Effects of hypothalamic and thalamic lesions on prolactin secretion in goldfish ( Carassius auratus)

The effects of hypothalamic and thalamic lesions on serum and pituitary prolactin levels in goldfish were studied. A radioimmunoassay was used to measure prolactin levels. Lesions in the nucleus lateral tuberis (NLT) pars anterioris, NLT pars posterioris, NLT pars inferioris, nucleus anterior tuberis, or in the nucleus preopticus did not affect serum or pituitary polactin levels compared to sham or normal control groups. Lesions in the NLT pars lateralis caused a significant increase in serum prolactin, but had no effect on pituitary prolactin levels. This suggests that the NLT pars lateralis is the origin of a factor that normally inhibits prolactin release from the pituitary. Large lesions that destroyed the medial thalamic and anterior hypothalamic region dorsal to the NLT caused a significant decrease in serum prolactin, but had no significant effect on pituitary prolactin levels. It is suggested that the lesions in this region may have interrupted neural afferents to the NLT pars lateralis that normally inhibit secretion of a prolactin inhibitory factor.