Modulation of pyramidal response in the rat sensorimotor cortex after combined stimulation of the lateral hypothalamus and the sensorimotor cortex

It was shown during experiments on unrestrained rats that rhythmic stimulation of the pyramidal tract produced a statistically significant increase in the functional activity of neuronal populations of the sensorimotor cortex, manifesting as potentiation of the primary, positive phase of pyramidal cortical response. Combined rhythmically matched stimulation of the pyramidal tract and of the lateral hypothalamus leads to statistically significant enhancement in potentiation of the positive phase of pyramidal cortical response compared with effects produced independently of hypothalamic involvement. When stimulation of the pyramidal tract and the lateral hypothalamus are combined with stimulation applied at the same periodicity to the sensorimotor cortex, a further statistically significant enhancement in potentiation of the positive phase of pyramidal cortical response is seen in addition to the potentiating effect produced by hypothalamic stimulation.Institute for Brain Research of the All-Union Scientific Center of Mental Health, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 367–373, May–June, 1986.     

Karyometric characteristics of the rat sensorimotor cortex in non-uniform gamma irradiation

Neurocyte nuclei increase in volume without structural changes in karyoplasm at early times after gamma-irradiation of rat head with doses of 50 to 100 Gy. Irradiation of 200 Gy causes a diminution of the nuclei volume while at a dose of 400 Gy the nuclei do not change their volume. A dose as high as 1000 Gy causes severe changes in the karyoplasm leading to nucleus swelling. At later times (24-72 h), the increase in the nuclei volume is associated with the changes in the karyoplasm structure. At one and the same dose, radiation causes either a decrease (irradiation of the head) or increase (exposure of the body) in the neurocyte nuclei volume. At early times after wholebody uniform irradiation no karyometric changes are detected. The nucleus swelling is more pronounced at lower dose-rates.     

Neuronal activity of the sensorimotor area of the rabbit cerebral cortex in zoosocial behavior

The present study was aimed to investigate the neural activity during competitor relationships in the social interactions and operant feeding behaviour. In experiments on three pairs of rabbits the activity of 32 sensory-motor cortex neurones were analyzed. 21 neurones were found specialized relatively to different acts of social behaviour. They did not participate in provision for "individual" types of behaviour.     

Reliability and representational bandwidth in the auditory cortex

It is unclear why there are so many more neurons in sensory cortex than in the sensory periphery. One possibility is that these "extra" neurons are used to overcome cortical noise and faithfully represent the acoustic stimulus. Another possibility is that even after overcoming cortical noise, there is "excess representational bandwidth" available and that this bandwidth is used to represent conjunctions of auditory and nonauditory information for computation. Here, we discuss recent data about neuronal reliability in auditory cortex showing that cortical noise may not be as high as was previously believed. Although at present, the data suggest that auditory cortex neurons can be more reliable than those in the visual cortex, we speculate that the principles governing cortical computation are universal and that visual and other cortical areas can also exploit strategies based on similarly high-fidelity activity.     

Ultrastructure of distal nephron cells in rat renal cortex

Distal nephron segments in the rat renal cortex contain distal convoluted tubule cells (DCT cells), connecting tubule cells (CNT cells), intercalated cells (I cells), and principal cells (P cells). The present study was carried out to expand present knowledge on the ultrastructure of these cells. The cells were sampled from superficial cortex and analyzed by electron microscopy. Several morphometric parameters were determined and statistical comparison between cell types was performed. Significant structural differences between the cell types were demonstrated. DCT cells showed the highest volume density of mitochondria whereas the amplification of basolateral membranes was higher in CNT cells than in I and P cells. The surface density of the membrane that bounds intermediate vesicles in the apical cytoplasm was twofold higher in I cells than in the other cell types. The morphological differentiation found in the present study adds to available evidence indicating a functional differentiation between the cell types and provides a reference for structure-function correlations in these cells.     

Connections between the parietal cortex with the lateral suprasylvian gyrus (Clare-Bishop area) and auditory cortex in cats

Projections between areas 5 and 7 and the lateral suprasylvian gyrus (Clare-Bishop area) were investigated using anterograde degeneration techniques. This showed a topographic organization of projections from areas 5 and 7 to the lateral suprasylvian gyrus. Area 5 association fibers terminate mainly in the anterior portion of the lateral suprasylvian gyrus; this corresponds to the intermediate zone and anterior section of the posterior suprasylvian region. Area 7 efferents are located more caudally, terminating in the posterior section of the intermediate zone and in the posterior region, excluding the outer posterior limits. Fields 5 and 7 give rise to single efferent fibers terminating in the auditory cortex. Fibers from area 5 terminate in the medial ectosylvian and medial, sylvian gyri, i.e., in zones Al and AII or areas 22 and 50. A projection from area 7 terminates at the superior border of the medial ectosylvian gyrus, corresponding to the upper limit of zone A1 or areas 22 and 50.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 739–745, November–December, 1990.     

