Further characterization of the major forms of reptile beta-endorphin

β-Endorphin inhibits phagocytic activity of lizard splenic phagocytes through μ receptor-coupled adenylate cyclase-protein kinase A signaling pathway

The receptor-coupled intracellular signaling mechanism of endogenous opioid peptide β-endorphin (β-end) is explored for the first time in ectothermic vertebrates using wall lizard as a model. β-End inhibited the percentage phagocytosis and phagocytic index of lizard splenic phagocytes in a dose-dependent manner. The inhibitory effect of β-end on phagocytosis was completely antagonized by non-selective opioid receptor antagonist naltrexone and also by selective μ-receptor antagonist CTAP. However, selective antagonists for other opioid receptors like NTI for δ-receptor and NorBNI for κ-receptor did not alter the effect of β-end on phagocytosis. This suggests that β-end mediated its inhibitory effect on phagocytic activity of splenic phagocytes exclusively through μ opioid receptors. The μ opioid receptor-coupled downstream signaling cascade was subsequently explored using inhibitors of adenylate cyclase (SQ 22536) and protein kinase A (H-89). Both SQ 22536 and H-89 abolished the inhibitory effect of β-end on phagocytosis in a concentration-related manner. Implication of cAMP as second messenger was corroborated by cAMP assay where an increase in intracellular cAMP level was observed in response to β-end treatment. It can be concluded that β-end downregulated the phagocytic activity of lizard splenic phagocytes through μ opioid receptor-coupled adenylate cyclase-cAMP-protein kinase A pathway.

Analyzing the evolution of beta-endorphin post-translational processing events: studies on reptiles

In many cartilaginous fishes, most ray-finned fishes, lungfishes, and amphibians, the post-translational processing of POMC includes the monobasic cleavage of beta-endorphin to yield an opioid that is eight to ten amino acids in length. The amino acid motif within the beta-endorphin sequence required for a monobasic cleavage event is -E-R-(S/G)-Q-. Mammals and birds lack this motif and as a result beta-endorphin(1-8) is a not an end-product in either group. Since both mammals and birds were derived from ancestors with reptilian origins, an analysis of beta-endorphin sequences from extant groups of reptiles should provide insights into the manner in which beta-endorphin post-translational processing mechanisms have evolved in amniotes. To this end a POMC cDNA was cloned from the pituitary of the turtle, Chrysemys scripta. The beta-endorphin sequence in this species was compared to other reptile beta-endorphin sequences (i.e., Chinese soft shell turtle and gecko) and to known bird and mammal sequences. This analysis indicated that either the loss of the arginine residue at the cleavage site (the two turtle species, chick, and human) or a substitution at the glutamine position in the consensus sequence (gecko and ostrich) would account for the loss of the monobasic cleavage reaction in that species. Since amphibians are capable of performing the beta-endorphin monobasic reaction, it would appear that the amino acid substitutions that eliminated this post-translational process event in reptilian-related tetrapods must have occurred in the ancestral amniotes.

Trends in the evolution of the proopiomelanocortin gene

The POMC gene is perhaps the most extensively studied member of the opioid/orphanin gene family. In Phylum Chordata this gene has been characterized in representatives of every class within the Gnathostomata, as well as in one representative agnathan vertebrate, the marine lamprey. This review provides a systematic overview of trends in the evolution of the melanocortins (ACTH/alpha-MSH, beta-MSH, gamma-MSH, and delta-MSH) and beta-endorphin in gnathostomes, and advances the hypothesis that the appearance of gamma-MSH occurred early in the radiation of the gnathostomes. A summary of the extensive work on POMC genes in the marine lamprey is also provided, as well as a reevaluation of the conserved regions in the sequence of CLIP (corticotropin-like-intermediate lobe peptide) in the POMC sequences of the various groups of gnathostomes.

The posttranslational modification of beta-endorphin in the intermediate pituitary of the toad, Bufo marinus, includes processing at a monobasic cleavage site

Fractionation of an acid extract of 15 B. marinus intermediate pituitaries by a combination of gel filtration chromatography and cation exchange chromatography revealed one major and five minor forms of beta-endorphin in this tissue. Based on reversed-phase HPLC and immunological properties, as well as amino acid composition and primary sequence analysis, it was deduced that the sequence of the major form of B. marinus beta-endorphin is N-acetyl-YGGFMTPE. Overall, the steady-state analyses of the minor forms of beta-endorphin indicated that the posttranslational processing of beta-endorphin in the toad intermediate pituitary includes endoproteolytic cleavage at both paired basic and monobasic cleavage sites.

