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The conditional placing reflex was studied in chronic experiments on cats. Neuronal activity of the midbrain periaqueductal grey matter was recorded under conditions of extinction, differentiation and conditional inhibition. Neuronal reactions preceded the conditioned and voluntary movements by 400-800 ms and lasted for 1-2 s in 69 units from total numbers 182 (36.7%). This reactions appeared 200 ms earlier than corresponding neuronal reactions of the motor cortex. 58 neurons (30.9%) were excited by auditory stimuli with latencies 10-50 ms for 2-6 s. 19 neurons (10.1%) were activated by auditory stimuli and conditioned movement. Responses to isolated auditory stimulation were absent in 42 neurons (22.3%), but some of the neurons showed long-lasting (minutes) changes of the background activity under repeated conditioned stimulation. The extinction, differentiation and conditioned inhibition caused specific changes in activity of different neuronal groups. A conclusion is made that the periaqueductal grey matter participated in reflex performance as well as in its inhibition. The functional independence of the first and second neuronal groups in extinction and restoration of conditional reflex is shown.
Conditioned reflex facilitation occurs when the amplitude of the eyeblink (EB) unconditioned reflex (UR) is increased as a result of prior pavlovian conditioning. Prepulse modification of the EB reflex is produced by preceding the unconditioned stimulus (US) by a brief low-level neutral stimulus. This study examined both conditioned EB facilitation and prepulse modification in rabbits with either medial prefrontal (mPFC) lesions or sham lesions. Conditioned reflex facilitation was assessed by comparing EB UR amplitude prior to and after pavlovian EB conditioning. Animals that received CS/US paired presentations showed evidence of conditioned reflex facilitation, but animals with unpaired training did not. However, this increase in EB UR magnitude in the paired groups was smaller in animals with mPFC lesions, compared to those with sham lesions. In two subsequent experiments different groups of sham and lesion animals received an intense burst of white noise preceded by tones with different interstimulus interval durations to assess prepulse modification. Unlike conditioned facilitation, prepulse modification was unaffected by mPFC lesions.
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Studies in rabbits of the time course of the formation of conditioned reflex switching of homogeneous reflexes showed that learning involved three main stages, characterized by the extent of stability of the conditioned reflexes, their interaction, and the level of switching. Formation of conditioned reflex switching was found to involve transfer of motor learning and interference of motor reflexes.
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The protein content in neurons of areas CA-1 and CA-3 of the dorsal hippocampus has been determined by means of cytointerferometry in rats during elaboration of unlocal alimentary instrumental reflex (ULAIR) and local alimentary instrumental reflex (LAIR) on the background of increased and normal serotonine content in the brain. It has been found that during the ULAIR elaboration the hippocampal neurons react by an increase of dry mass, during the LAIR elaboration-by its decrease. Under condition of serotonine excess in the brain the changes of dry mass in hippocampal neurons during elaboration of the two reflexes are opposite to these observed during the ULAIR and LAIR elaboration with normal serotonine content.
The defensive conditioned reflex with two-way avoidance was developed in rats in a shuttle-box. Immediately and 30 min after learning the animals were decapitated and synaptosomes were isolated from the whole brain and brain cortex. Using [14C] and [3H]-noradrenaline (NA), the processes of uptake, spontaneous and potassium depolarization-induced (60 mM KCl) release of NA by brain synaptosomes of trained and control animals were studied in vitro. Immediately after learning the inhibition of NA uptake was observed, but 30 min following learning the ability of synaptosomes to take up NA was recovered to the initial level. Thirty minutes after learning the potassium depolarization-induced release of NA previously taken up by synaptosomes increased as compared to the control. NA spontaneous release did not change under these conditions. With the increase of Ca2+ concentration in the incubation medium from 1.2 mM to 2.4 mM, the induced NA release from brain synaptosomes of trained and control animals regularly increased. Changes in NA release and uptake are specific for the development of conditioned reflex
Changes in conditioned reflex spike activity of neurons in the sensorimotor cortex were studied during microiontophoretic application of agonists and antagonists of glutamate and GABAergic transmission. The results of these experiments showed that the glutamate ionotropic receptors (AMPA and NMDA) of neurons in the sensorimotor cortex were intensely activated by the arrival of a conditioned signal in the cortex. This response included not only large pyramidal neurons of the deep cortical layers, but also the surrounding inhibitory interneurons. The existence of constant tonic inhibitory regulation of the activity of large pyramidal neurons by the surrounding inhibitory cells was demonstrated, along with the active involvement of this inhibition in organizing the excitatory responses of neurons in the sensorimotor cortex during a conditioned reflex.
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The effects of nicergoline and piracetam on the learning of avoidance response and its restoration after disturbance produced by unexpected changes of the previously established cause-effect relations in experimental environment were studied. It was found that both drugs improve the learning, nicergoline being the most active in the initial period of training, meanwhile piracetam--beginning from the third day. The drugs prevent disturbance of the avoidance response but piracetam is more effective.
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