Brain muscarinic receptor subtypes mediating water intake and Fos following cerebroventricular administration of bethanecol in rats.
BACKGROUND
The brain regions and receptor subtypes involved in water intake following central cholinergic stimulation have been incompletely characterized.


OBJECTIVE
To examine whether drinking and brain Fos-immunoreactivity (ir) induced in rats by central administration of bethanecol is reversed by either the preferential M1 antagonist pirenzepine, the M3 antagonist 4-DAMP, or their combination.


METHODS
Male Sprague-Dawley rats were surgically implanted with cerebroventricular cannulae. The muscarinic agonist, bethanecol was used as the dipsogenic agent. Either nonselective (atropine) or selective muscarinic receptor antagonists were injected together with bethanecol to determine blockade of drinking. In parallel studies, Fos-ir was assessed in discrete brain regions.


RESULTS
Bethanecol-induced drinking was completely blocked by atropine or by a combination of pirenzepine and 4-DAMP; these latter antagonists alone produced sub-total inhibition of drinking. In contrast, water intake induced by angiotensin II was unaffected by combination of pirenzepine and 4-DAMP. Fos-ir was induced by bethanecol in many brain regions previously implicated in body fluid regulation, including subfornical organ and the magnocellular supraoptic and paraventricular hypothalamic nuclei. Induced Fos-ir was substantially but not completely prevented by co-injection of either pirenzepine or 4-DAMP, but their combination did not seem markedly more effective than either alone.


CONCLUSIONS
Drinking induced by brain muscarinic receptor stimulation seems to proceed by a combination of M1 and M3 receptor subtypes. Drinking induced by angiotensin II occurs independently of this mechanism. Fos-ir induced in fluid-related brain regions by bethanecol either uses additional receptor type(s) or is less easily blocked than drinking behavior.
Rowland
Neil E
NE
Department of Psychology, University of Florida, P.O. Box 112250, Gainesville, FL 32611-2250, USA. nrowland@ufl.edu
Farnbauch
Laura J
LJ
Robertson
Kimberly L
KL
D000818:Animals; D001285:Atropine / Q000008:administration & dosage / Q000494:pharmacology; D018723:Bethanechol / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004327:Drinking Behavior / Q000187:drug effects; D007276:Injections, Intraventricular; D008297:Male; D018721:Muscarinic Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D018727:Muscarinic Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D010880:Piperidines / Q000008:administration & dosage / Q000494:pharmacology; D010890:Pirenzepine / Q000008:administration & dosage / Q000494:pharmacology; D016760:Proto-Oncogene Proteins c-fos / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000502:physiology; D014867:Water
D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D010880:Piperidines; D016760:Proto-Oncogene Proteins c-fos; D011976:Receptors, Muscarinic; D018723:Bethanechol; D014867:Water; D010890:Pirenzepine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium