Brain stem influences on the parasympathetic supply to the urinary bladder of the cat

(1)The brain stem of anaesthetized cats has been mapped between Horsley-Clark planes APO and P8.5 with electrical stimuli of low intensity in order to determine the areas which can produce excitatory of inhibitory influences on the spontaneously contracting, sympathetically denervated, urinary bladder. (2) Two inhibitory areas were found. The first extended from P3.0 to P8.5 and at all levels was coincident with the midline raphe nuclei. The second area occurred largely 2-3 mm lateral to the midline, in the area of the nucleus reticularis pontis caudalis rostrally, and the nuclei reticularis gigantocellularis and parvocellularis caudally. Both of these areas were found to inhibit bladder contractions with threshold stimulus parameters of 20-60 microamperemeter, 400 microseconds, 20 Hz. (3)One excitatory area was found, largely 3-4 mm lateral to the midline. This area appeared large and diffuse in the lateral reticular formation. It is possible that it originated in the pontine micturition centre in the rostral pontine tegmentum. Caudally, it shifted to occupy a ventrolateral position. This excitatory area was in close approximation to, and was probably interspersed with, the lateral inhibitory area. (4) In decerebrate preparations the areas that produced excitation or inhibition had the same distribution as those found in anaesthetized animals. (5) Single shock stimulation (100 microamperemeter, 400 microseconds, 0.5 Hz repetition frequency in the excitatory area could produce firing in pelvic nerve efferents to the bladder at latencies of 60-110 ms. The amplitude of such responses was dependent on the level of intravesical pressure. (6) Stimulation of the inhibitory areas produced no evoked responses in the pelvic nerve efferents, but could inhibit reflexly evoked responses in this nerve. The similarity in the time courses of the inhibitory effects from the two areas raises the possibility that one acts via the other.