Structural/functional disturbances in the rat sensorimotor cortex evoked by low-intensity environmental factors

The effect of low-frequency continuous vabration, hypokinesia, and shielding from the geomagnetic field were studied on 424 albino mongrel male rats. The action of these low-intensity factors of a different nature caused changes first of all in the microcirculatory bed (MCB) of the cerebral cortex. Structural disturbances, as well as the disturbances of redox metabolism in the neurons appeared close to those observed during hypoxia of a different origin; they obviously resulted from the disturbances of the MCB functions, which caused discrepancy between the needs for energy supply and the transport system state. Specificities of the disturbances evoked by different factors can be related to desynchronization of the biorhythms (e.g., caused by deprivation of the geomagnetic field).     

Sources of thalamo-cortical afferents of the forelimb representation area in the first somatosensory zone of the cat cerebral cortex

Retrogradely labeled thalamic neurons—the sources of afferents in the focus of peak activity induced by radial nerve stimulation—were investigated in adult cats by means of microiontophoretic horseradish peroxidase injection into the first somatosensory zone of the cerebral cortex. Labeled cells were found mainly in the ventroposterolateral and a smaller proportion in the posteroventral medial thalamic nuclei. Labeled neurons were distributed in groups differing in their morphological parameters within these nuclei.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 154–160, March–April, 1988.     

Analysis of the reactivity of the sensorimotor neurons of the rat cerebral cortex to acetylcholine

Several types of cholinoceptive neurons have been identified in rat's sensomotor cortex according to response character to ionophoretical application of acetylcholine. The neurons investigated form continuous range according to duration of the excitatory component of reaction to transmitter application. It has been suggested that the duration of this component reflects the important functional properties of the nerve cell.     

Dreamed movement elicits activation in the sensorimotor cortex

Since the discovery of the close association between rapid eye movement (REM) sleep and dreaming, much effort has been devoted to link physiological signatures of REM sleep to the contents of associated dreams [1-4]. Due to the impossibility of experimentally controlling spontaneous dream activity, however, a direct demonstration of dream contents by neuroimaging methods is lacking. By combining brain imaging with polysomnography and exploiting the state of "lucid dreaming," we show here that a predefined motor task performed during dreaming elicits neuronal activation in the sensorimotor cortex. In lucid dreams, the subject is aware of the dreaming state and capable of performing predefined actions while all standard polysomnographic criteria of REM sleep are fulfilled [5, 6]. Using eye signals as temporal markers, neural activity measured by functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS) was related to dreamed hand movements during lucid REM sleep. Though preliminary, we provide first evidence that specific contents of REM-associated dreaming can be visualized by neuroimaging.     

The participation of the cholinergic system of the rat sensorimotor cortex in regulating different types of movements

To study the role of the cholinergic system of the sensorimotor cortex in regulation of different manipulatory movements and locomotion of Wistar rats, the effects of injections of cholinergic drugs (a cholinergic agonist carbachol and an antagonist scopolamine) into the area of forepaw representation in the sensorimotor cortex on motor activity and performance of manipulatory movements (with prolonged and short pushing) were analyzed. The drugs were injected via special cannulae stereotaxically implanted into the cortex during surgery carried out under Nembutal anesthesia. Carbachol injections (0.03-3 micrograms in 1 microliter of physiologic solution) into the cortex resulted in a significant slowing down of both types of movements as well as an increase in locomotion in the open-field test. Injections of scopolamine (0.3-3 micrograms) into the same cortical area were accompanied by an increase in the number of fast manipulatory movements without significant changes in locomotor activity. The obtained evidence suggests that the cholinergic system of the sensorimotor cortex indifferent manners regulates the innate (locomotion) and acquired movements which require different periods of maintaining the muscle tone of the forepaw (short-time periods for the usual movements necessary for food taking from the narrow horizontal tube and prolonged periods for the learned slow movements with additional tactile and tonic components).     