Detection of N-acetylated forms of alpha-MSH and beta-endorphin in the intermediate pituitary of the holostean fishes, Lepisosteus spatula, Lepisosteus osseus, and Amia calva

Acid extracts of the intermediate pituitaries of the gars, L. spatula and L. osseus, were fractionated by Sephadex G-50 column chromatography and analyzed by radioimmunoassay. This procedure revealed that immunoreactive forms of N-acetylated beta-endorphin- and alpha-MSH-sized material were present in equimolar amounts and represented the major end products of the POMC biosynthetic pathway in these species. Cation-exchange chromatography indicated that multiple N-acetylated forms of beta-endorphin were present in the intermediate pituitaries of the two species of gar, and that these forms differed in their net positive charge and in their apparent molecular weight. Reversed-phase HPLC analysis of the alpha-MSH-related material indicated that up to 90% of the total MSH in the pituitary of the gar was N-acetylated. Furthermore, the predominant form of alpha-MSH in both species of gar was N,O-diacetyl-ACTH(1-13)-NH2. Nearly identical results were obtained following the analysis of alpha-MSH-related peptides in the intermediate pituitary of the bowfin, A. calva. The pattern of posttranslational processing of POMC observed in the intermediate pituitaries of holostean fishes is very similar to the processing events observed in lungfishes, turtles, and mammals; hence, the processing of POMC has been remarkably conserved during vertebrate evolution.

Differential N-acetylation of alpha-MSH and beta-endorphin in the intermediate pituitary of the turtle, Pseudemys scripta

Steady-state analyses of the intermediate pituitary of the turtle, Pseudemys scripta, indicated that alpha-MSH-sized immunoreactive forms and beta-endorphin-sized immunoreactive forms are major end products of melanotropic cells. Three forms of alpha-MSH-related immunoreactivity were detected. The two major forms had the same reversed-phase HPLC properties as synthetic N,O-diacetyl-ACTH(1-13)-NH2 and N-acetyl-ACTH(1-13)-NH2. These forms accounted for 97% of the total alpha-MSH-related immunoreactivity detected. A minor peak of ACTH(1-13)-NH2 was also detected. Multiple forms of beta-endorphin-related immunoreactivity were detected, which varied in net positive charge (+1 to +5), apparent molecular weight (2.4 to 3.5 kDa), and degree of N-terminal acetylation. Although N-acetylated forms of beta-endorphin were detected in the turtle intermediate pituitary, the major forms of turtle beta-endorphin were nonacetylated. These features of the turtle intermediate pituitary POMC-specific N-acetylation mechanism are similar to, yet distinct from, the POMC N-acetylation mechanisms observed for mammals. These data suggest that POMC-specific N-acetylation mechanisms were present in reptiles prior to the divergence of the anapsid and synapsid lines.

Detection and partial characterization of proopiomelanocortin-related end-products from the pars intermedia of the toad, Bombina orientalis

Steady-state analyses were performed on the proopiomelanocortin (POMC)-related end-products present in acid extracts of the pars intermedia of the anuran amphibian, Bombina orientalis. Sephadex G-75 gel filtration chromatography indicated that immunoreactive alpha-MSH-sized material and N-acetylated beta-endorphin-related material are the major POMC-related products present in this tissue. The alpha-MSH-sized immunoreactivity was further fractionated by reversed phase HPLC. The major peak of immunoreactivity isolated by this procedure eluted with the same retention time as synthetic ACTH(1-13)amide. Cation exchange chromatography supported the conclusion that the major storage form of alpha-MSH in the pars intermedia of Bombina is ACTH(1-13)amide. Analysis of Bombina pars intermedia in culture indicated that mono-acetylated and di-acetylated alpha-MSH were the major forms of alpha-MSH secreted into the medium. The major peak of N-acetylated beta-endorphin-related material was further analyzed by cation exchange chromatography and Sephadex G-25 gel filtration column chromatography. The major storage form of beta-endorphin in this tissue is N-acetylated, has a net positive charge at pH 2.75 of +1, and has an apparent molecular weight of 1.2K. The beta-endorphin present in the pars intermedia of this tissue does not undergo further N-acetylation at the time of secretion. These results indicate that in the pars intermedia of the archaeobatrachian, Bombina orientalis, the N-acetylation of alpha-MSH is a cosecretory processing event, whereas N-acetylation of beta-endorphin is a post-translational processing event. These results are compared to other archaeobatrachian and neobatrachian pituitary POMC systems that have been analyzed.

