Contrasting interactions of the locus coeruleus as compared to the ventral noradrenergic bundle with CNS and pituitary pools of vasopressin, dynorphin and related opioid peptides in the rat

30 years of dynorphins--new insights on their functions in neuropsychiatric diseases

Since the first description of their opioid properties three decades ago, dynorphins have increasingly been thought to play a regulatory role in numerous functional pathways of the brain. Dynorphins are members of the opioid peptide family and preferentially bind to kappa opioid receptors. In line with their localization in the hippocampus, amygdala, hypothalamus, striatum and spinal cord, their functions are related to learning and memory, emotional control, stress response and pain. Pathophysiological mechanisms that may involve dynorphins/kappa opioid receptors include epilepsy, addiction, depression and schizophrenia. Most of these functions were proposed in the 1980s and 1990s following histochemical, pharmacological and electrophysiological experiments using kappa receptor-specific or general opioid receptor agonists and antagonists in animal models. However, at that time, we had little information on the functional relevance of endogenous dynorphins. This was mainly due to the complexity of the opioid system. Besides actions of peptides from all three classical opioid precursors (proenkephalin, prodynorphin, proopiomelanocortin) on the three classical opioid receptors (delta, mu and kappa), dynorphins were also shown to exert non-opioid effects mainly through direct effects on NMDA receptors. Moreover, discrepancies between the distribution of opioid receptor binding sites and dynorphin immunoreactivity contributed to the difficulties in interpretation. In recent years, the generation of prodynorphin- and opioid receptor-deficient mice has provided the tools to investigate open questions on network effects of endogenous dynorphins. This article examines the physiological, pathophysiological and pharmacological implications of dynorphins in the light of new insights in part obtained from genetically modified animals.

Locus ceruleus and immunity. III. Compromised immune function (antibody production, hypersensitivity skin reactions and experimental allergic encephalomyelitis) in rats with lesioned locus ceruleus is restored by magnetic fields applied to the brain

This study deals with the relationship between the immunosuppression induced by electrolytic lesions placed into the nucleus locus cerules and the immunopotentiation produced by micromagnets implanted to the parietal area of the skull. The following groups of rats were set up: LC, rats with lesioned locus ceruleus; ShL, sham-lesioned animals bearing non-magnetic beads in the brain parietal region; M, rats with micromagnets of 60 mT influx density in the parietal part of the skull; LCM, animals with impaired locus ceruleus and magnetic beads placed in the parietal area of the skull; and IC, intact control rats. Animals of all groups were tested for plaque-forming cell response, circulating antibodies to sheep red blood cells and bovine serum albumin, Arthus and delayed hypersensitivity skin reactions to bovine serum albumin and old tuberculin, and experimental allergic encephalomyelitis. In LC-rats, humoral and cell-mediated immune reactions were compromised. On the other hand, immune responses in M-rats were significantly potentiated. In LCM-rats, however, the immunosuppression induced by destruction of the locus ceruleus was abrogated by prolonged exposure of the brain parietal region to the magnetic fields, i.e. immune reactivity of LCM-rats was quite similar to that of control IC- and ShL-animals. Several mechanisms may account for the immunomodulating effects produced by lesioning of the locus ceruleus and exposure of the brain to magnetic fields. Noradrenergic, serotoninergic, dopaminergic and peptidergic neurotransmitters, as well as growth hormones and immunopeptides, produced within the central nervous system or elsewhere, may be implicated as necessary for the interactions among the brain, immune apparatus and magnetic fields.

Oxytocin administered intrathecally preferentially increases heart rate rather than arterial pressure in the rat

Oxytocin was administered intrathecally at a dose of 6.5 nmol to the 9th or 2nd thoracic level of the spinal cord in the rat. This increased heart rate but had no effect on arterial pressure. The increase in heart rate began within 1 and 5 min and reached a peak at 10-30 min; the maximum increase, at 10 min after administration, at the second thoracic level was 65.4 +/- 13.8 (S.E.M.) bpm (n = 9). When administration was at the 9th thoracic level the change at 10 min was 36.9 +/- 18.0 bpm (n = 14). Administration of hexamethonium systematically, to block nicotinic transmission in autonomic ganglia, prevented the cardioacceleration in response to intrathecal administration of oxytocin. When 6.5 nmol of oxytocin were administered i.v., there was an immediate decrease in heart rate by 42.5 +/- 16.5 bpm (n = 4) and an increase in systolic (6.3 +/- 6.4 mm Hg) and in diastolic (38.8 +/- 8.3 mm Hg) pressures (n = 4); this effect lasted 5-10 min. Administration of 1.625 nmol of oxytocin at the 9th thoracic level had an effect qualitatively similar to that seen with the higher dose, but the response was smaller in magnitude and more delayed in onset; 0.65 nmol of oxytocin were without effect. Transfer of label to the blood after intrathecal administration of [125I]oxytocin indicated that the level in the blood reached a maximum of 0.6% of the total injected by 30 min after administration. It is concluded that the intrathecal administration of reached a maximum of 0.6% of the total injected by 30 min after administration. It is concluded that the intrathecal administration of oxytocin increases heart rate via an action in the spinal cord, presumably on sympathetic preganglionic neurons. Our results are consistent with earlier suggestions that oxytocin may be a chemical mediator of synaptic transmission onto sympathetic preganglionic neurons.

Electrical stimulation of the ventral noradrenergic tract (VNAT) releases hypothalamic noradrenaline and stimulates prolactin secretion in ovariectomized female rats treated with oestrogen

Electrical stimulation of the ventral noradrenergic tract (VNAT) caused a significant fall in the hypothalamic content of noradrenaline in ovariectomized female rats which had been treated with oestrogen. No similar effect was observed in the cerebral cortex, which implies that the stimulation did not affect the dorsal noradrenergic tract. In parallel experiments with groups of similarly treated rats, VNAT stimulation was found to increase release of prolactin from the pituitary gland, and this increase was significantly enhanced in animals which had been stressed by fasting for 3 days.

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)

Intracerebral injection of different antibodies against endogenous opioids suggests alpha-neoendorphin participation in control of feeding behaviour

The mechanism of feeding behaviour of rats was examined. We used antibodies to different opioid peptides in order to reduce the tonic activity of various endogenous opioid peptide systems that may underly appetite. Unilateral microinjection of anti-alpha-neoendorphin antibodies into various areas of the ventromedial hypothalamus (VMH) inhibited food and water intake up to 45% in deprived animals. Injections outside this area failed to affect feeding. Administration of anti-beta-endorphin antibodies into the VMH moderately attenuated appetite. A considerable decrease of food and water intake was observed only upon injection of this antibody into the nucleus periventricularis hypothalami, a region generally believed to be involved with feeding. A marginal reduction of appetite was observed with anti-dynorphin antibodies injected into the VMH. These data may suggest that alpha-neoendorphin is involved in the control of food and water intake in the VMH.