Effects of the cocaine- and amphetamine-regulated transcript peptide on the turnover of dopamine in tuberoinfundibular neurons and serum prolactin levels: studies using estrogen, melanin concentrating hormone, and melanocortin

Abstract

Effects of the cocaine- and amphetamine-regulated transcript (CART) peptide on tuberoinfundibular dopaminergic (TIDA) neurons were examined in female and male Sprague–Dawley rats in the morning and afternoon. We also examined the blocking effects of melanin concentrating hormone (MCH) and the antagonists of α-melanocyte stimulating hormone (α-MSH), SHU9119 and HS014, on stimulation induced by the CART peptide in TIDA systems. Intracerebroventricular administration of 1 μg CART peptide (55–102) at 45 min, either in the morning or afternoon, produced an increase in the median eminence (ME) DOPAC (3,4-dihydroxyphenylacetic acid) level and a corresponding decrease in serum prolactin (PRL) levels. This resulted from stimulation of TIDA neurons regardless of castration, and whether or not male and female rats were estrogen-primed. The stimulatory effects of the CART peptide on ME DOPAC levels were similar in the morning and afternoon in both male and female rats. Central treatment with 1 μg SHU9119, HS014, or MCH significantly decreased the ME DOPAC levels and elevated serum PRL levels in female rats. However, only MCH prevented the stimulatory effect of the CART peptide on TIDA neurons. These results indicate that stimulation by the CART peptide on TIDA neurons is gender-independent; and this stimulatory effect can be blocked by MCH, but not the antagonists of α-MSH.