Comparison of the distribution of dynorphin systems and enkephalin systems in brain

Postnatal development of multiple opioid receptors in rat brain

Recent studies have demonstrated that opioid receptors may be functional at early stages of ontogeny, and may modulate specific developmental functions. It is presently unknown, however, which particular opioid receptor subtype(s) may be involved. In the pre-ent study, we have used selective radioligand binding conditions in combination with quantitative autoradiography to examine the ontogeny of mu-, kappa- and delta-opioid receptors in the developing rat brain. Membrane binding data indicate that the affinities of mu-, kappa- and delta-sites for radiolabeled drugs are similar in neonatal and adult rats. mu- And kappa-receptors are present in significant densities during early neonatal periods, while delta-receptors appear much later. Autoradiographic data indicate that mu- and kappa-receptors appear early in the development of several brain regions, including the neostriatum, olfactory tubercle and rostral midbrain, and later in other regions such as the thalamus and hypothalamus. Whereas the densities of kappa-binding sites remain relatively constant throughout development, there is a transient appearance and/or redistribution of mu-receptors in several brain areas. delta-Receptors are present in low densities in the basal forebrain at birth. The level of delta-receptor binding increases markedly during the third postnatal week in all brain areas examined. The early appearance of mu- and kappa-receptors during the ontogeny of the brain suggests that these receptors, at least in part, mediate the developmental actions of exogenous and endogenous opioids.

Expression of opioid peptides in tumors

We looked for opioid peptides and their precursors in 108 tumors of both neuroendocrine and nonneuroendocrine origin, using a monoclonal "pan-opioid" antibody, 3-E7, which recognizes the tetrapeptide Tyr-Gly-Gly-Phe (the sequence responsible for pharmacologic activity in all known opioid peptides), in conjunction with polyclonal antibodies directed against representative peptides of each of the three precursors (alpha-endorphin, [met]enkephalin-Arg-Gly-Leu, and dynorphin B). Using the avidin-biotin immunoperoxidase technique, we observed consistent cytoplasmic immunoreactivity (at least focally) in all of 15 adrenal pheochromocytomas, all of 6 thyroid medullary carcinomas, and all of 5 pituitary adenomas. Opioid staining was also observed in parathyroid adenomas (8 of 9), pancreatic islet-cell tumors (7 of 10), carcinoid tumors from various sites (18 of 26), and paragangliomas (1 of 2). There was no immunoreactivity in pulmonary small-cell carcinomas, Merkel-cell tumors of skin, neuroblastomas, or any of the non-neuroendocrine tumors examined. The expression of alpha-endorphin, [met]enkephalin-Arg-Gly-Leu, and dynorphin B varied from tumor to tumor; however, positive staining with the "pan-opioid" antibody was found in each tumor containing at least one of the three precursors. Opioid peptide immunoreactivity was also detected in non-neoplastic cells of the adrenal medulla, pancreatic islets, pituitary, intestinal and bronchial mucosa, and intestinal myenteric plexuses. We conclude that opioid expression within tumors is most likely due to enhanced expression of a normal cell product and that opioid peptides are useful markers of neuroendocrine differentiation in many tumors.

Selective effects of beta-endorphin infused into the hypothalamus, preoptic area and bed nucleus of the stria terminalis on the sexual and ingestive behaviour of male rats

beta-Endorphin was infused bilaterally into the medial preoptic area-anterior hypothalamic continuum at doses of 5, 10 and 40 pmol each side. The highest dose selectively abolished mounting, intromitting and ejaculating in sexually experienced male rats paired with an oestrous female. Males infused with 40 pmol beta-endorphin still followed the female, investigated her anogenital region and other parts of her body, but made abortive attempts to mount. A dose of 5 pmol beta-endorphin had no effect, but 10 pmol proved partially effective. The same males, in other tests, were allowed to ingest a highly preferred, sweet, non-calorific solution (acesulfame-K) in the absence of a female. beta-Endorphin infusions (up to 40 pmol) into the same area of the hypothalamus had no effect on this behaviour. Control males allowed simultaneous access both to an oestrous female and to the sweet solution copulated normally but reduced their ingestive behaviour, despite there being sufficient time during tests for both to occur. beta-Endorphin (40 pmol) infused into the preoptic area-anterior hypothalamic continuum under these conditions suppressed sexual interaction, but ingestion of acesulfame-K increased to values observed when the female was absent. beta-Endorphin infused into neighbouring areas of the brain had different behavioural effects. Sexual behaviour was not inhibited, and ingestion of acesulfame-K was unaltered, when beta-endorphin was infused either into the bed nucleus of the stria terminalis or the rostral ventromedial hypothalamus. However, infusions of cholecystokinin-8 into the ventromedial hypothalamus suppressed acesulfame-K ingestion in most animals, showing that the cannulae were placed in an area regulating ingestive behaviour. The inhibition of sexual behaviour after preoptic area-anterior hypothalamic continuum infusions of beta-endorphin was prevented by either pretreating rats with 1 mg/kg naloxone intraperitoneally, or by infusing a putative delta opiate receptor blocker (0.5 pmols ICI 174864) into the preoptic area-anterior hypothalamic continuum 5 min prior to beta-endorphin treatment. ICI 174864 administered alone significantly increased mount rate and reduced the post-ejaculatory refractory period in copulating males. These experiments suggest that there is both neurochemical and neuroanatomical specificity relating beta-endorphin to sexual behaviour in the male rat.

Nicotine-induced alterations in brain regional concentrations of native and cryptic Met- and Leu-enkephalin

The distribution of cryptic forms (larger enkephalin-containing peptides) in neostriatum, hypothalamus, spinal cord T3-L1 and neurointermediate lobe of pituitary were determined by radioimmunoassay. Optimal conditions for enzymic hydrolysis of the cryptic enkephalins by trypsin and carboxypeptidase B were established. The proportion of total Met- and Leu-enkephalin represented by native pentapeptide varied markedly among these central nervous system regions. Also, the distributions of native and cryptic Met-enkephalin were distinct from that of Leu-enkephalin. Chromatographic separation by HPLC of immunoreactive Met-enkephalin peptides revealed only two peaks corresponding to Met-enkephalin and Met-enkephalin sulfoxide in rather equal amounts. Hydrolysis of cryptic Met-enkephalin also produced only two HPLC-separable peaks of immunoreactive Met-enkephalin, again corresponding to Met-enkephalin and Met-enkephalin sulfoxide. Bioactivity of cryptic striatal Met-enkephalin after hydrolysis was demonstrated by antinociception and catalepsy in rats following its intracerebroventricular injection. Repeated short-term administration of nicotine, 0.1 mg/kg IP six times at 30 min intervals, produced significant increases in native and cryptic Met-enkephalin in striatum, consistent with an increase in neuronal release of Met-enkephalin together with increases in synthesis and processing of proenkephalin A in this brain region. This regimen of nicotine also decreased levels of native Met-enkephalin and of both native and cryptic Leu-enkephalin in neurointermediate lobe, consistent with nicotine-induced release of both proenkephalin A- and prodynorphin-derived peptides from neurointermediate lobe.

