Multi-dimensional analyses of behavior in mice treated with U-50,488H, a purported kappa (non-mu) opioid agonist

The effects of U-50, 488H (trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl ]-benzeneacetamide, methane sulfonate, hydrate), a purported selective kappa (non-mu) opioid agonist on spontaneous locomotor activity were investigated using a multi-dimensional behavioral analyzer (Animex II). U-50,488H (1 mg/kg) failed to affect behavior in mice, however, 3 mg/kg significantly reduced rearing and grooming. In addition, 10 mg/kg markedly reduced linear locomotion, rearing and grooming. The behavioral depression induced by U-50,488H (10 mg/kg) was reversible by the opioid antagonist Mr2266 (10 mg/kg). These results suggest that the selective activation of the kappa (non-mu) opioid receptor by U-50,488H decreases linear locomotion, rearing and grooming in mice.     

Involvement of kappa-opioid receptors and sigma receptors in memory function demonstrated using an antisense strategy

Although antinociceptive effects of U-50,488H (trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl] cyclohexyl) benzeneacetamide methanesulfonate and (-)-pentazocine have been reported to influence kappa-opioid receptors, the involvement of kappa-opioid receptors in learning and/or memory is still controversial. We have recently reported that the memory improving effect of (-)-pentazocine was antagonized by sigma1 receptor antagonist. In this study, we examined the effects of several antisense oligodeoxynucleotides (antisenses) to kappa1-opioid receptors and sigma1 receptor on memory and nociceptive function. Male ddY mice were treated subcutaneously (s.c.) with scopolamine (1.65 mumol/kg) and/or test drugs 30 min before a Y-maze test. U-50,488H significantly improved the scopolamine-induced impairment of spontaneous alternation behavior. Twenty micrograms of antisense targeting exons 2 and 3 of the kappa1-opioid receptor significantly reversed the effects of U-50,488H, but antisense targeting exon 1 and mismatch sense did not. The antisense targeting exon 3 was most effective. These antisenses themselves did not affect normal mice, indicating that kappa1-opioid receptors do not tonically regulate memory function. All three antisenses equally prevented U-50,488H-induced antinociceptive effects in the acetic-acid-induced writhing test. Pretreatment with antisense targeting sigma1 receptors (AS-sigma1) completely prevented the memory-improving effects of (-)- and (+)-pentazocine, although U-50,488H ameliorated the scopolamine-induced impairment of spontaneous alternation behavior in AS-sigma1-treated mice. These results suggest that kappa1-opioid receptors containing different exons have a distinct function in memory and nociceptive functions. Furthermore, kappa-opioid receptors agonist showing analgesic effects act on kappa-opioid receptors or sigma receptors and play important roles only when memory function is impaired, but the two neuronal systems regulate memory function independently.     

Differential effects of central injections of D1 and D2 receptor agonists and antagonists on male sexual behavior in Japanese quail

A key brain site in the control of male sexual behavior is the medial pre‐optic area (mPOA) where dopamine stimulates both D1 and D2 receptor subtypes. Research completed to date in Japanese quail has only utilized systemic injections and therefore much is unknown about the specific role played by dopamine in the brain and mPOA in particular. The present study investigated the role of D1 and D2 receptors on male sexual behavior by examining how intracerebroventricular injections and microinjections into the mPOA of D1 and D2 agonists and antagonists influenced appetitive and consummatory aspects of sexual behavior in male quail. Experiments 1 and 2 investigated the effects of intracerebroventricular injections at three doses of D1 or D2 agonists and antagonists. The results indicated that D1 receptors facilitated consummatory male sexual behavior, whereas D2 receptors inhibited both appetitive and consummatory behaviors. Experiment 3 examined the effects of the same compounds specifically injected in the mPOA and showed that, in this region, both receptors stimulated male sexual behaviors. Together, these data indicated that the stimulatory action of dopamine in the mPOA may require a combined activation of D1 and D2 receptors. Finally, the regulation of male sexual behavior by centrally infused dopaminergic compounds in a species lacking an intromittent organ suggested that dopamine action on male sexual behavior does not simply reflect the modulation of genital reflexes due to general arousal, but relates to the central control of sexual motivation. Together, these data support the claim that dopamine specifically regulates male sexual behavior.     

