Sensomotor Cortex Research Articles

Ultrastructure of axosomatic junctions on neurons of the rat sensomotor cortex and celiac ganglia from the age aspect

Previous investigations have shown that axosomatic junctions are not numerous on pyramidal neurons [2, 12] and are rare on neurons of sympathetic ganglia [3, 8, 13, 14]. Our observations showed that there are 3.70  0.22 axosomatic junctions with a junction length of 0.85  0.05 D and with an area of axon of 0.53  0.06 D2 per 10Dperimeter of a pyramidal neuron in young rats. The corresponding figures for old rats were 3.50  0.23 and 0.94  0.09 D and 0.58 i 0.08 ~2. In the celiac ganglia of young rats there were 1.5  0.44 axosomatic junctions per neuron and 2.35  0.47 in old rats. The axon diameter was 0.58  0.035 in the young rats and 0.77 f 0.033 ~ in the old. Axons forming synapses were found mainly in transverse section (Figs. 2 and 4). These transverse profiles could belong to "en passant" terminals and to terminal axon expansions.

Effect of mebicar on focal epileptic activity

Effect of mebicar on the epileptic activity (EA) and frequency of interepileptic activity discharges (IEAD) was studied in experimental focal cortical epilepsy induced by penicillin application to the sensomotor cortex of conscious rats. Mebicar in a dose of 300--100 mg/kg induced a dose-dependent suppression of EA in the presence of the increased frequency of IEAD. During rhythmic stimulation of some areas of the thalamus mebicar completely abolished high-frequency EA, promoting consecutive alternating on the electrocorticogram of periods of responses to each stimulus with dead bands. The antiepileptic effect of mebicar was compared with that of diazepam in the similar model of epilepsy. It is suggested that the action of mebicar on the focus of epileptic activity in the cerebral cortex is related to the potentiation of synaptic inhibition of the neurons in the focus of epileptic activity.

Antidromic action potentials as a manifestation of trace excitation.

1. As a result of low-frequency subconvulsive electrical stimulation of the sensomotor cortex of an unanesthetized, uncurarized rabbit, groups of AP spreading antidromically along the axons to the soma of callosal neurons located in the opposite hemisphere arose spontaneously after single stimulation. 2. Groups of spontaneous antidromic AP were recorded in the region of the cortex after disappearance of seizure activity, induced by application of penicillin, in it. 3. It is suggested that the phenomena discovered reflect the long-lasting preservation of increased excitability of terminals of cortical neurons after the action of the electrical stimulus of penicillin has ended.

Ultrastructural changes in synapses of the rabbit sensomotor cortex during stimulation of the reticular formation

Ultrastructural changes were studied in synapses of the sensomotor cortex of rabbits during short-term (25 stimuli during 1 day) and long-term stimulation of RF (400 stimuli in the course of 7–8 days). 1. Short-term stimulation of RF led to the development and increased complexity of structures of the synapses, in the form of the appearance of numerous axon terminals forming several active zones with the postsynaptic neuron, and to an increase in the number of synaptic vesicles in the axon terminals. 2. During long-term stimulation of RF further transformations took place in the synapses, namely an increase in the area of the active zones and a decrease in the number of synaptic vesicles in the axon terminals. 3. The submicroscopic changes observed in the synaptic apparatus during stimulation of RF are regarded as a process of intensification of the functional activity of the synaptic apparatus of the sensomotor cortex with the bringing of new interneuronal connections into operation. 4. Structural and functional transformations in the synaptic apparatus of rabbits take place throughout the cross-section of the sensomotor cortex, but predominantly at the upper level (layers I–IV), which suggests that nonspecific afferent endings are distributed throughout all layers of the sensomotor cortex but are represented chiefly in the upper layers.

Physiological analysis of the effect of micropolarization on trace processes.

1. The combination of rhythmic lifting of one forelimb and simultaneous continuous pressor stimulation of the same limb in cats leads to the formation of a conditioned motor reflex to time. Trace motor responses in the assigned rhythm can be detected either during continuous pressor stimulation or during micropolarization of the sensomotor or motor cortex, the body of the caudate nucleus, corpus callosum, and mesencephalic reticular formation by currents of 0.3–1.5 μA. 2. A combination of rhythmic lifting of the forelimb with continuous micropolarization of the sensomotor cortex in the region of representation of the lifted limb by a current of 0.5–1.5 μA also leads to formation of a conditioned reflex to time. Trace motor responses are detected to continuous micropolarization of this same cortical area alone or to subthreshold pressor stimulation of the trained limb alone. 3. It is suggested that these phenomena may have a common physiological mechanism: prolonged activation (through pressor stimulation or micropolarization) of sensory and motor cortical projections of the proprioceptive stimulus facilitates the formation of a trace reflex, such as a conditioned reflex to time.

Organization of single unit responses in the sensomotor cortex to combined stimulation of brain structures.

