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Aging impairs methamphetamine-induced free-running and anticipatory locomotor activity rhythms in rats
1Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kyushu University, Fukuoka, Japan.
Abstract:
In the present experiment, under drinking of 0.01% methamphetamine (MA), young rats exhibited free-running locomotor rhythm ranging from 24.6 to 30.9 h period under light-dark cycle. In contrast, 24-month-old rats showed a low activity and did not exhibit MA-induced free-running rhythm. When MA was injected at a fixed time of day (14:00), young rats exhibited intense locomotor activity from 1-2 h before drug-injection time. This preinjection activity was still detected on the withdrawal day. In addition, intense locomotor activity was observed for 12:00-17:00, even on the withdrawal day (MA-associated anticipatory activity). Thus, MA-associated activity of the withdrawal day became an another good index for MA anticipatory activity rhythms whereas old rats did not exhibit this anticipatory activity. The present study suggests that aging strongly impairs the manifestation of MA-induced free-running and anticipatory activity rhythms in rats.
Insights
Young rats show altered activity rhythms when exposed to methamphetamine (MA). Aging significantly impairs these methamphetamine-induced rhythms, including free-running and anticipatory activity, in older rats.
Area of Science:
- Neuroscience
- Chronobiology
- Pharmacology
Background:
- Methamphetamine (MA) is a psychostimulant known to affect locomotor activity and circadian rhythms.
- Aging is associated with various physiological changes that can impact drug responses and biological rhythms.
Purpose of the Study:
- To investigate the effects of methamphetamine on locomotor activity rhythms in young versus aged rats.
- To determine if aging impairs the development of MA-induced free-running and anticipatory activity rhythms.
Main Methods:
- Young and aged rats were administered methamphetamine (0.01% in drinking water or daily injection).
- Locomotor activity was monitored under a light-dark cycle to assess free-running and anticipatory rhythms.
- Activity patterns were analyzed during drug administration and withdrawal phases.
Main Results:
- Young rats exhibited MA-induced free-running locomotor rhythms (24.6-30.9 h period).
- Aged rats showed low activity and did not exhibit MA-induced free-running or anticipatory rhythms.
- Young rats displayed MA-associated anticipatory activity before injections, which persisted during withdrawal.
Conclusions:
- Aging significantly impairs the manifestation of MA-induced free-running locomotor activity rhythms.
- Aging also hinders the development of MA-associated anticipatory activity rhythms.
- These findings highlight the impact of aging on psychostimulant-induced circadian rhythm alterations.