Prolonged posttetanic potentiation in slices of mouse hippocampus with the "kindling" phenomenon

The characteristics of long-term potentiation (LTP) in Schaffer collaterals--CA1 system were compared in hippocampal slices from mice of control group and mice with pentylenetetrazol (PTZ) kindling, induced by daily i.p.-injection of 30 mg/kg of PTZ. The increase in LTP mean magnitude was found in the preparation from kindled mice. The enhancement of the paired-pulse potentiation was also shown in these slices. It is suggested that both the increase in LTP and paired-pulse potentiation are due to the depression of an inhibition in intrahippocampal synaptic systems.     

The effect of exogenous gangliosides on the dynamics of the development of prolonged posttetanic potentiation]

In hippocampal slices of rats was studied the influence of different gangliosides on the dynamics of development of long-term post-tetanic potentiation (LPTP) in the pyramidal cell layer of the CA3 area at stimulation of the mossy fibers. Each ganglioside was shown to change synaptic efficiency specifically after the tetanic stimulation. Incubation of hippocampal slices with monosialoganglioside GM1 induced the rapid increase of population spike amplitude in the pyramidal neurons being of higher level in comparison to that of the active control up to the end of the experiment. Disialoganglioside GD1b increased the amplitude of the summary cellular response to a lesser degree than GM1, but contributed to its conservation up the control level in the course of the whole recording period. Gangliosides GD1a and GT1b induced inhibitory action on LPTP decreasing population spike value lower than that of both the control and initial levels, GT1b causing more rapid decrease of amplitudes of cellular responses than GD1a. A conclusion was drawn on the participation of gangliosides in the mechanisms of synaptic plasticity. The differential influence of various kinds of gangliosides on the LPTP dynamics was found out. The possible mechanisms of these reactions are discussed.     

Caudate-cortical connections in the cat brain

By means of optical and electron microscopic methods, the cortical fields from the ipsilateral hemisphere was analysed in the cat after electrocoagulation of the dorsal part in the nucleus caudatus (NC). Degenerating axonal preterminals and terminals were detected in the preparations impregnated after Nauta--Gygax and Wiitanen's methods and in electronograms. To exclude degeneration of cortical and projective thalamic fibrillae from the great number of regenerated conductors, additional operations were performed on the same cats--thalamic and ventral NC nuclei were damaged and coagulative electrode was inserted into the dorsal NC a month before the last operation.     

Effect of an excess of serotonin in the brain on consolidation of temporary connections]

As a result of intravenous administration of 100 mg/kg of 5-oxytryptophane (5-OTP) to mice, the serotonin content in the brain rises in ten minutes by 35 to 37 per cent, and in an hour, by 58 to 60 per cent, and declines in a day to its initial level. In case of elaboration of passive avoidance reflexes (PAR) an hour after 5-OTP injection, their preservation considerably decreases in a day's time, while 5-OTP administration immediately following PARs elaboration does not affect their preservation. However, 5-OTP injected after PARs elaboration to animals subjected to preliminary cooling, sharply deteriorates their preservation. These facts in conjunction with the previously obtained date attest that excess of serotonin in the brain has a negative effect on the earliest stages of consolidation. When the animals are cooled and the brain temperature is reduced, the consolidation processes are retarded; as a result, the temporary connections prove to be still vulnerable to the action of serotonin excess set up after PAR elaboration.     

Generalized posttetanic changes in the excitatory postsynaptic and acetylcholine-evoked currents in snail neurons

Heteroreceptor posttetanic changes in excitatory postsynaptic currents (EPSC) and inward currents evoked by the local iontophoretic application of acetylcholine (ACh) on the dorsal surface of PLa3 and PRa3 Helix lucorum neurons were studied. The following changes in the currents were revealed over the course of 1-1.5 h after tetanization. The rhythmical ACh application (0.5-1.0 cps, 10-40 s) evokes potentiation of the orthodromic EPSC. The tetanic orthodromic stimulation of one of the nerves (n. intestinalis, n. pallialis dexter, or n. pallialis sinister; 1-5 cps, 1-2 min) causes the potentiation of the ACh current and also heterosynaptic depression of the EPSC. It is concluded that activation of subsynaptic and nonsynaptic neurotransmitter chemoreceptors evokes the development of generalized posttetanic changes in neuronal responses.     

