EFFECT OF SULFAMETHAZINE ON SEXUAL PRECOCITY AND NEUROPEPTIDE-Y NEURONS WITHIN THE TUBEROINFUNDIBULAR REGION OF THE CHICK BRAIN

Neuropeptide Y (NPY) has been implicated in the sexual maturation proc ess in chicks and other species. This study attempted to identify spec ific neural sites where NPY could influence gonadotrophin-releasing ho rmone (GnRH) neurons during maturation as evidenced by immunocytologic al changes. To do this sulfamethazine (SMZ), an antibiotic known to ad vance sexual maturation in male chicks, was used to elicit early teste s development, One week posthatch, 20 chicks were fed either a control ration or one with 0.2% SMZ for 2 weeks or 5 weeks, At 3 and 6 weeks of age, birds were perfused through the heart, brains removed, and pre pared for immunocytochemical assay for either NPY or GnRH. Results sho wed that chicks given SMZ had significantly greater testes weight comp ared to controls at both ages (p less than or equal to 0.05) while bod y weight did not differ significantly between these groups at either a ge, The results of cell quantification showed no difference in the num ber of GnRH neurons between the SMZ chicks and controls in either the bed nucleus of the pallial commissure or the anterior lateral thalamic nucleus (LA) at 3 or 6 weeks of age, There was a significantly greate r number of GnRH neurons found within the LA of 6-week compared to 3-w eek-old control chicks. A ratio of the mean width of the external zone (EZ) of median eminence (ME) to the total width of ME showed no signi ficant difference between the experimental and control animals at eith er 3 or 6 weeks of age, The ratio EZ/ME did, however, increase as a fu nction of age, The results of the assay for immunoreactivity to NPY sh owed no significant difference in the number of NPY neurons found with in the nucleus marginalis tractus opticus between treatment groups at either age. A highly significant increase in NPY neurons was found wit hin the infundibular nucleus (IN) and the internal zone of the ME of S MZ-treated chicks compared to controls at 3 weeks of age, Data suggest that NPY-like neurons within the IN complex may serve an important ro le regarding the early stages of sexual maturation in chicks. (C) 1997 Elsevier Science Inc.