1. A temporary connection is formed, as reflected in single unit activity and evoked potentials (EPs) in the sensomotor cortex of waking, unimmobilized rabbits, during paired combination of stimulation of the medial lemnicus (ML), reticular tegmental nucleus (RF), and pyramidal tract (PT). The temporary connection is manifested in the dynamics of evoked responses and in changes in electrical activity in the place of usual application of the second stimulus when it is withheld. 2. In response to a combination of stimuli as indicated above the change in singleunit responses affects mainly the late components and occurs twice or three times more often than to simple repetition of the same stimulus. The dynamics of responses to combined stimuli is most clearly defined if the first stimulus consists of stimulation of RF or ML. On omission of the second stimulus, one-third of the neurons develop changes in discharge frequency, corresponding in time mainly to the late component of the response to the second stimulus. 3. Combined evoked potentials to a combination of stimuli undergo similar changes to those in single unit responses. On omission of the second stimulus a complex series of electrical waves consisting of elements of true reproduction of EP and waves outwardly differing in character from EPs to real stimuli develops in the place of its usual application in 75% of cases.

Lipid peroxidation in a focus of hyperactivity in the rat cerebral cortex

It is shown that lipid peroxidation (LPO) can participate in the mechanism of development of paroxysmal activity in the rat cerebral cortex. The appearance of epileptic activity as a result of application of the sodium salt of penicillin to the surface of the sensomotor cortex led to a sharp rise in LPO products in the fraction of unpurified synaptosomes isolated from a focus of hyperactivity. Preliminary injection of the antioxidant α-tocopherol into rats abolished the LPO activation effect and considerably reduced the number of paroxysms recorded on the electrocorticogram during existence of the focus.

Effect of repetitive stimulation on cortical single unit activity

Activity of single units in the visual and sensomotor cortex of an uncurarized, unanesthetized rabbit was recorded by means of two independent microelectrodes during photic stimulation at different frequencies. Trace effects characterized by repetition of the temporal structure of afferent stimulation and by an increase in the level of intercellular correlation were discovered mainly on analysis of distant interneuronal relations after stimulation with frequencies of 2 and Hz. Stimulation at a frequency of 8 Hz did not evoke trace effects.

Possible use of an analgesic (fentanyl) during electrophysiological investigations of the cerebellar cortex

The effect of the central analgesic fentanyl on evoked potentials and responses of single Purkinje cells in the cerebellar cortex to stimulation of the sensomotor cortex and of somatic nerves was investigated in unanesthetized cats. Injection of fentanyl in an analgesic dose (10–30 µg/kg, intravenously) had no appreciable effect on evoked potentials and led only to very slight changes in spontaneous activity and responses of Purkinje cells. As a rule fentanyl, in a dose of 30 µg/kg, depressed, but in a dose of 10 µg/kg, facilitated responses and spontaneous activity of Purkinje cells. This effect of fentanyl is negligible compared with the action of barbiturate anesthetics on responses of cerebellar cortical neurons. Consequently, fentanyl can be used for analgesia during electrophysiological investigations of the cerebellar cortex in unanesthetized cats.

Microiontophoretic study of the mechanism of action of gamma-hydroxybutyric acid

The effect of gamma-hydroxybutyric acid (GHBA) on extracellularly recorded spontaneous unit activity in the sensomotor cortex was studied by microiontophoresis in rabbits. GHBA reduced the discharge frequency of most neurons. Bicuculline, a specific blocker of gamma-aminobutyric acid (GABA), prevented the inhibitory effect of GHBA. This indicates that competitive relations may arise between GHBA and GABA while they interact with the common receptor. The conditions for the appearance of such relations are discussed.

Glial-vascular reactions to angiotensin II in the rat brain

Reactions of the glia and blood vessels in the sensomotor cortex of adult rats to intraperitoneal injection of angiotensin II were studied electron-microscopically. Repeated injections of the hormone led to edema of increasing severity of the astrocytes, constriction of the lumen of the capillaries, and changes in the structure of their endothelium. It is suggested that these disturbances may be the cause of the cerebrovascular insufficiency and of functional changes in the CNS.

Increased ATP-hydrolase activity of brain mitochondria induced by chlorpromazine (electron-cytochemical study)

The location of Mg-activated ATPase was determined in mitochondria of the sensomotor cortex of WAG rats 3 h after administration of chlorpromazine (15 mg/kg). Besides normal mitochondria without the reaction product, modified mitochondria also were observed with the product of the ATPase reaction variously localized in them. No precipitate was found in the mitochondria of intact animals. It is suggested that two factors are concerned in the increase in ATP-hydrolase activity of the mitochondria induced by chlorpromazine: depression of glycolytic and respiratory activity of the cells by the neurol eptic and increased permeability of the mitochondrial membranes.

Changes in sensomotor cortical evoked potentials during electric acupuncture in rabbits

Electrical acupuncture stimulation of tsu-san-li points in rabbits caused gradual disappearance of the second positive wave of the EP and the EEG desynchronization reaction in the sensomotor cortex, and also disappearance of the response of tachycardia to, electrodermal stimulation, indicating the development of a state of analgesia in the animals. Discontinuation of the electric acupuncture led to gradual recovery of the indices mentioned above.

