Endogenous opiates: 1991

The opioid peptide dynorphin suppresses pituitary-ovary axis in the tilapia Oreochromis mossambicus

The opioid peptides are involved in the regulation of neuroendocrine functions in vertebrates. Nonetheless, the influence of an opioid peptide, dynorphin A (DYN), on reproduction in fish is understudied. The aim of this work was to study the influence of DYN on the pituitary-ovary axis in Oreochromis mossambicus. Daily injections (ip) of 250 μg DYN kg^-1 body weight for 22 days during the ovarian cycle caused a reduction in the intensity and the per cent area of luteinizing hormone (LH) immunoreactive content in the proximal pars distalis region of the pituitary gland compared with an intense immunostaining in time-matched controls. In the ovary, DYN treatment caused a decrease in the number of stage I (previtellogenic) follicles compared with time-matched controls. No difference was observed in the number of stage IV (vitellogenic) follicles among different experimental groups, whereas the numbers of stage II and stage III follicles (previtellogenic) were higher in DYN-treated fish than in time-matched controls. Nonetheless, there was a reduction in the number of stage V (preovulatory) follicles in DYN-treated fish compared with time-matched controls. Taken together, these results indicate that DYN exerts an inhibitory effect on follicular recruitment at the late vitellogenic stage, through the suppression of LH secretion in fish.

Influence of endomorphins along the pituitary-ovary axis in the Mozambique Tilapia Oreochromis mossambicus

Endomorphins (EM-1 and EM-2) are the tetrapeptides involved in pain and neuroendocrine responses with a high affinity for μ-opioid receptors in vertebrates. However, their role in fish reproduction is not clear. The aim of this study was to investigate the influence of EM-1 and EM-2 on the pituitary-ovary axis in the Mozambique tilapia Oreochromis mossambicus. The experimental set-up consisted of four groups, namely, initial controls, controls, EM-1- and EM-2-treated groups (n = 10 in each group consisting of two replicates). Although the number of stage IV (vitellogenic) follicles was significantly lower (P < 0.05) in controls compared to initial controls, the stage V (preovulatory) follicles were present in controls in contrast to their absence in initial controls. Treatment of 40 μg EM-1/0.1 ml saline/fish/day for 22 days resulted in significant increase (P < 0.05) in the number of stage I follicles compared to controls. While similar treatment of EM-2 did not significantly alter the number of stage I follicles compared to controls, the number of stage II follicles was significantly lower (P < 0.05) in this group compared to those of controls and EM-1 treated fish. The number of stage III and IV follicles did not significantly differ among controls, EM-1- and EM-2-treated groups. However, a significant reduction (P < 0.05) in the mean number of stage V follicles was observed in EM-1- and EM-2-treated fish compared to controls. These changes were concomitant with significant reduction (P < 0.05) in the intensity and the percent area of immunoreactivity of luteinizing hormone (LH) secreting cells in the proximal pars distalis (PPD) of the pituitary gland and significantly higher (P < 0.05) percent occurrence of follicular atresia in EM-1- and EM-2-treated fish compared to those of controls. Taken together, these results suggest an inhibitory effect for endomorphins along the pituitary-ovary axis, for the first time in fish.

Opioid modulation of cell proliferation in the ventricular zone of adult zebra finches (Taenopygia guttata)

Besides modulating pain, stress, physiological functions, motivation, and reward, the opioid system has been implicated in developmental and adult mammalian neurogenesis and gliogenesis. In adult male songbirds including zebra finches, neurons generated from the ventricular zone (VZ) of the lateral ventricles are incorporated throughout the telencephalon, including the song control nuclei, HVC, and area X. Although the endogenous opioid met-enkephalin is present in neurons adjacent to the VZ and is upregulated in song control regions during singing, it is not known whether the opioid system can modulate adult neurogenesis/gliogenesis in zebra finches. We used quantitative RT-PCR and in situ hybridization to demonstrate that μ- and δ-opioid receptors are expressed by the VZ of adult male zebra finches. Treating cultured VZ cells from male birds with the opioid antagonist naloxone led to an increase in cell proliferation measured by 5-bromo-2-deoxyuridine incorporation, whereas administering met-enkephalin had the opposite effect, compared with saline-treated cultures. Systemically administering naloxone (2.5 mg/kg body wt) to adult male zebra finches for 4 d also led to a significant increase in cell proliferation in the ventral VZ of these birds, compared with saline-treated controls. Our results show that cell proliferation is augmented by naloxone in the VZ adjacent to the anterior commissure, suggesting that the endogenous opioids modulate adult neurogenesis/gliogenesis by inhibiting cell proliferation in songbirds.

