Cholinergic modulation in the olfactory bulb influences spontaneous olfactory discrimination in adult rats

Eur J Neurosci. 2006 Dec;24(11):3234-44. doi: 10.1111/j.1460-9568.2006.05212.x.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholine / metabolism*
  • Action Potentials / drug effects
  • Action Potentials / physiology
  • Afferent Pathways / cytology
  • Afferent Pathways / drug effects
  • Afferent Pathways / metabolism*
  • Animals
  • Cholinergic Fibers / drug effects
  • Cholinergic Fibers / metabolism*
  • Cholinergic Fibers / ultrastructure
  • Cholinesterase Inhibitors / pharmacology
  • Male
  • Muscarinic Antagonists / pharmacology
  • Neurons / drug effects
  • Neurons / metabolism
  • Nicotinic Antagonists / pharmacology
  • Odorants
  • Olfactory Bulb / cytology
  • Olfactory Bulb / drug effects
  • Olfactory Bulb / metabolism*
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Muscarinic / drug effects
  • Receptors, Muscarinic / metabolism
  • Receptors, Nicotinic / drug effects
  • Receptors, Nicotinic / metabolism
  • Septal Nuclei / cytology
  • Septal Nuclei / drug effects
  • Septal Nuclei / metabolism
  • Smell / drug effects
  • Smell / physiology*
  • Synaptic Transmission / drug effects
  • Synaptic Transmission / physiology

Substances

  • Cholinesterase Inhibitors
  • Muscarinic Antagonists
  • Nicotinic Antagonists
  • Receptors, Muscarinic
  • Receptors, Nicotinic
  • Acetylcholine