Effect of dizocilpine (MK-801) on analgesia and tolerance induced by U-50,488H, a κ-opioid receptor agonist, in the mouse

The effect of dizocilpine (MK-801), anN-methyl-D-aspartate (NMDA) receptor antagonist, on the analgesic response to U-50,488H, a κ-opioid receptor agonist, and tolerance to the analgesic effect of U-50,488H was determined in mice. The doses of MK-801 used were 0.03–0.30 mg/kg, whereas U-50,488H was administered at a dose of 25 mg/kg. Intraperitoneal (i.p.) administration of U-50,488H (25 mg/kg) produced analgesia as evidenced by the delay in the tail-flick latency in the mouse and lasted for a period of 240 min. MK-801 (0.03–0.30 mg/kg, i.p.) given 30 min prior to the injection of U-50,488H did not modify U-50,488H-induced analgesia. Twice daily administration of U-50,488H (25 mg/kg) for 9 days produced tolerance to its analgesic action. Administration of MK-801 (0.03 and 0.10 mg/kg) injected 30 min before each injection of U-50,488H prevented the development of tolerance to its analgesic effect. The higher dose, 0.3 mg/kg, of MK-801 had a minimal effect on U-50,488H tolerance. It is concluded that MK-801 in doses which do not affect U-50,488H-induced analgesia blocks the development of tolerance to its analgesic action in mice. These studies suggest that NMDA receptors play a crucial role in the development of tolerance to κ-opioid agonist in mice.     

U-50,488H inhibits dynorphin and glutamate release from guinea pig hippocampal mossy fiber terminals.

The selective kappa opioid agonist U-50,488H was tested for its ability to modulate the potassium-induced rise of cytosolic Ca2+ in, and transmitter release from, guinea pig hippocampal mossy fiber synaptosomes. U-50,488H dose dependently inhibited the potassium-induced rise in synaptosomal free Ca2+ levels. This inhibition was attenuated by the selective kappa opioid antagonist nor-binaltorphimine, but was insensitive to naloxone and the sigma opioid antagonist ICI 174,864. U-50,488H also dose dependently depressed the potassium-induced release of L-glutamate and dynorphin B-like immunoreactivity from mossy fiber synaptosomes in a nor-binaltorphimine-sensitive manner. This is the first report to confirm the presence of a presynaptic kappa opioid receptor in the hippocampal mossy fiber-CA3 synapse and the nature of its influence on neurotransmitter release. The present results may be used to suggest that endogenous dynorphin peptides interact with this kappa opioid receptor to autoregulate the excitatory mossy fiber synaptic input.     

U-50,488, a selective kappa opioid agonist: Comparison to other reputed kappa agonists

1. U-50,488 is a structurally novel, non-mu opioid. In the present experiments it was compared to the reputed kappa opioid agonists, ketazocine, ethylketocyclazocine and bremazocine as regards analgesic cross tolerance to morphine and U-50,488, antagonism of analgesia by naloxone and MR-2266 (in vivo pA2 determination), and narcotic antagonist properties (antagonism of morphine analgesia and precipitation of abstinence in morphine-dependent mice). 2. The analgesic mechanism of bremazocine was similar to that of U-50,488 but the former compound had, in addition, considerable mu-antagonist activity. The analgesic mechanisms of the ketazocines were less selective; both shared both mu and kappa agonist properties. U-50, 488, however, had no such mu agonist or antagonist effects and thus is a more selective kappa agonist. 3. This compound and its congeners may prove useful in the elucidation of the functions of kappa receptors in the central nervous system.     

