Vasopressinergic mechanisms in the nucleus reticularis lateralis in blood pressure control.
We sought to determine whether arginine vasopressin (AVP) modulates arterial pressure (AP) by a receptor-mediated action in the nucleus reticularis rostroventrolateralis (nRVL). Immunocytochemical labeling with an antiserum against a synthetic AVP conjugate revealed a discrete although modest presumptive neuropeptidergic innervation of the nRVL. Electron microscopic analysis of vasopressinergic processes in the nRVL revealed that AVP-like immunoreactivity (AVP-LI) was primarily in axons and axon terminals. Immunoreactive terminals contained numerous small clear vesicles and large dense core vesicles and formed synapses with unlabeled dendrites. In the nRVL, retrograde transport-immunofluorescence data demonstrated close appositions between vasopressinergic beaded processes and a compact subambigual column of reticulospinal neurons labeled by deposits of cholera toxin beta-subunit into the thoracic spinal cord. Similar methods were used to define the origins of the AVP-afferent projection to nRVL. These retrograde transport-immunofluorescence studies demonstrated numerous retrogradely labeled neurons in the hypothalamus, including the paraventricular nucleus (PVN), after injections of a retrograde tracer, Fluoro-Gold into the ventrolateral medulla. However, double-labeled neurons were rare and confirmed a diffuse AVP afferent innervation of the sympathoexcitatory area. Microinjection of AVP into the nRVL in anesthetized rats produced a large dose-related increase in AP different from control at a dose of 1 pmol or higher. AVP injected intravenously elevated AP only at significantly higher doses. Microinjections of AVP into the nucleus tractus solitarii (NTS) had a smaller effect whereas into the caudal ventrolateral medulla exerted no effect on AP. Bilateral microinjections of an AVP antagonist, d(CH2)5[Tyr(Me)2]AVP into the nRVL produced no change in AP but blocked the increase produced by subsequent injections of AVP. An acute hemorrhage produced by withdrawal of 2 ml of blood from the femoral vein did not alter AP. However, bilateral microinjections of the AVP antagonist into the nRVL 5 min after hemorrhage decreased AP. In contrast, the AVP-antagonist injected intravenously after hemorrhage had no effect on AP. Our data suggest that under conditions demanding increased sympathetic drive to maintain AP, such as hemorrhage, a functional AVP receptor mechanism via terminals in the nRVL may be activated to restore normal levels of AP.
Gómez
R E
RE
Instituto de Investigaciones Cardiológicas, Buenos Aires, Argentina.
Cannata
M A
MA
Milner
T A
TA
Anwar
M
M
Reis
D J
DJ
Ruggiero
D A
DA
D000818:Animals; D001127:Arginine Vasopressin / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000032:analysis* / Q000494:pharmacology / Q000502:physiology; D001370:Axonal Transport; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D001794:Blood Pressure / Q000187:drug effects; D001921:Brain / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006470:Hemorrhage / Q000503:physiopathology; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D008845:Microinjections; D009474:Neurons / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013569:Synapses / Q000502:physiology / Q000648:ultrastructure
D001127:Arginine Vasopressin; C025043:vasopressin, 1-(1-mercaptocyclohexaneacetic acid)-2-(O- methyl-L-tyrosine)-8-L-arginine-