N-acetylation and C-terminal proteolysis of beta-endorphin in the anterior lobe of the horse pituitary

beta-Endorphin is post-translationally processed to both N-acetylated and C-terminally shortened derivatives in the anterior lobe of the horse pituitary, a processing pattern qualitatively different from that of the rat and virtually every other mammalian species. Thus, separation of the molecular forms of beta-endorphin using gel filtration and ion exchange chromatography showed that the horse anterior lobe primarily contains beta-endorphin-1-31 and N-acetyl-beta-endorphin-1-27 along with smaller amounts of beta-lipotropin, beta-endorphin-1-27, and N-acetyl-beta-endorphin-1-31 and -1-26, in contrast to the rat anterior lobe, which contains approximately equal amounts of beta-lipotropin and beta-endorphin-1-31. Immunohistochemical experiments using an antiserum which specifically recognizes N-acetylated beta-endorphin peptides confirmed that N-acetyl-beta-endorphin immunoreactivity is present in the anterior lobe of the horse, but not the rat. The intermediate lobe of both species primarily synthesizes N-acetylated, C-terminally shortened beta-endorphin peptides, and while distinct species differences do occur, they were relatively minor, consisting of quantitative differences in the relative proportion of each peptide. These results are consistent with earlier reports that beta-endorphin processing in the rat pituitary is tissue specific; the anterior and intermediate lobes produce entirely different sets of beta-endorphin peptides. In the equine pituitary, however, both pituitary lobes produce the same multiple beta-endorphin forms, possessing both opioid and nonopioid properties, although their relative amounts differ.

Detection of N-acetylated forms of beta-endorphin and nonacetylated alpha-MSH in the intermediate pituitary of the toad, Bufo marinus

Steady-state analysis of the acid extracts of the intermediate pituitary of the toad, Bufo marinus, revealed the presence of multiple forms of beta-endorphin and alpha-MSH. Approximately 98% of the immunoreactive beta-endorphin was N-acetylated. The major form of N-acetylated beta-endorphin, which represented 81.5% of the total beta-endorphin recovered from this tissue, had an apparent molecular weight of 1.2 kDa and a net charge of +1 at pH 2.75. Approximately 98% of the immunoreactive alpha-MSH present in the Bufo intermediate pituitary had reverse phase HPLC properties similar to the nonacetylated form of alpha-MSH, ACTH(1-13)amide. These observations are in agreement with studies on the intermediate pituitary of the frog, Xenopus laevis, which have shown that the N-acetylation of alpha-MSH in this species is a cosecretory processing event, whereas the N-acetylation of beta-endorphin is a posttranslational processing event (2, 5, 15). These observations indicate that the N-acetylation of beta-endorphin and alpha-MSH occurs at distinct subcellular sites in intermediate pituitary cells of anuran amphibians. The Bufo intermediate pituitary will serve as a good model system for studying these novel N-acetyltransferase reactions.

Characterization of beta-endorphin in human pituitary by fast atom bombardment mass spectrometry of trypsin-generated fragments

