neuropeptide-y and bretylium

The antidysrhythmic bretylium is useful experimentally because it selectively abolishes neurotransmitter release from sympathetic peripheral nerve terminals. Its mechanism of action seemed settled, but recent results from optical monitoring of single terminals now suggests a new interpretation.. Orthograde transport of a dextran-conjugated Ca(2+) indicator to monitor Ca(2+) in nerve terminals of mouse isolated vas deferens with a confocal microscope. In some experiments, local neurotransmitter release was detected by monitoring neuroeffector Ca(2+) transients (NCTs) in adjacent smooth muscles, a local measure of purinergic transmission. Sympathetic terminals were identified with catecholamine fluorescence (UV excitation) or post-experiment immunohistochemistry.. Bretylium (10 microM) abolished NCTs at 60/61 junctions over the course of 2 h, indicating effective abolition of neurotransmitter release. However, bretylium did not abolish the field stimulus-induced Ca(2+) transient in most nerve terminals, but did increase both action potential delay (by 2+/-0.4 ms) and absolute refractory period (by 4+/-2 ms). Immunohistochemistry demonstrated that 85-96% of terminals orthogradely filled with a dextran-conjugated fluorescent probe contained Neuropeptide Y (NPY). A formaldehyde-glutaraldehyde-induced catecholamine fluorescence (FAGLU) technique was modified to allow sympathetic terminals to be identified with a Ca(2+) indicator present. Most terminals contained catecholamines (based on FAGLU) or secrete ATP (as NCTs in adjacent smooth muscle cells are abolished).. Bretylium can inhibit neurotransmitter release downstream of Ca(2+) influx without abolishing the nerve terminal action potential. Bretylium-induced increases in the absolute refractory period permit living sympathetic terminals to be identified.

Topics: Action Potentials; Adenosine Triphosphate; Animals; Bretylium Compounds; Calcium Signaling; Catecholamines; Immunohistochemistry; Male; Mice; Mice, Inbred BALB C; Microscopy, Confocal; Neuropeptide Y; Neurotransmitter Agents; Presynaptic Terminals; Sympathetic Nervous System; Synaptic Transmission; Time Factors; Vas Deferens

In an attempt to understand the changes of circulating neuropeptide Y (NPY) during hypoxia, the plasma level of NPY was investigated by radioimmunoassay. Exposure of rats to hypobaric hypoxia at an altitude of 18,000 ft for 4 weeks causes an increase of pulmonary pressure and an elevation of plasma NPY-like immunoreactivity (NPY-LI). However, the systemic blood pressure was not elevated by this chronic hypoxia. Also, plasma noradrenaline (NA) estimated by chromatographic analysis (HPLC-ECD) was not markedly raised. Failure of bretylium and guanethidine, sympathetic neuron blockers, in reducing the plasma NPY-LI level of these rats ruled out the participation of adrenergic nervous terminals. Adrenal medulla seems responsible for this elevation of plasma NPY-LI because this magnitude disappeared in adrenalectomized rats. These data suggest that chronic hypoxia induced an elevation of circulating NPY from the adrenal gland of rats.

Topics: Adrenal Glands; Adrenalectomy; Animals; Blood Pressure; Bretylium Compounds; Chromatography, High Pressure Liquid; Female; Guanethidine; Hypoxia; Male; Neuropeptide Y; Norepinephrine; Radioimmunoassay; Rats; Rats, Inbred Strains