Electrophysiological analysis of efferent neurons of cat associative parietal cortex

We have studied in acute experiments the neurons of the associative parietal cortex in the cat, using the microelectrode take-off technique. We identified the efferent neurons sending axons to the sensomotor cortex, the red nucleus, and the pontine nuclei by antidromic stimulation. We investigated the collateral branching of axons of neurons projected simultaneously into two of the formations mentioned, using the impulse collision technique. We studied the characteristics of the spatial distribution of efferent neurons in the parietal cortex.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 72, No. 7, pp. 865–873, July, 1986.     

Antidromal and synaptic activation of neurons of the associative parietal cortex of the cat brain elicited by spike activity from the intrinsic nuclei of the pons

Acute experiments were performed on cats with intracellular recording of efferent and unidentified neurons of the anterior suprasylvian and posterior lateral gyri of the parietal cortex, to study the antidromal and synaptic responses to stimulation of the lateral and medial groups of intrinsic nuclei of the pons. Oligo- and polysynaptic components were detected, along with complex EPSP due to convergence of axons from fast- and slow-conducting neurons. Antidromal and synaptic responses were demonstrated in the same parietal cortex neurons, demonstrating a double connection between the intrinsic nuclei of the pons and the associated parietal cortex. The possible pathways of these connections are discussed, along with their features and importance in the functioning of pontocortical connections. Laboratory for Central Nervous System Physiology, L. A. Orbel' Institute of Physiology, Armenian National Academy of Sciences, Erevan. Translated from Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 82, No. 1, pp. 10–17, January, 1996.     

Pre-movement activity of neurons in the parietal associative cortex of the cat during different types of voluntary movement

Pre-movement activation of electromyographic spike activity of 201 neurons of field 5 was studied in cats trained to carry out a stereotypical act (lifting the anterior footpad to press a pedal) in response to a conditioned stimulus (experimental series 1) and without a conditioned stimulus (self-initiated movement, experimental series 2). In series 1, 69.2% of neurons were activated and 13.5% were inhibited before the movement. Prior changes in activity were also seen in intersignal movements, with activation of 40.6% and inhibition of 21.7% of neurons. The time parameters of excitatory and inhibitory responses in both situations were similar, with pre-movement intervals of 19-1640 msec. In series 2, pre-movement inhibition was seen rather more frequently than activation (36.7% and 33.7% respectively). The earliest changes were inhibitory, occurring some 1800 msec before movements, while excitatory changes occurred only 880 msec before movement. These data indicate the involvement of the parietal associative area in the cat not only in executing, but also in preparing for different types of movement, including self-initiated movements, and that inhibition has an active role in this process. Department of Human and Animal Physiology and Biophysics (Director V. G. Sidyakin), Simferopol State University. Translated from Fiziologicheskii Zhurnal im. I. M. Sechenova, Vol. 81, No. 4, pp. 70–75, April, 1995.     

Interhemispheric asymmetry of associative responses in the cat parietal cortex

The asymmetry of associative responses in the parietal region of the cortex was experimentally studied during visual and auditory stimulation of tubocurarineimmobilized cats at various intensities with the multiple recording of evoked potentials (EP). The left-handed asymmetry of the early and late components of associative responses was established. It was shown that the zones of convergence of visual and auditory information are also asymmetric and predominate in the left hemisphere. By contrast to the projection regions, no strength or transcallosal modulation of the interhemispheric asymmetry could be found in the parietal cortex. The data obtained indicate the applicability of the principle of functional asymmetry to the activity of paired segments of associative cortical systems in animals.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 68, No. 6, pp. 729–737, June, 1982.     

Pyramidal and non-pyramidal projection from cortical areas 4 and 6 to the red nucleus in the cat

The pyramidal tract (PT) and the red nucleus (RN) of cats were stimulated electrically to identify by antidromic invasion PT and non-PT neurons projecting from cortical areas 4 and 6 to the RN. A main result was that the input to RN is much stronger from PT neurons than that of non-PT neurons in area 4, and vice versa in area 6.     

Transcranial magnetic stimulation to right parietal cortex modifies the attentional blink

The attentional blink (AB) reflects a limitation in the ability to identify multiple items in a stream of rapidly presented information. Repetitive transcranial magnetic stimulation (rTMS), applied to a site over the right posterior parietal cortex, reduced the magnitude of the AB to visual stimuli, whilst no effect of rTMS was found when stimulation took place at a control site. The data confirm that the posterior parietal cortex may play a critical role in temporal as well as spatial aspects of visual attention.     