A novel mass spectrometric method possessing a high level of structural specificity is described for characterization in biological fluids and tissues of endogenous beta-endorphin of the human amino acid sequence (beta h-EP). The method is based upon purification of tissue extracts by an RP-HPLC gradient, followed by trypsinolysis of that particular HPLC fraction corresponding to the elution time of synthetic beta h-EP. The tryptic digest of that endogenous beta h-EP fraction was purified further by a second RP-HPLC gradient. A unique tryptic fragment selected from the second gradient was analyzed by fast atom bombardment mass spectrometry and B/E linked-field scan MS/MS techniques to provide molecular weight and amino acid sequence-determining fragment ion information, respectively, of that fragment. Collectively, these independent analytical methodologies provided unequivocal structure evidence for the presence of endogenous beta h-EP in human pituitary. The method was established first by utilizing synthetic beta h-EP to optimize experimental parameters, and then applied to the analysis of beta h-EP in post-mortem human pituitary extracts. The suitability of the present method for semi-quantitation of tissue extracts is also demonstrated. The corresponding detection limit of the synthetic beta h-EP was 90 fmol, and human pituitary contained 1.5 pmol of beta h-EP mg-1 protein. The method can be extended readily to the analysis of beta-endorphin derived from other species and tissues.

Distribution of mu, delta, and kappa opiate receptor types in the forebrain and midbrain of pigeons

Ligands that are highly specific for the mu, delta, and kappa opiate receptor binding sites in mammalian brains have been identified and used to map the distribution of these receptor types in the brains of various mammalian species. In the present study, the selectivity and binding characteristics in the pigeon brain of three such ligands were examined by in vitro receptor binding techniques and found to be similar to those reported in previous studies on mammalian species. These ligands were then used in conjunction with autoradiographic receptor binding techniques to study the distribution of mu, delta, and kappa opiate receptor binding sites in the forebrain and midbrain of pigeons. The autoradiographic results indicated that the three opiate receptor types showed similar but not identical distributions. For example, mu, delta, and kappa receptors were all abundant within several parts of the cortical-equivalent region of the telencephalon, particularly the hyperstriatum ventrale and the medial neostriatum. In contrast, in other parts of the cortical-equivalent region of the avian telencephalon, such as the dorsal archistriatum and caudal neostriatum, only kappa receptors appeared to be abundant. Within the basal ganglia, all three types of opiate receptors were abundant in the striatum and low in the pallidum. Within the diencephalon, kappa and delta binding was high in the dorsal and dorsomedial thalamic nuclei, but the levels of all three receptor types were generally low in the specific sensory relay nuclei of the thalamus. Kappa binding and delta binding were high, but mu was low in the hypothalamus. Within the midbrain, all three receptor types were abundant in both the superficial and deep tectal layers, in periventricular areas, and in the tegmental dopaminergic cell groups. In many cases, the distribution of opiate receptors in the pigeon forebrain generally showed considerable overlap with the distribution of opioid peptide-containing fiber systems (for example, in the striatal portion of the basal ganglia), but there were some clear examples of receptor-ligand mismatch. For example, although all three receptor types are very abundant in the hyperstriatum ventrale, opioid peptide-containing fibers are sparse in this region. Conversely, within the pallidal portion of the basal ganglia, opioid peptide-containing fibers are abundant, but the levels of opiate receptors appear to be considerably lower than would be expected. Thus, receptor-ligand mismatches are not restricted to the mammalian brain, since they are a prominent feature of the organization of the brain opiate systems in pigeons.(ABSTRACT TRUNCATED AT 400 WORDS)

Forms of immunoreactive beta-endorphin in the intermediate pituitary of the holostean fish, Amia calva

Acid extracts of the intermediate pituitary of the holostean fish, Amia calva, were fractionated by gel filtration chromatography and analyzed with radioimmunoassays specific for N-acetylated beta-endorphin and C-terminally amidated alpha-MSH. In these extracts beta-endorphin-related immunoreactive material and alpha-MSH-related immunoreactive material were present in roughly equimolar amounts. The immunoreactive beta-endorphin-sized material was tested for opiate receptor binding activity using a beta-endorphin radioreceptor assay. The results of these studies were negative. The immunoreactive beta-endorphin-sized material was further analyzed by cation exchange chromatography at pH 2.5. Two major and three minor peaks of immunoreactive material were isolated. Peak 5 exhibited a net charge of +7 at pH 2.5 and represented 53% of the total immunoreactivity recovered. Peak 2 with a net charge of +3 at this pH represented 38% of the total immunoreactivity recovered. The minor forms, Peaks 1, 3 and 4, exhibited net charges of +2, +4 and +6, respectively. The apparent molecular weights of Peaks 2 and 5 were determined on a Sephadex G-50 column. Peak 2 had an apparent molecular weight of 2.7 Kd and Peak 5 had an apparent molecular weight of 3.5 Kd. Reverse phase HPLC analysis of Peak 5 indicates that this form of Amia beta-endorphin had chromatographic properties similar to salmon beta-endorphin II. These results would suggest that N-terminal acetylation and C-terminal proteolytic cleavage are important post-translational modifications of the forms of Amia beta-endorphin.

