Stimulatory Role of Prolactin on the Development of Tuberoinfundibular Dopaminergic Neurones in Prepubertal Female Rats: Studies with Cysteamine and Somatostatin

Abstract

Cysteamine, a potent depletor of prolactin and somatostatin, was used to determine the role of prolactin and somatostatin in the control of central dopamine neurones in prepubertal rats. Cysteamine (100 mg/kg, i.p., twice daily) was injected for 7, 14 or 21 days in 28-day-old Sprague-Dawley female rats in one study and for 3 days in 35-day-old rats in another. In control rats, the 3, 4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminence increased threefold from day 35 to day 49, and serum prolactin concentration increased about 50%. Cysteamine lowered serum prolactin concentrations to 20%, and median eminence DOPAC and dopamine levels to 32-50% of control levels in both studies. The DOPAC levels in the nucleus accumbens and striatum were also lowered, while both DOPAC and dopamine in the paraventricular nucleus and periventricular nucleus (A14) were increased by cysteamine. A single injection of rat prolactin (0.01, 0.1 or 1 mg/kg) significantly increased DOPAC or DOPA levels in the median eminence, nucleus accumbens and striatum, but not in the paraventricular nucleus or A14 at 14 h later in 28-day old female rats or in 40-day-old rats pretreated with cysteamine. In contrast, central injection of somatostatin dose (0.001-1 microg/rat) and time (30-90 min) dependently decreased the DOPAC levels in the median eminence, paraventricular nucleus and A14 and increased those in the nucleus accumbens and striatum of adult female rats. These results indicate that serum prolactin is important for the maturation and maintenance of dopamine systems in the median eminence, nucleus accumbens and striatum, while somatostatin exhibits inhibitory and stimulatory effects on hypothalamic and midbrain dopamine systems, respectively.

Pivotal roles of α‐melanocyte‐stimulating hormone and the melanocortin 4 receptor in leptin stimulation of prolactin secretion in rats

“…1981; Arbogast and Voogt 1991; Phelps et al . 1995), although some investigators reported that PRL can stimulate both the nigrostriatal and mesolimbic DA systems (Chen and Ramirez 1988, 1989; Shieh and Pan 1999). Although we cannot provide any clear explanations for this discrepancy, it is possible that the degree of hyperprolactinemia may be responsible.…”

“…Although we cannot provide any clear explanations for this discrepancy, it is possible that the degree of hyperprolactinemia may be responsible. In the latter three studies that reported PRL's stimulating effects on the nigrostriatal and mesolimbic DA neurons, large doses of ovine or rat PRL were administered exogenously (Chen and Ramirez 1988, 1989; Shieh and Pan 1999).…”

Circadian Rhythms of Neuroendocrine Dopaminergic Neuronal Activity in Ovariectomized Rats

“…TIDA axons terminate on a fenestrated capillary bed within the external zone of the median eminence (ME) which drains into long portal vessels (LPV) that transport DA to the AL of the pituitary gland [10, 11, 12, 13]. The role of TIDA neurons as the primary source of DA inhibiting PRL secretion is well established [14, 15, 16, 17, 18]. However, a growing importance has been assigned to THDA and PHDA in the regulation of PRL secretion [9, 14, 19].…”

Effects of Prolactin-Releasing Peptide on Tuberoinfundibular Dopaminergic Neuronal Activity and Prolactin Secretion in Estrogen-Treated Female Rats

“…Thick (600 Ìm), coronal sections were made by using a tabletop freezing microtome, thawmounted onto slides, and kept frozen over dry ice. The ME and striatum (ST) were removed from the sections using a modified micropunch technique [33], and stored individually in 40 Ìl solution containing 0.775 mM sodium octylsulfate, 0.5 mM EDTA, 0.17 M NaH 2 PO 4 , and 10% methanol at pH 2.8.…”