Effect of maternal hypoxia on neurogenesis of the cerebral cortex of the progeny in rats (autoradiographic study)

On the 15th day of pregnancy rats were exposed for 2 h to the action of hypoxia equivalent to an altitude of 8000 m, and on the 18th day of pregnancy they were given three injections of [3H]thymidine. A quantitative autoradiographic study was made of the cerebral cortical neurons of the progeny at the age of 30 days. Rats surviving intrauterine hypoxia were shown to have a significantly higher percentage of labeled nerve cells in layers II, III, and V of the sensomotor cortex than in the control. A difference in the intensity of labeling also was found. It is suggested that maternal hypoxia can delay differentiation and maturation of cerebral cortical neurons in the progeny.

Single unit responses of the dental projection area of the rabbit sensomotor cortex to photic, acoustic, and nociceptive stimulation of the dental pulp

In experiments on waking rabbits interaction between acoustic (tones, clicks), photic, and nociceptive excitation arising during stimulation of the dental pulp on sensomotor cortical neurons in the region of representation of dental afferents was investigated by a microelectrode technique. Bisensory and polysensory convergence of excitation was shown to take place on the cells in this region. It is suggested that convergence of excitation lies at the basis of the mechanisms of formation of the integral systemic nociceptive response to stimulation of the dental receptors.

Effect of artificial gravity in space flight on the content of water-soluble proteins in nerve tissue structures

The content of water-soluble proteins was investigated in the gray and white matter of the spinal cord, the spinal ganglia, and the sensomotor cortex of rats after a space flight lasting 18.5 days. The content of water-soluble proteins in the gray and white matter of the spinal cord and in the spinal ganglia of rats exposed to the action of weightlessness was significantly reduced after 4.5–9.5 h. In rats kept under conditions of artificial gravity during flight the content of water-soluble proteins was reduced in the white matter of the spinal cord. In animals kept previously under conditions of weightlessness 25 days after space flight a significant increase was found in the level of, water-soluble proteins in the gray matter of the spinal cord. In the gray matter of the sensomotor cortex of rats kept under conditions of weightlessness or of artificial gravity no changes were found (compared with controls kept in the ordinary animal house) in the content of water-soluble proteins whether 4.5–9.5 or 25 days after the satellite has landed.

Role of cholinergic mechanisms in the mechanism of action of bicuculline

The hypothesis of a possible role of cholinergic structures in the mechanism of the action of bicuculline was tested by screening and electrophysiological methods. Neither muscarinic (M-) nor nicotinic (N-) cholinolytics (benactyzine, atropine, aprophen,* and pediphen†) abolished convulsions produced in mice by bicuculline. Meanwhile substances inducing the accumulation of γ-aminobutyric acid (GABA) in the brain, such as aminohydroxyacetic acid (AHAA) and depakine, had a well marked protective action against bicuculline convulsions. The electrophysiological experiments also showed that the M-cholinolytic benactyzine does not abolish the effects of bicuculline. Bicuculline was shown to reduce the depression of the test response in the recovery cycle of the primary response of the rat sensomotor cortex when intervals between stimuli measured 40–125 msec, whereas benactyzine reduced the late facilitation of the test response when intervals between stimuli measured 150–300 msec. No interaction could be found between benactyzine and bicuculline by this test. It was concluded from these results that the effects of bicuculline are produced by blockade of postsynaptic GABA receptors and are not connected with the activity of cholinergic structures.

Projection of dental receptors in the rabbit sensomotor cortex

In experiments on rabbits the topical organization of dental representation in the cortex was studied by the evoked potentials method. Each tooth was shown to be locally represented in the sensomotor cortex. During stimulation of threshold strength these zones do not overlap one another. Topographically the dental projection region occupies a territory including areas ParI, Praecag, Preacgr, and PC.

Evoked potentials in the sensomotor cortex during the avoidance reaction in dogs.

1. The formation of an avoidance reaction on the basis of a stable escape reaction leads to loss of the signal meaning of the first pulse of the series of stimulating current. 2. The projection structures of the working limb perform mainly efferent functions in the avoidance reaction.

Slow potentials and spike activity of cortical neurons during development of internal inhibition.

1. During the formation of different forms of internal inhibition to unreinforced flashes similar changes in electrical activity are observed in the cortex of waking rabbits, in the form of weakening of EP and a decrease in the activation of neurons of the sensomotor cortex and strengthening of the late components of EP with a corresponding alternation of inhibition and an increase in the discharge frequency of neurons in the visual cortex. 2. When reinforcement stimuli were used in the experiments (the formation of delaying inhibition, conditioned inhibition, differentiation) and in the first stage of extinction, changes in electrical indices are located mainly in the analyzer of the conditioned stimulus. 3. During prolonged repetition of unreinforced stimuli the changes in electrical activity become more generalized. High-amplitude polyrhythmic waves of potentials, which correspond to irregular grouped discharges of neurons, separated by inhibitory pauses, develop in the cortical representation of both conditioned and reinforcing stimuli. 4. The results are evidence in support of the view that during the formation of internal inhibition conditions favorable for strengthening of hyperpolarization are created in the cortex and, possibly, in other brain structures; recurrent inhibition probably plays an important role in the organization of this hyperpolarization.