New Evidence For The Innervation Of The Mammalian Anterior Pituitary

It is universally acknowledged that the anterior pituitary is regulated by hypothalamic hormones released at the median eminence and carried to the gland via the portal system. In resent years, Ju and his colleugues have postulated the hypothesis of neural-humoral dual regulation of the mammalian anterior pituitary, which serves as an important modification of classical theory. The hypothesis has been formulated based on a body of powerful evidence, among which, of pivotal significance is the discovery of synaptic contacts between the peptidergic nerve fibers and the gland cells of the anterior pituitary in the dog. The fibers were found to make synaptic contacts most frequently, if not exclusively, with corticotrophs and somatotrophs, and more with corticotrophs. It was thus speculated that there might be two phases of stress response in the dog: an immediate neural phase followed later by a humoral one. The environment of the dog is very different from that of the laboratory rat, which may be reflected in the way their anterior pituitaries are regulated. To determine whether there might be differences in the synaptic control of the anterior pituitary of these two species, we studied the synaptic relationship between substance P(SP) like-immunoreactive(LI) nerve fibers and gland cells of the anterior pituitary in the rat. The galanin (GAL)-LI nerve fibers were also investigated in the anterior pituitary of normal and adrenalectomized rat, and synaptophysin (SYN) immunoreactivity in the anterior pituitary of the monkey. The results showed that firstly, the SP-LI nerve fibers were found to make synapses with every type of the gland cells, strongly supporting the hypothesis of neural-humoral dual regulation of the mammalian anterior pituitary.