Opioid receptor subtypes associated with ventral tegmental facilitation and periaqueductal gray inhibition of feeding

Eating was induced in sated animals by lateral hypothalamic electrical stimulation following central microinjections of mu- (morphine), delta-([D-Pen2,D-Pen5]enkephalin) or kappa-(U-50,488H) receptor agonists, or saline. With stimulation intensity fixed at a moderate level, time to eat 3 45-mg food pellets decreased with increases in stimulation frequency, approaching an asymptote near 7 s at ca. 70 Hz. Ventral tegmental injections (8 but not 0.8 nmol) of each of the 3 drugs reduced the minimum frequency required to produce eating of 3 pellets within 20 s and reduced the frequency at which asymptotic performance was produced; the drugs were equally effective at these doses. Naloxone (2 mg/kg) reversed the effects of each drug; naloxone was slightly more effective against morphine than against DPDPE or U-50,488H. These data suggest that all 3 receptor classes may contribute to the ventral tegmental facilitation of feeding. Periaqueductal gray injections (16 but not 1.6 nmol) of morphine had the opposite effect; they increased the stimulation frequency required to cause eating of 3 pellets in 20 s, and decreased the speed of eating across all stimulation frequencies. Periaqueductal gray injections of the delta- and kappa-agonists were each without effect. These data indicate that the periaqueductal gray inhibition of feeding is mediated solely by mu-receptors and their associated periaqueductal gray circuitry.

Differential effects of mu and kappa opioid analgesics on cerebral glucose utilization in the rat

The autoradiographic 2-deoxy-D-[1-(-14)C]glucose ([14C]2-DG) method was used to map the effects of subcutaneous (s.c.) morphine (8.0 mg/kg), oxymorphone (0.4 mg/kg) and nalbuphine (16.0 mg/kg) on local cerebral glucose utilization (LCGU), an index of local brain function. At the dosages administered, effects of the opioid agonists on LCGU were very restricted. The mu agonists, injected 15 min before [14C]2-DG, decreased LCGU in thalamic nuclei, including some of those which have been implicated in somatosensory processing, and in the dorsal tegmental nucleus. Nalbuphine did not produce these effects, but stimulated LCGU in nuclei of the spinal tract of the trigeminal nerve and in the globus pallidus. All of the effects on LCGU were blocked by prior administration of naloxone (1.0 or 10.0 mg/kg, s.c., 5 min before morphine or nalbuphine, respectively). Our findings suggest that different supraspinal mechanisms are involved in the actions of mu vs kappa opioids, and indicate that the [14C]2-DG procedure might be helpful in elucidating the anatomical areas involved.

Effects of naloxone on hippocampal seizure activity

Although the presence of several types of opiate receptors and ligands has been demonstrated within the hippocampus, little is known about the circumstances in which endogenous opiates may be released. Previous studies have suggested that opiates may be involved in producing seizure activity within the hippocampus, or alternatively, that they may be released by seizure activity within the limbic system to prolong the period of postictal depression and thereby prevent the recurrence of seizures during this period. In this experiment we examined the effect of opiate receptor blockade produced by 20 mg/kg ip naloxone on the duration of afterdischarge produced by high-frequency hippocampal stimulation and on inhibition of subsequent seizure activity in male Sprague-Dawley rats. Contrary to the stated hypotheses, naloxone had no effect on either measure.

An in vitro autoradiographic analysis of mu and delta opioid binding in the hippocampal formation of kindled rats

Recent studies have shown that opioid peptide levels are altered in hippocampal formation of kindled animals. We therefore studied the distributions of mu and delta opioid binding sites in hippocampal formation of kindled and control rats using quantitative in vitro autoradiography. Animals received daily stimulations of the amygdala until they experienced 3 class 5 seizures. Paired control animals underwent implantation of electrodes but were not stimulated. Mu binding sites were labeled with 125I-FK-33824. Twenty-four hours after the last kindled seizure, mu binding was decreased by 32% in stratum pyramidale of CA1 and stratum radiatum of CA2 and by 17-27% throughout most of the rest of CA1, CA2, and CA3. Few, if any, differences were seen between kindled and control animals at 7 or 28 days after the last kindled seizure. Delta binding sites were labeled with 125I-[D-Ala2,D-Leu5]enkephalin in the presence of the morphiceptin analog PL-032. Twenty-four hours after the last kindled seizure, delta binding was decreased only in stratum moleculare of the dentate gyrus. Seven days after the last kindled seizure, delta binding was decreased by 11-17% throughout CA1, CA3, and the dentate gyrus. At 28 days after the last seizure, however, no differences were found between kindled and control animals. Since the decreases in mu and delta opioid binding are transient, they are unlikely to be the molecular basis of the permanent kindling phenomenon. Rather, these changes in opioid binding may represent responses to repeated seizures.

The distribution of proenkephalin-derived peptides in the central nervous system of turtles

The present study was carried out to examine if peptides similar to the various opioid peptide products of mammalian proenkephalin are present in the turtle central nervous system and to determine their distribution. Antisera against several enkephalin peptides were used: leucine-enkephalin (LENK), methionine-enkephalin (MENK), methionine-enkephalin-arg6-phe7 (MERF), methionine-enkephalin-arg6-gly7-leu8 (MERGL), Peptide E (PEPE), and BAM22P. Their specificity and cross-reactivity were carefully examined. The results indicated that LENK, MENK, and MERF (or highly similar peptides) are present in the turtle central nervous system, and that a peptide showing immunological similarity to BAM22P and PEPE also appeared to be present. In contrast, MERGL did not appear to be present. The distributions of the immunoreactive labeling for LENK, MENK, MERF, BAM22P, and PEPE were indistinguishable, and double-label studies showed that LENK, MERF, and BAM22P were colocalized within individual neurons and fibers. Although all of the above substances were observed in the same cell groups, there was some regional variation, in terms of which enkephalin peptide appeared to be most abundant. The distributions of these enkephalin peptides were very similar to those previously described in mammals and birds. Enkephalin was more abundant in the basal ganglia than in overlying telencephalic regions. Within the basal ganglia, enkephalin was present in striatal neurons and fibers and in pallidal fibers, thereby suggesting the existence of an enkephalinergic striatopallidal projection. Sensory relay nuclei of the thalamus were generally poor in enkephalinergic fibers, whereas the hypothalamus was rich in enkephalinergic neurons and fibers. Enkephalinergic neurons and fibers were present in the midbrain central gray. As is true of neurons of the nucleus spiriformis lateralis of the avian pretectum, the neurons of the homologous cell group in turtles, the dorsal nucleus of the posterior commissure of the pretectum, were found to contain enkephalin and have an enkephalinergic projection to the deep layers of the ipsilateral tectum. Enkephalinergic neurons and fibers were also abundant in the entry zones of the trigeminal nerve and dorsal root fibers of the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Intranigral dynorphin-1-13 suppresses kindled seizures by a naloxone-insensitive mechanism

Numerous lines of evidence indicate that the substantia nigra (SN) facilitates the propagation of seizures in kindling and in other seizure models. Intranigral injection of dynorphin-1-13 exerted a potent seizure suppressant action in kindled rats. This seizure suppressant action was dose dependent, spatially specific for the area of the SN and was not blocked by naloxone (2 mg/kg i.p.). This finding extends previous work indicating that treatments which reduce SN output exert an anticonvulsant action and further suggests that opioid peptides endogenous to the SN may regulate seizure susceptibility in the kindling model.

