The Hypothalamic Paraventricular Nucleus: Relationship to Brain and Pituitary Pools of Vasopressin and Oxytocin as Compared to Dynorphin, β-Endorphin and Related Opioid Peptides in the Rat

Abstract

The present study examines the relationship of the hypothalamic paraventricular nucleus (PVN) to discrete brain and pituitary pools of immunoreactive (ir) vasopressin (VP), oxytocin (OT) and particular opioid peptides in the rat. Selective, bilateral destruction of the PVN resulted in a parallel depression in levels of ir-VP, ir-OT, ir-dynorphin (DYN), ir-DYN_1–8 and ir-α-neo-endorphin (α-NE) in the neurointermediate lobe of the pituitary, whereas in its anterior counterpart no decrease in the content of any of these peptides was seen. In contrast, the content of ir-β-endorphin (β-EP) in the neurointermediate lobe was not significantly altered. Further, a rise in levels of ir-β-EP in the anterior lobe, together with a fall in these in systemic plasma, was found. In the hypothalamus, in distinction to ir-metenkephalin (ME), a diminution in the content of ir-VP, ir-OT, ir-DYN, ir-DYN_1–8, ir-α-NE and, in addition, ir-β-EP was observed. In the septum, midbrain and medulla/pons, however, a selective depression in levels of ir-VP (and, as measured in the medulla/pons, of ir-OT) was seen: the content of ir-DYN, ir-DYN_1–8, ir-α-NE, ir-β-EP and ir-ME was unchanged in these tissues. These data indicate that: (1) the PVN is an important contributor to neurointermediate lobe, but not anterior lobe, pools of ir-VP, ir-OT, ir-DYN, ir-DYN_1–8 and ir-α-NE in contrast to ir-β-EP. (2) the PVN provides a mayor input of ir-VP (and ir-OT), in contrast to ir-DYN, ir-DYN_1–8, ir-α-NE, ir-β-EP and ir-ME, to the septum, midbrain and medulla pons. (3) although coexisting with ir-VP in a hypothalamo-neural lobe tract partially derived from the PVN, ir-DYN, ir-DYN_1–8 and ir-α-NE exist independently of the PVN-originating VP-containing neurons which innervate extrahypothalamic brain tissue. (4) the PVN may interact with hypothalamic ir-β-EP and plays a facilitatory role in the tonic regulation of adenohypophyseal secretion of ir-β-EP into the systemic circulation.

Beta Endorphin and Dynorphin Levels in Rat Pituitary and Hypothalamus: Age Studies

“…In contrast, the molecular forms of DYN in the AP differed from those in HT and the N-IL and showed a changing distribution after 3 months. There are a number of reports linking DYN in the HT and N-IL with vasopressin [17], and more recently on the immunocytochemical localization of DYN in the AP gonadotrope [14], The physiological significance of these findings remains unclear at this time, since there is a 'paucity of data concerning the functions of dynorphins' [8], and other agerelated data are to our knowledge presently unavailable.…”

Immunoreactive Dynorphin Is Regulated by Estrogen in the Rat Anterior Pituitary

“…More recently, dynorphin gene expression in pituitary gon adotrophs has been demonstrated by the combination of quantitative Northern blot analysis and immunocytochemistry [12]. Neural lobe dynorphin, in contrast, appears to originate in the magnocellular neurons of the supraoptic and paraventricular nuclei [28,29], and appears to be co secreted with vasopressin from the same source [14]. Ra diofrequency lesions of the medial basal hypothalamus thus not surprisingly reduce N-IL levels of both ir-dyn and AVP, but do not affect AP ir-dyn levels [27]; N-IL levels of ir-dyn, but not those in AP, move in parallel with those of AVP in a variety of situations and in response to a variety of endocrine manipulations [10].…”

“…Molineaux and co-workers origiReceived: November 26, 1986 Accepted after revision: June 1, 1987 nally reported [18] anterior lobe dynorphin to consist of dynorphin 1 -32 (dyn 32), the 4-kdalton form ; in subsequent studies, however, they have found a higher molecular weight species [17]. In the N-IL there have been a variety of studies showing that dynorphin immunoreactivity was co released with A VP [10,14,16].In the present studies we have determined the effect of ovariectomy and estrogen replacement on levels of irdynorphin in the AP, N-IL and hypothalamus of female rats. We have used two antisera, one specific for dynorphin A 1-8 (dyn 8), and the other recognizing dynorphin A 1-13 (dyn 13) and longer forms.…”

Naloxone Effects on Plasma Vasopressin and Oxytocin Concentrations Elevated by Histamine, Nicotine, Isoproterenol and an Acute Increase in [NaCl] in Cerebrospinal Fluid

“…We conclude that endogenous opioid peptides inhibit release of oxytocin in vivo by an effect on the final common pathway, i.e. the magnocellular neuron or on pituicytes in the neural lobe.A growing body of evidence supports a role for endoge nous opioid peptides in attenuating release of vasopressin and oxytocin from the hypothalamo-neurohypophysial sys tem [ 16,32] during osmotic and nonosmotic stimulation (22,27], Opioid peptides are localized both within magnocellu lar neurons that synthesize either vasopressin or oxytocin (13,35,36] and in the surrounding hypothalamus [15,17,18,25], In addition, opiate receptors are present in the neural lobe of the pituitary [28,34] and in the supraoptic and par aventricular nuclei of the hypothalamus [34]. Thus, both the cell bodies and nerve terminals of magnocellular neurons are sites where opioid peptides could attenuate secretion of neurohypophysial hormones.…”