Effects of antimuscarinic cholinergic drugs injected systemically or into the hippocampo-entorhinal area upon passive avoidance learning in young rats

Abstract

Passive avoidance learning was significantly impaired by atropine (5 mg/kg, IP) or scopolamine (0.5 mg/kg), but not by methyl-atropine (5 mg/kg) or methyl-scopolamine (0.5 mg/kg), from postnatal day 15 on. In contrast, an improvement was observed, not significant at 11 days and significant at 13 days, probably due to nonspecific effects. Retention of the response increased from 6 h at 13 days, to 24 h at 17 days. In treated rats, retention was abolished at 13 and 15 days, and impaired at 17 and 20 days. Acquisition of the response was also significantly impaired by bilateral injections of atropine (1, 5, and 20 micrograms) into the posteroventral hippocampo-entorhinal (VHE) area, from day 15 on. Concomitantly, extinction was accelerated. At 14 days, atropine had no influence. At 13 days, a facilitatory action was observed, with better acquisition and greater resistance to extinction, possibly linked to affective changes. The results confirm that central muscarinic cholinergic mechanisms are involved in passive avoidance learning from postnatal day 15 on, and demonstrate that some pathways of this system are located in the VHE area, become efficient at 15 days, and improve markedly between 17 and 18 days.

Enhancement of passive avoidance learning through small doses of intra‐amygdaloid physostigmine in the young rat. Its relation to the development of acetylcholinesterase

“…The same disruptive effect is also observed in young mice (Ray & Nagy, 1978) and rats (Blozovski, Cudennec, & Garrigou, 1977;Blozovski & Hennocq, 1982;Feigley, 1974;Wilson & Riccio, 1976) …”

“…This dye had been added in our previous microinjection experiments (Blozovski & Hennocq 1982), and was shown to produce no alteration of the animal's behavior and learning capabilities. The two studied physostigmine doses (0.1 and 0.2 pg on each side) were chosen for the 20-day group where they were administered in 0.1 p L of 0.9% saline.…”

Conditional hyperthermia in response to atropine associated with a hypothermic drug

“…Thus the thermic shift in response to atropine alone does not stem merely from experience with the drugs, nor from some sort of physiological synergism. It is of some interest to note that learning was obtained here despite atropine's known capacity to retard the acquisition or performance of a learned response at lower doses than 10 mg/kg (e.g., Blozovski and Hennocq 1982;Bure~ovfi et al 1964;Whitehouse 1964Whitehouse , 1967Whitehouse et al 1964).…”

Mediation of passive avoidance learning by nicotinic hippocampo‐entorhinal components in young rats

“…Effectively, the VHE muscarinic mechanisms become involved in passive avoidance on Day 15 (Blozovski & Hennocq, 1982). Synapse elimination of previously formed contacts has been demonstrated in the central nervous system of developing organisms (Mariani, 1983).…”