Perturbations in fluid balance induced by medially placed forebrain lesions

Acute and chronic effects on the fluid balance of radio-frequency forebrain lesions were studied in the goat. Medial lesions which involved practically the entire anterior wall of the third cerebral ventricle cause persistent loss of thirst and lack of significant antidiuretic hormone (ADH) release in response to hypernatraemia and plasma hyperosmolality. As acute response to such lesions an uncompensated, temporary water diuresis was seen, which rapidly caused pronounced hypernatraemia and hypovolaemia. Lesions extending laterally to encroach upon the supraoptic nuclei resulted in persistent signs of weak, inappropriate ADH secretion (=impaired water diuresis, renal salt wasting, and pronounced hyponatraemia during hydration). Forebrain damage, mainly restricted to the septal region, caused hyperdipsia. In some goats, obvious post-lesioning increase in salt appetite was observed which could not be coreelated to the extent of their forebrain damage. The results are discussed in relation to hypothalamic syndromes in man and previous studies on central control of fluid balance in the goat.