The role of the medial geniculate bodies in analyzing sounds]

Elaboration and manifestation of motor alimentary conditioned reflexes were studied after a lesion of medial geniculate bodies (MGB) in adult cats. No substantial disturbance were recorded of the capacity for pitch analysis. In the case of more extensive MGB lesions, there were some difficulties in the elaboration of tone differentiations but not in their achievement. Additional temporo-parietal cortical ablation drastically reduced the animals' capacity for anlysing sound frequencies and more profoundly disturbed their capacity for inhibitory reactions.     

Participation of the thalamic reticular nucleus in the shaping of the interrelations of the mesencephalic reticular formation and the lateral geniculate body

On the awake rabbits and cats under nembutal anesthesia it has been shown that the reticular nucleus of the thalamus takes considerable part in the formation of reticulogeniculate response of the lateral geniculate body (LGB) to electrostimulation of the mesencephalic reticular formation. It is assumed that the reticular nucleus of the thalamus takes basic part in a realization of "rapid" physical influences of the reticular formation on the LGB.     

Effect of extracellular polarization on unit activity in the lateral geniculate bodies

Unit responses of the lateral geniculate bodies (LGB) to polarization of the cells through the recording microelectrode were investigated in acute experiments on cats anesthetized with Nembutal. Under the influence of anodic polarization the firing rate of the LGB cells clearly increased. Complete adaptation of the cells to the polarizing current was not observed during the time intervals investigated (5–10 min). Cathodic polarization by a current of 5–50 nA induced inhibitory effects; neurons with a single type of spontaneous activity under these circumstances generated volleys of 2–5 spikes. Off-responses were recorded in 75–85% of neurons. It is postulated that complex changes in unit activity produced by polarization may be due to the structural characteristics of the functional connections of the LGB neurons investigated. The change to grouped activity on the part of many of the neurons under the influence of cathodic polarization is evidently explained by the specific functional pattern of the synaptic system of the LGB cells.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 2, pp. 130–140, March–April, 1972.     

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.     

Effect of pentobarbital on neurones in the reticular formation of the brain stem: ionophoretic study in the rat

The effect of ionophoretically applied pentobarbital (PB) upon neurones in the nucleus reticularis gigantocellularis of the rat was studied. PB applied through a micropipette depressed the spontaneous activity of 81% of the neurones tested; the remaining neurones did not change their firing rates. Regardless of current intensities used for PB ejection (5-60 nA) there was no increase in the firing rate during PB administration. The depression was dependent upon both the control firing rate and the PB dose; a total depression of activity was observed at currents between 40 and 60 nA. EC50 (15.5 nA, about 5 X 10(-5) mol.l-1--the drug concentration was approximated theoretically) was assessed from the dose-response curve. Repeated application resulted in a shift of EC50 towards higher current values (desensitization). The Hill coefficient was calculated in conformity with the classical theory. From its value (1.4), it may be assumed that the occupation of only one subunit of the binding site is enough to give a response. Possible mechanisms of action of PB upon neurones are discussed.     

Effect of local cooling of the cortex on evoked potentials in the reticular formation in response to somatosensory stimulation

Potentials evoked in nuclei of the reticular formation by electrodermal stimulation of the limbs were investigated in acute experiments on unanesthetized, immobilized rats during cooling of the somatosensory cortex in the area of representation of one forelimb. Evoked potentials in the reticular formation were found to depend on the degree of cold inhibition of the cortical primary response to the same stimulation. The peak time of the main negative wave increased from 40–50 to 60–80 msec with a simultaneous decrease in its amplitude or its total disappearance in the case of deep cooling of the cortex. Cooling of the cortex had a similar although weaker effect on the earlier wave of the evoked potential with a peak time of 14 msec, recorded in the ventral reticular nucleus. In parallel recordings of potentials evoked by stimulation of other limbs they remained unchanged at these same points of the reticular formation or were reduced in amplitude while preserving the same temporal parameters. Cooling of the cortex thus selectively delays the development and reduces the amplitude of the response to stimulation of the limb in whose area of representation transformation of the afferent signal into a corticofugal volley is blocked. Consequently the normal development of both late and early components of the potential evoked in the reticular formation by somatic stimulation requires an additional volley, descending from the cortex, and formed as a result of transformation of the same afferent signal in the corresponding point of the somatosensory cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 32–38, January–February, 1981.     