A quantitative light microscopic analysis and ultrastructural description of cholecystokinin-like immunoreactivity in the spinal trigeminal nucleus of the rat

The spinal trigeminal nucleus is involved in orofacial sensory transmission. Cholecystokinin octapeptide has been identified in axons in this nucleus and appears to play a role in the transmission of orofacial sensation from the trigeminal ganglia to the spinal trigeminal nucleus. Although cholecystokinin has been reported in axonal processes within the spinal trigeminal nucleus at the light microscopic level, nothing is known about the synaptic relationships of these cholecystokinin axons. The goals of this study were to quantitatively determine the volume fraction of cholecystokinin-like immunoreactive cell bodies and fibers in the three subnuclei of the spinal trigeminal nucleus, to provide the first ultrastructural description of cholecystokinin-like immunoreactive processes within these subnuclei and to analyse the synaptic relationships of cholecystokinin-like immunoreactive processes within the spinal trigeminal nucleus neuropil. Cholecystokinin-like immunoreactivity was localized by the peroxidase-antiperoxidase method or the peroxidase labeled, avidin-biotin technique and quantified at the light microscopic level by point counting. Immunoreactive fibers were present in all three subnuclei, but the greatest volume fraction of immunoreactive axons was obtained in laminae I and II of the nucleus caudalis. No immunoreactive cell bodies were evident in any of the subnuclei. The majority of immunoreactive profiles in all three subnuclei were identified ultrastructurally as axon terminals that contained both small and medium sized agranular vesicles and infrequently, large dense core vesicles. These immunoreactive terminals were usually found in close contact with non-immunoreactive dendrites with which they were observed to form asymmetric synapses. Immunoreactive terminals were occasionally observed to contact the cell bodies of large non-immunoreactive neurons on the border of laminae I and II in the nucleus caudalis. These results indicate that cholecystokinin-like immunoreactive processes are present throughout the spinal trigeminal nucleus, and in nucleus caudalis show a distribution similar to that reported for the spinal cord dorsal horn. Immunoreactive axons make synaptic contact with both the dendrites and perikarya of spinal trigeminal nucleus neurons. No axoaxonic synapses were observed. These findings suggest that cholecystokinin plays an important role in spinal trigeminal nucleus function. The possible colocalization of cholecystokinin and substance P in the spinal trigeminal nucleus, and the possible role of cholecystokinin in attenuating the action of opioids in the spinal trigeminal nucleus are also discussed.

Comparison of met-enkephalin-, dynorphin A-, and neurotensin-immunoreactive neurons in the cat and rat spinal cords: I. Lumbar cord

This study compared the distribution of methionine enkephalin-, dynorphin A 1-8-, and neurotensin-immunoreactive (IR) perikarya in laminae I and IV-VII of selected segments of lumbar spinal cord of cat(L5) and rat(4). Immunoreactive neurons for each peptide were found throughout the dorsal horn and dorsal lamina VII but were quantified only within laminae I and IV-VII. In lamina I, both large (greater than 20 micron) and small (less than 20 micron) IR neurons were identified. Large IR neurons for each peptide in both species resembled Waldeyer neurons studied by Golgi stain and were outnumbered by small IR neurons. Comparison among the laminae of the distribution of met-enkephalin IR neurons showed a similar pattern in the two species with the majority of IR neurons (greater than 65%) in laminae V and VI. Differences in laminar distribution occurred between species for the other peptides. Dynorphin IR neurons were greatest in number in lamina V in rat but greatest in number in laminae I and V in cat. Neurotensin IR neurons occurred predominantly in cat lamina I but were nearly equal in density in rat laminae I and VI. The topographic distribution of each peptide in laminae V and VI was similar between the two species with IR neurons occurring laterally in lamina V and more medially in lamina VI. Comparisons between species of the numbers of IR neurons/segment indicated distinct relationships for each peptide. The number of met-enkephalin IR neurons in laminae of cat L5 was generally two times greater than the number of IR neurons in the same laminae of rat L4, except in laminae I and IV, where the numbers were nearly equal. In contrast, the number of dynorphin IR neurons in cat laminae was generally one-half the number in rat, except in lamina I, where the number in cat was two times greater than rat. A high degree of variability occurred in laminar comparisons of neurotensin IR neurons. Neurotensin IR neurons in lamina I of cat outnumbered those of rat 2:1, but in laminae IV-VII, the ratio of cat to rat IR neurons varied from 1:1 to 1:20. The met-enkephalin, dynorphin, and neurotensin IR neurons quantified in this study may be interneurons or may serve as projection neurons to brainstem and/or thalamic nuclei. The observed differences in distribution may be relevant to differences in spinal cord physiology in the two species.

The role of reward pathways in the development of drug dependence

In commenting on the discovery of "opiate" receptors, Goldstein (1976) said: "It seemed unlikely, a priori, that such highly stereospecific receptors should have been developed by nature to interact with alkaloids from the opium poppy" (p. 1081). Endogenous opioid peptides and opioid receptor systems have now been identified in invertebrates that are unlikely to have had ancestors exposed to opium poppies (Kavaliers et al., 1983; Kream et al., 1980; Leung and Stefano, 1984; Stefano et al., 1980). Moreover, endogenous opioids play a role in stress-induced feeding in the slug (Kavaliers and Hirst, 1986) just as they play a role in stress-induced feeding in rodents (Lowy et al., 1980; Morley and Levine, 1980). If we are to understand the actions of opiates and other drugs of abuse we must understand them in terms of their abilities to interact with neural systems that evolved in the service of primitive biological functions, long before any serious incidence of addiction itself. The most primitive axes of the biological substrates of behavior are the axes of approach and withdrawal. Addictive drugs appear to be able to activate the mechanisms of approach, which is termed "positive reinforcement" and to inhibit the mechanisms of withdrawal, which is termed "negative reinforcement." Anatomically distinct sets of pathways have evolved to serve these two forms of reward. Activation of the medial forebrain bundle and associated structures serves positive reinforcement and induces forward locomotion. Approach and forward locomotion are the unconditioned responses to positive reinforcing stimuli such as food and sex partners, and approach to environmental objects and positive reinforcement is induced by electrical stimulation of this structure. The locomotor stimulating effects and the positive reinforcing effects of opiates and psychomotor stimulants result from their activation of this mechanism; stimulants activate the mechanism at the level of dopaminergic synapses of the nucleus accumbens, frontal cortex, and perhaps other forebrain structures, while opiates activate the system at two points: at the level of the dopaminergic synapse and at the level of the afferents to the dopaminergic cell bodies. Ethanol, nicotine, caffeine and phencyclidine stimulate both locomotor activity and dopamine turnover, but their sites of interaction with reward pathways have not yet been identified. Benzodiazepines and barbiturates stimulate locomotor activity without stimulating dopamine turnover; they may interact with reward pathways at a synapse efferent to the dopaminergic link in the pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Antidiuretic effects of methionine-enkephalin and 2-D-alanine-5-methionine-enkephalinamide microinjected into the hypothalamic supraoptic and paraventricular nuclei in a water-loaded and ethanol-anesthetized rat

Effects of methionine-enkephalin (ME) and 2-D-alanine-5-methionine-enkephalinamide (DAMEA) microinjected into the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei, which contain neurons synthesizing and releasing antidiuretic hormone, upon the outflow and the osmotic pressure of urine and the other visceral functions were studied in a rat which was loaded with water and anesthetized with ethanol. These opioid peptides when microinjected into the SON or PVN induced potent antidiuretic effects in dose-dependent and time-dependent manners with no significant effects on the other visceral functions. The approx. ED50 values for DAMEA were 1.3 (in the SON) and 0.7 (in the PVN) nmol, and the values for ME were 110 (in the SON) and 60 (in the PVN) nmol. The antidiuretic effects showed slow onset and long duration, with a minimal urine outflow at approx. 0.5 hr after microinjection and an approx. 2 hr-duration. The effects induced by the opioid peptides were inhibited by pretreatment with naloxone or atropine, without effects of pretreatment with alpha- or beta-adrenoceptor antagonists, suggesting that the antidiuretic effects were mediated through an opioid receptor having low sensitivity to naloxone and also possibly mediated through a muscarinic receptor which was stimulated probably by the ACh released by the opioid peptides.

