Distribution of Somatostatin Immunoreactivity in Sheep Hypothalamus: A Comparison with That of the Rat

The distribution of somatostatin immunoreactivity was determined throughout the hypothalamus of the sheep and comparisons were made with the known distribution of somatostatin immunoreactivity in the rat. Immunopositive perikarya were present in the sheep periventricular region from as far rostral as the supraoptic recess of the third ventricle to the posterior optic chiasm. In the basal hypothalamus, a thick shell of immunopositive neurons surrounded the ventromedial nucleus (VMH), and there were also neurons in the caudal arcuate nucleus. Somatostatin immunoreactive fibres were concentrated in the dorsal VMH and arcuate nucleus as well as in the median eminence. The distribution in sheep was similar to that in rats, butimmunoreactive neurons around sheep VMH were distinctive, a characteristic that might relate to differences in growth hormone physiology in this species.