Stimulatory role of prolactin on the development of tuberoinfundibular dopaminergic neurones in prepubertal female rats: Studies with cysteamine and somatostatin

Cysteamine, a potent depletor of prolactin and somatostatin, was used to de termine the role of prolactin and somatostatin in the control of central do pamine neurones in prepubertal rats. Cysteamine (100 mg/kg, i.p., twice dai ly) was injected for 7, 14 or 21 days in 28-day-old Sprague-Dawley female r ats in one study and for 3 days in 35-day-old rats in another. In control r ats, the 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the median eminen ce increased threefold from day 35 to day 49, and serum prolactin concentra tion 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 stri atum were also lowered, while both DOPAC and dopamine in the paraventricula r nucleus and periventricular nucleus (A14) were increased by cysteamine. A single injection of rat prolactin (0.01, 0.1 or 1 mg/kg) significantly inc reased DOPAC or DOPA levels in the median eminence, nucleus accumbens and s triatum, 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 co ntrast, central injection of somatostatin dose (0.001-1 mu g/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 accumben s and striatum of adult female rats. These results indicate that serum prol actin is important for the maturation and maintenance of dopamine systems i n the median eminence, nucleus accumbens and striatum, while somatostatin e xhibits inhibitory and stimulatory effects on hypothalamic and midbrain dop amine systems, respectively.