Differential effects of LY235959, a competitive antagonist of the NMDA receptor on κ-opioid receptor agonist induced responses in mice and rats

The effects of the competitive antagonist of the N-methyl-d-aspartate (NMDA) receptor, LY235959, were determined on the analgesic and hypothermic effects as well as on the development of tolerance to these effects of U-50,488H, a κ-opioid receptor agonist in mice and rats. In the mouse, a single injection of LY235959 given 10 min prior to U-50,488H did not modify the analgesic action of the latter. Similarly, chronic administration of LY235959 twice a day for 4 days did not modify U-50,488H-induced analgesia in mice. Repeated pretreatment of mice with LY235959 dose-dependently attenuated the development of tolerance to the analgesic actions of U-50,488H. In the rat, LY235959 by itself produced a significant analgesia and prior treatment of rats with LY235959 enhanced the analgesic action of U-50,488H. Similar effects were seen with the hypothermic action. Pretreatment of rats with LY235959 attenuated the development of tolerance to the analgesic but not to the hypothermic action of U-50,488H. These results provide evidence that LY235959 produces differential actions on nociception and thermic responses by itself and when given acutely with U-50,488H in mice and rats. However, when the animals are pretreated with LY235959, similar inhibitory effects are observed on the development of tolerance to the analgesic action of U-50,488H in both the species. These studies demonstrate an involvement of the NMDA receptor in the development of κ-opioid tolerance and suggest that the biochemical consequences of an opioid's interaction with the opioid receptor are not the only factors that contribute to the acute and chronic actions of opioid analgesic drugs.     

Developmental changes in opiate-induced analgesia in deer mice: sex and population differences

We examined developmental changes in nociception and mu (morphine) and kappa (U-50,488) opiate-induced analgesia in male and female deer mice of two different populations; Peromyscus maniculatus artemisiae from a mainland region and P. m. angustus from a small island. Both populations displayed significant developmental changes in nociception and morphine (10 mg/kg) and U-50,488 (10 mg/kg)-induced analgesia. Basal thermal response latencies (nociceptive responses) and the levels of mu and kappa opiate-induced analgesia increased over 14-35 days of age, with maximum analgesic responses in adults (35+ days of age). In both of the populations, young (neonatal-weaning) male mice displayed significantly higher thermal response latencies and greater levels of naloxone (1.0 mg/kg) antagonized opiate-induced analgesia than young females. There were also population differences in the levels of analgesia, the insular mice displaying greater mu and lower kappa opiate-induced analgesic responses than the mainland animals. The population differences in mu and kappa opiate-induced analgesia were evident in young and adult mice of both sexes. These results show that there are significant sex and population differences in nociception and opiate-induced analgesia in young (neonatal-weaning) and adult deer mice.     

Morphine injected into the paraventricular nucleus of the hypothalamus prevents noncontact penile erections and impairs copulation: involvement of nitric oxide.

Male rats show four to six penile erection episodes when put in the presence of an inaccessible receptive female for 80 min. These noncontact erections occur concomitantly with an increase in nitric oxide production in the paraventricular nucleus of the hypothalamus. This is shown by the increases in the NO2- and NO3- concentrations in the paraventricular dialysate obtained from these males by in vivo microdialysis. The NO2- concentration increased from 0.75 +/- 0. 10 microm to 2.89 +/- 0.39 microm and that of NO3- from 4.13 +/- 0. 58 microm to 9.5 +/- 1.2 microm. Morphine (0.5, 1 and 5 microg), given unilaterally into the paraventricular nucleus 15 min before the introduction of the receptive female, prevented the NO2- and NO3- increases, and noncontact erections, dose-dependently. In contrast, the kappa opioid receptor agonist U-69 593 (5 microg) was ineffective. The effects of morphine on NO2- and NO3-, and on noncontact erections, were prevented by the opiate receptor antagonist naloxone (10 microg) injected into the paraventricular nucleus 15 min before morphine. The NO2- and NO3- concentrations were also increased in the paraventricular dialysate of male rats during copulation, i.e. when in copula penile erections occurred. As found with noncontact erections, morphine, but not U-69 593, injected into the paraventricular nucleus prevented the NO2- and NO3- increases and impaired copulatory behaviour, and naloxone prevented these responses when given before morphine. Although some diffusion of the opiate to surrounding brain areas cannot be completely ruled out, the present results suggest that morphine acts through mu receptors in the paraventricular nucleus to impair noncontact erections and copulation. These effects of morphine are apparently mediated by a prevention of the increased nitric oxide production that occurs in the paraventricular nucleus of the hypothalamus of male rats during sexual activity.     

