Evidence for a selective processing of proenkephalin B into different opioid peptide forms in particular regions of rat brain and pituitary

Dynorphin(1-8) immunoreactivity in brainstem and hypothalamic nuclei of normotensive and age-matched hypertensive rat strains

The concentration of dynorphin (1-8) immunoreactivity [ir-dyn(1-8)] was measured in 10 hypothalamic and 11 brainstem nuclei of Sprague-Dawley (SD) and 6- and 14-week old Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats. The highest concentrations of ir-dyn(1-8) were found in the lateral preoptic and lateral hypothalamic areas of the hypothalamus and the solitary tract nucleus of the brainstem. Levels of the peptide were low in other brainstem nuclei compared to hypothalamic areas. There was a significant reduction in ir-dyn(1-8) concentrations at 14 weeks of age compared to 6 weeks of age in all 9 nuclei examined in SH and WKY rats. However, there were no differences between the strains at either age. These changes may be related to the increase in blood pressure that occurs in both SH and WKY rats over this age range although other factors must also be involved to produce the higher blood pressure levels of the SH rat.

Proenkephalin is processed in a projection-specific manner in the rat central nervous system

The biosynthesis and posttranslational proteolytic processing of proenkephalin was studied in three projection systems in the rat central nervous system--the caudate-putamen to the globus pallidus, the paraventricular nucleus of the hypothalamus to the median eminence, and the mossy fiber system of the granule cells of the hippocampus. By using the techniques of in vivo radiolabeling and sequential high-performance liquid chromatographic purification coupled with chemical modification, the biosynthesis of six radiolabeled [Met]enkephalin-containing peptides--[Met5]enkephalin, [Met5,Arg6,Gly7,Leu8]enkephalin, [Met5,Arg6,Phe7]enkephalin, metorphamide, peptide E, and BAM 18P--was followed. In each projection system, radiolabeled enkephalins were purified to constant radiochemical specific activity. However, the posttranslational processing of proenkephalin was found to differ between these three systems, as judged by the relative ratio of these peptides. These findings imply that specific, different physiologies and behaviors may be elicited by the enkephalins based upon the specific [Met]enkephalin-containing peptides that are cleaved from proenkephalin and released in synaptic terminal fields.

Opioid peptides in Huntington's disease: alterations in prodynorphin and proenkephalin system

The concentrations of dynorphin A1-8 and Met-enkephalin-Arg6-Gly7-Leu8 were measured in the basal ganglia of postmortem brains from patients with Huntington's disease (HD) and from control subjects. A significant reduction of dynorphin A1-8 concentration was found in caudate nucleus, putamen, external globus pallidus and substantia nigra of HD brains. Levels of Met-enkephalin-Arg6-Gly7-Leu8 were reduced in HD caudate nucleus, putamen, internal and external globus pallidus. These data indicate that both the prodynorphin and proenkephalin opioid peptide system are affected in the basal ganglia in HD.

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.

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.

Isolation and structure of a C-terminally amidated nonopioid peptide, amidorphin-(8-26), from bovine striatum: a major product of proenkephalin in brain but not in adrenal medulla

We have isolated and sequenced a C-terminally amidated peptide from bovine striatum. The peptide was purified to homogeneity by adsorption to XAD-2 resins and four different HPLC steps. Amino acid composition analysis and gas-phase sequence analysis revealed identity of this peptide with residues 8-26 of the proenkephalin-derived opioid peptide amidorphin, which we have recently isolated from bovine adrenal medulla. C-terminal amidation of amidorphin-(8-26) from bovine striatum was demonstrated by its stability to carboxypeptidase A digestion and full crossreactivity in a radioimmunoassay that required the C-terminal amide group as part of the recognition site. The nonopioid peptide amidorphin-(8-26), which lacks the N-terminal [Met]enkephalin sequence of amidorphin, is a major product of the opioid peptide precursor proenkephalin in the brain. In the adrenal medulla, however, where amidorphin occurs in remarkably high concentrations, amidorphin-(8-26) could not be detected. This is indicative of differential post-translational processing of proenkephalin in different tissues. In the brain, as opposed to the adrenal medulla, amidorphin is further processed at the typical cleavage signals of two basic residues, giving rise to the nonopioid peptide amidorphin-(8-26) and, possibly, to the opioid peptide [Met]enkephalin. Thus, proenkephalin in the brain might be considered as a precursor in which an opioid peptide is linked with a nonopioid peptide of possibly different biological function.