Isolation of immunoreactive beta-endorphin-related and Met-enkephalin-related peptides from the posterior pituitary of the amphibian, Xenopus laevis

Acid extracts of the posterior pituitary of the amphibian, Xenopus laevis, were analyzed with two heterologous region specific beta-endorphin RIAs. Following gel filtration chromatography and cation exchange chromatography four peaks of immunoreactivity were detected. All four peaks were detected with a N-acetyl specific beta-endorphin RIA. Peak I represented 92% of the total immunoreactivity isolated following cation exchange chromatography. This peak had a net positive charge at pH 2.5 of +1 and an apparent molecular weight of 1.4 Kd. Following reverse phase HPLC, Peak I fractionated into two peaks: Peak Ia and Peak Ib. Both peaks were detected with the N-acetyl specific beta-endorphin RIA and a Met-enkephalin RIA, however, neither peak co-migrated with either Met-enkephalin or N-acetyl-beta-endorphin(1-16). At present it is not clear whether Peak I is derived from pro-opiomelanocortin or one of the other opioid polyproteins. Peaks II, III, and IV represented 8% of the total immunoreactivity recovered following cation exchange chromatography. These peaks had net positive charges of +3, +4, and +5, respectively, and apparent molecular weights of 2.8, 3.2, and 3.5 Kd, respectively. These apparently N-acetylated beta-endorphin-sized forms are minor end products of the pro-opiomelanocortin biosynthetic pathway.

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)

Evidence for the presence of adrenocorticotropic and opiate-like hormones in the brains of two sea snakes, Hydrophis cyanocinctus and Lapemis hardwickii

The brain acetone powders of the sea snakes Hydrophis cyanocinctus and Lapemis hardwickii were extracted with a mixture of acetone:water:hydrochloric acid (40:21:1 by volume) and the extracts were then added to a copious volume of acetone, in accordance with the method of C. H. Li (1952, J. Amer. Chem. Soc., 74, 2134) for preparing adrenocorticotropin and beta-endorphin from mammalian pituitaries. The resultant precipitate, designated acid acetone powder, possessed adrenocorticotropic activity as evidenced in its ability to stimulate corticosterone production in isolated rat adrenal decapsular cells and lipolysis in isolated hamster adipocytes, and in its cross-reactivity in an ACTH radioimmunoassay. The presence of opioid molecules was indicated by activity in opiate radioreceptor assay using either 3H-D-Ala2-D-Leu5 enkephalin or [3H]naloxone as ligand and rat brain membranes. The brain acetone powders possessed neither "lactogenic" nor "somatogenic" activity as evidenced by their inability to displace the primary ligand in the rat hepatic prolactin receptor- and growth hormone receptor-binding assays, respectively.

Hormones with adrenocorticotropic and opiate-like activities from the carp (Cyprinus carpio) pituitary

Carp (Cyprinus carpio) pituitary acetone powder was extracted with a mixture of water, hydrochloric acid and acetone. An acid acetone powder was formed by adding the pituitary extract into a large volume of chilled acetone and subsequently recovering the precipitate. The powder was subjected to ion exchange chromatography on CM cellulose. Fractions adsorbed on the ion exchanger exhibited ACTH-like activity as evidenced in the ability to stimulate lipolysis in isolated hamster adipocytes and corticosterone production in isolated rat adrenal decapsular cells and also in cross-reactivity in an ACTH-specific radioimmunoassay. A portion of the ACTH-like bioactivity and immunoactivity was unadsorbed on the ion exchanger. Opiate-like activity in opiate receptor binding assay, employing [3H]D-ala2-D-leu5 enkephalin or [3H]naloxone as ligand, also resided in fractions adsorbed on CM cellulose. The data indicate a separation of ACTH-like and opiate-like activities, and the presence of opiate-like molecules with different affinities of binding to mu and delta opiate receptors.

