ABSTRACT
A discrimination conditioned active avoidance reflex (CAAR) model in a T maze was used in 18 rats to study the effects of bilateral microinjections of the selective muscarinic M1 receptor blocker pirenzepine into the neostriatum on the acquisition of the CAAR and behavior in an open field test. There was sharp degradation of learning of the CAAR and a significant improvement in motor activity both in the open field test and in the maze itself in rats given bilateral microinjections (pirenzepine, 0.004 mg) into the neostriatum as compared with intact controls. This suggests that changes in motor behavior (a sharp increase in locomotor activity) may be among the reasons for difficulty in learning the CAAR in rats after pirenzepine microinjections. Another reason for difficulty in learning the CAAR in these animals may be impairment of the perception of the conditioned signals (a flashing light) and poor differentiation. This is particularly indicated by the delay in the start chamber (double that seen in intact animals) on presentation of conditioned signals despite the high level of motor activity. These results and published data provide evidence for the complex nature of changes induced by blockade of muscarinic M1 receptors in the neostriatum.
Subject(s)
Behavior, Animal/physiology , Locomotion/physiology , Motor Activity/physiology , Neostriatum/physiology , Pirenzepine/administration & dosage , Receptor, Muscarinic M1/antagonists & inhibitors , Receptor, Muscarinic M1/metabolism , Animals , Behavior, Animal/drug effects , Locomotion/drug effects , Male , Microinjections , Motor Activity/drug effects , Muscarinic Antagonists/administration & dosage , Neostriatum/drug effects , Rats , Rats, Sprague-DawleyABSTRACT
In simulated discrimination conditioned reflex of active avoidance (CRAA) in T-maze, the effect of bilateral microinjections of the muscarinic receptor M1 selective blocker pirenzepine on the CRAA formation and behaviour in the "open filed" test, was studied in rats. A sharp worsening of the CRAA learning and a significant increase in the motor activity were shown to occur in rats following the microinjections as compared with control rats. The change in the motor responses seems to account for the worsening of the CRAA learning. Another reason of the phenomenon could involve a disorder in perception of conditioned signals and their poor differentiation. The data obtained and the literature data suggest a complex character of changes induced by the blockade of the M1 muscarinic receptors of the neostriatum.
Subject(s)
Motor Activity/drug effects , Muscarinic Antagonists/pharmacology , Neostriatum/drug effects , Pirenzepine/pharmacology , Receptor, Muscarinic M1/drug effects , Animals , Avoidance Learning/drug effects , Conditioning, Classical/drug effects , Discrimination, Psychological/drug effects , Male , Maze Learning/drug effects , Microinjections , Neostriatum/physiology , Rats , Rats, Sprague-DawleyABSTRACT
Chronic experiments were performed on four dogs using a model of an operant defensive reflex associated with maintaining a flexion posture to study the effects of bilateral intraneostriatal microinjection of the non-selective muscarinic receptor agonist carbachol, the selective D2 dopamine receptor blocker raclopride, and the selective M1 muscarinic receptor blocker pirenzipine on the performance of the operant defensive reflex and differentiation of signals. The results show that microinjection of carbachol induced increases in the tonic component and inhibition of the phasic component of the reflex, an ordering rearrangement of the posture, and increases in the amplitudes of its components. Raclopride microinjection gave similar but less marked results. The greatest effects with both substances were seen using differential stimuli. There were sharp increases in the process of differentiation of sound signals. Pirenzipine microinjections gave the opposite result. These data are assessed on the basis of concepts of the existence of two efferent outputs from the neostriatum with opposite effects on their targets and the roles of muscarinic and dopamine receptors in triggering and blocking these effects.
Subject(s)
Avoidance Learning/physiology , Conditioning, Operant/physiology , Motor Skills/physiology , Neostriatum/physiology , Receptors, Muscarinic/physiology , Animals , Carbachol/administration & dosage , Conditioning, Operant/drug effects , Dogs , Dopamine Antagonists/administration & dosage , Microinjections , Motor Skills/drug effects , Muscarinic Agonists/administration & dosage , Muscarinic Antagonists/administration & dosage , Neostriatum/drug effects , Raclopride/administration & dosage , Receptors, Muscarinic/drug effects , gamma-Aminobutyric Acid/metabolismABSTRACT
In four dogs, microinjections of carbacholine enhanced the tonic component and inhibited the physical component of the instrumental defence reflex, put in order the posture, and increased its components' amplitude. Microinjections of raclopride yielded a similar though a less obvious result. Differentiation stimuli provided the greatest effect of both substances. A sharp improvement occurred in differentiation of sound signals. Microinjections of pyrenzepine yielded an opposite result. The data obtained are explained proceeding from the idea of a presence of the neostriatum's two efferent outputs exerting opposite effects on their targets, and the role of muscarine and dopamine receptors in their triggering and blockade.