Paracrine interactions in the anterior pituitary

The topographical affinity between certain cell types in rat anterior pituitary as well as the presence of biogenic amines, neuropeptides, growth and tissue factors in specific cell types suggest participation of paracrine control mechanisms in the regulation of anterior pituitary hormone secretion. Due to the recent advances in the separation of pituitary cell types and the development of three-dimensional cell cultures, direct experimental evidence for control by intercellular messengers has become available. The stimulation of PRL release from superfused pituitary cell aggregates by LHRH has been shown to be mediated by gonadotrophs. Gonadotrophs appear to secrete a factor with PRL-releasing activity. Gonadotrophs also modulate the stimulation of PRL release by angiotensin II. Interaction of somatotrophs with an unknown small-sized cell type strongly amplifies the GH response to adrenaline, GRF and VIP. The latter phenomenon requires the permissive action of glucocorticoids. Some of these in vitro observations can be correlated with recently reported in vivo actions of LHRH, PRL and angiotensin II and with pathophysiological changes in the pituitary.

Distribution of immunoreactive alpha-neo-endorphin in the rat brain

The distribution of immunoreactive alpha-neo-endorphin (alpha-Neo) in the rat brain was demonstrated by means of highly specific radioimmunoassay (RIA). The highest concentrations of immunoreactive (ir) alpha-Neo (100 pmol/g tissue) were found in the substantia nigra, the hypothalamic supraoptic nucleus (86 pmol/g) and the preoptic area (63 pmol/g); medium levels were found in the basal ganglia, mesencephalic reticular formation, nucleus accumbens and hippocampus. Other structures contained less alpha-Neo-ir. The possible anatomical interaction between alpha-Neo and monoaminergic nerve terminals or cell bodies in some structures is discussed.

Characterization of proenkephalin B-derived opioid peptides in the human hypothalamo-neurohypophyseal axis

Proenkephalin B-derived opioid peptides, such as dynorphin1-17, dynorphin1-8, dynorphin B, alpha-neo-endorphin and beta-neo-endorphin in the human hypothalamo-neurohypophyseal tract were quantitated and characterized by the combined use of various radioimmunoassays, gel filtration, high performance liquid chromatography and enzymatic cleavage. Chromatographic analysis of immuno-reactive peptide levels determined that, in each case, these were comprised almost exclusively of the authentic peptides both in the neurohypophysis and hypothalamus. Concentrations of authentic proenkephalin B-peptides were 100-5000-fold lower in the human as compared to the rat neurohypophysis. However, in the paraventricular nucleus (PVN), supraoptic nucleus (SON) and certain other nuclei of the human hypothalamus concentrations of authentic peptides were found to be in the same range as those in the rat hypothalamus. The ratio of proenkephalin B-peptides in PVN and SON to those of the neurohypophysis in the rat was ca. 1:50. Conversely, in man these ratios were shown to be 80:1 for dynorphin B, 6:1 for alpha-neo-endorphin and 1:1 for all other peptides evaluated. Examination of postmortem degradation of peptides indicated that these lower levels in the neurohypophysis are not due to a higher rate of postmortem breakdown. Since levels of both vasopressin and beta-endorphin were very high, these deficits in proenkephalin B-peptides were selective and do not represent a generalized property of the human pituitary. Experiments involving enzymatic cleavage demonstrated the occurrence of higher molecular weight forms containing the Leu-enkephalin sequence which were not recognized by the antisera employed.(ABSTRACT TRUNCATED AT 250 WORDS)