Characterization of endorphins from the pituitary of the spiny dogfish Squalus acanthias

Opioid-like immunoreactive material was extracted from the pituitary and brain of the Spiny Dogfish Shark Squalus acanthias. The immunoreactive material in the pituitary extracts was purified to apparent homogeneity by reverse phase high performance liquid chromatography and subsequently characterized by amino acid analysis, Edman degradation and fast atom bombardment mass spectrometry. The largest opioid-like peptide isolated contained 30 amino acids and showed 80 percent homology with salmon endorphin-II but less than 50 percent homology with human beta-endorphin. Three structural variants of this molecule were also characterized. These variants were shown to be shorter N-terminal fragments, two of which corresponded to cleavage products at the single basic residues arginine and lysine. Cleavage at a single lysine residue has not been reported for posttranslational processing of beta-endorphin in mammals and could represent a modification seen only in lower vertebrates. The remaining fragment corresponded to a loss of 3 residues from the C-terminus of the parent molecule. No alpha-N-acetylated peptides were detected. These results provide the first unequivocal confirmation of beta-endorphin in an elasmobranch and provide evidence of novel N-terminal variants of beta-endorphin.

Localization of neurons containing pro-opiomelanocortin-related peptides in the hypothalamus and midbrain of the lizard, Anolis carolinensis: evidence for region-specific processing of beta-endorphin

Immunohistochemical analyses of the lizard-brain, following colchicine pretreatment, revealed two populations of POMC-producing cell bodies located in medial-basal hypothalamus and the mesencephalic tegmentum. Analyses of extracts of lizard brain regions by radioimmunoassay and gel filtration chromatography indicate that beta-endorphin-sized and alpha-MSH-sized peptides are the major POMC-related end products. Evidence is presented for region-specific processing of beta-endorphin in the lizard brain.

Proopiomelanocortin peptide immunocytochemistry in rhesus monkey brain

The immunocytochemical distribution of proopiomelanocortin (POMC) peptides (beta-endorphin, ACTH, alpha-MSH, 16K fragment) was studied in the brain of the rhesus monkey (Macaca mulatta). Some animals were administered colchicine intracerebroventricularly prior to sacrifice to enhance the visualization of perikaryal immunoreactivity. Immunoreactive perikarya are localized to hypothalamic infundibular nucleus, giving rise to several distinct projections. Rostral projections extend through midline diencephalic and preoptic areas, and enter the telencephalon. Along this course, immunoreactive fibers are seen in midline hypothalamic and preoptic nuclei, nucleus of the diagonal band, olfactory tubercle, nucleus accumbens, bed nucleus of stria terminalis, septum, and other limbic structures in telencephalon. Caudal to the anterior commissure, some fibers ascend dorsally to enter the midline thalamus, which they innervate. Lateral projections of the infundibular perikarya course through the medial-basal hypothalamus, dorsal to the optic tracts, and enter the amygdala region where they innervate more medially situated amygdaloid nuclei. Caudal projections of the POMC neurons also extend through midline diencephalon, some coursing along a periventricular path to innervate midline hypothalamic and thalamic nuclei. This projection extends into the mesencephalic substantia grisea centralis and may also contribute to the innervation of more dorsally situated nuclei in the pons and medulla, such as the parabrachial nuclei and nucleus tractus solitarius. Other caudal projections originating in the hypothalamus course through the ventral tegmentum of mesencephalon and pons and may contribute to the innervation of midline raphe and other ventrally situated nuclei in the pons and medulla. The distribution of immunoreactive perikarya and fibers in the brain of rhesus monkey is strikingly similar to that found in the rat brain. However, subtle differences appear to exist in the innervation patterns of particular brain regions.

