title: Involvement of opioid receptors in N-methyl-D-aspartate-induced arterial hypertension in periaqueductal gray matter.
abstract: Arterial hypertension induced by microinjections of N-methyl-D-aspartate (NMDA) (2 nmol/rat) into the midbrain periaqueductal gray matter was used to assess the involvement of opioid receptors (mu, delta and kappa) in modulating pressor periaqueductal gray neurons. Groups (n = 5-8) of urethane-anaesthetised rats received, 5 min before NMDA, microinjections of selective opioid receptor antagonists in the periaqueductal gray area and arterial blood pressure was monitored. Pretreatments with naloxone (5 nmol/rat), a non selective mu receptor antagonist, or naltrindole hydrochloride (5 nmol/rat), a selective delta receptor antagonist, significantly (P < 0.05) decreased by 31% and 37%, respectively, NMDA-induced hypertension. The latency for the maximum increase of NMDA-induced hypertension was also significantly (P < 0.05) increased with naloxone. Pretreatment with nor-binaltorphimine (5 nmol/rat), a selective kappa receptor antagonist, only increased the latency of NMDA-induced hypertension. Each opioid antagonist failed per se to alter arterial blood pressure. Microinjection of morphine (13 nmol/rat), a non selective mu receptor agonist, significantly decreased (P < 0.05) by 57.5% NMDA-induced arterial hypertension and this effect was antagonised by naloxone. Combined pretreatments in the periaqueductal gray area with naloxone and the GABAA antagonist bicuculline (2.5 nmol/rat; 5 min before naloxone) antagonised the effect of naloxone on NMDA-induced hypertension. In contrast, bicuculline significantly (P < 0.05) potentiated morphine-induced decrease of NMDA hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Institute of Pharmacology and Toxicology, Faculty of Medicine and Surgery, II University of Naples, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Maione
authors.forename: J
authors.initials: J
authors.lastname: Leyva
authors.forename: M
authors.initials: M
authors.lastname: Pallotta
authors.forename: L
authors.initials: L
authors.lastname: Berrino
authors.forename: V
authors.initials: V
authors.lastname: De Novellis
authors.forename: F
authors.initials: F
authors.lastname: Rossi
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D006973:Hypertension / Q000139:chemically induced* / Q000503:physiopathology*; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000502:physiology*
chemical_list: D011957:Receptors, Opioid; D016202:N-Methylaspartate