The cellular mechanism for the formation of lamellar bodies in type-II pneumocytes in rat lungs]

Pneumocyte type II cells from lungs of native rats and of rats that inspired a hypoxic mixture of gases were investigated by transmission electron microscopy. In cells of experimental rats, membrane structures were found that well compare with lamellar bodies. Experimental results and analysis of literature allowed to put forward a hypothesis about the cell mechanism of formation of lamellar bodies from the spiral twisted membranes of the endoplasmic reticulum.     

Radiation-induced formation of apoptotic bodies in rat thymus

The process of interphase death of thymocytes in whole-body X-irradiated rats were studied. Cell size distribution analysis indicates that cell fragments (= apoptotic bodies) appeared in the thymus and increased in number depending on dose (200-1000 R) and time (2-6 hr) after irradiation with corresponding decrease in normal-size thymocytes. Occurrence of nuclear fragmentation in association with the cellular fragmentation was proved with cytofluorometric determination of DNA content in individual cells. Scanning electron microscopic observations also revealed extensive fragmentation of cells in the irradiated rat thymus. The results show clearly that cells as well as nuclei fragment rapidly into smaller pieces of various sizes in the irradiated rat thymus as commonly observed with apoptosis.     

Effect of phosphocreatine on reflex activity of the brain stem reticular formation

The effects of phosphocreatine (PCr) on startle reflexes, known to be relayed through the brain stem reticular formation (RF), were investigated on chloralose-anesthetized rats. PCr (10^–6 to 10^–3 M) was either applied superficially to the bottom of the fourth ventricle or microinjected into the reticular gigantocellular nucleus. The PCr effect was found to depend on its concentration. At low concentrations (10^–6 to 10^–5 M), PCr markedly facilitated the reflexes; sometimes its application gave rise to additional, later and longer, discharges following startle reflexes, whereas an inhibitory effect predominated at higher PCr concentration (10^–4 to 10^–3 M). Possible mechanisms of PCr action on the studied reflexes are discussed.Neirofiziologiya/Neurophysiology, Vol. 25, No. 3, pp. 272–278, 1993.     

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.     

Ageing and monoamine turnover in the lateral geniculate nucleus and visual cortex of the rat

The effects of ageing on the turnover of dopamine, noradrenaline and serotonin in the lateral geniculate nucleus and the visual cortex were evaluated, using high performance liquid chromatography (HPLC) with electrochemical detection. Compared to adult animals, aged rats showed more changes in the visual cortex than in the lateral geniculate nucleus, with dopamine turnover decreased in both structures and noradrenaline turnover unaltered. Changes in serotonin turnover were witnessed only in the visual cortex. A decrease in the monoamine oxidase-A to -B ratio was also observed with increased age for both the lateral geniculate nucleus and visual cortex.     

Effect of strychninization of the rabbit visual cortex on evoked activity in the lateral geniculate body

Changes in the parameters of responses of "low-frequency" and "high-frequency" neurons evoked in the lateral geniculate body by flashes or electrical stimulation of the optic nerve were investigated in immobilized and anesthetized rabbits after strychninization of the visual cortex. Under these conditions mainly an increase in the mean discharge frequency in the responses and a decrease in their latent periods were found in the "low-frequency" neurons, probable evidence of dominance of corticofugal facilitation. In most "high-frequency" neurons, on the other hand, the mean discharge frequency in the responses decreased and the latent periods were increased, evidence of dominance of corticofugal inhibition. It is suggested that reciprocal corticofugal influences exist on neurons connected with central and peripheral channels of the visual projection pathway.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow, Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 459–466, September–October, 1976.