Regional distribution of a novel pituitary protein (7B2) in the rat brain

The regional distribution of a novel pituitary protein (7B2) in the rat brain was studied using a specific and sensitive radioimmunoassay. Immunoreactive (IR)-7B2 was distributed throughout the brain, with the highest concentrations in the pituitary, hypothalamus and basal ganglia. Immunoreactive 7B2 from the brain and other tissues had an apparent molecular weight of around 20,000 as estimated by SDS-polyacrylamide gel electrophoresis as observed with other tissues. In homozygous Brattleboro rats which do not synthesize vasopressin or its associated neurophysin, IR-7B2 levels in the brain and pituitary gland were shown to be similar to those of control animals. Furthermore, the molecular weight of 7B2 in the brain and pituitary gland of homozygous Brattleboro rats was similar to that of control animals.

Assessment of dynorphin-A depletion in the anorexia of Walker-256 tumor bearing rats

Rats bearing the Walker-256 (W-256) tumor display an anorexic profile which resembles that of normal animals forced to drink 2% NaCl [2,24], a regimen which depletes neurohypophyseal dynorphin-A (DYN) [3,9]. As expected, the naloxone reversible feeding induced by 2-deoxy-D-glucose (2-DG) was attenuated (36%) in the W-256 tumor bearing rats (TBR). Interestingly, immunoreactive (ir) levels of dynorphin-A 1-17 (DYN-17) and its postulated breakdown product, dynorphin-A 1-18 (DYN-8), were also reduced in the neurohypophysis of W-256 TBR by 42 and 50%, respectively. However, ir-DYN levels were not reduced in TBR in those brain regions which are probably involved in the regulation of appetite (e.g., hypothalamus). 2-DG itself did not consistently affect ir-DYN levels in any tissue for either controls or TBR. The ratio of DYN-8 to DYN-17 did not change in response to any treatment, including the depletion of both peptides from the NIL of TBR. In summary, the present data do not support DYN depletion as being a factor which contributes to the anorexia of the W-256 TBR.

Sequence and expression of the rat prodynorphin gene

We report here the isolation of a lambda genomic clone that contains the nucleotide sequence coding for the main exon of the rat prodynorphin (proenkephalin B) gene. This exon codes for the majority of the translated region of prodynorphin mRNA including the opioid peptides alpha-neo-endorphin, dynorphin A, and dynorphin B. The entire 3' untranslated region is also contained on the lambda clone. Nucleotide sequence comparison with the main exon of the human prodynorphin gene reveals both structural and sequence homology. RNA blot analysis reveals that prodynorphin transcripts can be seen in numerous regions of the rat brain and in the adrenal gland, spinal cord, testis, and anterior pituitary.

Degradation of alpha and beta neo-endorphin by rat brain membrane peptidases

Fractionation of Triton-solubilized rat brain membranes on diethylaminoethyl-cellulose resolves two peptidases which hydrolyze beta-neo-endorphin. One of these peptidases was identified as Angiotensin Converting Enzyme by (a) its sensitivity to inhibition by the specific inhibitors MK422 and captopril, (b) by the identification of reaction products, and (c) by comparison to authentic angiotensin converting enzyme. In contrast, alpha-neo-endorphin hydrolysis by angiotensin converting enzyme could not be detected. The second enzyme active on beta-neo-endorphin was identified as an aminopeptidase. This aminopeptidase is identical to the previously described enkephalin-degrading aminopeptidase. The possible involvement of these enzymes in the metabolism of opioid peptides is discussed.