Steroidal modulation of the regulatory neuropeptides: luteinizing hormone releasing hormone, neuropeptide Y and endogenous opioid peptides

Recent studies show that a large number of neuropeptides may play important roles in the hypothalamic control of reproduction and related sexual, feeding and locomotor behaviours. Based on the evidence summarized here we propose that gonadal steroids may exert a "trophic" influence on the regulatory peptides namely LHRH, NPY and EOP locally in the hypothalamus.

Behavioral effects of centrally administered dynorphin and [D-ala2-D-leu] enkephalin (DADLE) in rats

Dynorphin and [D-ala2-D-leu]enkephalin (DADLE) were administered directly into the cerebrolateral ventricles of rats and effects on various indices of sensorimotor function and retention of a passive avoidance task were measured. Dynorphin markedly suppressed exploratory motor activity and decreased responsiveness to an acoustic stimulus. Although increases in latency to respond to a noxious thermal stimulus were seen in rats after dynorphin, these changes were always associated with alterations in motor capacity. Injection of dynorphin immediately after a passive avoidance training trial had no significant effect on retention 1 week later. The physiological effects of DADLE were clearly different than those of dynorphin. DADLE produced a biphasic decrease followed by an increase in motor activity and an increased acoustic startle reactivity. DADLE had no effect on reactivity to a noxious thermal stimulus. Posttrial administration of DADLE significantly impaired retention of a step-through passive avoidance task 1 week after training. These data indicate different neurobiological roles for kappa and delta opiate receptors in the central nervous system.

Striato-nigral dynorphin and substance P pathways in the rat. I. Biochemical and immunohistochemical studies

The effect of striatal ibotenic acid lesions on dynorphin-, substance P- and enkephalin-like immunoreactivities in the substantia nigra has been studied with immunohistochemistry as well as biochemistry. A comparison was made with the effects produced by intranigral ibotenic acid lesion and by 6-hydroxy-dopamine injection into the medial forebrain bundle. In addition, the effect of the striatal lesions on nigral glutamic acid decarboxylase (GAD)-positive structures was analysed with immunohistochemistry. The effect of the lesions was analysed functionally in the Ungerstedt rotational model, in order to obtain a preliminary evaluation of the extent of the lesions. The striatal lesions produced a parallel depletion of dynorphin and substance P levels in the substantia nigra, pars reticulata, ipsilateral to the treated side, which was dependent upon the extent and location of the lesion. Ibotenic acid lesions into the tail and the corpus of the striatum produced stronger nigral-peptide depletion than lesions in the head and the corpus of the striatum. Comparison of placement of lesions and localization of depleted area in the substantia nigra revealed a topographical relationship. Furthermore, the nigral depletion patterns of dynorphin and substance P were similar. The immunohistochemical analysis revealed that also GAD-positive fibers in the pars reticulata to a large extent disappeared after striatal lesions, in parallel to the dynorphin- and substance P-positive fibers. However, the depletion was less pronounced for GAD than for the peptides, probably related to presence of local GABA neurons in the zona reticulata of the substantia nigra. These results indicate that with the types of lesion used in this study it is not possible to provide evidence for a differential localization within the striatum of dynorphin-, substance P- and GABA-positive cell bodies projecting to the substantia nigra. The radioimmunoassay showed that (Leu)- but not (Met)-enkephalin was affected to the same extent as the dynorphin peptides, supporting the view that (Leu)-enkephalin in the pars reticulata of the substantia nigra is derived from proenkephalin B and not from proenkephalin A. In the immunohistochemical analysis (Met)-enkephalin-like immunoreactivity could only be detected in the pars compacta of the substantia nigra and did not seem to be affected by any of the lesions. The striatal lesions produced a behavioural asymmetry, which could be disclosed by stimulating the rats with apomorphine, which produced ipsilateral rotation.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of somatostatin on the vagal motor neuron in the rat

Somatostatin-14 (SOM) effects on electrical properties of membrane in rat brainstem slice preparations were studied in vitro by intracellular recording. Vagal motoneurons in the nucleus dorsalis motoris nervi vagi (DMV) were hyperpolarized by SOM. SOM increased both negativity of membrane potential and input membrane conductance, and decreased synaptic noise. The effects persisted during synaptic blockade by tetrodotoxin (TTX) or [Ca]o-free-high-[Mg]o perfusion. The reversal potential of the hyperpolarization induced by SOM depended on [K]o concentration. Hill's coefficient calculated from the dose-response curve was 2. The results suggest that SOM may inhibit visceral organ functions through the DMV.

Coexistence of enkephalin and dynorphin immunoreactivities in neurons in the dorsal gray commissure of the sixth lumbar and first sacral spinal cord segments in rat

The dorsal gray commissure (DGC) of the sixth lumbar (L6) and first sacral (S1) spinal cord segments in the rat has been shown to contain several different peptides, including enkephalin (ENK) and dynorphin (DYN). The present study was conducted to determine if DYN and ENK immunoreactivities coexist in neurons in the DGC in L6 and S1. Coexistence was determined using the elution/restaining technique of Tramu in which sections were stained first with anti-DYN then with anti-ENK after elution of the DYN antiserum. The number and location of DYN-immunoreactive cells was compared to the number and location of ENK-immunoreactive cells using photographic negatives. Of 67 ENK-immunoreactive cells counted in 20 sections through L6, 54 also contained DYN immunoreactivity. Of 100 ENK-immunoreactive cells counted in 47 sections through S1, 95 also contained DYN immunoreactivity. No cells with only DYN immunoreactivity were seen. S1 was found to contain a significantly greater number (P less than 0.005) of ENK-immunoreactive cells that also contained DYN than L6. The results of these studies indicate that ENK and DYN immunoreactivities coexist in most, but not all, neurons in the DGC of L6 and S1 and that a difference exists between L6 and S1 in the extent of coexistence of these peptides. Further studies are necessary to determine if coexistence of opioids is limited only to autonomic regions of the nervous system and also to define the functional significance of this coexistence.

Identification of the tridecapeptide dynorphin B (rimorphin) within perikarya of rat duodenum

Using an immunofluorescence microscopic staining technique, the opioid peptide dynorphin B (rimorphin) was revealed within neuronal cell bodies of the rat duodenum. Dynorphin B immunoreactive perikarya were revealed in the myenteric and submucousal plexus as well as in the longitudinal muscle layer. They were large in diameter and round in shape and they contained a large round nucleus. Because no dynorphin B immunofluorescent nerve fibre and terminal could be noted it might be that dynorphin B is further cleaved by proteases into the bioactive opioid pentapeptide Leu-enkephalin and dynorphin B(6-13). These findings might also indicate that dynorphin B is processed within duodenal perikarya and that it has important physiological roles in the rat duodenum.