Beta-endorphin/ACTH immunocytochemistry in the CNS of the lizard Anolis carolinensis: evidence for a major mesencephalic cell group

The immunocytochemical distribution of beta-endorphin and other proopiomelanocortin (POMC) peptides in the central nervous system of the lizard Anolis carolinensis was determined. Colchicine pretreatment was used to enhance perikaryal immunoreactivity. A major finding of this study is the localization of a previously undetected mesencephalic cell group which exhibits immunoreactivity to beta-endorphin, ACTH, and alpha-MSH. The perikarya of these neurons are large, bipolar, and situated in the mesencephalic tegmental area. They appear to project to the mesencephalic central gray and other brainstem structures. In contrast, the immunoreactive parvicellular perikarya of the medial-basal hypothalamus, corresponding to the POMC perikarya of the rodent arcuate nucleus, exhibit major rostral projections to various telencephalic and diencephalic structures. The exact extent of fiber projections and innervation patterns arising from either of these two groups is not clear at this time and will require further analyses. Scattered fiber immunoreactivity was also seen in the medial cerebral cortex and the striatal complex, regions which apparently are not innervated by beta-endorphin fibers in the rodent brain. Also, no immunoreactivity was seen to an antiserum to the 16K peptide of POMC. Other similarities and differences in the brain distribution of POMC in reptiles and mammals are discussed.

In vitro synthesis of ACTH- and beta-endorphin-related substances in the pars distalis of Anolis carolinensis

In order to investigate the biosynthesis of ACTH- and beta-endorphin-related substances in the pars distalis of Anolis carolinensis, explants of pars distali were incubated for 24 hr in a complete medium which contained [3H]tyrosine. Acid extracts of the incubates were immunoprecipitated with either an affinity-purified ACTH antiserum or an affinity-purified beta-endorphin antiserum and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Three distinct peaks of ACTH-related material were detected. The major peak comigrated with human ACTH(1-39), while two minor peaks corresponded in apparent molecular weight to ACTH biosynthetic intermediate and precursor-sized material. Three peaks of beta-endorphin-related material were also detected. The major peak comigrated with beta-endorphin(1-31), while two minor peaks corresponded to beta-lipotropin (LPH) and precursor-sized material. Sequential immunoprecipitation experiments indicated that the precursor-sized material had antigenic determinants for both ACTH and beta-endorphin. In addition this peak was identical in apparent molecular weight to the common precursor for alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin in the pars intermedia of A. carolinensis (R.M. Dores, Peptides 3, 925-935). Analysis of extracts of reptile pars distalis by gel-filtration chromatography revealed a single peak of naloxone-reversible opiate bioactivity which coeluted with the peak of beta-endorphin-sized immunoreactivity. On a molar basis there is tenfold more opiate bioactivity in the reptile pars distalis than in the reptile pars intermedia.

Biosynthesis of multiple forms of beta-endorphin in the reptile intermediate pituitary

Fractionation of the beta-endorphin-sized material from freshly dissected reptile intermediate pituitaries by ion exchange chromatography on sulfopropyl Sephadex (SP) revealed at least three distinct forms of immunoreactive beta-endorphin. These forms eluted at 0.25 M NaCl, 0.28 M NaCl, and 0.32 M NaCl and represent respectively, 6%, 65% and 29% of the total immunoreactivity. Only the 0.28 M NaCl peak and the 0.32 M NaCl peak exhibited naloxone reversible opiate bioactivity when tested in the isolated guinea pig ileum bioassay system; taking into account the molar amount of immunoreactive peptides the 0.32 M NaCl peak was 6 fold more potent than the 0.28 M NaCl peak. Intermediate pituitaries in culture were incubated with either [3H]tyrosine, [3H]arginine, or [35S]methionine for periods up to 24 hours and beta-endorphin-sized peptides were prepared by immunoprecipitation and gel filtration. Fractionation of the labeled beta-endorphin-sized peptides by ion exchange chromatography yielded profiles nearly identical to the immunoassay analyses of freshly dissected tissue. Further analysis of the major labeled forms of reptile beta-endorphin by chromatography on Sephadex G-50 equilibrated in 6 M guanidine HCl indicated that the 0.32 M NaCl peak had an apparent molecular weight of 3500 +/- 100 and the 0.28 M NaCl peak had an apparent molecular weight of 3200 +/- 100. Furthermore, pulse/chase experiments showed that the 0.32 M NaCl peak was the precursor for the 0.28 M NaCl peak. These results coupled with the relative opiate bioactivities of the major argue that the principal post-translational modification of reptile beta-endorphin is COOH-terminal proteolytic cleavage.