Abstract
Active shock avoidance was used to explore the impact
of behavioural stimulation on the neurochemistry
of the suprachiasmatic nucleus. We have found
previously that the expression of muscarinic acetylcholine
receptors in the suprachiasmatic nucleus of
young rats was significantly enhanced 24 hours after
fear conditioning. Here, we investigated whether this
observation is age-dependent. We used 26 month-old
Wistar rats with a deteriorated circadian system, and
compared them with young rats (4 months of age)
with an intact circadian system. Vasopressin, representing
a major output system of the suprachiasmatic
nucleus, was studied in addition to muscarinic receptors.
Young rats showed a significant increase in
immunostaining for muscarinic acetylcholine receptors
24 h after training, corroborating earlier observations.
Aged rats did not show such an increase. In
contrast, aged rats did show an increase in vasopressin
immunoreactivity 24 h after fear conditioning,
both at the level of content and cell number, while
young rats did not reveal a significant rise. Thus, it
seems that these two neurochemical systems in the
suprachiasmatic nucleus are regulated independently.
The results further demonstrate that the circadian
pacemaker is influenced by fear conditioning in an
age-dependent manner.
Age-dependent expression changes of circadian system-related genes reveal a potentially conserved link to aging