Distribution of dynorphin and enkephalin peptides in the rat brain

The neuroanatomical distribution of dynorphin B-like immunoreactivity (DYN-B) was studied in the adult male and female albino rat. The distribution of DYN B in colchicine- and noncolchicine-treated animals was also compared to that of another opioid peptide derived from the prodynorphin precursor dynorphin A (1-8) (DYN 1-8), and an opioid peptide derived from the proenkephalin precursor met-enkephalin-arg-gly-leu (MERGL). DYN B cell bodies were present in nonpyramidal cells of neo- and allocortices, medium-sized cells of the caudate-putamen, nucleus accumbens, lateral part of the central nucleus of the amygdala, bed nucleus of the stria terminalis, preoptic area, and in sectors of nearly every hypothalamic nucleus and area, medial pretectal area, and nucleus of the optic tract, periaqueductal gray, raphe nuclei, cuneiform nucleus, sagulum, retrorubral nucleus, peripeduncular nucleus, lateral terminal nucleus, pedunculopontine nucleus, mesencephalic trigeminal nucleus, parabigeminal nucleus, dorsal nucleus of the lateral lemniscus, lateral superior olivary nucleus, superior paraolivary nucleus, medial superior olivary nucleus, ventral nucleus of the trapezoid body, lateral dorsal tegmental nucleus, accessory trigeminal nucleus, solitary nucleus, nucleus ambiguus, paratrigeminal nucleus, area postrema, lateral reticular nucleus, and ventrolateral region of the reticular formation. Fiber systems are present that conform to many of the known output systems of these nuclei, including major descending pathways (e.g., striatonigral, striatopallidal, reticulospinal, hypothalamospinal pathways), short projection systems (e.g., mossy fibers in hippocampus, hypothalamo-hypophyseal pathways), and local circuit pathways (e.g., in cortex, hypothalamus). The distribution of MERGL was, with a few notable exceptions, in the same nuclei as DYN B. From these neuroanatomical data, it appears that the dynorphin and enkephalin peptides are strategically located in brain regions that regulate extrapyramidal motor function, cardiovascular and water balance systems, eating, sensory processing, and pain perception.

Effects of opioid peptides on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Effects of opioid peptides on immunoreactive corticotropin-releasing factor (I-CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. beta-Endorphin (0.3 - 30 nM), dynorphin (0.3 - 30 nM) and FK 33-824 (1 - 10 microM) suppressed basal I-CRF release in a dose-dependent fashion. At 2.2 nM concentrations of these peptides, mean percent inhibition was 56% for beta-endorphin; less than 5% for alpha-endorphin; 44% for dynorphin; 23% for leucine-enkephalin; 6% for methionine-enkephalin; less than 5% for FK 33-824; and less than 5% for D-ala2, D-leu5-enkephalin. The inhibitory effects of beta-endorphin and enkephalins were completely blocked by naloxone, but those of dynorphin were only partially blocked. These results suggest that opioid peptides act through opioid receptors and inhibit I-CRF release from the hypothalamus under our conditions. Therefore, endogenious opioid peptides may have a physiological role in the CRF-releasing mechanism of the hypothalamus.

Centrally-administered opioid selective agonists inhibit drinking in the rat

The effects of intracerebroventricular injection of mu (morphine), kappa (dynorphin-(1-13), ethylketocyclazocine, and U50,488H), and delta ([D-Pen2, D-Pen5]enkephalin) opioid agonists on water intake of 14 hr water deprived rats was studied. All agonists caused a dose related decrease in time spent drinking, with a rank order potency of dynorphin-(1-13) greater than morphine greater than ethylketocyclazocine greater than [D-Pen2, D-Pen5]enkephalin = U50, 488H. With the exception of morphine, all of the compounds increased the latency to begin drinking, but only at the highest doses tested. The rank order potency for this endpoint was dynorphin-(1-13) = ethylketocyclazocine greater than [D-Pen2, D-Pen5]enkephalin greater than U50, 488H. The potent inhibition of drinking following centrally-given dynorphin-(1-13), at doses that did not affect the latency to begin drinking, supports a role for endogenous dynorphin in the homeostatic control of water balance. This function may not be primarily mediated through activation of a kappa opioid receptor since dynorphin-(1-13) was 80-230 times more potent than the selective kappa agonist, U50,488H or ethylketocyclazocine.

Changes in the immunoreactivities of an opioid peptide leumorphin in the hypothalamus and anterior pituitary during the estrous cycle of the rat and their relation to sexual behavior

Leumorphin, an opioid peptide whose functions are unknown, is found in mammalian brain and pituitary and stimulates lordosis behavior in estrogen-treated female rats. To elucidate the role of leumorphin in the physiological control of female sexual behavior, the levels of immunoreactive (ir) leumorphin as well as ir dynorphin (dynorphin A) were measured in the rat brain and pituitary during the estrous cycle. There was a clear variation of ir leumorphin in the hypothalamus and anterior pituitary during the estrous cycle. The levels of ir leumorphin in the hypothalamus and anterior pituitary on the afternoon of proestrus were significantly higher (P less than 0.01) than those on the afternoons of estrus and metestrus. The rise in the hypothalamic levels of ir leumorphin on the afternoon of proestrus was correlated with the receptivity of lordosis during the estrous cycle. Furthermore, there was a close correlation with ir dynorphin levels. These findings are in agreement with studies demonstrating a common precursor for leumorphin and dynorphin. Ir leumorphin in the hippocampus and neurointermediate pituitary did not change significantly during the estrous cycle. Because the leumorphin antiserum used recognizes rimorphin (dynorphin B) 1.78 times more than porcine leumorphin on a molar basis, high performance-gel permeation chromatography was done on pooled extracts of hypothalamus taken at proestrus and estrus. The peak in the leumorphin-like substance in the activation of sexual behavior is discussed.

Neuronal architecture in the rat central nucleus of the amygdala: a cytological, hodological, and immunocytochemical study

The organization of neurons in the rat central nucleus of the amygdala (CNA) has been examined by using Nissl stain and immunocytochemical and retrograde tracing techniques. Four main subdivisions were identified on the basis of quantitative analyses of Nissl-stained material: medial (CM), lateral (CL), lateral capsular (CLC), and ventral (CV). An intermediate subdivision (CI), previously described by McDonald ('82), was apparent only in animals that had HRP-WGA injected into the bed nucleus of the stria terminalis. Large populations of neurotensin-, corticotropin-releasing factor (CRF)-, and enkephalin-immunoreactive neurons were present within the lateral divisions (mainly CL), although they were also seen within CM. Somatostatin-immunoreactive neurons were distributed mainly within CL and CM. Within CL, neurotensin- and enkephalin-immunoreactive neurons were more numerous laterally whereas CRF- and somatostatin-immunoreactive neurons were more numerous medially. Substance P-immunoreactive neurons were almost exclusively confined to CM. Only a few cholecystokinin- and vasoactive-polypeptide-immunoreactive neurons were seen in the CNA, and they were observed within CL, CV, and CM. The majority of neurons projecting to the dorsal medulla, hypothalamus, and ventral tegmental area were located within CM, although a significant number of cells were also seen within CL. Efferent projections to the bed nucleus of the stria terminalis were found to arise from neurons located within all subdivisions of the CNA. Thus, the distributional patterns of peptidergic and efferent neurons were not confined to individual cytoarchitectonically- defined subdivisions of the CNA. Rather, the results suggest overlapping medial to the lateral trends. Comparisons with the results of previous studies indicate that peptidergic and afferent terminal distribution patterns are more restricted to individual cytoarchitectonically defined subregions of the CNA. These observations suggest that the detailed cytoarchitecture of the CNA more likely reflects the functional integration of afferents rather than the organization of the CNA output neurons.