Direct connections of the hippocampus with the retrosplenial cortex in rats

Connections of the retrosplenial cortex with the hippocampus in rats were investigated by the method of retrograde axonal transport of horseradish peroxidase (HRP). If a crystal of HRP was introduced into the dorsocaudal part of the retrosplenial cortex, HRP-labeled cells were found in the rostral pole of hippocampal area CA₃ and in the presubiculum. After iontophoretic injection of HRP into the rostral pole of the hippocampus, HRP-labeled cells were found in layers V and VI of the retrosplenial cortex and in the presubiculum. The results are evidence of reciprocity of direct connections between the rostral pole of the hippocampus and the retrosplenial cortex, and also of the existence of direct efferents of the dorsal subiculum to the rostral pole of the hippocampus.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 102–107, January–February, 1985.     

Microchromatographic study of proteins in hippocampal field CA3 during prolonged posttetanic potentiation in surviving sections

A study was made of 3H-leucine incorporation into water- and tween-soluble proteins of the hippocampal CA3 field under the development of prolonged post-tetanic potentiation (PPTP) because of stimulation of mossy fibers. The mixture of supernatant proteins was assayed by ion-exchange microchromatography while each fraction was evaluated for the radioactive label incorporation. In the course of the assay of the chromatograms obtained, no significant alterations in the protein spectrum were found during the development of the PPTP. Substantial changes were identified in the rate of the labeled leucine incorporation in the acid part of the spectrum represented by acid proteins and polypeptides including brain specific ones. It is assumed that the development of the PPTP in the hippocampal pyramids is associated with activation of the proteins under consideration.     

Activation of pyramidal neurons by intrinsic longitudinal connections in the hippocampus

In the guinea pig, EPSPs and population spikes were found to be generated in the apical dendrites of pyramidal neurons of middle and ventral hippocampus, in response to dorsal hippocampal commissure (PSD) stimulation, without any involvement of dentate gyrus granule cells of corresponding segments. These long-latency synaptic effects were evoked only by repetitive (0.2-2.0 c/sec) PSD stimulation and showed increasing latency in ventral direction. A cross section between dorsal and middle hippocampus was followed by the disappearance of the responses ventrally to the section. The results show that the postsynaptic discharge of dorsal pyramidal neurons is transferred to more ventral hippocampal segments by an intrahippocampal longitudinal association system.     

Effect of pH of the external solution on posttetanic hyperpolarization of the denuded nerve

Changes in posttetanic hyperpolarization of the frog sciatic nerve during a change in pH of the external solution from 5.3 to 9.0 were studied. Reducing the pH of the external solution was shown to lead to an increase in the amplitude and time constant of posttetanic hyperpolarization of the nerve, and an increase in pH led to a decrease in the time constant and a considerable weaking or complete abolition of posttetanic hyperpolarization. It is concluded that these changes in posttetanic hyperpolarization of the nerve related to the pH of the external solution are probably the result of a change in the stoichiometry of the active transport of sodium and potassium ions and the consequent electrogenicity of the potassium — sodium pump.I. N. Ul'yanov Ul'yanovsk Pedagogic Institute. Translated from Neirofiziologiya, Vol. 8, No. 2, pp. 177–182, March–April, 1976.     

