Cellular distribution of beta-endorphin-like substance in the rat pituitary and brain

Presence of pro-opiomelanocortin mRNA in the rat medial prefrontal cortex, nucleus accumbens and ventral tegmental area: studies by RT-PCR and in situ hybridization techniques

Pro-opiomelanocortin (POMC) is a large proteic precursor which originates several biologically actives neuropeptides, such as beta-lipotropin (beta-LPH), beta-endorphin (beta-END), adenocorticotropic hormone (ACTH) and alpha-melanocyte-stimulating hormone (alpha-MSH). The arcuate nucleus of the hypothalamus is the main POMC producing cell group in brain and innervates several areas of the limbic system and brainstem. POMC-derived neuropeptides have been related to several motivated and rewarding behaviours, including sexual facilitation, feeding, and drug addiction. However, POMC mRNA has not been detected in regions of the dopaminergic mesocorticolimbic system, which represents the most important reward pathway. The aim of this work was to investigate if POMC mRNA is expressed in the medial prefrontal cortex (mPFC), the nucleus accumbens (NAcc) and the ventral tegmental area (VTA) of the rat. We used the reverse transcriptase reaction coupled to the polymerase chain reaction (RT-PCR). We also used the in situ hybridization technique to study the regional distribution of POMC mRNA in the same regions. We report that RT-PCR amplification of extracted RNA with two different pairs of primers generates the predicted 94bp and 678bp POMC-PCR products. Both the amplification of RNA obtained from the rat glial C-6 cell line (which does not express POMC mRNA) and the omission of reverse transcriptase from the RT reaction of rat brain samples showed no amplification products. We have shown for the first time that the rat medial prefrontal cortex, the nucleus accumbens and the ventral tegmental area contain POMC mRNA. This mRNA is in low concentration, ranging from 21% to 31% with respect to the hypothalamus. In situ hybridization experiments showed that POMC mRNA is homogeneously distributed in these areas. The presence of POMC mRNA in regions of the mesocorticolimbic system could have functional implications in motivated behaviours.

Beta-endorphin modulation of interferon-gamma, perforin and granzyme B levels in splenic NK cells: effects of ethanol

The effects of ethanol and beta-endorphin (beta-EP) on productions of cytolytic factors granzyme B, perforin and IFN-gamma in splenic rat NK cells were determined. Intracranial administration of beta-EP increased protein and mRNA levels of cytolytic factors in NK cells. Chronic ethanol feeding reduced the basal and beta-EP-induced levels of cytolytic factors in NK cells. In vitro treatment of beta-EP on NK cells increased the levels of perforin, granzyme B and IFN-gamma and their mRNA transcripts, whereas ethanol pre-treatment prevented beta-EP effects on cytolytic factors in these cells. These results suggest that beta-EP and ethanol interact to regulate NK cell functions.

Detection of pro-opiomelanocortin mRNA in human and rat caudal medulla by RT-PCR

Pro-opiomelanocortin (POMC) mRNA has been localized in the NTS of the rat, but not in the human or other species. Here, we report that RT-PCR amplification of human caudal medulla RNA generated a distinct band on agarose gels corresponding in size and sequence to the predicted 742-bp POMC PCR product. The 742-bp signal was undetectable following amplification of cortex, amygdala or caudate nucleus RNA. An homologous, 678-bp band was amplified from rat caudal medulla and, unexpectedly, from other brain regions. Competitive RT-PCR demonstrated that POMC cDNA from rat cortex, striatum and cerebellum was 17%, 22% and 45% of caudal medulla levels. These data indicate that the POMC gene is expressed in human caudal medulla and suggest that small amounts of POMC mRNA are present in regions other than the hypothalamus and NTS of rat brain.

Involvement of beta-endorphin in the modulation of paw inflammatory edema in the rat

This study investigates the role of the opiod receptors and of the opioid peptide beta-endorphin in the development of yeast-induced inflammation in the rat paw. Pretreatment with the opioid receptor antagonist naltrexone (10 mg/kg i.p.) exacerbates the paw edema, while morphine pretreatment (5 and 10 mg/kg) reduces it. In addition, the intravenous injection of a specific anti-beta-endorphin antibody aggravates the yeast-induced inflammation. On the contrary, both the kappa-opioid receptor antagonist MR 1452 (2.5, 5 and 10 mg/kg i.p.) and the delta-opioid receptor antagonist ICI 174-864 (2.5, 5 and 10 mg/kg i.p.) do not interfere with the inflammatory process. After intraplantar injection, naltrexone, morphine and the anti-beta-endorphin antibody do not interfere with the yeast-induced inflammatory edema. Our data suggest that beta-endorphin exerts an inhibitory regulation on the inflammatory responses through the activation of mu-opioid receptors probably located on immune cells, rather than in the paw.