Quantitative autoradiographic analysis of mu and delta opioid binding sites in the rat hippocampal formation

The distributions of mu and delta opioid binding sites were studied in rat hippocampal formation by using quantitative in vitro autoradiography. Mu binding sites, labeled with 125I-FK-33824, showed a highly organized laminar distribution. Binding was greatest at the foot of the obliterated hippocampal fissure in stratum lacunosum-moleculare of CA3. Stratum pyramidale and stratum lacunosum-moleculare of CA2 and stratum pyramidale of CA3 were next highest in mu binding, followed by stratum oriens and stratum radiatum of CA2, stratum oriens of CA3, and stratum pyramidale of CA1. The distribution of delta binding sites, labeled with 125I-D-ala2-D-leu5-enkephalin in the presence of the unlabeled mu receptor ligand PL-032, was similar to the distribution of mu binding in that binding within each region was greatest in a band centered over stratum pyramidale and in stratum lacunosum-moleculare. Over all, delta binding was greatest in CA2 followed by CA3 and then CA1. Compared to mu binding, delta binding was relatively enriched in stratum moleculare of the dentate gyrus. These laminar distributions correlate reasonably well with the distribution of enkephalin immuno-reactivity in hippocampal formation, although binding was surprisingly low in stratum lucidum, an area rich in dynorphin and enkephalin immunoreactivity.

Design and interpretation of opiate antagonist trials in dementia

In view of the reports of possible beneficial effects of naloxone in dementia, rationales and strategies for studying endogenous opiate systems are reviewed. Important considerations in the design and interpretation of clinical investigations using naloxone are also reviewed. The nature and distribution of endogenous opiate systems are summarized from an historical perspective. Endogenous opiate systems are distributed throughout the central nervous system and play important roles in a variety of brain functions, including memory and learning. In view of this, several rationales are evident for studying endogenous opiate systems in dementia, since it is a syndrome in which structures known to contain opiate systems are disturbed, functions modulated by opiate systems are disturbed, and other neurotransmitter systems (functionally linked to endogenous opiate systems) are disturbed. Different strategies for studying endogenous opiate systems are reviewed, including examination of body fluids and pharmacologic challenge studies. Naloxone hydrochloride, a competitive opiate receptor antagonist, is a commonly used pharmacologic agent. The design of a multidose naloxone study of 12 dementia patients is discussed, with reference to the pharmacokinetics, pharmacodynamics, and specificity of naloxone as well as to the nature of the dependent measures selected for this study. No cognitive benefit was observed in this study. Behavioral arousal was observed at naloxone doses, with more evident psychomotor retardation at higher doses. These findings are contrasted with the results of naloxone challenges in other studies. The varying effects of naloxone within and across populations can be conceptualized in terms of the basic and clinical considerations previously discussed. The importance of dose-finding studies is stressed for this and other drug trials.

Distribution of immunoreactive metorphamide (adrenorphin) in discrete regions of the rat brain: comparison with Met-enkephalin-Arg6-Gly7-Leu8

The distribution of immunoreactive (ir)-metorphamide (adrenorphin) in 101 microdissected rat brain and spinal cord regions was determined using a highly specific radioimmunoassay. The highest concentration of metorphamide in brain was found in globus pallidus (280.1 fmol/mg protein). High concentrations of ir-metorphamide (greater than 120 fmol/mg protein) were found in 9 nuclei, including central amygdaloid nucleus, lateral preoptic area, anterior hypothalamic nucleus, hypothalamic paraventricular nucleus, interpeduncular nucleus, periaqueductal grey matter and nucleus of the solitary tract. Moderate concentrations of the peptide (between 60 and 120 fmol/mg protein) were found in 47 brain nuclei such as nucleus accumbens, bed nucleus of stria terminalis, several septal and amygdaloid nuclei, most of the hypothalamic nuclei, ventral tegmental area, red nucleus, raphe nuclei, lateral reticular nucleus, area postrema and others. Low concentrations or ir-metorphamide (less than 60 fmol/mg protein) were measured in 41 nuclei, e.g., cortical structures, hippocampus, caudate nucleus, thalamic nuclei, supraoptic nucleus, substantia nigra, vestibular nuclei, cerebellum (nuclei and cortex). The olfactory bulb has the lowest metorphamide concentration (5.8 fmol/mg protein). Spinal cord segments exhibit very low peptide concentrations.

Comparison of the substance P- and dynorphin-containing projections to the substantia nigra: a radioimmunocytochemical and biochemical study

A series of knife cuts were made in the striatonigral pathway and changes in dynorphin B (Dyn) and substance P (SP) input to the substantia nigra were examined using radiolabeled antibodies and radioimmunoassay (RIA). Cryostat cut sections were incubated with primary antibody followed by a secondary antibody labeled with 125I. Apposition of the radiolabeled sections to LKB Ultrofilm generated an image that was qualified by computerized optical densitometry. The striatonigral system served as a model system for comparing the quantitative capabilities of radioimmunocytochemistry with RIA. The results indicated a strong correlation between optical densitometry measurements and RIA for both Dyn (r = 0.97) and SP (r = 0.98) antisera. This suggests that radioimmunocytochemistry may be used for quantitative, as well as, qualitative descriptions of the distribution of tissue antigens. Knife cuts separating the rostral caudate putamen from the substantia nigra resulted in less than 40% depletion of dynorphin and substance P in the nigra pars reticulata, leaving the levels of both peptides relatively unchanged in the pars lateralis. More caudal knife cuts resulted in progressively greater depletions of both peptides in the pars reticulata and pars lateralis.

Conversion of dynorphin-(1-9) to [Leu5]enkephalin by the mouse vas deferens in vitro

The inhibitory action of dynorphin-(1-9) on the electrically stimulated mouse vas deferens was seen to be antagonised by the delta-selective opioid antagonist ICI 174864. The observed delta-receptor mediated responses were partially, but not totally, prevented by peptidase inhibitors which protect the C- and N-termini of dynorphin-(1-9). [3H]Dynorphin-(1-9) is rapidly degraded by slices of vasa deferentia of the mouse. The major product of this metabolism co-elutes with [Leu5]enkephalin on reverse phase HPLC. It is concluded that a major component of the inhibitory effects of dynorphin-(1-9) on the mouse vas deferens is mediated by degradation to [Leu5]enkephalin which in turn acts through delta-receptors. It is possible that in other in vitro and in vivo systems, the effects produced by dynorphin-(1-9) might be similarly mediated by delta-receptor activation.

Release of immunoreactive Met-enkephalin from the spinal cord by intraventricular beta-endorphin but not morphine in anesthetized rats

Effect of beta-endorphin and morphine injected intraventricularly on the release of immunoreactive Met-enkephalin, Leu-enkephalin and dynorphin1-13 from the spinal cord was studied in anesthetized rats. Intraventricular beta-endorphin, 16 micrograms, caused a marked spinal release of immunoreactive Met-enkephalin and to a much lesser extent, of immunoreactive Leu-enkephalin while intraventricular morphine, 40 micrograms, did not cause any significant release of immunoreactive enkephalins. The release of immunoreactive Met-enkephalin was not blocked by the pretreatment with 5 mg/kg naloxone, i.p. Immunoreactive dynorphin1-13 was not released by either beta-endorphin or morphine. High performance liquid chromatographic analysis indicated that immunoreactive Met-enkephalin released by beta-endorphin had a retention time identical to [3H]Met-enkephalin. These findings in conjunction with previous pharmacological studies suggest different modes of pharmacological action for beta-endorphin and morphine.

