Cholinergic modulation in the olfactory bulb influences spontaneous olfactory discrimination in adult rats.
Cholinergic neuromodulation in the olfactory bulb has been hypothesized to regulate mitral cell molecular receptive ranges and the behavioral discrimination of similar odorants. We tested the effects of cholinergic modulation in the olfactory bulb of cannulated rats by bilaterally infusing cholinergic agents into the olfactory bulbs and measuring the rats' performances on separate spontaneous and motivated odor-discrimination tasks. Specifically, 6 microL/bulb infusions of vehicle (0.9% saline), the muscarinic antagonist scopolamine (7.6 mM and 38 mM), the nicotinic antagonist mecamylamine hydrochloride (3.8 mM and 19 mM), a combination of both antagonists, or the acetylcholinesterase inhibitor neostigmine (8.7 mM) were made 20 min prior to testing on an olfactory cross-habituation task or a rewarded, forced-choice odor-discrimination task. Spontaneous discrimination between chemically related odorants was abolished when nicotinic receptors were blocked in the olfactory bulb, and enhanced when the efficacy of cholinergic inputs was increased with neostigmine. Blocking muscarinic receptors reduced but did not abolish odor discrimination. Interestingly, no behavioral effects of modulating either nicotinic or muscarinic receptors were observed when rats were trained on a reward-motivated odor-discrimination task. Computational modeling of glomerular circuitry demonstrates that known nicotinic cholinergic effects on bulbar neurons suffice to explain these results.
Mandairon
Nathalie
N
Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA. nm243@cornell.edu
Ferretti
Casara Jean
CJ
Stack
Conor M
CM
Rubin
Daniel B
DB
Cleland
Thomas A
TA
Linster
Christiane
C
D000109:Acetylcholine / Q000378:metabolism*; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000344:Afferent Pathways / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002799:Cholinergic Fibers / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000494:pharmacology; D009812:Odorants; D009830:Olfactory Bulb / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism; D012686:Septal Nuclei / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D012903:Smell / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
D002800:Cholinesterase Inhibitors; D018727:Muscarinic Antagonists; D018733:Nicotinic Antagonists; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D000109:Acetylcholine