Identification of a respiratory related area in the rat insular cortex

The aim of this study was to map areas within the rat insular cortex from which respiratory responses originate and compare those sites with gastrointestinal control regions. The insular cortex was systematically microstimulated and histological location of responsive sites determined. Increased inspiratory airflow and decreased respiratory cycle duration were considered to be respiratory excitatory responses. The responses were localized in dysgranular and agranular insular cortex at levels caudal to the joining of the anterior commissure. More rostrally, respiratory inhibitory responses were elicited: these were manifested as a decrease in inspiratory airflow without a significant alteration in respiratory cycle duration. Respiratory inhibitory responses were usually accompanied by changes in gastric motility. These results suggest that the respiratory area in the rat insular cortex consist of two distinct zones which overlap a region modulating the gastrointestinal activity.     

Laminar analysis of the origin of the various components of evoked potentials in slices of rat sensorimotor cortex

In slices of rat sensorimotor cortex, extracellular field potentials evoked by electrical stimulation of the white matter were recorded at various cortical depths. In order to determine the nature of the various components, experiments were performed in 3 situations: in a control perfusion medium, in a solution in which calcium ions have been replaced by magnesium ions to block synaptic transmission, and in cortices in which the pyramidal neurons of layer V had been previously induced to degenerate.In the control situation, the response at or near the surface was a positive-negative wave. From a depth of about 150 μm downwards, the evoked response consisted usually of 6 successive components, 3 positive-going, P11, P3 and P6 and 3 negative-going, N2, N4 and N5. P1 and N4 were apparent in superficial layers only. The amplitude of the remaining waves variable in the cortex but all diminished near the white matter.The early part of the surface positive wave arises from a non-synaptic activation of superficial elements, probably apical dendrites. The late part of the surface positive wave and the negative wave are due to the synaptic activation of neurons located probably in layer III.The large negative wave N2 represents principally the antidromic activation of cell bodies and possibly of proximal dendrites of neurons situated in layers III, IV and V, through the compound action potentials of afferent and efferent fibers may contribute to a reduced part to its generation.The late components N4 to P6 are post-synaptic responses. The negative component N5, the amplitude of which is largest in layers III and IV, represents excitatory responses of neurons located at various depths in the cortex. The nature of the positive component P6 is less clear, although the underlying mechanism might be inhibitory synaptic potentials.     

N-Acetyl-aspartyl-glutamate in the rat dorsal striatum: topographical distribution and effect of sensorimotor cortex lesions

The dipeptide N-acetyl-aspartyl-glutamate (NAAG) has been proposed as putative neurotransmitter of some corticostriatal projections. To further explore this possibility, endogenous NAAG levels were measured in various microdissected striatal regions in normal animals and in those with bilateral lesion of sensorimotor cortex. In intact rats there was a rostro-caudal gradient for NAAG, with highest concentrations in the more caudal portions of the striatum without significant differences between the medial and lateral regions. Decortication induced no significant changes in peptide concentration in any of the striatal regions or in the respective crude synaptosomal (P2) fractions. However, decorticated animals showed a large degree of deafferentation as evidenced by a marked and significant decrease in [³H]glutamate uptake as well as in glutamate levels measured in striatal homogenates or in crude synaptosomal fractions. No changes in striatal dopamine levels were observed in lesioned animals. Thus, these findings are not in favor of the existence of corticostriatal projections arising from the sensorimotor cortex using NAAG as neurotransmitter.     

Perceiving time to collision activates the sensorimotor cortex

The survival of many animals hinges upon their ability to avoid collisions with other animals or objects, or to precisely control the timing of collisions. Optical expansion provides a compelling impression of object approach and in principle can provide the basis for judgments of time to collision (TTC) [1]. It has been demonstrated that pigeons [2] and houseflies [3] have neural systems that can initiate rapid coordinated actions on the basis of optical expansion. In the case of humans, the linkage between judgments of TTC and coordinated action has not been established at a cortical level. Using functional magnetic resonance imaging (fMRI), we identified superior-parietal and motor-cortex areas that are selectively active during perceptual TTC judgments, some of which are normally involved in producing reach-to-grasp responses. These activations could not be attributed to actual movement of participants. We demonstrate that networks involved in the computational problem of extracting TTC from expansion information have close correspondence with the sensorimotor systems that would be involved in preparing a timed motor response, such as catching a ball or avoiding collision.     

Oscillatory interactions between sensorimotor cortex and the periphery

Field potential recordings from motor cortex show oscillations in the beta-band (approximately 20 Hz), which are coherent with similar oscillations in the activity of contralateral contracting muscles. Recent findings have revised concepts of how this activity might be generated in the cortex, suggesting it could achieve useful computation. Other evidence shows that these oscillations engage not just motor structures, but also return from muscle to the central nervous system via feedback afferent pathways. Somatosensory cortex has strong beta-band oscillations, which are synchronised with those in motor cortex, allowing oscillatory sensory reafference to be interpreted in the context of the oscillatory motor command which produced it.