Regulation of G-PROTEIN mRNA abundancy and cAMP accumulation after long-term opioid incubation in primary cultures of astroglia from the rat cerebral cortex.

Primary astroglial cultures were incubated with delta (10(-6) M DPDPE) or kappa (10(-5) M U-50,488H) receptor agonists for 5 days. Thereafter, the acute inhibitory actions of delta or kappa receptor agonists on forskolin stimulated cAMP accumulation were assayed. The G alpha s, G alpha i-1 and G alpha i-2 mRNA levels were quantified after 5 days of either delta or kappa receptor agonist treatment using a solution hybridization, RNase protection assay. Pronounced effects were observed after 5 days of kappa receptor agonist [10(-5) M U-50,488H] incubation. This treatment resulted in an attenuation in the acute inhibitory action of delta and kappa receptor agonists. Furthermore, a decreased stimulatory action of forskolin was seen. Similar effects were also seen after delta receptor stimulation. We also investigated the effects after 24 h and 3 days of incubation with the kappa receptor agonist (10(-5) M) U-50,488H. The 24 h incubation resulted in a decreased sensitivity to the acute inhibitory action of delta and kappa receptor agonists in the astroglial cultures. This effect was further accentuated after the 3 days of incubation with 10(-5) M U-50,488H. No significant change was seen in the basal accumulation of cAMP after incubation with the kappa agonist U-50,488H. However, after 5 days of incubation with the delta agonist DPDPE, a significantly increased basal accumulation of cAMP was seen in the astroglial cultures. After 5 days of delta or kappa agonist incubation, an increase in G alpha s mRNA level and a decrease in G alpha i-2 mRNA level was seen compared with controls. No statistically significant alterations in the amount of G alpha i-1 mRNA were seen. The data obtained in the present study indicate that the effects of long-term opioid treatment alters the sensitivity of glial cell opioid receptors. Furthermore, long term opioid treatment induces alterations in glial G-protein mRNA levels.     

Dopamine modulates male sexual behavior in Japanese quail in part via actions on noradrenergic receptors

In rats, dopamine (DA) facilitates male sexual behavior through its combined action on D1- and D2-like receptors, in the medial preoptic area (MPOA) as well as other brain areas. In Japanese quail, systemic injections of dopaminergic drugs suggested a similar pharmacology but central injections have never been performed. Recent electrophysiological experiments demonstrated that DA effects in the MPOA of quail are mediated mainly through the activation of alpha2-noradrenergic receptors. Previous studies of DA action on behavior used specific dopaminergic agonists/antagonists and therefore unintentionally avoided the potential cross-reaction with alpha2-receptors. The present study was thus designed to investigate directly the effects of DA on male sexual behavior and to test whether the interaction of DA with heterologous receptors affects this behavior. Intracerebroventricular (i.c.v.) injection of DA or NE inhibited copulation in a dose-dependent manner. Systemic injections of yohimbine, an alpha2-noradrenergic antagonist, modulated copulation in a bimodal manner depending on the dose injected. Interestingly, a behaviorally ineffective dose of yohimbine markedly reduced the inhibitory effects of DA when injected 15min before. Together, these results show for the first time that i.c.v. injections of DA itself inhibit male sexual behavior in quail and suggest that the interaction of DA with alpha2-receptors has behavioral significance.     