Stimulation of mu and delta opioid receptors induces hyperalgesia while stimulation of kappa receptors induces antinociception in the hot plate test in the naked mole-rat (Heterocephalus glaber)

The antinociceptive effects of highly selective mu (DAMGO), delta (DPDPE) and kappa (U-50488 and U-69593) opioid agonists were evaluated following intraperitoneal (i.p.) administration in the naked mole-rat. A hot plate test set at 60 degrees C was used as a nociceptive test and the latency to the stamping of the right hind paw (response latency) was used as the end-point. DAMGO (5-10 mg/kg) and DPDPE (2.5-5 mg/kg) caused a naloxone-reversible significant decrease in the mean response latency. Subcutaneous injection of naloxonazine (20 mg/kg) 24h prior to the administration of DAMGO (5 mg/kg) also blocked the reduction in the response latency observed when DAMGO was injected alone. On the contrary, U-50488 (2.5-5 mg/kg) or U-69593 (0.08 or 0.1 mg/kg) caused a naloxone-reversible significant increase in the mean response latency. These results showed that activation of mu or delta receptors caused hyperalgesia, whereas activation of kappa receptors caused antinociception in the hot plate test in naked mole-rat. This suggests that mu and delta receptors modulate thermal pain in a different way than kappa receptors in the naked mole-rat. It is not possible at the moment to point out how they modulate thermal pain as little is known about the neuropharmacology of the naked mole-rat.

ACTH and beta-endorphin in transcendental meditation

We have evaluated the effect of Transcendental Meditation (TM) on the hypothalamo-hypophyseal-adrenal axis diurnal rhythms through the determination of hormone levels. Blood samples were taken at 0900 hours. and at 2000 hours. These samples were taken from 18 healthy volunteers who regularly practice TM and from nine healthy non-meditators. Cortisol, beta-endorphin, and adrenocorticotropic hormone (ACTH) were measured at both hours. TM practitioners showed no diurnal rhythm for ACTH and for beta-endorphin (ACTH, pg/mL, mean +/- SE; 13.8+/-1.2 - 12.1+/-1.5/beta-endorphin, pg/mL; 14.4+/-1.5 - 17.2+/-1.9, at 0900 hours and 2000 hours, respectively), in contrast to control subjects, who showed normal diurnal rhythm for these hormones and for cortisol (ACTH, pg/mL; 19.4+/-1.9 - 11.9+/-2.2/beta-endorphin, pg/mL; 25.4+/-1.7 - 17.7+/-1.1/Cortisol, ng/mL; 201.4+/-13.2 - 71.3+/-6.5, at 0900-2000 hours, respectively, p < 0.01 in the three cases). Practitioners of TM with similar anxiety levels to those of the control group showed a different pattern in the daytime secretion of pituitary hormones. TM thus appears to have a significant effect on the neuroendocrine axis. Because cortisol levels had a normal pattern in the TM group, these results may be due to a change in feedback sensitivity caused by this mental technique.

Food cravings, endogenous opioid peptides, and food intake: a review

Extensive research indicates a strong relationship between endogenous opioid peptides (EOPs) and food intake. In the present paper, we propose that food cravings act as an intervening variable in this opioid-ingestion link. Specifically, we argue that altered EOP activity may elicit food cravings which in turn may influence food consumption. Correlational support for this opioidergic theory of food cravings is provided by examining various clinical conditions (e.g. pregnancy, menstruation, bulimia, stress, depression) which are associated with altered EOP levels, intensified food cravings, and increased food intake.

