Depression by p-methoxyphenylethylamine of sympathetic reflex firing elicited by electrical stimulation of the carotid sinus nerve or pelvic nerve

Effects of clonidine on the lumbar sympathetic pathways to the large intestine and urinary bladder of the cat

The effects of clonidine on lumbar sympathetic outflow to the colon and urinary bladder were examined by recording drug-induced changes in spontaneous postganglionic firing and spinal viscero-sympathetic reflexes in the lumbar colonic and hypogastric nerves of the cat. Clonidine in doses between 2--40 micrograms/kg produced a dose dependent depression of spontaneous and evoked discharges in efferents of the hypogastric nerve but did not alter activity in the lumbar colonic nerves. Clonidine also reduced arterial blood pressure and spontaneous firing in the renal nerves. These data coupled with previous observations in this laboratory indicate that spinal sympathetic pathways can exhibit a considerable variation in the sensitivity to the depressant actions of clonidine. This variation in sensitivity may reflect the relative importance of noradrenergic inhibitory mechanisms in the respective pathways.

Reflex activation of sympathetic pathways to vesical smooth muscle and parasympathetic ganglia by electrical stimulation of vesical afferents

1. Activation of the sympathetic input to the urinary bladder by electrical stimulation of afferent fibres in the pelvic nerve evoked three responses: (1) an initial transient rise in intravesical pressure, (2) an inhibition of neurally evoked bladder contractions and (3) an inhibition of transmission in vesical parasympathetic ganglia. Similar responses were elicited by stimulation of the hypogastric nerve. 2. The reflex responses were observed in acute spinal preparations (T10-T12) and in cats with intact spinal cords, but were abolished by bilateral transection of the hypogastric nerves. 3. The inhibition of bladder contractions was antagonized by the administration of propranolol (200-400 mug, I.A.), a beta-adrenergic blocking agent. The inhibition of ganglionic transmission was antagonized by dihydroergotamine (30-75 mug, I.A.), an alpha-adrenergic blocking agent. The initial rise in intravesical pressure was not antagonized by either agent. 4. Electrical stimulation of other afferents (carotid sinus nerve and sciatic nerve) did not consistently elicit responses in the urinary bladder. However, stimulation of these afferents as well as pelvic nerve afferents evoked reflex firing in nerve filaments on the surface of the urinary bladder. The firing was abolished by transection of the ipsilateral hypogastric nerve. 5. It is concluded that stimulation of vesical afferents activates a spinal sympathetic reflex which results in closing of the internal urethral sphincter and a depression of bladder activity. The latter occurs by a direct depression of detrusor smooth muscle as well as a block of the neural input to the bladder. This vesico-sympathetic reflex represents a negative feed-back mechanism which may have an important role in the maintenance of urinary continence.