Hypothalamic catecholamine histofluorescence in dwarf mice

Summary Brains of growth hormone (GH)-and prolactin (PRL)-deficient Ames (df/df) and Snell (dw/dw) dwarf mice and normal mice of the same strains were examined for catecholamine (CA) histofluorescence, with particular emphasis upon the hypothalamic tuberoinfundibular (A12) (arcuate nucleus/median eminence) region, which plays a role in the regulation of both GH and PRL. Dwarfs and normal animals of both types also were treated with a drug regimen to deplete sequentially neuronal CA stores (reserpine), inhibit CA oxidation (nialamide) and load dopaminergic A12 cells with exogenous transmitter (norepinephrine), in order to test viability and axonal transport capacity of A12 neurons. In both types of dwarfs, compared with normals, fluorescence was markedly reduced in the zona externa of the median eminence, which is normally rich in terminals from A12 neurons. Fluorescence in the median eminence was particularly weak in Ames dwarfs, and A12 perikarya were difficult to discern in this group. Snell dwarfs showed reduced fluorescence of A12 perikarya when compared with the brightly fluorescent perikarya seen in normal mice. In supraoptic and paraventricular nuclei, and in the zona interna of the median eminence, CA fluorescence attributable to NE was comparable among dwarfs and normals; fluorescence of dopaminergic perikarya in substantia nigra was also unaffected in dwarfs. Exogenously administered NE effected enhanced fluorescence of A12 Perikarya in normal mice and in Snell dwarfs; NE treatment in the Ames dwarf, however, failed to increase significantly the faint fluorescence of A12 cell bodies. The results indicate that dopaminergic A12 neurons in Snell dwarf mice are present and viable. Reduction in DA in the median eminence in both genetic dwarfs and failure of CA uptake in Ames dwarfs may indicate altered axon morphology or transport capacity, and/or abnormal DA biosynthesis, which may be more severe in Ames than in Snell dwarfs. Thus, genetic alteration in differentiation of pituitary cells may play a significant role in development of the CA systems in the hypothalamus.Supported by PHS Grants HD 18243 (CP), NS15816 and AG00847 (JRS) and HS12671 (AB).