BDNF produces analgesia in the formalin test and modifies neuropeptide levels in rat brain and spinal cord areas associated with nociception

Previous studies have demonstrated an antinociceptive effect of brain-derived neurotrophic factor (BDNF) following infusion into the midbrain, near the periaqueductal grey and dorsal raphe nuclei. BDNF administration attenuated the behavioural response in the tail-flick and hot-plate tests, two models employing a phasic, thermal high-intensity nociceptive stimulus; the present studies extend our previous findings to include a model of moderate, continuous pain resulting from a chemical stimulus, the formalin test. Midbrain infusion of BDNF decreased the behavioural paw flinch response to subcutaneous formalin injection in both the early and late phases of the test. As our previous studies showed that BDNF-induced analgesia was reversible by naloxone, we have examined the effects of BDNF administration on brain and spinal cord levels of neuropeptides involved in the modulation of nociceptive information, including the endogenous opioid peptides, met-enkephalin and beta-endorphin, as well as substance P and neuropeptide Y (NPY). At the site of infusion, within the PAG and dorsal raphe, BDNF increased the level of beta-endorphin by 63%, but had no effect on substance P, metenkephalin or NPY levels. In the dorsal spinal cord, substance P (113% increase), beta-endorphin (97% increase) and NPY (64% increase) were elevated, although ventral spinal cord levels of these peptides remained unchanged. These studies demonstrate a modulatory effect of BDNF on relevant neuropeptides within areas of the brain and spinal cord involved in the processing of nociceptive information.

Production of immunoreactive adrenocorticotropin and beta-endorphin by hypothalamic and extrahypothalamic brain cells

Despite many in vivo studies, little is known about brain regulation of POMC synthesis or regulation of secretion of POMC-related peptides. To test the hypothesis that dissociated brain cells in culture can produce and release POMC-related peptides, immunoreactive (IR)-adrenocorticotropin (ACTH) and beta-endorphin were measured in cells and media of dissociated cell cultures incubated up to 38 days. Fetal rat hypothalamic and extrahypothalamic forebrain cells were maintained in serum free medium. IR-ACTH and beta-endorphin were measured by radioimmunoassay in concentrated cells and media after various incubation times using two ACTH (mid-portion = R4; carboxy-portion directed = KEND) antisera and a beta-endorphin antiserum. IR-ACTH and IR-beta-endorphin in hypothalamic and extrahypothalamic cells and in media (cumulative) were greater than quantities in cells before culture. Peak hypothalamic cellular content of IR-ACTH (5.3 fmol/10(6) cells-R4; 4.7 fmol/10(6) cells-KEND) and content of IR-beta-endorphin (32.0 fmol/10(6) cells) occurred on days 16, 9 and 23, respectively. Peak extrahypothalamic content of IR-ACTH (2.9 fmol/10(6) cells-R4; 1.0 fmol/10(6) cells-KEND) and content of IR-beta-endorphin (10.8 fmol/10(6) cells) was also seen on different days, was lower than hypothalamic content and was not always concurrent with peak hypothalamic content. Gel filtration chromatography revealed that the predominant forms of IR-ACTH and IR-beta-endorphin in hypothalamic cell extracts co-eluted with synthetic ACTH1-39 and beta-endorphin. Changes in molar ratios of IR-ACTH and IR-beta-endorphin also suggested a differential regulation of different POMC derivatives.

CONCLUSIONS

(1) IR-ACTH and IR-beta-endorphin are produced by hypothalamic and extrahypothalamic forebrain cells in culture: and (2) dissociated brain cell cultures can be used as a potential model for studying regulation of POMC-related peptides in brain.