Opposite effects of opiate agonists on metabolic weight loss in mice

Morphine (M) produced a dose-related decrease in metabolic weight loss (MWL) over a three-hour period, despite the fact that it significantly enhanced locomotor activity in male mice. This conservation of energy was specific to opioid receptors because naltrexone HCl (N) blocked it. These receptors were localized mainly to the periphery because a form of N that does not enter the brain, MR2663 BR (QN) eliminated the conservation response and instead increased MWL. The increase in MWL induced by M plus QN was blocked by MR2266 (MR), a specific kappa receptor antagonist. We suggest that this increase is due to the unmasking of a kappa opioid system located in the brain that acts to enhance energy expenditure. In support of this idea, administration of the kappa receptor agonist U-50,488H (U) produced a dose-related increase in MWL to levels nearly twice that of saline controls, while markedly reducing locomotor activity. These actions were blocked by MR but not by N. They were not blocked by QN and this suggests they originate mainly in the brain. Increasing amounts of M caused increasing inhibition of metabolic weight loss induced by a constant amount of U. This supports the idea of an antagonistic relationship between the two opioid systems.     

kappa-Opioid receptors in the substantia nigra pars reticulata mediate the U-50,488-induced locomotor activity of preweanling rats

The purpose of the present study was to determine the neuroanatomical location where kappa-opioid receptor stimulation induces locomotor activity in the preweanling rat. To confirm that the U-50,488-induced locomotor activity of preweanling rats is mediated by kappa-opioid receptors, 18-day-old rats were initially injected with vehicle or the kappa-opioid receptor agonist U-50,488 (5 mg/kg, s.c.) followed, 15 min later, by an injection of the kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI; 0, 2, 4, 8, or 12 mg/kg, s.c.). In subsequent experiments, 18-day-old rats were injected with vehicle or U-50,488 (5 mg/kg, s.c.) 15 min prior to bilateral administration (0.25 or 0.5 microl per side) of nor-BNI (0, 5, 10, or 20 microg) into the substantia nigra pars reticulata (SNR) or medial dorsal striatum (MDS). In the final experiment, 18-day-old rats received bilateral administration (0.25 microl per side) of vehicle or U-50,488 (0.0, 0.8, 1.6, or 3.2 microg) into the SNR. Results showed that systemically administered nor-BNI (0-12 mg/kg, s.c.) produced a dose-dependent reduction in the U-50, 488-induced locomotor activity of preweanling rats. The site of action for U-50,488's locomotor-activating effects appeared to be the SNR, because (a) bilateral administration of nor-BNI (5, 10, or 20 microg) into the SNR caused a complete attenuation of U-50, 488-induced locomotion, and (b) bilateral administration of U-50,488 into the SNR caused a dose-dependent increase in the locomotor activity of preweanling rats. Striatal injections of nor-BNI did not affect U-50,488-induced locomotor activity. When these findings are considered together it is apparent that stimulation of kappa-opioid receptors in the SNR is both necessary and sufficient for the occurrence of U-50,488-induced locomotor activity in the preweanling rat.     

U-50,488H into A10 reduces haloperidol-induced elevations of accumbens dopamine.

Injections of kappa (k) opioid agonists into the A10 ventral tegmental area (VTA) induce behavioral inhibitions and decreased interest in incentive stimuli, behavioral changes indicative of decreased mesolimbic dopamine (DA) transmission. In seeming contrast, three separate laboratories have recently reported that intra-VTA injections of k agonists do not affect nucleus accumbens septi (NAS) basal levels of extracellular DA. In the present experiment, we investigated whether intra-VTA injections of a k agonist would decrease pharmacologically-stimulated increased levels of extracellular NAS DA. It was found that intra-VTA injections of the k agonist U-50,488H significantly attenuated haloperidol-induced elevations of DA, as measured by in vivo microdialysis.     