Effect of ethanol drinking and naltrexone on subsequent drinking in rats

The effects of several days of oral ethanol drinking paired with naltrexone (NTX) on subsequent ethanol drinking were investigated in rats. We hypothesized that repeated pairings of NTX combined with forced oral ethanol intake would extinguish ethanol drinking so that when NTX injections were terminated, voluntary oral ethanol drinking would be suppressed. Thirty-two male. Long-Evans rats were provided with alternate days of either 8% ethanol solution or water as the sole source of fluid. Intraperitoneal injections of 0, 2.5, or 5.0 mg of NTX hydrochloride were administered on the ethanol days. Following the termination of injections, rats were returned to unrestricted access to water and ethanol and 24-h measurements of fluid intake were recorded. NTX decreased ethanol intake 4 h, but not 24 h, after NTX injections. Despite the consumption of significant amounts of ethanol during NTX treatment, there was no change in voluntary oral ethanol intake patterns after NTX injections were terminated (reinstatement of voluntary ethanol drinking). Thus, NTX's reduction in ethanol intake was limited in duration and did not result in long-term extinction of ethanol drinking behavior.

Taste preferences and food intake

Sensory responses to the taste, smell, and texture of foods help determine food preferences and eating habits. However, sensory responses alone do not predict food consumption. The view that a "sweet tooth" leads to obesity through excess sugar consumption is overly narrow. In reality, there are multiple links between taste perceptions, taste preferences, food preferences, and food choices and the amount of food consumed. Taste responses are influenced by a range of genetic, physiological, and metabolic variables. The impact of taste factors on food intake further depends on sex and age and is modulated by obesity, eating disorders, and other pathologies of eating behavior. Food preferences and food choices of populations are further linked to attitudinal, social, and--probably most important--economic variables such as income. Nutrition education and intervention strategies aimed at improving population diets ought to consider sensory pleasure response to foods, in addition to a wide range of demographic and sociocultural variables.

Distribution of catecholamine-synthesizing enzymes and some neuropeptides in the median eminence-arcuate nucleus complex (MEARC) of the immature female pig

The presence of the catecholamine-synthesizing enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (D beta H) and some neuropeptides, including neuropeptide Y (NPY), Leu5-enkephalin (LENK), vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), substance P (SP), galanin (GAL) and somatostatin (SOM) was investigated in nerve fibres and perikarya of the median eminence-arcuate nucleus complex (MEARC) of the sexually immature female pigs by means of the immunohistochemical avidin-biotin complex method. Although immunoreactivities to all the studied substances were found in nerve fibres of the porcine MEARC, there were differences in the distribution and density of particular subsets of nerve fibres within the complex. While loose D beta H-immunoreactive (D beta H-IR) and dense TH-, NPY- and VIP-IR nerve meshworks occurred predominantly in the internal layer of the MEARC, nerve fibres immunoreactive to TH, CGRP, SOM, SP and LENK were more numerous in the external than in the internal layer of the median eminence (ME). Numerous TH-, D beta H-, NPY-, VIP-, SP- and CGRP-IR perivascular nerve fibres were also observed within both layers of the median eminence. There were also differences in the distribution of a particular subset of neurons within the porcine MEARC: NPY-, VIP-, GAL-, SP- and TH-IR (but not D beta H-IR) perikarya were found in the arcuate nucleus, while in the median eminence only subpopulations of NPY-, VIP and GAL-IR neurons were observed.

Distribution and changes in mu- and kappa-opiate receptors during the midlife neurodevelopmental period of Coho salmon, Oncorhynchus kisutch

