Early Postnatal Administration of Growth Hormone Increases Tuberoinfundibular Dopaminergic Neuron Numbers in Ames Dwarf Mice

Abstract

Hypothalamic tuberoinfundibular dopaminergic (TIDA) neurons secrete dopamine, which inhibits pituitary prolactin (PRL) secretion. PRL has demonstrated neurotrophic effects on TIDA neuron development in PRL-, GH-, and TSH-deficient Ames (df/df) and Snell (dw/dw) dwarf mice. However, both PRL and PRL receptor knockout mice exhibit normal-sized TIDA neuron numbers, implying GH and/or TSH influence TIDA neuron development. The current study investigated the effect of porcine (p) GH on TIDA neuron development in Ames dwarf hypothalamus. Normal (DF/df) and dwarf mice were treated daily with pGH or saline beginning at 3 d of age for a period of 42 d. After treatment, brains were analyzed using catecholamine histofluorescence, tyrosine hydroxylase immunocytochemistry, and bromodeoxyuridine (BrdU) immunocytochemistry to detect BrdU incorporation. DF/df males and df/df treated with pGH experienced increased (P </= 0.01) weight gain compared with those treated with saline. DF/df had greater (P </= 0.01) TIDA neuron numbers than df/df, regardless of treatment. TIDA neuron number in pGH-treated df/df was greater (P </= 0.01) than in saline-treated df/df. Zona incerta and periventricular dopamine neurons were not affected by treatment or genotype. There was no effect of genotype or treatment on BrdU incorporation in the arcuate nucleus, median eminence, or periventricular region surrounding the third ventricle. Saline-treated df/df experienced decreased (P </= 0.05) dentate gyrus BrdU incorporation compared with saline-treated DF/df. In the lateral ventricle, pGH-treated males had greater BrdU immunoreactivity than pGH-treated females. The results show an effect of pGH on TIDA neuron development, although this effect is less potent than that of PRL, and likely GH-induced preservation of TIDA neurons rather than generation of new TIDA neurons via neurogenesis.