Effects of morphine and naloxone on thresholds of ventral tegmental electrical self-stimulation

The involvement of opioid systems in self-stimulation reward was investigated by studying the effects of the opioid antagonist naloxone (10 mg/kg s.c.) and graded doses of morphine (0.3-5.0 mg/kg s.c.) on intracranial electrical self-stimulation (ICSS) in rats with electrodes in the ventral tegmental area. Lever pressing for ICSS was analyzed using three different procedures: determination of response rate i.e. the number of responses to high and threshold currents, measuring threshold current when response rate was kept low and relatively constant, determination of 'behavioural' threshold using a two-lever procedure in which a response on one lever resulted in a reset of the decreasing current to a high current contingent on a response to the other lever. It was found that low doses of morphine increased the response rate of ICSS behaviour and decreased the threshold whereas the higher doses decreased the response rate but also decreased the threshold current when measured with a rate insensitive procedure. Naloxone raised the threshold for ICSS and caused a corresponding decrease of response rate. In a second series of experiments in which the behaviour of rats which had been tested in one procedure was analysed using one of the other methods, it was observed that naloxone caused smaller changes, while the effects of morphine were at least comparable to those observed in the first series of experiments. The present data suggest that response rate insensitive procedures to analyse ICSS should be preferred to response rate sensitive ones, especially when the interaction of depressant drugs such as morphine with reward mechanisms is investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny and regional distribution of proenkephalin- and prodynorphin-derived peptides and opioid receptors in rat hippocampus

Levels of prodynorphin- and proenkephalin-derived peptides were determined in whole hippocampus of prenatal and early postnatal rats and in five regions of the hippocampus of the adult rat. Using autoradiography, opioid receptor subtypes were localized in coronal sections of adult hippocampus. The opioid peptides are present in very low concentrations in prenatal hippocampus, with only dynorphin B and alpha-neo-endorphin being present in significant amounts. The main increase in concentrations of the opioid peptides occur between day 7 and 14 postnatally, when dynorphin A, dynorphin A-(1-8), dynorphin B and alpha-neo-endorphin reach their adult levels. beta-Neo-endorphin and [Met]enkephalyl-Arg-Gly-Leu do not reach their maximal level until later in development. There is a distinct differential distribution of the opioid peptides in the subregions of the hippocampus; the subiculum and CA1 are relatively poor in prodynorphin-derived peptides but do contain significant amounts of [Met]enkephalin and [Leu]enkephalin. Very high concentrations of dynorphin B and alpha-neo-endorphin are present in region CA4. Dynorphin A-(1-8) and [Met]enkephalin have their highest concentrations in the dentate gyrus. There is a 5-fold higher concentration of [Met]enkephalin in the ventral hippocampus compared to the dorsal hippocampus. A similar trend is seen with dynorphin A-(1-8) but not with the other opioid peptides. The most abundant opioid receptor population in the hippocampus is of the mu type and it is densest in and around stratum pyramidale of the region CA3. There are relatively few kappa opioid receptors in the rat hippocampus. These results indicate the presence of at least two independent opioid neuronal systems (enkephalin and dynorphin) in rat hippocampus and the presence of mu-, delta- and kappa-opioid receptor subtypes.

Colocalization of dynorphin-A(1-17) and dynorphin-A(1-8) within some perikarya of rat duodenum: immunohistochemical evidence for the presence of two separate dynorphinergic systems

Adjacent serial sections through the rat duodenum were alternately stained for immunofluorescence microscopic studies with specific anti-sera directed to the opioid peptides dynorphin-A(1-17) and dynorphin-A(1-8), respectively. This resulted in the evidence that two separate dynorphinergic neuron populations are present there: intramural neurons, revealing a colocalization of dynorphin-A(1-17) and dynorphin-A(1-8), were round, contained a large and round nucleus and were lying sporadically in the longitudinal muscle layer as well as bulb-shaped neurons expressing only a dynorphin-A(1-8) immunoreactivity. The latter were recognized abundantly in the myenteric plexus. Myenteric plexus nerve fibres and terminals were immunoreactive for dynorphin-A(1-8), but not for dynorphin-A(1-17). Dynorphin-A(1-8) immunostained nerve terminals formed close contacts with large non-dynorphinergic myenteric plexus perikarya. These findings might indicate that dynorphin-A(1-8) is processed directly from its prodynorphin ('preproenkephalin B') precursor within myenteric plexus perikarya and indirectly via dynorphin-A(1-17) within intramural perikarya, indicating the presence of two separate dynorphinergic systems in the rat duodenum.

Autoradiographic localization of benzomorphan binding sites in rat brain

The benzomorphan subpopulation of opiate binding sites was labeled by [3H]diprenorphine in the presence of unlabeled ligands selected to quench mu and delta opiate binding sites. The distribution of benzomorphan binding sites was then localized autoradiographically. Areas particularly enriched in these sites were nucleus solitarius, nucleus ambiguus, substantia gelantinosa of the trigeminal nerve, the habenula, and the medial nucleus of the amygdala. Within hippocampal formation, binding was relatively enhanced in the pyramidal and granule cell layers. Within the basal ganglia, binding was greatest in the dorsomedial caudate nucleus and least in the globus pallidus. No 'patches' of increased binding were present in the striatum. The interstitial nucleus of the stria terminalis and the medial preoptic nucleus also showed significant binding. This distribution differs from the distributions of mu, delta and kappa opiate binding and is quite similar to the distribution of beta-endorphin immunoreactivity. These observations support the hypothesis, based on biochemical studies in brain membranes, that benzomorphan binding sites may represent the ligand recognition sites of putative epsilon receptors.

Opiates and opioid peptides modify sensory evoked potentials and synaptic excitability in the rat dentate gyrus

The effects of morphine and the synthetic opioid peptide D-Ala2-MePhe4-Met-O-ol-enkephalin (FK 33-824) on averaged (AEPS) potentials evoked by a tone and extracellular synaptic potentials (EPSs) in the perforant path, recorded from the outer molecular layer (OM) of the dentate gyrus, were examined in rats trained to respond in an auditory discrimination task. Potentials evoked by a tone were systematically altered by both peripheral (intraperitoneal) and central (intracerebroventricular) administration of opioids. The short-latency negative (N1) component of the average evoked potential was increased in amplitude and the longer-latency negative (N2) component was decreased in amplitude by administration of opioids. At the same time, perforant path extracellular synaptic potentials were enhanced after administration of opioids. The changes in the average evoked potential and extracellular synaptic potentials in the perforant path were reversed by subsequent administration of naloxone. The significance of these results is discussed in terms of a possible role of endogenous opioid peptides in modulating the synaptic efficacy of the perforant path during the transmission of sensory information to the hippocampus from the entorhinal cortex.

Time of origin of opioid peptide-containing neurons in the rat hypothalamus

By using a combined technique of immunocytochemistry and [3H]thymidine autoradiography, we have determined the "birth date" of opioid peptide-containing neurons in several hypothalamic nuclei and regions. These include proopiomelanocortin (POMC) neurons (represented by ACTH immunoreactivity) in the arcuate nucleus; dynorphin A neurons in the supraoptic and paraventricular nuclei and the lateral hypothalamic area; and leu-enkephalin neurons in the periventricular, ventromedial, and medial mammillary nuclei, as well as in preoptic and perifornical areas. Arcuate POMC neurons were born very early in embryonic development, with peak heavy [3H]thymidine nuclear labelling occurring on embryonic day E12. Supraoptic and paraventricular dynorphin A neurons were also labelled relatively early (peak at E13). The lateral hypothalamic dynorphin A neurons showed peak heavy labelling also on day E12. By contrast, leu-enkephalin neurons in the periventricular nucleus and medial preoptic area exhibited peak heavy nuclear labelling on day E14. Furthermore, perifornical and ventromedial leu-enkephalin neurons were also born relatively early (peak on days E12 and E13, respectively). However, the leu-enkephalin neurons in the medial mammillary nucleus were born the latest of all cell groups studied (i.e., peak at E15). The results indicate a differential genesis of these opioid peptide-containing neuronal groups in different hypothalamic nuclei and regions.