A general procedure for analysis of proenkephalin B derived opioid peptides

Tryptic digestion followed by radioimmunoassay for (Leu)enkephalin-Arg6 has been used in this study as a general method to detect the presence of all possible products containing the enkephalin sequence from the opioid peptide prohormone, proenkephalin B. Tissue extracts of human hypothalamus and pituitary were examined. Gel filtration was used to separate the different precursor products according to molecular weight. The elution profile was also monitored with highly sensitive radioimmunoassays for dynorphin A and dynorphin B, respectively. Immunoreactive dynorphin A appeared in three peaks with the approximate molecular weight of 1000, 2000 and 5000. Immunoreactive dynorphin B partly occurred in other peaks, 1500, 5000 and 10 000 dalton. Profiles obtained by measuring immunoreactive (Leu)enkephalin-Arg6 in all fractions from gel filtration after trypsin digestion showed a more complex pattern compared to the profiles of immunoreactive dynorphin A and dynorphin B. The major peaks coincided with dynorphin A and dynorphin B but high levels of immunoreactive (Leu)enkephalin-Arg6 were also generated from higher molecular weight regions (MW greater than 5000).

Dynorphin-A (1-8) is contained within perikarya, nerve fibres and nerve terminals of rat duodenum

By the use of well-characterized antibodies against porcine dynorphin-A(1-8), an endogenous opioid peptide, and the use of a modified immunofluorescence microscopic technique, dynorphin-A(1-8) stained perikarya, nerve fibres, and nerve terminals were visualized in the rat duodenum. Dynorphin-A(1-8) immunoreactive perikarya were revealed with certainty only in the myenteric plexus, while dynorphinergic nerve fibres could bee seen in the myenteric plexus and circular muscle layer, but not in the longitudinal muscle layer and submucous plexus. Dynorphin-A(1-8) immunofluorescent nerve endings were in close contacts with submucosal blood vessels, probably arterioles, and Brunner's gland cells. These findings suggest that the opioid peptide dynorphin-A(1-8) might be synthetized within myenteric plexus perikarya of the rat duodenum and that it might modulate the peristaltic activity, intestinal blood pressure, and production of mucopeptides synthetized within Brunner's gland cells.

Analysis of opioid and non-opioid end products of pro-dynorphin in the substantia nigra of the rat

The substantia nigra is among the richest pro-dynorphin terminal field regions in the rat brain. We therefore contrasted processing in this area to the known processing in the posterior pituitary. Fractionation of acid extracts of the posterior pituitary by gel filtration followed by analysis by radioimmunoassay indicated that the molar ratio of dynorphin A(1-17) to dynorphin A(1-8) averaged 1:2. The levels of dynorphin A-related end products to alpha-neo-endorphin and bridge peptide (a 2K nonopioid end product of pro-dynorphin) were approximately equimolar; however, the levels of dynorphin B-sized material were 50% lower than dynorphin A levels. Similar analyses of acid extracts of the substantia nigra also indicated that the levels of dynorphin A, alpha-neo-endorphin, and bridge peptide were approximately equimolar. In this terminal field the levels of dynorphin B-sized material were approximately 60% lower than dynorphin A. A striking feature of the nigral system was that the molar ratio of dynorphin A(1-17) to dynorphin A(1-8) averaged 1:16. Thus, in the nigra, dynorphin A(1-17) is primarily a biosynthetic intermediate rather than as an end product.

Prodynorphin immunoreactivity is located in different neurons than proenkephalin immunoreactivity in the cerebral cortex of rats

Reported here is a description of the distribution and cellular morphology of neurons containing dynorphin B immunoreactivity (IR) and a comparison with cells containing bovine adrenal medullary peptide IR in the cerebral cortex of colchicine treated rats. Dynorphin B-IR was found in bipolar and multipolar cells in neocortical layers II-III and V-VI and in pyramidal and polymorph cells in olfactory cortical layers II and III. In the hippocampus, dynorphin B-IR was found in dentate granule cells and multipolar cells. In Fisher rats, dynorphin B was also found in cells in the subiculum and in CA1. The extensive regional overlap in the distribution of cortical neurons containing prodynorphin and proenkephalin in IR prompted a detailed comparison of their localization. In double immunostained tissue, dynorphin B-IR was demonstrated to occur in different neurons than those containing BAM22P-IR in the cerebral cortex and hippocampus of rats.

