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Delayed effects of acute oral and chronic inhalational exposure to methylparathion on learning and memory in rats
J George1, C Andrade, T Joseph
1Department of Pharmacology, St. John's Medical College, Bangalore, India.
Abstract:
Impairment of acquisition phase of the learning process was observed in rats even at 3 weeks after single oral exposure to the near-lethal dose of commercial grade methylparathion (MP) followed by atropine resuscitation. Though there was a trend towards memory impairment in this group of animals, memory retention was not significantly affected. Chronic inhalational exposure to MP (one exposure/day for 3 weeks) did not significantly alter learning or memory. No significant alteration in red blood cell or brain acetylcholinesterase levels were observed in either of the two groups. It appears that behavioural effects can persist even 3 weeks after exposure to acute near-lethal doses of the pesticide, as occurs in the clinical situation of suicidal attempts; while repeated exposure to no-observed-effect-level doses as occurs in farm and factory workers, may not be associated with behavioural changes.
Insights
Single high-dose methylparathion (MP) exposure impaired learning in rats for weeks, but chronic low-dose exposure did not. Acetylcholinesterase levels remained unchanged, suggesting persistent behavioral effects from acute MP poisoning.
Area of Science:
- Neuroscience
- Toxicology
- Environmental Health
Background:
- Methylparathion (MP) is an organophosphate pesticide.
- Acute MP poisoning can occur in suicidal attempts.
- Chronic low-level MP exposure is common for agricultural and factory workers.
Purpose of the Study:
- To investigate the long-term behavioral effects of acute and chronic methylparathion exposure in rats.
- To assess the impact of methylparathion on learning, memory, and acetylcholinesterase levels.
Main Methods:
- Rats received a single oral near-lethal dose of methylparathion followed by atropine resuscitation.
- Rats underwent chronic inhalational exposure to methylparathion (daily for 3 weeks).
- Learning and memory were assessed using behavioral tests; acetylcholinesterase levels were measured in red blood cells and brain tissue.
Main Results:
- Single oral exposure to a near-lethal dose of methylparathion caused significant impairment in the acquisition phase of learning, persisting for at least 3 weeks.
- Memory retention showed a trend towards impairment but was not statistically significant after acute exposure.
- Chronic inhalational exposure to methylparathion did not significantly alter learning or memory.
- No significant changes in red blood cell or brain acetylcholinesterase levels were observed in either exposure group.
Conclusions:
- Behavioral deficits, specifically in learning acquisition, can persist for weeks after a single acute near-lethal exposure to methylparathion.
- Chronic, low-level exposure to methylparathion at no-observed-effect levels may not be associated with significant behavioral changes or altered acetylcholinesterase activity.
- Findings suggest distinct neurotoxicological profiles for acute versus chronic methylparathion exposure relevant to different human exposure scenarios.