Modulation of lordosis behaviour in the female rat by corticotropin releasing factor, beta-endorphin and gonadotropin releasing hormone in the mesencephalic central gray

A possible functional relationship between corticotropin-releasing factor (CRF) and opiate peptide neuronal systems (beta-endorphin, dynorphin1-17 and Met-enkephalin) and their interactions with gonadotropin releasing hormone (GnRH) in the mesencephalic central gray (MCG) for the regulation of lordosis behaviour was assessed in ovariectomized, oestrogen-treated and oestrogen-progesterone-treated female rats. Lordosis behaviour triggered by male mounting was inhibited in a dose-dependent fashion by CRF microinfused into the MCG in both oestrogen-treated and oestrogen-progesterone-treated female rats. This CRF-induced inhibition of lordosis could be overcome by a pre-infusion of naloxone or anti-beta-endorphin-globulin (anti-beta-end-G) directly into the MCG but not by anti-Met-enkephalin globulin (anti-enk-G) or anti-dynorphin1-17 globulin (anti-dynor-G). Supporting data indicate that the facilitation of lordosis behaviour induced by treatment with naloxone or anti-beta-end-G alone but not with anti-enk-G or anti-dynor-G may be due to enhanced GnRH release. This results from the action of these substances in overcoming the inhibition of GnRH secretion mediated specifically by beta-endorphin but not by Met-enkephalin or dynorphin1-17 in the MCG. These studies together with previous data showing that GnRH can overcome the abolition of lordosis by beta-endorphin in the MCG, indicate a close relationship between beta-endorphin (but not Met-enkephalin or dynorphin) and GnRH systems in the MCG in the control of lordosis behaviour. Thus, the inhibition of lordosis by CRF and the complete reversal of this blockade by naloxone or anti-beta-end-G may suggest that CRF could enhance the release of beta-endorphin from fibres in the MCG; beta-endorphin then inhibits lordosis by inhibiting the release of GnRH. However, a direct inhibitory effect of CRF on GnRH release is also likely since anti-CRF-gamma-globulin (anti-CRF-G) infused into the MCG produced a long-lasting facilitation of lordosis which can be blocked by an antagonist analogue of GnRH; in addition, previous studies have shown that GnRH infused into the MCG completely overcame the CRF-induced abolition of lordosis and potentiated lordosis to high levels. These results suggest that there may be functional neuroanatomical relationships between CRF, beta-endorphin and GnRH neuronal systems in the MCG in the control of female sexual behaviour. Neither Met-enkephalin nor dynorphin1-17 appear to participate in such mechanisms.

Methionine and leucine enkephalin in rat neurohypophysis: different responses to osmotic stimuli and T2 toxin

Specific radioimmunoassays were used to measure the effects of hypertonic saline (salt loading), water deprivation, and trichothecene mycotoxin (T2 toxin) on the content of methionine enkephalin (ME), leucine enkephalin (LE), alpha-neoendorphin, dynorphin A, dynorphin B, vasopressin, and oxytocin in the rat posterior pituitary. Concentrations of vasopressin and oxytocin decreased in response to both osmotic stimuli and treatment with T2 toxin, but the decrease was greater with osmotic stimulations. Similarly, concentrations of LE and dynorphin-related peptides declined after salt loading and water deprivation; LE concentrations also decreased after treatment with T2 toxin. The concentration of ME decreased after water deprivation, did not change after salt loading, and increased after T2 toxin treatment. The differentiating effects of these stimuli on the content of immunoreactive LE and ME are consistent with the hypothesis that LE and ME may be localized in separate populations of nerve endings with different roles in the posterior pituitary.

Increased dynorphin immunoreactivity in spinal cord after traumatic injury

Opiate antagonists, at high doses, have been shown to improve physiological variables and outcome after experimental spinal injury. Dynorphin appears to be unique amongst opioids in producing hindlimb paralysis after intrathecal injection. Taken together, these findings suggest a possible pathophysiological role for endogenous opioids, particularly dynorphin, in spinal injury. In the present studies we examined the relationship between changes in dynorphin immunoreactivity (Dyn-ir) in rat spinal cord after traumatic injury and the subsequent motor dysfunction. Trauma was associated with significantly increased Dyn-ir at the injury site, but not distant from the lesion. Dyn-ir was found elevated as early as 2 h and as late as 2 weeks after trauma, and was significantly correlated with the degree of injury. These data are consistent with the hypothesis that dynorphin systems may be involved in the secondary injury that follows spinal trauma.

Corticotropin-releasing factor: immunohistochemical colocalization with adrenocorticotropin and beta-endorphin, but not with Met-enkephalin, in subpopulations of duodenal perikarya of rat

By the use of two different double-staining techniques (simultaneous staining of adjacent serial sections and the double-staining elution method) it was possible to demonstrate that a corticotropin-releasing factor (CRF) immunofluorescence co-existed with an adrenocorticotropin (ACTH) and beta-endorphin (beta-END) immunoreactivity, but not with a Met-enkephalin (Met-ENK) immunostaining, within perikarya subpopulations of both the myenteric and submucousal plexus of the rat duodenum. Not a single Met-ENK-positive neuronal cell body was stained also for CRF, ACTH or beta-END. Even nerve fibres, localized in both the myenteric plexus and closely to submucousal blood vessels (probably arterioles), revealed a CRF immunofluorescence, which is also colocalized with an beta-END staining. These results are quite different to the recent observations in the mammalian hypothalamus, suggesting that some myenteric and submucousal plexus neurons may synthesize CRF as well as beta-END and ACTH, but not Met-ENK. The colocalized peptides might be concomitantly released into the synaptic cleft after terminal stimulation.

The effects of neurotensin, vasoactive intestinal polypeptide and other neuropeptides on the secretion of somatostatin from cerebral cortical cells

We have examined the effects of several neuropeptides on the release of immunoreactive somatostatin from cerebral cortical cells in vitro. Neurotensin and vasoactive intestinal polypeptide induced large increases in somatostatin release, whereas cholecystokinin, gonadotropin releasing hormone and Met-enkephalin induced only modest increases. Thyrotropin releasing hormone and insulin had no effect. These results demonstrate a complex interaction amongst neuropeptides in the cerebral cortex, which must be considered in future studies of the roles of peptides in cortical function.

Endogenous opioid immunoreactivity in rat spinal cord following traumatic injury

It has been postulated that endogenous opioids play a pathophysiological role in spinal cord injury, based on the therapeutic effects of the opiate receptor antagonist naloxone in certain experimental models. The high doses of naloxone required to exert a therapeutic action suggest that naloxone's effects may be mediated by non-mu opiate receptors, such as the kappa receptor. This notion is supported by recent pharmacological studies demonstrating that an opiate antagonist more active at kappa sites is effective and far more potent than naloxone in improving outcome after spinal cord injury. Moreover, dynorphin--postulated to be the endogenous ligand for the kappa receptor--is unique among opioids in producing hindlimb paralysis following intrathecal administration in the rat. In the present studies we have examined changes in endogenous opioid immunoreactivity following traumatic spinal cord injury in the rat. Dynorphin A was found to increase progressively with graded injury; changes were restricted to the injury segment and adjacent areas and were time dependent. Dynorphin A-(1-8) showed no marked changes. Methionine and leucine enkephalin were either unaltered or reduced at the injury site; changes were not well localized and were not clearly related to the injury variables. These findings provide further support for a potential pathophysiological role of prodynorphin-derived peptides in spinal cord injury.