CNS tissue levels of dynorphin-A immunoreactivity and the anorexia associated with sodium chloride imbibition in the rat

Forced imbibition of increasing concentrations of sodium chloride (NaCl) in rats reduced daytime 2-deoxy-D-glucose (2-DG) induced feeding in a concentration dependent manner. Pituitary neurointermediate lobe (NIL) levels of immunoreactive (ir)-dynorphin-A 1-17 and 1-8 were also decreased by the NaCl regimen in a concentration dependent manner. However, there was no significant association between the reduction of NIL dynorphin levels and the suppression of 2-DG induced feeding on a within-animal basis. NaCl imbibition did not affect levels of either ir-dynorphin-A 1-17 or 1-8 in the hypothalamus, cerebral cortex, hippocampus, medulla/pons or anterior pituitary. Neither the acute changes following 2-DG administration, nor the comparison of ir-dynorphin-A 1-8/1-17 ratios appeared useful for the assessment of dynorphin-A turnover. Thus, the present results did not support the hypothesis that anorexia of NaCl treated animals results from the depletion of dynorphin-A.

Steady state levels of pro-dynorphin-related end products in the striatum and substantia nigra of the adult rhesus monkey

Analysis of an acid extract of the striatum of the rhesus monkey revealed that the molar ratio of dynorphin A(1-8)-sized material and dynorphin (A(1-17)-sized material is approximately 1:1. In addition, the molar ratios of the dynorphin A-related end products to both dynorphin B(1-13)-sized material and alpha-neo-endorphin-sized material were approximately 1:1. Fractionation of an acid extract of the substantia nigra by gel filtration and reverse phase HPLC revealed the following molar ratios for pro-dynorphin-related end products. The molar ratio of dynorphin A(1-8) to dynorphin A(1-17) is approximately 6:1. The molar ratios of dynorphin A-related end products to dynorphin B(1-13) and alpha-neo-endorphin were approximately 0.5 and 0.8, respectively. Comparisons between proteolytic processing patterns of pro-dynorphin in the striatum and the substantia nigra of the rhesus monkey are considered. In addition, comparisons between pro-dynorphin processing in the substantia nigra of the rhesus monkey and the substantia nigra of the rat are discussed.

Prodynorphin peptide immunocytochemistry in rhesus monkey brain

The present study describes the immunocytochemical distribution of peptides derived from the prodynorphin precursor in the brain of the rhesus monkey (Macaca mulatta). Animals were treated with colchicine (intracerebroventricularly) prior to perfusion to enhance the observation of perikaryal immunoreactivity. Using antisera generated against dynorphin A(1-17), dynorphin B(1-13), and prodynorphin(186-208) (or bridge peptide), the anatomical distribution of dynorphin systems was mapped. The results indicate a widespread neuronal localization of immunoreactivity from the cerebral cortex to the caudal medulla. Anti-dynorphin B and anti-bridge peptide sera proved useful for the demonstration of neuronal perikarya, while the dynorphin A antiserum was best for localizing terminal projection fields. Immunoreactive perikarya are located in numerous brain loci, including the cingulate cortex, caudate nucleus, amygdala, hypothalamus (especially the magnocellular nuclei), thalamus, substantia grisea centralis, parabrachial nucleus, nucleus tractus solitarius, and other nuclei. In addition, fiber and terminal immunoreactivity are seen in varying densities in the striatum and pallidum, substantia innominata, hypothalamus, substantia nigra pars reticulata, parabrachial nucleus, spinal trigeminal nucleus, and other areas. The distribution of prodynorphin peptides in the brain of the monkey is similar to that described for the rat brain; however, significant differences also exist. Other interspecies differences in the anatomy of prodynorphin and proenkephalin neuronal systems in the monkey and human brain are further discussed.