Topography in the preoptic region: differential regulation of appetitive and consummatory male sexual behaviors

Several studies have suggested dissociations between neural circuits underlying the expression of appetitive (e.g., courtship behavior) and consummatory components (i.e., copulatory behavior) of vertebrate male sexual behavior. The medial preoptic area (mPOA) clearly controls the expression of male copulation but, according to a number of experiments, is not necessarily implicated in the expression of appetitive sexual behavior. In rats for example, lesions to the mPOA eliminate male-typical copulatory behavior but have more subtle or no obvious effects on measures of sexual motivation. Rats with such lesions still pursue and attempt to mount females. They also acquire and perform learned instrumental responses to gain access to females. However, recent lesions studies and measures of the expression of the immediate early gene c-fos demonstrate that, in quail, sub-regions of the mPOA, in particular of its sexually dimorphic component the medial preoptic nucleus, can be specifically linked with either the expression of appetitive or consummatory sexual behavior. In particular more rostral regions can be linked to appetitive components while more caudal regions are involved in consummatory behavior. This functional sub-region variation is associated with neurochemical and hodological specializations (i.e., differences in chemical phenotype of the cells or in their connectivity), especially those related to the actions of androgens in relation to the activation of male sexual behavior, that are also present in rodents and other species. It could thus reflect general principles about POA organization and function in the vertebrate brain.     

The interaction between kappa-opioid agonist, U-50, 488H, and kainic acid: behavioral and histological assessments

The effects of a selective kappa-agonist, U-50,488H, on systemic kainic acid-induced behavioral and histological changes were studied in rats. U-50,488H inhibited kainic acid-induced wet dog shakes in a naloxone reversible manner; however, U-50,488H did not protect rats against kainic acid-evoked behavioral seizures. As revealed by histological analysis, kainic acid caused edema and severe neuronal damage in several brain regions, notably in CA1 but also in the CA3 fields of both hippocampi. Pretreatment of rats with U-50,488H markedly protected hippocampal neurons, especially those in CA1, against kainic acid-induced neurotoxicity. Naloxone by itself had little effect on kainic acid-induced seizures or hippocampal neuron loss. Naloxone plus U-50,488H resulted in less severe seizures and, consequently, less hippocampal cell loss than after kainic acid alone. These data indicate that U-50,488H can markedly attenuate the neurotoxic and behavioral consequences of systemic kainic acid administration. However, the mechanism of these effects requires further study with more specific opioid antagonists.     

Morphine can produce analgesia via spinal kappa opioid receptors in the absence of mu opioid receptors

Previous studies have demonstrated the virtual lack of analgesia in mu opioid receptor knockout mice after systemic administration of morphine. Thus, it has been suggested that analgesic actions of morphine are produced via the mu opioid receptor, despite its ability to bind to kappa and delta receptors in vitro. However, it is not clear whether the results of these studies reflect the effect of morphine in the spinal cord. In the present study, we report study of the analgesic actions of spinally-administered morphine and other opioid receptor agonists in mu opioid receptor knockout and wild type mice. Morphine produced a dose-dependent antinociceptive effect in the tail flick test in the knockout mice, although higher doses were needed to produce antinociception than in wild type mice. The antinociceptive effect of morphine was completely blocked by naloxone (a non-selective opioid antagonist) and nor-binaltorphimine (nor-BNI, a selective kappa-opioid receptor antagonist), but not by naltrindole (a selective delta-opioid receptor antagonist). U-50,488H (a selective kappa-opioid receptor agonist) also produced a dose-dependent antinociceptive effect in knockout mice but presented lower analgesic potency in knockout mice than in wild type mice. Analgesic effects of [d-Pen2,d-Pen5]enkephalin (DPDPE, a selective delta-opioid receptor agonist) were observed in wild type mice but abolished in knockout mice. SNC80 (a selective delta-opioid receptor agonist) was not antinociceptive even in wild type mice. The present study demonstrated that morphine can produce thermal antinociception via the kappa opioid receptor in the spinal cord in the absence of the mu opioid receptor. Lower potency of U50,488H in mu opioid receptor knockout mice suggests interaction between kappa and mu opioid receptors at the spinal level.     

