AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 2 215-R221, Copyright © 1983 by American Physiological Society
Effect of clorgyline (a MAO type A inhibitor) on locomotor activity in the Syrian hamster
L. Tamarkin, C. J. Craig, N. A. Garrick and T. A. Wehr
Syrian hamsters in a lighting schedule of 14 h of light per day (LD 14:10)
and housed in cages equipped with running wheels exhibited a clear onset of
locomotor activity during the 1st h after lights off. Implantation of
osmotic minipumps containing clorgyline (2 mg . kg-1 . day-1), an
irreversible inhibitor of monoamine oxidase type A, caused a 1.5-h delay in
the onset of wheel running by the 7th day of treatment. Increasing dosages
of clorgyline (0.5, 1, 2, or 4 mg . kg-1 . day-1) caused increasing delays.
Hamsters shifted from LD 14:10 to LD 10:14 underwent a 3-h advance in the
onset of wheel running. Animals treated with clorgyline (2 mg . kg-1 .
day-1) exhibited a markedly slowed rate of advance in activity onset, which
did not prevent the short photoperiod from inhibiting reproductive
function. Additionally, removal of the pineal gland did not affect
wheel-running onset and did not prevent the delay in activity onset during
clorgyline treatment. Hamsters in LD 14:10 were "released" into constant
darkness (DD) for 3 days to prevent masking of activity onsets and offsets
by light. Delays in activity onset in LD 14:10 caused by clorgyline (2 mg .
kg-1 . day-1) persisted when these animals were released into DD. Activity
offset in LD 14:10 occurred at lights on before and during clorgyline
treatment but was delayed when the treated animals were maintained in DD.
Drug-induced delays in both activity onset and offset suggest that
clorgyline is not simply shortening the duration of activity or changing
the expression of activity relative to the light-dark cycle, but is
delaying the phase position of the circadian rhythm in locomotor activity.
Clorgyline may act directly on the central oscillatory mechanism that
drives the rhythm.
