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Deficits in passive avoidance learning in young rats following mecamylamine injections in the hippocampo-entorhinal
Insights
Nicotinic receptors in the young rat
Area of Science:
- Neuroscience
- Developmental Psychology
- Pharmacology
Background:
- Passive avoidance learning is crucial for survival.
- Cholinergic systems play a role in learning and memory.
- The posteroventral hippocampo-entorhinal (VHE) area is implicated in memory formation.
Purpose of the Study:
- To investigate the role of nicotinic cholinergic sites in the VHE area in passive avoidance learning in young rats.
- To determine the age- and dose-dependency of nicotinic antagonist effects on passive avoidance.
Main Methods:
- Rats aged 11, 13, 16, and 20 days were injected with mecamylamine hydrochloride (a nicotinic antagonist) into the VHE area.
- Animals were trained on a cool-draft-stimulus passive avoidance task.
- Acquisition and resistance to extinction were measured.
Main Results:
- Nicotinic blockade impaired passive avoidance acquisition and reduced resistance to extinction.
- Deficits were age-dependent, with younger rats (11 and 13 days) being more sensitive.
- Dose-dependency was also observed, with higher doses causing greater impairment.
Conclusions:
- Nicotinic cholinergic sites in the VHE area are critical for early passive avoidance learning in rats.
- These nicotinic mechanisms appear to be essential for the emergence of passive avoidance behavior.
- Muscarinic cholinergic mechanisms develop later and become more important for this behavior in this region.
Abstract:
Young rats 11, 13, 16, and 20 days old were injected bilaterally with the nicotinic antagonist mecamylamine hydrochloride (5, 50, and 100 micrograms on each side) into the posteroventral hippocampo-entorhinal (VHE) area and trained on a "cool-draft-stimulus" passive avoidance task. The data showed impaired acquisition and reduced resistance to extinction. The deficits observed were age- and dose-dependent, rats being highly sensitive to the drug when 11 and 13 days old and decreasingly responsive up to day 20. The results may indicate that nicotinic cholinergic sites in the VHE area mediate passive avoidance learning in the young rat as soon as acquisition emerges. Muscarinic cholinergic mechanisms only develop later in this region, becoming progressively more important for passive avoidance behavior.