Induction of proenkephalin in tuberoinfundibular dopaminergic neurons by hyperprolactinemia: the role of sex steroids.

Abstract

The observation that tuberoinfundibular dopaminergic (TIDA) neurons of pregnant, pseudopregnant, lactating, and aged rats express enkephalins suggested that chronically elevated PRL levels, which are characteristic for these animals, are essential for the induction of proenkephalin gene expression in TIDA neurons. The present studies investigated further the role of PRL in this phenomenon. Elevated PRL levels were achieved either experimentally by implanting anterior pituitaries under the kidney capsule of intact or hypophysectomized female rats or by using lactating rats. For controls, the elevated PRL levels were reduced with bromocryptine, a dopamine receptor agonist. The role of sex steroids in PRL-induced enkephalin gene expression was also studied in cycling, sex hormone-treated, hypophysectomized or ovariectomized rats, pituitary-implanted/sex hormone-treated rats, and ovariectomized mothers. Enkephalin immunoreactivity was detected by immunocytochemistry and enkephalin messenger RNA with in situ hybridization histochemistry using 35S- or digoxigenin-labeled riboprobes. Enkephalin or its messenger RNA was present in TIDA neurons in all experimental animals with elevated PRL levels. Although estradiol had no or only a minor effect on PRL-induced enkephalin gene expression, progesterone supported the effect of PRL. The present observations suggest that the expression of enkephalin in TIDA neurons is PRL dependent and supported by sex steroids, primarily progesterone.

Altered Gene Expression Profiles of the Hypothalamic Arcuate Nucleus of Male Mice Suggest Profound Developmental Changes in Peptidergic Signaling

“…Cell types expressing Penk in the mouse ARC may include tuberoinfundibular dopaminergic neurons. In female rats, these neurons respond with enhanced Penk gene expression to hyperprolactinemia [56]. In addition, Penk is also coexpressed with neuronal nitric oxide synthase in the ARC of rats, whereas Penk-immunoreactive neurons in the infundibular nucleus of human males exhibit an overlap with KP and NKB neurons [57]; of note, in mice KP/met-enkephalin colocalization has only been observed in the rostral periventricular area of the third ventricle, but not in the ARC [58].…”

The Effects of Anti-TNF-α Antibody on Hyperprolactinemia-Related Suppression of hCG-Induced Testosterone Release in Male Rats

“…Meanwhile, the kidney harboring the grafts was also examined. The extent of vascularization and size of the viable grafted pituitary tissue were confirmed grossly and, later, microscopically by a method described previously [12]. AP gland grafted animals whose plasma PRL concentrations had increased by at least 50% above the mean control concentration were retained for further experiments.…”

Nicotinamide promotes long‐term survival and extensive neurite outgrowth in ultimobranchial C cells cultured from chick embryos

“…The expression of tyrosine hydroxylase, proenkephalin, and POMC mRNA in cultured C cells indicates that these cells make up a neuroendocrine cell population that synthesizes catecholamines, similar to adrenal chromaffin cells. Furthermore, the cultured C cells resemble catecholaminergic neurons, in that tyrosine hydroxylase and proenkephalin are expressed in the sympathetic ganglia and hypothalamic nuclei and POMC is expressed in the hypothalamic arcuate nucleus (Laurent‐Huck et al, 1991; Tyrrell and Landis, 1994; Merchenthaler et al, 1995; Fang et al, 1998; Emsberger et al, 2000). Intense green fluorescence for dopamine is observed in the C cells of adult chicken ultimobranchial glands that are freeze dried and fixed in paraformaldehyde vapor (Kameda et al, 1988).…”