Localization and quantitation of dynorphin B in the rat hippocampus

The present study measures the content of dynorphin B in the rat hippocampus, and localizes the dynorphins within the intrinsic hippocampal neuronal circuitry. The level of dynorphin B, which is representative of the prodynorphin-derived peptides, was markedly depleted by intrahippocampal injection of colchicine, which destroyed the great majority of the hippocampal granule cells and the associated mossy fiber pathway. The hippocampus contralateral to the injection demonstrated a slight, non-significant rise in dynorphin B levels after colchicine. Entorhinal cortical lesions ablating the perforant pathway input to the hippocampus did not significantly alter dynorphin B levels in the hippocampus. Unilateral fimbrial transection caused a small but significant increase in dynorphin B on the side of the lesion relative to the unlesioned side, but neither side was significantly different from control.

Differential effects of various opioid peptides on vasopressin and oxytocin release from the rat pituitary in vitro

Dynorphin (1-17), and to a lesser extent, beta-endorphin and [Leu]enkephalin (10(-6) M each) decreased the spontaneous release of vasopressin (VP) from the rat neurointermediate pituitary in vitro, whereas the oxytocin (OT) release remained unchanged. Naloxone, however, did not significantly alter the spontaneous VP and OT release. Dynorphin (1-17) (10(-7) M) increased the electrically evoked release of VP and OT, while 10(-6) M had a significant, somewhat less pronounced stimulatory effect only on VP, but not on OT release. The opiate inactive fragment [des-Tyr1]dynorphin (1-17) did not change the evoked VP and OT release, indicating that the dynorphin effect was mediated by opiate receptors. beta-Endorphin (10(-6) M and 10(-7) M) did not alter the evoked VP and OT secretion. 10(-6) M [Leu]enkephalin induced a stimulation of the evoked OT, but not VP release; 10(-7) M [Leu]enkephalin had no effect, neither on VP nor on OT release. The opiate antagonist naloxone (10(-5) M) induced an increase in the evoked VP and, even more pronounced, OT release. In a concentration of 10(-6) M, however, naloxone only increased the evoked OT release. When naloxone and dynorphin (1-17) were concomitantly applied, their stimulatory effects on the evoked VP and OT release were additive. Similarly to the effects of naloxone, addition of a monoclonal antibody which binds to the common N-terminal sequence of all endogenous opioid peptides, resulted in a marked increase in the evoked secretion of VP and, to an even more pronounced degree, of OT.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasopressin and oxytocin in the rat spinal cord: distribution and origins in comparison to [Met]enkephalin, dynorphin and related opioids and their irresponsiveness to stimuli modulating neurohypophyseal secretion

Immunoreactive-vasopressin, -oxytocin, -dynorphin, -dynorphin-(1-8), -alpha-neo-endorphin and -[Met]enkephalin were, in each case, present in greater concentrations in dorsal as compared to ventral, and lumbo-sacral as compared to cervico-thoracic, spinal cord. These differences were significantly more pronounced for vasopressin and oxytocin than for the other peptides. Lesions of the hypothalamic paraventricular nucleus depleted levels of immunoreactive-vasopressin and -oxytocin throughout the cord whereas levels of the opioid peptides therein were unaffected. In contrast, destruction of either the supraoptic or suprachiasmatic nucleus failed to change the content of immunoreactive-vasopressin, -oxytocin or any of the opioid peptides in the cord. Dehydration for 3 days depressed levels of immunoreactive-vasopressin, -oxytocin and -dynorphin in the neurointermediate lobe of the pituitary. In distinction, the levels of these were not modified in the spinal cord. Further, treatment with the synthetic corticosteroid, dexamethasone, elevated levels of immunoreactive-vasopressin, -oxytocin and -dynorphin in the neurointermediate pituitary whereas these were unaffected in the spinal cord. It is concluded that vasopressin and oxytocin in the spinal cord are predominantly derived from the paraventricular nucleus, localized in dorsal lumbo-sacral regions of the cord and insensitive to endocrinological manipulations. These pools may, thus, be modulated differently from their counterparts in the neurohypophysis and have a differing role, possibly in the control of the primary processing, autonomic or motor junctions. Further, there is no evidence from these or our prior studies for a close interrelationship of spinal cord vasopressin with dynorphin-related peptides (or oxytocin with [Met]enkephalin), likewise in contrast to the neurohypophysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution and characterization of opioid peptides derived from proenkephalin A in human and rat central nervous system

