Volume-evoked micturition reflex is mediated by the ventrolateral periaqueductal gray in anesthetized rats

The central pathway of the micturition reflex in the rat was investigated functionally by acute blockade of synaptic neurotransmission using microinjection of cobalt chloride into the periaqueductal gray or pontine tegmental region. In 27 urethan-anesthetized (1.2 g/kg ip) rats, the bladder pressure response to continuous infusion of the bladder with saline (0.1-0.25 ml/min) was assessed. Electromyographic activity of external urethral sphincter and arterial blood pressure were also monitored. Bladder contractions and external urethral sphincter activity were reversibly attenuated after unilateral or bilateral stereotaxic injections of 10 mM cobalt chloride into the caudal (bregma -7.80 to -8.80) ventrolateral periaqueductal gray as well as into Barrington's nucleus. Blood pressure was not affected by injection into either area. The results demonstrate that the caudal ventrolateral periaqueductal gray, in addition to Barrington's nucleus, is a critical part of the long-routed micturition reflex circuitry in the anesthetized rat.