Diencephalic Mechanism of Control of the Urinary Bladder of the Cat ‡

It has long been known that at the level of the midbrain pontine junction there is a neural mechanism essential for micturition. Contraction of the urinary bladder in response to increased intravesicular pressure is abolished in the cat following a subcollicular, but not after an intercollicular decerebration.' Electrical stimulation of the brain stem at the level of the inferior colliculus evokes bladder contraction, whereas bilateral chronic lesions in this area results in making cats incapable of completely emptying the bladder.2 These experiments led Barrington to the conclusion that this area constitutes a reflex micturition mechanism. The presence of Barrington's micturition center in the brain stem has since been confirmed.89'12 In recent years, however, many investigators have stimulated more rostral portions of the brain and observed contractions of the bladder. These reactive regions are the rostral portion of the midbrain, and the posterior and anterior hypothalamus,' septum pellucidum and medial preoptic area,5"' the putamen and pallidum and the area around them as well as the genual gyrus," and the cruciate sulcus.9 Each of these areas described is in proximity to another reactive area, and therefore it is difficult to determine whether responses obtained by stimulation of the hypothalamus are due to excitation of cells or of fibers constituting a descending pathway. It is the purpose of this investigation to clarify this point by comparing (i) the bladder responses obtained following electrical stimulation of the hypothalamus in cats having chronic lesions at the preoptic level with (ii) the responses obtained in normal animals.