Quantitative analysis of the distribution of the motor cortex representations of the fore-and hindlimbs in the red nucleus of the cat

A quantitative analysis of the distribution of corticorubral fibers was performed after precise electrolytic lesioning of the lateral and medial margins of the posterior sigmoid gyrus — the motor representations of the fore-and hindlimbs respectively — in cats. The cortical representations of the forelimbs were found to project to the whole of the rostrocaudal extent of the red nucleus (RN). The number of efferent fibers terminating at the rostral margin of the RN was almost twice that terminating in the caudal third of the RN. Efferent fibers of the cortical representation of the hindlimbs did not project to the rostral two thirds of the RN but ended in its caudal third; the number of projecting corticorubral fibers was the same as the number running from the cortical representation of the forepaws to the caudal third of the RN. The significantly (almost double) greater number of fibers running from the cortical representation of the forelimbs in comparison with the number directed from the representation of the hindlimbs found in the present study is probably evidence of the greater functional importance of corticorubral connections in movement reactions performed by the forelimbs. __________ Translated from Morfologiya, Vol. 131, No. 2, pp. 29–31, March–April, 2007.     

Responses of cat vestibular neurons to stimulation of the frontal cortex

Summary To study the neural basis for the regulation of vestibulocollic reflexes during voluntary head movements, the effects of stimulation of the precruciate cortex near the presylvian sulcus (neck area of the motor cortex) and the frontal eye fields (FEF) on vestibular neurons were studied in cerebellectomized cats anesthetized with chloralose. Neurons were recorded in the medial and descending vestibular nuclei and antidromically identified from C₁. Stimulation of the FEF and precruciate cortex fired 29 and 13% of neurons that did not exhibit spontaneous activity. About 80% of spontaneously discharging neurons were influenced by stimulation of either of the two. Stimulation of the precruciate cortex or FEF suppressed or facilitated labyrinthine evoked monosynaptic activation of vestibulospinal neurons, suggesting that the frontal cortical neurons have the properties to regulate the vestibulocollic reflexes.     

Characteristics of neuronal responses in the sensorimotor cortex of the cat to monaural and binaural stimulation

The dependence of neuronal responses in the sensorimotor cortex (SMC) of the cat upon localization parameters of dichotically presented auditory signals was studied in acute experiments. Binaural stimulation was more effective than either monaural stimulation. It was shown that spatial-localization parameters of auditory-stimulus source such as interaural differences in intensity and time are reflected by the characteristics of neuronal responses in the SMC; moreover, in 67–88% of cases the most pronounced responses were observed for small, close to zero, temporal and amplitudinal interaural shifts. It was found that SMC neuronal background activity may be altered by signals simulating directed movement of the sound source in the horizontal plane.Translated from Fiziologicheskii Zhurnal SSSR imeni I. M. Sechenova, Vol. 65, No. 6, pp. 801–811, June, 1979.     

Two modes of cerebellar input to the parietal cortex in the cat

Summary The characteristics of cerebellar input to the parietal cortex through the ventroanterior-ventrolateral (VA-VL) complex of the thalamus were investigated in the adult cat by using combined electrophysiological and anatomical methods. Two distinct parietal regions were activated by stimulation of the cerebellar nuclei (CN). In the first region located in the depth of the bank of the ansate sulcus, stimulation of the CN induced early surface positive-deep negative potentials and late surface negative-deep positive potentials. In this cortical area, potentials of similar shape and time course were evoked at a shorter latency by stimulation of the ventrolateral part of the VA-VL complex where large negative field potentials were evoked by stimulation of the CN. After injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in this part of the VA-VL complex, axon terminals of thalamocortical (TC) fibers were found in layers I, III and IV in the depth of the bank of the ansate sulcus and layers I and III in the motor cortex. In the second region located in the suprasylvian gyrus, late surface negative-deep positive potentials were evoked by stimulation of the CN and similar potentials were evoked at a shorter latency from the dorsomedial part of the VA-VL complex where large cerebellar-evoked potentials could be recorded. PHA-L injection in this thalamic region stained TC fibers and their terminals in layer I of the suprasylvian gyrus, and in layers I and III of the motor cortex. The laminar distribution of TC axon terminals in two different regions of the parietal cortex could account for the depth profiles of the cerebellar- and the thalamic-evoked potentials in each region. These results show that cerebellar information is conveyed to two separate areas in the parietal cortex by two different TC pathways.     

