Receptor subtypes mediating depressor responses to microinjections of nicotine into medial NTS of the rat.
Microinjections (50 nl) of nicotine (0.01-10 microM) into the nucleus of the solitary tract (NTS) of adult, urethan-anesthetized, artificially ventilated, male Wistar rats, elicited decreases in blood pressure and heart rate. Prior microinjections of alpha-bungarotoxin (alpha-BT) and alpha-conotoxin ImI (specific toxins for nicotinic receptors containing alpha7 subunits) elicited a 20-38% reduction in nicotine responses. Similarly, prior microinjections of hexamethonium, mecamylamine, and alpha-conotoxin AuIB (specific blockers or toxin for nicotinic receptors containing alpha3beta4 subunits) elicited a 47-79% reduction in nicotine responses. Nicotine responses were completely blocked by prior sequential microinjections of alpha-BT and mecamylamine into the NTS. Complete blockade of excitatory amino acid receptors (EAARs) in the NTS did not attenuate the responses to nicotine. It was concluded that 1) the predominant type of nicotinic receptor in the NTS contains alpha3beta4 subunits, 2) a smaller proportion contains alpha7 subunits, 3) the presynaptic nicotinic receptors in the NTS do not contribute to nicotine-induced responses, and 4) EAARs in the NTS are not involved in mediating responses to nicotine.
Dhar
S
S
Department of Neurosurgery, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark, New Jersey 07103, USA.
Nagy
F
F
McIntosh
J M
JM
Sapru
H N
HN
D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002038:Bungarotoxins / Q000008:administration & dosage; D002121:Calcium Channel Blockers / Q000008:administration & dosage; D020916:Conotoxins / Q000008:administration & dosage; D018691:Excitatory Amino Acid Antagonists / Q000008:administration & dosage; D005973:Glutamine / Q000008:administration & dosage; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D018738:Hexamethonium / Q000008:administration & dosage; D008297:Male; D008464:Mecamylamine / Q000008:administration & dosage; D008845:Microinjections; D009538:Nicotine / Q000008:administration & dosage* / Q000037:antagonists & inhibitors; D018733:Nicotinic Antagonists / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar; D011978:Receptors, Nicotinic / Q000378:metabolism*; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism*; D064569:alpha7 Nicotinic Acetylcholine Receptor
D002038:Bungarotoxins; D002121:Calcium Channel Blockers; C579165:Chrna7 protein, rat; D020916:Conotoxins; D018691:Excitatory Amino Acid Antagonists; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C115558:conotoxin AuIB; C403530:nicotinic receptor alpha3beta4; D005973:Glutamine; C087686:alpha-conotoxin ImI; D018738:Hexamethonium; D008464:Mecamylamine; D009538:Nicotine