at 14 days of age. The present study, therefore, establishes a role for the kappa binding site in thermal analgesia in the tail flick test and differentiates its ontogenetic pattern from that of the mu receptor.

The effects of tifluadom and ketazocine on behaviour, dopamine turnover in the basal ganglia and local cerebral glucose utilization of rats.

The purpose of the present study was to evaluate the interrelation between behavioural effects of kappa-opiates and cerebral neurochemical correlates in rats. Administration of the kappa-opiates tifluadom (2.5 mg/kg i.p.) or ketazocine (5 mg/kg i.p.) caused a marked initial decrease in locomotor activity lasting about 15-20 min, followed by an increase in locomotor activity at about 40 min after drug administration. At 15 min after i.p. injections of the same drugs 3,4-dihydroxyphenylacetic acid concentrations, measured by HPLC, were slightly increased in the nucleus accumbens, but unchanged in the striatum; dopamine concentrations were unchanged in both regions. The rates of glucose utilization, determined by quantitative [14C]2-deoxyglucose autoradiography, were mainly unchanged except for the nucleus accumbens, which showed an increased glucose utilization after both drugs given i.v. Tifluadom also decreased rates of glucose utilization in the caudate nucleus and parietal, sensorimotor, olfactory and frontal cortices. The above-mentioned effects on behaviour and local cerebral glucose utilization could be prevented by naloxone (3 mg/kg). The data suggest that changes in locomotor activity, neurotransmitter metabolism and neuronal activity in the nucleus accumbens are interrelated and that opiate-induced akinesia is mediated via the nucleus accumbens.

Peptide and non-peptide opioid-induced hyperthermia in rabbits.

Intracerebroventricular administration of all three prototype non-peptide opioid receptor (mu, kappa and sigma) agonists, morphine, ketocyclazocine and N-allyl-normetazocine (SKF 10,047) induced hyperthermia in rabbits. Similar administration of peptide opioids like beta-endorphin (BE), methionine-enkephalin (ME) and its synthetic analogue D-ala2-methionine-enkephalinamide (DAME) also caused hyperthermia. As expected, the synthetic enkephalin DAME was more potent than the parent enkephalin. Of the three anion transport systems (iodide, hippurate and liver-like or L) present in the choroid plexus, it is suggested that only the L transport system seems to be important to ventricular inactivation of BE and DAME since iodipamide (an inhibitor of the L transport system) augmented the hyperthermia produced by BE and DAME. Prostaglandins (PG) and norepinephrine (NE) were not involved in peptide and non-peptide opioid-induced hyperthermia because a PG synthesis inhibitor, indomethacin, and an alpha-adrenergic receptor blocker, phenoxybenzamine, had no thermolytic effect on them. Likewise cAMP was not required since a phosphodiesterase inhibitor, theophylline, did not accentuate the hyperthermia due to peptide and non-peptide opioids. Naloxone-sensitive receptors were involved in the induction of hyperthermia by morphine. BE, ME and DAME since naloxone attentuated them. In contrast, the hyperthermic response to ketocyclazocine and SKF 10,047 were not antagonized by naloxone.

The influence of opiate agonists on day-night feeding rhythms in young and old mice.

Daily rhythms of feeding behavior and responses to ketocyclazocine, morphine and naloxone were measured in young (1-2 months) and old (24-30 months) male CF-1 mice. All of the mice consumed more food at night than in the day-time, though this nocturnal peak was markedly reduced in the old animals, who consumed more in the day. The young mice also displayed a significant nocturnal enhancement in ketocyclazocine- and morphine-stimulated feeding. This day-night rhythm in ingestive responses was absent in the old mice. In comparison to the young mice, the opiate-stimulated food consumptions of the old animals were reduced at all times. Additionally, the old animals failed to show any day-night variations in the suppressive effects of naloxone on deprivation-induced food intake that were displayed by the young animals.

Effects of neonatal spinal cord serotonin depletion on opiate-induced analgesia in tests of thermal and mechanical pain.