Parr-smolt transformation (PST) in coho salmon is associated with a plasma thyroid hormone (PT4) surge and a critical period of neural development that includes axonal sprouting, neurogenesis, and surges of select neurotransmitters. Here we provide a description of the selectivity, distribution, and the changes in the density of mu- and kappa-opiate receptors during PST, as revealed by quantitative in vitro autoradiography of [3H]Tyr-D-Ala-Gly-NMe-Phe-Gly-ol ([3H]DAMGO) and [3H]ethylketocyclazocine ([3H]EKC), respectively. The concentration of mu-receptors increased significantly in select cell groups in the early stages of parr-smolt transformation, until a peak was reached at the time coinciding with the peak of the PT4 surge. In other cell groups, the peaks occurred 1 or 2 weeks later. With one exception, this increase was followed by a decrease in concentration. The brain areas showing the highest concentrations are the dorsal nucleus of the ventral telencephalic area, the glomerular region, the granular layer of the valvula cerebelli, the nucleus diffuses of the inferior lobe, and the nucleus diffuses of the torus lateralis. Other regions with distinctly elevated mu-receptor concentrations are the stratum griseum centrale of the optic tectum and the preoptic area. The distribution of kappa-receptors is more diffuse, and the densities are considerably lower. The overlap in distribution of mu- and kappa-receptors is considerable, but significant exceptions are noted. For example, the dorsomedial nucleus of the dorsal telencephalic area, the habenular nucleus, and the dorsomedial nucleus of the thalamus exhibit a surge in density of kappa-receptors at the time of the PT4 surge, while the density of mu-receptors in these nuclei remain very low throughout parr-smolt transformation. The kappa-receptor containing cell groups are not identifiable until 3 weeks before the PT4 surge because of low densities. The most prominently labeled kappa-receptor regions are the ventral and dorsal nuclei of the ventral telencephalic area, the medial and dorsal zones of the dorsal telencephalic area, the optic tectum (all layers), the dorsomedial nucleus of the thalamus, the torus lateralis of the ventral hypothalamus, and the preoptic area. An increase of mu- and kappa-opiate receptor densities in specific brain regions may reflect roles in the alteration of brain organization, olfactory imprinting, neuroendocrine activity or other physiological activities. The overall distribution of these receptors are relatively more extensive in salmon than in other vertebrates so far studied.

State-dependent changes of brain endogenous opioids in mammalian hibernation

Endogenous opioids belonging to three opioid families were measured in different states of the hibernation cycle in brain of the Columbian ground squirrels. Using high-performance liquid chromatography-EC detection, the hypothalamic and septal concentrations of met-enkephalin were found to be significantly higher (p < 0.05) in the hibernating state than that in the nonhibernating state. In contrast, met-enkephalin content in the medulla decreased significantly during hibernation. Leuenkephalin content was only increased in the hypothalamus of hibernating animals. Using radioimmunoassay, dynorphin A-like immunoreactivity was observed to increase in the claustrum and striatum, whereas beta-endorphin-like peptides showed a significant increase in the hypothalamus during hibernation. It is evident that the changes in endogenous opioids in brain during hibernation are state dependent, type specific and region specific. These specific alterations of various endogenous opioids may imply their different roles in hibernation.

Metabolic determinants of binge eating

Binge-eating behavior is often thought to be the consequence of energy restriction and dietary restraint. However, evidence is accumulating that recurrent eating binges may be one behavioral mechanism in the expression of familial obesity, and may therefore precede the onset of dieting. The profile of patients with the DSM-IV binge-eating disorder resembles that of patients with familial obesity. There is further evidence for the involvement of the endogenous opiate peptide system. Binge-type foods are often rich in fat, sugar, or both. The opiate antagonist naloxone reduced the consumption of sweet high-fat foods in obese and lean female binge-eaters, though not in nonbinging controls. In contrast, obese as opposed to lean subjects were not differentially affected by naloxone. These data provide a psychobiological validation of the DSM-IV binge eating disorder and suggest that binge eating may be triggered by physiological events. As opposed to being the outcome of dieting, binge-eating episodes should be considered as its possible cause.

Behavioural effects of different intensities of formalin pain in rats

The effects of two concentrations of formalin (0.1% and 10%) on Licking, Flexing and Paw-Jerk, and standard measures of activity, were studied in male rats during three experimental conditions: Box, Open-Field and Novel Object. Pain-evoked responses were present in all formalin-injected animals, with greater intensity in the group injected with formalin 10%. In this group Rearing and Olfactory Exploration were reduced with respect to the controls, locomotion was inhibited to the point that it was virtually absent during the last part of the test. In contrast, the lower formalin concentration not only failed to inhibit the locomotor/exploratory behaviours but also appeared to induce a general activation of behaviour, as suggested by the longer durations of Pendulum, the absence of Sleeping-like episodes and the higher number of Approaches to the object found in this group. The results of the present experiment underline the importance of a detailed analysis of behaviour in animal models of pain and support the view that the intensity of pain plays a crucial role in its behavioural effects.

