Microinjection of L-glutamate into the nucleus tractus solitarii increases arterial pressure in conscious rats.
Microinjection of L-glutamate into the nucleus tractus solitarii (NTS) of anesthetized rats produces a fall in mean arterial pressure (MAP) similar to that observed during activation of baroreceptor afferents. In the present study we examined the effect of bilateral microinjections of L-glutamate through chronically implanted cannulae in the NTS of conscious freely moving rats. Group I (n = 6) was studied under conscious conditions and 24 h later the rats were anesthetized with urethane and the effects of L-glutamate re-examined. In conscious rats, L-glutamate (30 pmol to 5 nmol/100 nl) produced dose-dependent increases in MAP (+37 +/- 7 mmHg, 5 nmol), whereas under urethane anesthesia falls in MAP were observed (-11 +/- 3 mmHg, 5 nmol). Group II (n = 7) was studied under conscious conditions and 1 h later the rats were anesthetized with chloralose and the effects of L-glutamate re-examined. In this group of conscious rats L-glutamate (300 pmol to 5 nmol/100 nl) also produced dose-dependent increases in MAP (+37 +/- 5 mmHg, 5 nmol), whereas under chloralose anesthesia a dose-dependent depressor response was observed (-33 +/- 6 mmHg, 5 nmol). Saline microinjections into the NTS of conscious and anesthetized rats produced negligible effects. These data demonstrate that microinjection of L-glutamate into the NTS of rats produces a pressor response in conscious animals in contrast to depressor responses in animals anesthetized with chloralose or urethane.(ABSTRACT TRUNCATED AT 250 WORDS)
Machado
B H
BH
Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Brazil.
Bonagamba
L G
LG
D000768:Anesthesia, General; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D001933:Brain Stem / Q000033:anatomy & histology / Q000166:cytology; D003243:Consciousness; D004305:Dose-Response Relationship, Drug; D005971:Glutamates / Q000008:administration & dosage / Q000494:pharmacology*; D018698:Glutamic Acid; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D051381:Rats; D011919:Rats, Inbred Strains; D014520:Urethane
D005971:Glutamates; D014520:Urethane; D018698:Glutamic Acid