Intrinsic neuronal elements of the hypophyseal intermediate lobe.

The last neuron in the bovine hypophyseal neuroendocrine system is located in the intermediate lobe and not in the hypothalamus. Intrinsic neuronal elements, neurosensory and neurosecretory, of the intermediate lobe of the hypophysis are currently very relevant and they may be directly related to the chemically linked peptides including MSH, LPH, ACTH and the endorphins contained in the intermediate lobe. Hypothalamo-hypophyseal fibers innervating the intermediate lobe, subserve a trophic maintenance as well as a regulatory and feedback function. Variations in hypothalamic influences that tend to change the milieu interior of the intermediate lobe, activate the intrinsic neurosensory and neurosecretory elements. The neurosensory cell, an internuncial neuron, subserving a receptive function, analyzes and integrates changes in the environment of the lobe and sends either stimulatory or inhibitory impulses to the neurosecretory cell. Stimulatory impulses temporarily polarize the neurosecretory cell which eliminates specific materials that diffuse amongst intermediate lobe cells. The materials, in turn, stimulate certain intermediate lobe cells whose secretions are directed towards satisfying bodily functions as designated by the hypothalamus. The rather avascular intermediate lobe, utilizes intraglandular colloid, the holocrine secretion of the lobe, to transport its products to he cerebro-spinal fluid circulation and to the systemic venous circulation of the cavernous sinuses. When bodily functions registered by the hypothalamus (serving as a feedback organ) are satisfied, the hypothalamo-hypophyseal fibers readjust the lobe and the intrinsic elements are "turned off."