Molecular biology of the opioid receptors: structures, functions and distributions

Opiates like morphine and endogenous opioid peptides exert their pharmacological and physiological effects through binding to their endogenous receptors, opioid receptors. The opioid receptors are classified into at least three types, mu-, delta- and kappa-types. Recently, cDNAs of the opioid receptors have been cloned and have greatly advanced our understanding of their structure, function and expression. This review focuses on the recent advances in the studies on opioid receptors using the cloned cDNAs. We describe the molecular cloning of the opioid receptor gene family and studies of the structure-function relationships, modes of coupling to second messenger systems, pharmacological effects of antisense oligonucleotide and anatomical distributions of opioid receptors.

The effects of morphine treatment and morphine withdrawal on the dynorphin and enkephalin systems in Sprague-Dawley rats

The effect of morphine tolerance and withdrawal on prodynorphin peptides was studied in relevant brain areas and in the pituitary gland of male Sprague-Dawley rats, and compared with effects on the proenkephalin-derived peptide Met-enkephalin. After 8 days of morphine injections (twice daily), dynorphin A and B levels increased in the nucleus accumbens and dynorphin A levels increased also in the striatum. Morphine treatment increased striatal Met-enkephalin. Leu-enkephalinArg6 levels were reduced in the ventral tegmental area (VTA). Morphine-treated rats had very low Leu-enkephalinArg6 levels in the hippocampus as compared to saline control rats. Comparison of the relative amounts of dynorphin peptides and the shorter prodynorphin-derived peptides, Leu-enkephalinArg6 and Leu-enkephalin, revealed a relative increase in dynorphin peptides versus shorter fragments in the nucleus accumbens, VTA and hippocampus. Morphine-tolerant rats had lower levels of dynorphin A in both lobes of the pituitary gland, whereas hypothalamic dynorphin levels were unaffected by morphine. Leu-enkephalinArg6 levels were reduced in the hypothalamus, but not changed in the pituitary gland. Naloxone-precipitated withdrawal accentuated the increase in dynorphin A and B levels in the accumbens and dynorphin A levels in the striatum, while inducing an increase in enkephalin levels in the accumbens and Met-enkephalin in the VTA. In the hippocampus, Leu-enkephalinArg6 levels remained low in the withdrawal state. The low dynorphin levels in the anterior part of the pituitary gland were reversed by naloxone, whereas the low dynorphin A levels in the neurointermediate lobe were 0ven lower in the withdrawal state.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of preproenkephalin messenger RNA in the basal ganglia and limbic-associated regions of the monkey telencephalon

We studied the distribution of preproenkephalin messenger RNA in the monkey forebrain, using a free-floating method for in situ hybridization histochemistry. Autoradiographs reveal a high level of specific hybridization to preproenkephalin messenger RNA in the monkey striatum and forebrain regions. In the monkey striatum, the distribution of preproenkephalin messenger RNA is heterogeneous. There is variation in the general labeling pattern between regions of the striatum. For example, a particularly densely labeled area of preproenkephalin messenger RNA is observed in the ventral part of the caudal putamen. In addition, at the macroscopic level, there are patches of specific hybridization intermingled with areas containing less specific labeling. This forms a mosaic-like pattern. At the microscopic level, densely labeled individual cells are found among those with little or no specific labeling. Adjacent sections, processed for in situ hybridization and immunohistochemistry, show some correlation between the perikarya containing preproenkephalin messenger RNA and enkephalin-positive fibers in the striatum. Specific hybridization to preproenkephalin messenger RNA is evident throughout the cortical mantle, primarily concentrated in layers 2 and 3. Particularly high levels of preproenkephalin messenger RNA are found in specific limbic-associated cortices, including the piriform allocortex, the agranular area of the orbitofrontal cortex, the agranular insular cortex and the caudal field of the entorhinal cortex. Specific labeling is also present in the granular cell layer of the dentate gyrus and in the amygdaloid complex. This study reveals heterogeneous distribution of dense preproenkephalin messenger RNA in the basal ganglia and high levels of preproenkephalin messenger RNA in specific limbic-associated regions of the monkey telencephalon.

