Deficiency of Dopamine in the Median Eminence of Snell Dwarf Mice*

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Abstract
Catecholamine levels were measured in the median eminence, the intermedio-posterior lobe of the pituitary, and the hypothalamus of both male and female Snell dwarf mice and compared to the same parameters in normal mice of the same strain. Catecholamine levels were also examined in the striatum of female dwarfs. Dopamine (DA) levels in the median eminence of both male and female dwarf mice were severely deficient. Noradrenaline (NA) levels in this same region of the dwarf mouse brain were not different from normal. With the exception of the intermedio-posterior lobe of the pituitary of female dwarfs, both DA and NA levels in the other brain regions were comparable in dwarf and normal mice. The turnovers of DA and NA in the hypothalamus and telencephalon were not different in male Snell dwarfs vs. normal males. DA in the median eminence was also markedly depleted in the Ames dwarf mice, whose dwarfism is the result of a mutation on a different chromosome. Daily administration of ovine PRL or T4 for 2 weeks did not significantly influence DA levels in the media eminence of the female Snell dwarf mice, while GH replacement produced a vary small increase in median eminence DA. The implantation of a normal pituitary under the kidney capsule produced a very small but statistically significant increase in DA in the median eminence. These results suggest 1) that congenital PRL, GH, T4 deficiencies in mice are associated with extremely low levels of DA in the median eminence; 2) that the elevation of peripheral PRL or GH levels can only slightly increase DA in the median eminence of adult dwarfs; 3) that one or more of these hormones may be important at a critical time during the postnatal development of the tuberoinfundibular dopaminergic system; and 4) that the deficiency in median eminence DA is not due to a genetic deficiency of tuberoinfundibular dopaminergic system neurons, since it occurs in nonallelic Snell and Ames dwarfs.