Cocaine and kappa-opioid withdrawal in Planaria blocked by D-, but not L-, glucose

Planarians (Dugesia dorotocephala) that were exposed for 1 h to cocaine (80 microM) or to the kappa-selective opioid receptor agonist U-50,488H (1 microM) displayed an abstinence-induced withdrawal syndrome, indicative of the development of physical dependence, when they were tested in cocaine- (or U-50,488H-) free water, but not when they were tested in cocaine- (or U-50,488H-) containing water. The withdrawal was manifested as a significant (P<0.05) decrease in the rate of planarian spontaneous locomotor activity over a 5-min observation period, using a recently designed metric. Co-exposure of the planarians to D-glucose (1 microM) or to 2-deoxy-D-glucose (2-DG, 1 microM), but not to L-glucose (1 microM), significantly attenuated (P<0.05) the development of physical dependence, shown by an attenuated withdrawal syndrome, from cocaine and U-50,488H. These results suggest that either D-glucose and 2-deoxy-D-glucose compete with a common cocaine and kappa-opioid transport mechanism or that the development of physical dependence (or the inhibition of abstinence-induced withdrawal) in planarians requires energy supplied from glucose metabolism.     

Evaluation of U-50,488H analogs for neuroprotective activity in the gerbil.

U-50,488H, a kappa (kappa) opioid ligand with moderate potency at sigma (sigma) receptors, protects against mechanical and ischemia-induced injury. The purpose of this study was to evaluate the possibility that sigma-receptors may be involved in mediating the neuroprotective actions of U-50,488H. This possibility was examined by testing the potential of a series of U-50,488H analogs, which are potent sigma-ligands with minimal activity at kappa-opioid receptors, to protect against ischemia-induced neuronal damage in the gerbil. Like U-50,488H, BD-449 (20 mg/kg), the cis-diastereomer of U-50,4888H, protected against ischemia-induced neuronal damage as did BD-737 (50 and 30 mg/kg) and BD-738 (50 mg/kg). All 3 compounds interacted selectively with sigma-receptors. In contrast, BD-601 (50 mg/kg), did not protect against ischemia-induced neuronal damage, although it also interacted potently with sigma-receptors. One difference between the compounds that were neuroprotective and BD-601 is that only BD-601 produced sigma-like behavioral effects in the rat. Thus, it is possible that BD-601 may interact differently or at a different sigma-subtype than BD-449, BD-737 and BD-738 with sigma-receptors. However, these results clearly indicate that an interaction with kappa-opioid receptors is not required for anti-ischemic activity, and that sigma-receptors may play a role in neuroprotection.     

Site-specific effects of anosmia and cloacal gland anesthesia on Fos expression induced in male quail brain by sexual behavior

In rats, expression of the immediate early gene, c-fos observed in the brain following male copulatory behavior relates mostly to the detection of olfactory information originating from the female and to somatosensory feedback from the penis. However, quail, like most birds, are generally considered to have a relatively poorly developed sense of smell. Furthermore, quail have no intromittent organ (e.g., penis). It is therefore intriguing that expression of male copulatory behavior induces in quail and rats a similar pattern of c-fos expression in the medial preoptic area (mPOA), bed nucleus of the stria terminalis (BSTM) and parts of the amygdala. We analyzed here by immunocytochemistry Fos expression in the mPOA/BSTM/amygdala of male quail that had been allowed to copulate with a female during standardized tests. Before these tests, some of the males had either their nostrils plugged, or their cloacal area anesthetized, or both. A control group was not exposed to females. These manipulations did not affect frequencies of male sexual behavior and all birds exposed to a female copulated normally. In the mPOA, the increased Fos expression induced by copulation was not affected by the cloacal gland anesthesia but was markedly reduced in subjects deprived of olfactory input. Both manipulations affected copulation-induced Fos expression in the BSTM. No change in Fos expression was observed in the amygdala. Thus immediate early gene expression in the mPOA and BSTM of quail is modulated at least in part by olfactory cues and/or somatosensory stimuli originating from the cloacal gland. Future work should specify the nature of these stimuli and their function in the expression of avian male sexual behavior.