Molecular pharmacology of the opioid receptors

Opioid receptors are the primary sites of actions of opiates and endogenous opioid peptides, which have a wide variety of pharmacological and physiological effects. The opioid receptors are classified into at least three subtypes, mu, delta, and kappa, and their cDNAs have been cloned. In this review, we describe the molecular cloning of opioid receptor gene family and studies of the structure-function relationships, modes of coupling to second messenger systems, pharmacological effects of antisense oligonucleotides, and anatomical distribution of opioid receptor mRNAs.

The Tyr-MIF-1 family of peptides

A review of research on the Tyr-MIF-1 family of peptides is presented with emphasis on Tyr-MIF-1 and its structure, passage through the blood-brain barrier, and both opiate antagonist and agonist properties. Family members MIF-1, Tyr-W-MIF-1 and Tyr-K-MIF-1 are also included.

Endogenous opioid peptide level changes under electrostimulation and their assessment by the EEG

Endogenous opioid peptide (EOP) system plays an important role in the interaction of human organism with different stress factors, providing stress-limiting and stress-protective functions. Different kinds of electrostimulation seem to produce anti-stress and pain relief effects due to EOP system activation. The presented paper reviews recent literature concerning EOP system activation under electrostimulation and its reflections in the EEG characteristics. The results and opportunities of high resolution EEG structure analysis utilization for EOP level control, as well as for stress-induced state assessment and correction via resonance activation of brain EEG oscillators by means of frequency-tuned external stimulation are presented.

Differences between alcohol-preferring (AA) and alcohol-avoiding (ANA) rats in the prodynorphin and proenkephalin systems

The motivation to drink alcohol and the eventual risk of becoming addicted are in part genetically determined. Because opioid peptides are considered central to motivated behaviors, we have analyzed opioid peptides in relevant areas of the brain of two outbred lines of rats: the alcohol-preferring [Alko Alcohol (AA)] line who voluntarily drink alcohol and the alcohol-avoiding [Alko Non-Alcohol (ANA)] line with negligible intake. (Met)enkephalinArg6Phe7 (MEAP) was measured as a marker of proenkephalin, and dynorphin A, dynorphin B, and (Leu)enkephalinArg6 as markers of the prodynorphin system. The major line differences and effects of alcohol intake were observed in mesolimbic brain areas. The mesolimbic dopamine pathway, which projects from the ventral tegmental area (VTA) to the nucleus accumbens, is central in the reward system. Basal levels of MEAP and dynorphin peptides were low in the nucleus accumbens of AA rats, whereas (Leu)enkephalinArg6 levels were lower in the VTA of these rats. Alcohol drinking caused MEAP levels in the accumbens to rise, but had no effect on prodynorphin peptides. Opioids also influence the nigrostriatal dopamine pathway. However, this study showed no significant differences for any peptide between rat lines, or effect of alcohol intake, in either substantia nigra or striatum, except for a decrease of nigral and striatal (Leu)enkephalinArg6 levels in alcohol-drinking AA rats. Large line differences were observed in the pituitary gland. AA rats had high basal levels of MEAP, which became even higher after voluntary alcohol consumption for 4 weeks, and low levels of dynorphin peptides, not affected by alcohol drinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Combined effect of fluconazole and thymosin alpha 1 on systemic candidiasis in mice immunosuppressed by morphine treatments

Treatment of systemic infection with Candida albicans with a combination of an antifungal agent (i.e. fluconazole) and a thymus-derived immunostimulant (i.e. thymosin alpha 1 (T alpha 1)) in mice immunosuppressed by morphine treatments was investigated. In normal mice, fluconazole given after infection with 10(6) C. albicans cells was more effective than in mice treated with morphine. Combination treatment with fluconazole and T alpha 1 prolonged survival and reduced the fungal burden in the kidneys of immunosuppressed mice. We also investigated the influence of this combined treatment on killing properties of polymorphonuclear leucocytes (PMN) and natural killer (NK) cell activity, inhibited by morphine administrations. Treatment with T alpha 1 or fluconazole as single agents promoted a recovery of normal NK cell activity and intracellular killing of C. albicans by PMN, while the combination significantly increased both of these responses, probably through the modulation of lymphokine production. Our data suggest that the additive effect of T alpha 1 and fluconazole is due to a direct antifungal action and activation of the immunocompetence.

