title: Pressor effects of L-glutamate injected into the diagonal band of Broca of unanesthetized rats.
abstract: The diagonal band of Broca (dbB) is involved in central cardiovascular control. In the present study we compared the effects of microinjections of L-glutamate into the dbB of unanesthetized rats with those observed after the injection of L-glutamate into the same area in urethane-anesthetized rats. The microinjection of L-glutamate (10, 30, 100 or 200 nmol/200 nl) into the dbB of urethane-anesthetized rats caused dose-related short-lasting depressor responses The depressor responses to L-glutamate were accompanied by dose-related heart rate reduction. The cardiovascular response to the injection of L-glutamate (10, 30 or 100 nmol/200 nl) into the dbB of unanesthetized rats was characterized as a long-lasting pressor response without consistent heart rate changes. The pressor response was dose-related and presented an ED(50) of approximately 30 nmol/200 nl. The fact that the chemical stimulation of the dbB with L-glutamate caused only dose-related pressor responses in unanesthetized rats suggests that under normal conditions the dbB is predominantly a pressor area. After the characterization of the pressor response to L-glutamate microinjected into the dbB of unanesthetized rats we studied the mechanisms involved in the mediation of these responses. The pressor response to L-glutamate (30 nmol/200 nl) into the dbB was blocked by intravenous pretreatment with the vasopressin antagonist dTyr(CH(2))(5)(Me)AVP (50 microg/kg), suggesting the involvement of circulating vasopressin in this response. Further evidence of the involvement of the endocrine vasopressin system in the pressor response to L-glutamate injected into the dbB was provided by hypophysectomy since L-glutamate (30 nmol/200 nl) microinjection into the dbB of hypophysectomized rats caused only depressor responses. We presently report that chemical stimulation of the dbB with L-glutamate caused only pressor responses in unanesthetized rats that were mediated by vasopressin release into the systemic circulation. Additionally, the results confirmed the existence of an L-glutamate-sensitive depressor system in the dbB, which is predominant in urethane-anesthetized rats or may be evidenced in unanesthetized hypophysectomized rats.
authors.affiliation: Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Av Bandeirantes 3900, 14049-900, Ribeirão Preto, São Paulo, Brazil.
authors.forename: Rodrigo Fiacadori
authors.initials: RF
authors.lastname: Tavares
authors.forename: Fernando Morgan
authors.initials: FM
authors.lastname: de Aguiar Corrêa
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects* / Q000502:physiology; D020667:Diagonal Band of Broca / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000008:administration & dosage*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D008297:Male; D008845:Microinjections / Q000379:methods; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D014851:Wakefulness / Q000502:physiology*
chemical_list: D018698:Glutamic Acid