Abstract
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. (C) 2004 Wiley-Liss, Inc.
Original language | English |
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Pages (from-to) | 508-519 |
Number of pages | 12 |
Journal | Journal of Neuroscience Research |
Volume | 78 |
Issue number | 4 |
DOIs | |
Publication status | Published - 15-Nov-2004 |
Keywords
- active shock avoidance
- cholinergic signal transduction
- glial cells
- novelty
- passive shock avoidance
- cage change
- PASSIVE-AVOIDANCE
- CIRCADIAN-RHYTHMS
- RETENTION DEFICITS
- PERIODIC INTERVALS
- SYRIAN-HAMSTERS
- PHASE-SHIFTS
- BRAIN-STEM
- AGED RATS
- NEURONS
- FOREBRAIN