Species difference in the modulatory effect of kappa agonist on 5-HT release from ground squirrel and rat hippocampus

Inclusion of the kappa agonist U50488 in the perifusion medium enhanced K(+)-stimulated 5-HT release from ground squirrel hippocampal slices, but reduced 5-HT outflow in both young and old rats' hippocampal slices. The stimulatory effect of U50488 on 5-HT release from ground squirrel hippocampus was not significantly attenuated by the non-specific opioid antagonist naloxone (10(-5) M), but was completely reversed by the specific kappa antagonist nor-BNI (10(-6)M), and the voltage-dependent sodium channel blocker TTX (10(-6)M). In contrast, the inhibitory effect of U50488 on 5-HT release from the young rat hippocampus was attenuated by naloxone (10(-6)M), but not by nor-BNI (10(-6)M) or TTX (10(-6)M). These results illustrate a significant species difference in the modulatory effect of opioids on neurotransmitter release in the hippocampus.

Substance P inactivating enzymes in human cerebrospinal fluid

The Km and Vmax values were determined for enzymes in human lumbar cerebrospinal fluid (CSF) that inactivate synthetic substance P (SP = RPKPQQFFGLM-NH2) and produce metabolic products. For the human lumbar CSF samples analyzed in this study, Km = 2.24 +/- 0.93 mM and Vmax = 0.113 +/- 0.035 nmol/ml/min (n = 10; mean +/- SEM) for the rate of decrease of SP. HPLC analysis of the incubated synthetic peptide fragments demonstrated that the primary enzymatically produced fragment is SP(3-11), with minor amounts in decreasing order of SP(1-4), SP(1-7), and SP(1-9). Electrospray ionization mass spectrometry (ESI-MS) confirmed the appropriate molecular weights for the four peptides, SP(3-11), SP(1-4), SP(1-7), and SP(1-9). These data demonstrate that the primary enzyme in human lumbar CSF that acts on synthetic SP is a post-proline cleaving enzyme (PPCE).

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

In situ hybridization study of kappa-opioid receptor mRNA in the rat brain

Distribution of kappa-opioid receptor mRNA in rat brain was examined by in situ hybridization technique. kappa-Opioid receptor mRNA was expressed in various brain regions, especially intensely in the neocortex (layer V and VI), caudate-putamen, nucleus accumbens, preoptic area, paraventricular thalamic nucleus, amygdala, several nuclei of hypothalamus, ventral tegmental area and substantia nigra pars compacta.

Pyrogenic doses of intracerebroventricular interleukin-1 did not induce analgesia in the rat hot-plate or cold-water tail-flick tests

There are a few reports in the literature that cytokines can induce analgesia (5, 6, 18). The present study sought to characterize the analgesic effects of intracerebroventricularly (icv) administered interleukin-1 (IL-1) and interferon-alpha (IFN-alpha) in rats. In the cold-water tail-flick test (CWT), latency to tail withdrawal from a -3 degrees C liquid was timed; in the hot-plate test (HP), latency to a rear paw lick or a jump from a 55 degrees C surface was measured. In some experiments, core body temperature was also monitored with a rectal thermistor. In the CWT, human recombinant (hr) IFN-alpha induced a small, statistically significant effect at just one dose (15,000 U icv), but no dose of hr-IL-1 alpha (250-1000 U icv) or hr-IL-1 beta (125-2000 U icv) induced a significant effect at any time point. On the other hand, dose-related increases in body temperature were observed after icv injection of both IL-1 alpha and IL-1 beta. The largest hyperthermic effect was a 1.7 (+/- 0.15) degrees C rise 120 min after administration of 1000 U IL-1 beta. In a second analgesic assay, the HP, IL-1 beta was ineffective as well. Since IL-1 alone did not induce analgesia, we tested its capacity to potentiate morphine analgesia. Morphine (5.0 and 10 micrograms, icv) induced analgesia in the CWT (32.7 and 61.8% maximum analgesia, respectively); however, there was no significant effect of IL-1 beta on morphine-induced analgesia. In summary, we failed to find an analgesic effect of IL-1, alone or in combination with morphine, at doses which clearly had a physiological effect; this is in contrast to the reports cited above.