Changes in collagen metabolism during the chronic electrical stimulation of the midbrain reticular formation

The content of 11-hydroxycorticosteroids, free and bound hydroxyproline in the peripheral blood, as well as the level of free and net hydroxyproline in the aortic wall and myocardium of rabbits were studied in chronic prolonged electrical stimulation of the mesencephalon reticular system. The experiments have shown that electrical stimulation leads to the activation of adrenal cortex function and is accompanied by alterations in collagen metabolism, accumulation of collagen in the aorta and decreased collagen level in the myocardium.     

Evoked potentials in the parafascicular complex of the rabbit thalamus during peripheral noxious stimulation

Systematic research was conducted into the parafascicular complex of the nonspecific nociceptive system of the rabbit hypothalamus using a technique of evoked potentials. Two types of evoked response were recorded during electrocutaneous stimulation of the paw; a compound response consisting of early and late positive-negative potentials in the lateral region and a simple positive-negative evoked potential in the medial area. Evidence suggests a more complex organization of the thalamic parafascicular complex in leporines than previously supposed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 787–793, November–December, 1986.     

Immobilization stress-induced lesions of structures of the midbrain reticular formation

Emotional stress in rats resulted in blood-brain barrier increased permeability and brain parenchymal vessel disruptions. Stress induced microvascular damages were mainly observed in midbrain reticular formation. In this article the components of midbrain reticular formation were studied 1, 2, 4 and 6 weeks after immobilization stress. The destructive changes in some neurons, glia cells and myelin fibers were shown up to 6 weeks after immobilization. The signs of the recovery were also observed. It was supposed that the brain parenchymal vessel damages under emotional stress were due to the stress induced locus coeruleus dysfunctions.     

Correlation between bioelectrical processes of the cortex, thalamus, midbrain reticular formation during formation of a defensive conditioned reflex in rabbits]

EEG power spectra of the sensorimotor area of the neocortex, the dorsal hippocampus, midbrain reticular formation and anteroventral thalamic nucleus, as well as corresponding coherence functions and phase spectra, undergo changes during formation and performance of defensive conditioned reflex in rabbit. The conclusion is draen that in the process of conditioning a morphofunctional system of brain structures is established including the above mentioned formations. Their functional integration occurs on the basis of theta-rhythm. The execution of a conditioned act requires isorhythmicity of electrical processes within the theta-range in the studied structures and an adequate level of their excitability, which is manifested in the dominance of 6,0 c/s frequency.     

Evoked potentials during elaboration of fine differentiations

The paper deals with the character of changes in the EP form recorded from the visual cortex of a rat during elaboration of a system of positive and negative (with different degree of precision) conditioned defensive reflexes. It has been shown that in a state of a consolidated habit of pain stimulus avoidance in a shuttle box a negative component with peak latency up to 70 msec develops in EP to the differentiation stimulus of 0.5 c/s. This component is much less pronounced to the 2 c/s conditioned stimulus. When a more precise differentiation stimulus (1 c/s) was presented to the animal in this state the development of the studied component depended on the subsequent behavioural reaction: it developed if the animal reacted in the same way as to the differentiation stimulus. This fact suggests that the generation of this component is connected with the inhibitory processes developing at the time when the animal is choosing its behavioural reaction.     

Mechanism of the effect of the midbrain reticular formation on the hypothalamus-hypophysis-thyroid gland system]

The role of the posterior hypothalamic nuclei in the transmission of the influences of the mesencephalic reticular formation upon the thyroid hormone secretion was studied. Stimulation of the mesencephalic reticular formation in anesthetized cats was followed by the excitation of the thyroid hormoone secretion: the content of the blood protein-bound iodine was increased. This effect was eliminated after the bilateral coagulation of the posterior hypothalamic nuclei. These findings confirmed the hypothesis on the leading role of the posterior hypothalamic nuclpeus in the stimulation of the hormone secretion.     

Coherent analysis of the electrical activity of the rabbit brain during the formation of a motor polarization dominant

By the method of spectral-coherent analysis the dynamics was studied of successive changes in the structure the rabbit brain electrical activity coherent relations in the process of formation of motor polarization dominant created by DC anode action on the sensorimotor cortical region. It has been shown that at earlier stages, when the motor "dominant" reaction is absent, there appears an interhemispheric asymmetry in Coh spectra of electrical activity of the sensorimotor cortex and of the thalamus VPL. On the contrary, interhemispheric asymmetry in Coh spectra of electrical activity of the sensorimotor cortex and dorsal hippocampus CA3 field appears only at the stage when the motor "dominant" reaction is recorded. Asymmetry in alpha- and beta-frequencies ranges in biopotentials Coh spectra of the studied regions coinciding with the motor "dominant" reaction realization is connected with processes of movement organization.     

Evoked potentials during the elaboration of a conditioned reflex to hippocampal stimulation in rats

In experiments on 9 rats, the study of evoked potentials (EPs) of the CA1 field of the dorsal hippocampus to stimulation of its symmetrical part serving as a signal of drinking conditioned reflex (CR) showed that during reflex elaboration, the amplitude of the main EP components significantly decreased; CR did not appear when the population spike (PS) was absent in the hippocampal response. PS always accompanying CR was not specific only of it, it was also recorded at other behavioural reactions. Changes of fascia dentata EPs in the process of CR elaboration to stimulation of its symmetrical part consisted in decrease of the initial negative wave and increase of the positive one. The obtained data point to a significant reconstruction of excitatory and inhibitory inputs to the hippocampus and fascia dentata under the influence of conditioned activity.