Occurrence of beta-endorphin-like immunoreactivity in the brain of the teleost, Boops boops

By immunocytochemical methods the present study describes beta-endorphin-like immunoreactive substance in the brain of Boops boops. Beta-Endorphin-like neurons and fibers were detected in both dorsal and ventral components of the preoptic nucleus and in the nucleus lateralis tuberis. This localization has been discussed in relation to the presence, in the same area, of a well-defined neurosecretory system involved in hypophysial regulation. A beta-endorphin-like immunoreaction was also detected in the Purkinje cells and in processes within the cerebellum molecular layer. Although this last finding remains enigmatic it may suggest a neuromodulatory activity for cerebellum beta-endorphin-like substance. No immunoreaction was observed when the specific antiserum was absorbed with corresponding antigen and with beta-LPH. These tests led to the conclusion that the immunostaining reaction might correspond to a beta-endorphin- or lipotropin-like reaction. Further, the present results show the phylogenetic antiquity of a beta-endorphinergic or lipotropinergic system in the brain, with a stable evolutionary history as a hypophysial regulatory factor or neuromodulatory agent.

Prolonged disruption of plasma beta-endorphin dynamics following surgery

The purpose of the present study was to examine the effects of surgery on plasma beta-endorphin dynamics. Plasma beta-endorphin levels were measured by liquid chromatography/radioimmunoassay in seven patients undergoing elective surgery. Blood samples were obtained every 4 hr for two 24-hr periods: one beginning 48 hr before surgery and the other beginning 48 hr after surgery. Computer analysis of beta-endorphin levels as a function of clock time demonstrated a true circadian rhythm preoperatively with a mean of 28.0 +/- 5.9 pg/ml. In the postoperative period mean beta-endorphin levels were significantly elevated (85.6 +/- 20.7 pg/ml, P less than 0.005). Surgical procedures caused significant phase shifting in the grouped mean circadian rhythm of plasma beta-endorphin (mean = 2.4 hr). When the data was analyzed individually, plasma circadian rhythms were found to be totally abolished in the three patients with the longest operative times (mean = 3.8 hr) and significantly displaced in time in the remaining four patients. These prolonged alterations in plasma endogenous opioid peptide levels following surgery have not been previously reported, and should be considered in the management of the postsurgical patient.

ACTH-related peptide containing neurons within the medulla oblongata of the rat

Neurons containing antigenic determinants of 16 Kdalton fragment, ACTH, gamma-LPH, and beta-endorphin have been identified in the nucleus tractus solitarius and lateral reticular formation of the rat brainstem. Immunoreactive fibers extend longitudinally in dorsal and ventral midline tracts throughout the length of the brainstem, and are also concentrated in lateral reticular regions known to contain catecholamine nuclei. ACTH-containing neurons could participate with brainstem catecholamine cell groups in controlling visceral function.

Neuroanatomical methods for the quantitative evaluation of coexistence of transmitters in nerve cells. Analysis of the ACTH- and beta-endorphin immunoreactive nerve cell bodies of the mediobasal hypothalamus of the rat

A new statistical approach has been introduced to study in a quantitative way the coexistence of two neuromodulators in nerve cell bodies. The method has been exemplified on the ACTH-like and beta-endorphin-like immunoreactive nerve cell bodies of the mediobasal hypothalamus demonstrated by means of indirect immunofluorescence methodology. The method is based on the analysis of 3 adjacent sections which, in a random way, are stained with antiserum against neuromodulator 1, against neuromodulator 2 and with antisera against both neuromodulator 1 and neuromodulator 2. It could be shown that some neurons of the mediobasal hypothalamus do not contain at a detectable level both ACTH- and beta-endorphin-like immunoreactivity. The present method also involves an analysis of the two nerve cell groups by means of a morphometric procedure to collect additional information on the extent of coexistence. Thus, by this approach the gravity centers of the two cell groups can be calculated. The distances between the two gravity centers of the ACTH and beta-endorphin positive cell groups were significantly different at certain levels. The present method offers unique possibilities in increasing our understanding of the functional significance of coexistence of neuromodulators in one and the same nerve cell body since it makes possible a quantitative evaluation of coexistence. The usefulness of the present method is illustrated by the findings of a possible differential synthesis of ACTH- and beta-endorphin-like material in certain cell bodies of the mediobasal hypothalamus.