Isolated deficiency of tyrosine hydroxylase immunoreactivity in tuberoinfundibular neurons in pituitary prolactin-deficient Snell dwarf mice.

Light microscopic morphology and relative numbers of tyrosine hydroxylase (TH)-immunoreactive neurons were assessed in hypothalamus of hypopituitary Snell dwarf mice, compared with normal mice of the same strain. Qualitatively, a specific deficit in staining of tuberoinfundibular neurons was noted in dwarf hypothalamus; TH-positive terminals were absent in dwarf median eminence, and morphology of axons in this region was aberrant. Qualitative observations were supported by quantitative assessment of hypothalamic dopaminergic neuron groups. Dorsal and intermediate TH-positive cells numbered 80% of those normal mouse brain; tuberoinfundibular (A12) TH-positive neurons in dwarf hypothalamus were 2% of those in normal mouse brain. The results imply that absence of pituitary hormone feedback impedes both structural and biochemical development of hypophysiotropic hypothalamic neurons.