In various areas of rat and human brain and spinal cord the distributions of opioid peptides derived from the proenkephalin A precursor, the heptapeptide [Met]enkephalin-Arg6-Phe7 (MERF), the octapeptide [Met]enkephalin-Arg6-Gly7-Leu8 (MERGL), and bovine adrenal medulla dodecapeptide (BAM-12P), were determined by a combination of radioimmunoassay, gel filtration, and high-performance liquid chromatography. In the human central nervous system the highest concentrations were seen in the striatum (pallidum greater than caudate nucleus greater than putamen) and in substantia nigra, hypothalamus, and periaqueductal gray. Similarly, in rat brain high levels were found in striatum and hypothalamus. Bovine adrenal medulladocosa peptide (BAM-22P) only occurred in the rat brain, but could not be detected in human brain. No MERF, MERGL, BAM-12P, or BAM-22P could be found in either rat or human pituitary. In contrast to MERF, MERGL and BAM-12P, peptides derived from the proenkephalin B precursor, dynorphin1-8 and dynorphin B, showed high concentrations only in substantia nigra and pallidum, but quite low levels in the other regions of human brain and spinal cord. The present study provides evidence that the proenkephalin A precursor known from adrenal medulla also exists in the rat and human central nervous system. Moreover, the identification of BAM-12P in these tissues indicates that cleavage of the precursor molecule must also involve sites different from those with paired basic amino acids.

Distribution of immunoreactive dynorphin B in discrete areas of the rat brain and spinal cord

The distribution of immunoreactive (ir)-dynorphin B in 101 microdissected rat brain and spinal cord regions was determined using a specific radioimmunoassay. The highest concentration of dynorphin B in brain was found in the substantia nigra (1106.2 fmol/mg protein). Very high concentrations of ir-dynorphin B (greater than 400 fmol/mg protein) were also found in the lateral preoptic area, parabrachial nuclei and globus pallidus. Relatively high concentrations of ir-dynorphin B (250-400 fmol/mg protein) were found in 19 nuclei, including the periaqueductal gray matter, anterior hypothalamic nucleus, median eminence, nucleus accumbens and hippocampus. Moderate levels of the peptide (between 100 and 250 fmol/mg protein) were found in 42 brain nuclei such as the perifornical nucleus, nucleus of the diagonal band, medial forebrain bundle, and dorsal premamillary nucleus. Low concentrations of ir-dynorphin B (less than 100 fmol/mg protein) were found in 28 brain areas, e.g. cerebral cortical structures (parietal, cingulate, frontal), claustrum, olfactory bulb, lateral and periventricular thalamic nuclei. The cerebellar cortex has the lowest dynorphin B concentration (53.7 fmol/mg protein). Spinal cord segments exhibit low or moderate (cervical segment) levels of the peptide. The neurointermediate lobe of the pituitary gland is extremely rich in ir-dynorphin B (11,047.1 fmol/mg protein).

Immunoreactive peptides related to dynorphin B (= rimorphin) in the rat brain

We have developed a radioimmunoassay for synthetic dynorphin B, a novel opioid tridecapeptide, which shares a common precursor molecule with dynorphin1-17 (= dynorphin A) and the neo-endorphins. The levels of immunoreactivity towards this peptide in rat brain and pituitary show a pattern quantitatively and qualitatively similar to those found for dynorphin A and alpha-neo-endorphin in earlier studies. The antiserum used was highly specific with only dynorphin-32 and dynorphin B-29, both of which contain the dynorphin B sequence, showing substantial cross-reactivity. Gel filtration of whole rat brain extracts in combination with HPLC analysis provide strong evidence for the existence of these latter two peptides in rat brain.