Cardiovascular effects of noradrenaline microinjection into the medial part of the superior colliculus of unanesthetized rats.
The superior colliculus (SC) is a mesencephalic area involved in the mediation of defensive movements associated with cardiovascular changes. Noradrenaline (NA) is a neurotransmitter with an important role in central cardiovascular regulation exerted by several structures of the central nervous system. Although noradrenergic nerve terminals have been observed in the SC, there are no reports on the effects of local NA injection into this area. Taking this into consideration, we studied the cardiovascular effects of NA microinjection into the SC of unanesthetized rats. Microinjection of NA into the SC evoked a dose-dependent blood pressure increase and a heart rate decrease in unanesthetized rats. The pressor response to NA was not modified by intravenous pretreatment with the vasopressin v(1)-receptor antagonist dTyr(CH(2))(5)(Me)AVP, indicating a lack of vasopressin involvement in the response mediation. The effect of NA microinjection into the SC was blocked by intravenous pretreatment with the ganglionic blocker pentolinium, indicating its mediation by the sympathetic nervous system. Although the pressor response to NA was not affected by adrenal demedullation, the accompanying bradycardia was potentiated, suggesting some involvement of the sympathoadrenal system in the cardiovascular response to NA microinjection into the SC. In summary, results indicate that stimulation of noradrenergic receptors in the SC causes cardiovascular responses which are mediated by activation of both neural and adrenal sympathetic nervous system components.
Garcia Pelosi
Gislaine
G
Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Av. Bandeirantes 3900, 14040-900, Ribeirão Preto, São Paulo, Brazil. pelosigg@yahoo.com.br
Fiacadori Tavares
Rodrigo
R
Barros Parron Fernandes
Karen
K
Morgan Aguiar Corrêa
Fernando
F
D000313:Adrenal Medulla / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005730:Ganglionic Blockers / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D008845:Microinjections; D009638:Norepinephrine / Q000494:pharmacology*; D010425:Pentolinium Tartrate / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013477:Superior Colliculi / Q000187:drug effects*; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D005730:Ganglionic Blockers; D014662:Vasoconstrictor Agents; D010425:Pentolinium Tartrate; D009638:Norepinephrine