There is considerable evidence that serotonin (5-HT) is involved in the analgesic actions of various opiates. However, it is less clear which opioid receptor types interact with these descending systems and whether the various monoaminergic pathways are specific for different types of nociceptive signals. In the present study we lesioned the spinal cord serotonin pathways by neonatal spinal injections of 5,7-dihydroxytryptamine (5,7-DHT) and tested the analgesic effects of morphine and ketocyclazocine one and two weeks later using both mechanical and thermal noxious stimuli. The treatment depleted spinal cord serotonin by more than 90% while not affecting norepinephrine levels. The effects of morphine were greatly attenuated in the depleted animals when the thermal noxious stimulus was applied. The analgesic actions of morphine were only slightly affected when the mechanical stimulus was applied. The effects of ketocyclazocine were not reduced by the treatment. The results further buttress the conclusion that at least part of morphine's analgesic effects are mediated by descending serotonin systems and that these systems are primarily effective against a thermal stimulus. The data suggest that non-5-HT brainstem system(s) are involved in morphine-induced analgesia to a mechanical noxious stimulus.

Morphine- and ketocyclazocine-induced analgesia in the developing rat: differences due to type of noxious stimulus and body topography.

Patterns of morphine- and ketocyclazocine-induced analgesia in limb withdrawal and tail-flick tests of thermal and mechanical nociception were examined in the preweanling rat. In the forepaw test, morphine was more effective than ketocyclazocine with both thermal and mechanical stimuli. Both drugs first induced analgesia between 3 and 5 days of age. In the tail-flick test, ketocyclazocine-induced analgesia preceded morphine's effects against both thermal and mechanical stimuli by several days. Ketocyclazocine produced robust analgesia between 7 and 10 days of age, while the effects of morphine did not peak until day 14. In the hindpaw, morphine was more effective than ketocyclazocine against a higher intensity mechanical stimulus, while ketocyclazocine was more effective against a lower intensity mechanical stimulus. Morphine-induced analgesia was reversed by lower doses of naloxone than was ketocyclazocine-induced analgesia, regardless of body part tested, against all noxious stimuli. These findings demonstrate differences in morphine- and ketocyclazocine-induced analgesia that are dependent upon age, body topography, stimulus type and intensity and imply different physiologic roles of mu- and chi-opioid receptors in analgesia.

Analgesic effects of intraventricular and intrathecal injection of morphine and ketocyclazocine in the infant rat.

Little is known of the neural bases of analgesia in immature animals. This experiment examined the effects of intracerebroventricular (i.c.v.) and intrathecal (i.t.) administration of morphine or ketocyclazocine in tests of antinociception in rats aged 3 to 14 days of age. Analgesia tests were conducted using both thermal and mechanical (pressure) noxious stimuli applied to the forepaw, hindpaw or tail. In the 3-day-old morphine-injected i.c.v. produced analgesia in the forepaws when either the mechanical or thermal noxious stimulus was used. There was no effect when the hindpaw or tail was tested. At 10 days of age, when the mechanical stimulus was used, morphine was analgesic in tests on all three appendages but was only effective in the forepaw when the thermal stimulus was used. Morphine was fully effective in all tests with both stimuli at 14 days of age. Ketocyclazocine had no consistent effect when given i.c.v. When injected i.t., morphine produced analgesia in the forepaws in the thermal test at 4 days of age and in all appendages by 10 days. When the mechanical test was used, morphine was effective in all appendages at all ages tested. Ketocyclazocine was analgesic at all appendages for the mechanical stimulus at all ages but was only transiently effective in the thermal test. The results demonstrate differential development of analgesia mediated at different levels of the neural axis and are consistent with the development of descending inhibitory that may mediate analgesia induced by i.c.v. injections of morphine. Neural mechanisms that are involved in the analgesic effects of these drugs against the two types of stimuli are also developmentally distinct.

A kappa-selective opioidergic pathway is involved in the reversal of a behavioural effect of adrenalectomy.