Effect of neurogenic inactivity on posttetanic responses of rat fast muscle

At a short-term tetanic stimulation of fast muscle in response to subsequent single stimulation there is recorded a temporary increase of the strength of single contractions that returns to the initial background after 6–10 min. This phenomenon is called posttetanic potentiation (PTP) and is recorded only in fast muscles. The goal of the present work was a study of effect of motor innervation on the course of PTP in rat m. extensor digitorum longus (m. Edl). It has been established that the first signs of effect of motor denervation on the PTP course after section of sciatic nerve in the area of popliteal fossa are recorded as early as at the 4th day after denervation and are expressed in a decrease of strength of single contractions after cessation of tetanic stimulation. These changes reach its maximum at the 14–15th day after denervation when effect of PTP in denervated muscle does not appear at all. Pharmacological analysis of the studied phenomenon has shown that dantrolen (10 μM) suppresses amplitude of the single contraction, but does not prevent the appearance of PTP in intact muscle. In the denervated m. Edl, instead of the appearance of PTP, after a brief slight increase, a gradual decrease of the strength of contraction is recorded. Thus, it can be concluded that no significant PTP changes are present under action of dantrolen. It has been established that after the 10-min muscle incubation in Ringer’s solution with caffeine (4 mM), strength of the single contraction in intact and denervated muscles increases by approximately equal value. Tetanization of intact muscle increases strength of the single contraction approximately by 7% more than this occurs after incubation with caffeine, i.e., this substance reduces the capability of muscle for the appearance of PTP. On denervated muscle, caffeine increases strength of singly contraction, but does not potentiate development of PTP. The obtained data allow concluding about the existence of different mechanisms underlying the pretetatnic contraction and posttetanic potentiation of the single contraction. The main difference between two types of contractions can be recruiting of additional DICR-channels in the process of contraction under conditions of PTP.     

Effect of elimination of visual afferentation on electrical activity of various brain structures

Changes in spontaneous brain electrical activity were studied in experiments on rabbits totally blinded by enucleation befor acquiring vision, and on rabbits with direct vision excluded. Total exclusion of vision causes a sharp decrease in amplitude of electrical potentials in the cortex and subcortex. Depression of activity is greatest in the visual cortex and adjacent regions. Deprivation of direct vision also leads to definite changes in the EEG. The most marked changes are produced by restoration of normal vision. The possible mechanisms of the manifestation of depression in the brain electrical activity of animals with blocked visual function are discussed.Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 497–501, September–October, 1973.     

Effect of embryonic brain tissue transplantation on structural changes in the rat brain after craniocerebral trauma

The effect of homotopic allotransplantation of embryonic cerebral cortex tissue on structural changes in the brain were studied on rats who had suffered a severe craniocerebral trauma (CCT) and subsequent traumatonesis of an injured region. Using Nissl and Golgi-Cox techniques, we showed that the presence of a viable graft in the cavity created by the traumatonesis procedure prevented formation of coarse gliofibrous expansions and extensive dead zones within the perifocal region of the injury locus. Transplantation performed immediately after the CCT and traumatonesis appeared to be most effective. In this case, the graft growth was more intensive and it was better integrated into the recipient's brain; branching of neurons in the graft was more abundant, and their dendrites were densely covered with spines. Thus, the use of early transplantation prevents the development of destructive and dystrophic changes evoked by severe CCT and can be regarded as a promising direction in neurosurgical practice.Neirofiziologiya/Neurophysiology, Vol. 27, No. 5/6, pp. 350–360, September–December, 1995.     

Neurons forming striatonigral connections in the rat brain

Using the retrograde axonic transport of horseradish peroxidase method the striatal neurons projections to substance nigra have been studied in rats. After peroxidase injection into substance nigra a considerable number of small and medium sized neurons (10-20 mkm) become labelled in the ipsilateral striatum. Large labelled striatal cells (20-25 mkm) have been found. Among labelled striatal neurons multipolar cells with triangular and oval body prevailed. The number of cells with elongated multipolar or spindle-shaped body was less. The data obtained disprove the conception that only large ("giant") neurons form the efferent striatal pathways to substance nigra.