Locus coeruleus noradrenergic neurons as a micturition center

The micturition reflex arch is composed of an afferent pathway from the urinary bladder to the pontine micturition center via the pelvic nerve and spinal cord. The efferent pathway projects from the center to the bladder through the sacral parasympathetic center of intermediolateral column cells. The pontine micturition center is thought to be noradrenergic (NA) neurons in the locus coeruleus (LC) due to the following observations: (1) LC stimulation induces bladder contraction in cats, and this response is blocked by intrathecal application of alpha 1-adrenergic antagonist (prazosin), but not the alpha 2- nor beta-adrenergic antagonist. Although this contraction is not observed after NA depletion with reserpine, with subsequent i.v. injection of L-dopa a NA precursor induces recurrence of the response. (2) The micturition reflex induced by bladder distention is similarly reversed with alpha 1-adrenergic antagonist and chemical destruction of NA cells by injecting 6-hydroxydopamine in the LC. However, subsequently applied alpha 1-adrenergic agonist induces the contraction due to bladder distention. (3) LC stimulation elicits spike generation of sacral intermediolateral cells. Microiontophoretically applied alpha 1-adrenergic antagonist inhibits the LC stimulation-induced spikes of the neuron, which is not antidromically activated by pelvic nerve stimulation. However, spikes in neurons activated antidromically were not affected by the drug. This indicates that the former and latter neurons are interneuron and parasympathetic projecting neurons, respectively. The existence of NA terminals from the LC and alpha 1-adrenergic receptors in the intermediolateral column cells supports the concept that NA cells in the LC are units constituting the micturition center.