We have shown previously that adrenalectomized rats are immobile for only approximately 30% of a 5 min retest period, 24 h after an initial 15 min swimming exposure, compared with approximately 70% immobility for intact animals. The administration of ketocyclazocine, dynorphin-(1-17) or [Met5]enkephalin[Arg6,Phe7] immediately after initial exposure reversed the effect of adrenalectomy, whereas equimolar doses of morphine sulphate, [D-Ala2,D-Leu5]enkephalin and dynorphin-(1-8) were inactive. MR2266, a kappa-selective partial agonist/predominant antagonist, did not reverse immobility but antagonized the reversing effect of ketocyclazocine. In conjunction with our previous studies, we interpret these data to show that one of the opioidergic pathways for the incorporation of information post-stress is kappa-selective. This kappa selectivity in turn suggests a possible physiological role for prodynorphin-derived peptides in memory.

The forced swimming test: effects of glucose administration on the response to food deprivation and adrenalectomy.

Rats food deprived for 24 h prior to a 15 min swimming test have no difficulty in acquiring the immobile response but showed significantly reduced levels of immobility (40%) on retest compared with controls (70%). This effect of food deprivation was reversed, by glucose (100 mg/kg), dexamethasone (6 micrograms/rat) and ketocyclazocine (25 micrograms/rat). Adrenalectomised animals also acquire but cannot retain the immobile response, however, adrenalectomised rats given 1000 mg/kg glucose within 2 h of the initial swimming test are immobile for 75-85% of the retest period. We interpret these findings as suggesting a complex interplay of endocrine and metabolic factors are necessary for retention of the behavioural response.

The effect of the opioid-benzodiazepine, tifluadom, on ingestive behaviors.

A large body of evidence has suggested a role for the endogenous opiates and their receptors in the regulation of appetite. In this study, we report on the effects of tifluadom, a noval opiate with a benzodiazepine-like structure and preferential activity at the kappa opiate receptor, on ingestive behaviors. Tifluadom increases food intake in rats without altering water intake. Tifluadom's effect on feeding is more potent than that of morphine or ketocyclazocine and equivalent to that of butorphanol. The effect is partially resistant to naloxone antagonism. Tifluadom is more potent when administered subcutaneously than when given intraperitoneally. These data provide further support for the concept that kappa opiate receptors represent an important component of the natural feeding drive.

The thyroadrenal axis, food deprivation and retention of a behavioural response.

The effects of adrenalectomy on retention of the immobile response in the Porsolt swimming rat test are equally reversed by dexamethasone, ketocyclazocine and thyroxine; the effects of hypothyroidism are similarly equally well reversed by all three agents, or by adrenalectomy. Animals food deprived for 24 h lose the response, but retain it after 48 h food deprivation; the latter effect is blocked by adrenalectomy. These counterintuitive findings suggest hitherto unrecognized commonalities and/or interactions in the metabolic effects of the thyroid and adrenal glands.

The topography of cholinergic transmission in the mechanism of drug action at muscarinic synapses of the guinea-pig ileum.

The pharmacology of cholinergic neurogenic responses evoked by the participation of only the endings of axon terminals was compared to that of responses evoked by participation of the more proximal parts of the terminals also. Myenteric plexus-longitudinal muscle strips of the guinea-pig ileum were drawn through narrow orifices in 2 rubber membranes dividing a bath into 3 separate compartments. Oral segments were stimulated electrically by single impulses or by trains and local neurogenic contractions were evoked. The contractions of the aboral segment due to nerve impulses transmitted from the oral segment via the middle segment were also recorded. The opioid ligands ketocyclazocine and [D-Ala2,MePhe4,Met(O)5-ol]enkephalin and noradrenaline inhibited the twitches of the aboral segment evoked by oral segment stimulation more than the local twitches of the oral segment when these agents were applied directly to the respective compartments. The twitches of the aboral segment were also inhibited by the application of these drugs into the middle compartment adjusted to 10 mm width. Verapamil and the alkaline earth metal ions cobalt and lanthanum had similar effects. 4-Aminopyridine increased twitch amplitude more in the aboral segment than in the oral segment when applied directly; similar effects in the aboral segment were seen when the agents were applied to the middle compartment. The action of atropine, papaverine, d-tubocurarine and prostigmine did not discriminate between twitches in the oral and aboral segment when applied directly and all drugs except prostigmine were without effect when applied to the middle compartment.(ABSTRACT TRUNCATED AT 250 WORDS)