Habituation to a test apparatus during associative learning is sufficient to enhance muscarinic acetylcholine receptor-immunoreactivity in rat suprachiasmatic nucleus.
The suprachiasmatic nucleus (SCN) is engaged in modulation of memory retention after (fear) conditioning, but it is unknown which pathways and neurotransmitter system(s) play a role in this action. Here we examine immunocytochemically whether muscarinic acetylcholine receptors (mAChRs), mediating cholinergic signal transduction in the SCN, are involved. For this purpose, mAChR immunoreactivity (mAChR-ir) was studied in the SCN after various stages of passive shock avoidance (PSA) and active shock avoidance (ASA) training and, for ASA, at various posttraining time points. mAChR-ir was significantly enhanced in SCN neurons as a result of the training procedure, and the number of mAChR-positive glial cells in the SCN increased significantly. The increase in mAChR-ir as a result of PSA and ASA training was not due to fear conditioning or the number of correct avoidances (in case of ASA training) but rather to behavioral arousal as a consequence of (brief) exposure to a novel environment (the test apparatus). This finding was confirmed by a cage-change experiment in which the rats were allowed to stay in a novel cage for 15 min or 24 hr. Only the brief exposure to the fresh cage triggered alterations for SCN mAChRs 24 hr later. These results shed new light on a possible function of the cholinergic system in the SCN mediated by mAChRs in relation to modulation of memory processes and demonstrate that behavioral arousal during (the habituation stage of) a learning task is sufficient to alter the mAChR system in the SCN.
Van der Zee
Eddy A
EA
Department of Animal Behaviour, University of Groningen, Haren, The Netherlands. e.a.van.der.zee@biol.rug.nl
Biemans
Barbara A M
BA
Gerkema
Menno P
MP
Daan
Serge
S
D000704:Analysis of Variance; D000818:Animals; D001245:Association Learning / Q000502:physiology*; D001253:Astrocytes / Q000378:metabolism; D001362:Avoidance Learning / Q000502:physiology*; D001522:Behavior, Animal; D002452:Cell Count / Q000379:methods; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007150:Immunohistochemistry / Q000379:methods; D008297:Male; D009474:Neurons / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000502:physiology; D011976:Receptors, Muscarinic / Q000145:classification / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors
D005904:Glial Fibrillary Acidic Protein; D011976:Receptors, Muscarinic