Electrical stimulation of the hypothalamus and the mechanism of neural control of the adenohypophysis

Abstract

The means whereby the external environment influences the activity of most endocrine glands is unknown. There is no sound evidence that the thyroid, adrenal cortex or gonads possess a secretomotor nerve supply, and it is likely that the trophic hormones of the pituitary gland are the major factors which directly control their activity. The position regarding environmental influence over these glands would be clarified then if a neural or neuro-vascular connexion could be demonstrated between the adenohypophysis (anterior pituitary) and the central nervous system, particularly the hypothalamus.To investigate the control which the hypothalamus may exert over the secretion of the adenohypophysis a technique for applying prolonged electrical stimulation to these structures in conscious animals has been devised. By this method it is possible to stimulate up to six rabbits simultaneously for several hours daily over periods of weeks or months.

The effect of intrapituitary infusion of median eminence and other brain extracts on anterior pituitary gonadotrophic secretion

“…(2) All major vertebrate groups possess a vascular system carrying blood from the median eminence to the adenohypophysis (Green, 1951). (3) The evidence that electrical stimulation of the hypothalamus evokes ovulation in the rabbit, whereas similar stimulation applied directly to the anterior pituitary gland itself is ineffective (Markee et al 1946;Harris, 1948), is compatible with the view of humoral stimulation of the gland cells. (4) Permanent interruption of the hypophysial portal vessels (by pituitary stalk section or pituitary transplantation) results in a permanent and severe loss of ovarian activity; temporary interruption followed by regeneration of the portal vessels is often associated with a post-operative return of normal ovarian function.…”

60 YEARS OF NEUROENDOCRINOLOGY: The posterior pituitary, from Geoffrey Harris to our present understanding

“…Accordingly, with his student Barry Cross, Harris set out to test these two hypotheses. He had concluded (Harris 1948a) that direct electrical stimulation was ineffective in triggering secretion from the anterior pituitary, but the posterior pituitary was innervated by a nervous tract -the supraoptico-hypophysial tract. Cross & Harris (1950, 1952 showed that the electrical stimulation of this tract caused an increase in intramammary pressure in lactating rabbits, which suggested that the pituitary contains a releasable factor that can induce milk let-down.…”

The thyroxine ‘receptor’ of the thyroid‐pituitary system

“…Two to three days after the rabbits had received a dose of 2-5 ILc of carrierfree radio-iodine (1311) intramuscularly the observations started. The unanaesthetized rabbit was placed in a hammock and immobilized by restriction clamps (Harris, 1948a). The neck rested against the lead collimator of a scintillation counter.…”