Identification of two populations of corticothalamic neurons in cat primary somatosensory cortex

Summary Extracellular and intracellular recordings of corticothalamic (CT) cells were performed in the primary somatosensory cortex of the cat. CT neurons were antidromically activated by electrically stimulating the ventroposterior lateral (VPL) nucleus of the thalamus and were classified into two types according to their physiological properties. Type 1 had no spontaneous activity and no identifiable somatic receptive field. Type 2 fired action potentials spontaneously and responded to mechanical stimulation of the skin or underlying tissues. Axonal conduction velocities were slower for type 1 cells and their cell bodies were located slightly deeper in the cortex than those of type 2 cells. Both types of CT neurons exhibited inhibitory postsynaptic potentials in response to VPL stimulation but an early synaptic excitation and rebound discharge was observed almost exclusively in type 2 cells. These results suggest that only type 2 CT cells can modify the activity of thalamic neurons through a corticothalamic feedback loop.     

Age-related alterations in responses of the nucleus basalis magnocellularis neurons to frontal cortex stimulation in rats

The present study investigated the age-related alterations in responses of the nucleus basalis magnocellularis (nbM) neurons to frontal cortex (FCX) stimulation. Single unit extracellular recording from the nbM neurons were obtained with glass micropipettes in urethane-anesthetized rats. A total of 137 units were located within the nbM in the three age groups (young, 3 months; adult, 12 months; old, 24 months). FCX stimulation elicited responses in 91% of the 137 neurons. Most of them were excited. The frequency of occurrence of excitatory responses in the nbM neurons was decreased with aging. The thresholds and latencies of excitatory responses evoked by FCX stimulation were increased in old rats. The mean peak-firing rate of exciting phase was gradually reduced with aging. These findings indicate that there might be some functional changes in the nbM neurons with aging.     

Effects of electrical stimulation of the caudate nucleus on functionally identified neurons of the sensorimotor cortex in the cat brain

Paired stimulation was used to study the effects of the caudate nucleus on the specific and nonspecific responses of projection neurons of the sensorimotor cortex in the cat brain. Caudal influences on the neurons being studied had insignificant effects on specific peripheral evoked responses. Nonspecific peripherally evoked activity was in most cases inhibited by caudate spike activity, and the pattern of evoked activity underwent significant modulation in conditions of a constant type of peripherally evoked response. It is suggested that the caudate nucleus acts as a filter of proprioceptive information in the cortex or in pathways to the cortex: specific corticopetal information is passed unchanged, while nonspecific signals are predominantly inhibited or significantly modulated. Department of Human and Animal Physiology and Biophysics, M. V. Frunze State University, 4 Yaltinskaya Street, 333036 Simferopol’, Ukraine. Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 83, No. 1-2, pp. 117–121, January–February, 1997.     

Prefrontal cortex of the cat: Paucity of afferent projections from the parietal cortex

Summary Twenty-one cat brains with cortical injections of horseradish peroxidase resulting in labelled cells in the thalamic mediodorsal nucleus (MD) were screened for afferent projections from the parietal cortex. Contrary to expectation, nearly the whole prefrontal cortex (PFC) situated around the frontal pole was free of parietal afferents, while a small area in the anterior sylvian gyrus (orbito-insular subregion of PFC) consistently received afferents from the parietal cortex. The few afferents projecting to the cortex around the frontal pole originated exclusively from the convexity of the suprasylvian gyrus, while the great majority of the parietal neurons projecting to the anterior sylvian gyrus was situated within the fundus of the suprasylvian sulcus. While the main regions of the prefrontal cortex of the rhesus monkey receive a substantial projection from the parietal lobe, whereas the main regions of the cat's prefrontal cortex are free of afferents from the parietal cortex, possible differences in the parieto-prefrontal organization of both species are discussed. Furthermore, differences between the orbito-insular subregion and the rest of the PFC are emphasized.This study was carried out mainly at the University of Konstanz.Dr. B. Petrovi-Mini was a visiting scientist at the University of Konstanz. Research was supported in part by grant Ma 795 from the Deutsche Forschungsgemeinschaft (DFG)     

前庭神经核纤维与投射至纹状体的束旁核神经元的突触联系

目的：观察发自前庭神经内侧核的纤维末梢与投射至纹状体的丘脑束旁核神经元的突触联系。方法：采用15只Wistar大鼠,应用顺行和逆行标记技术,免疫组织化学和免疫电镜方法。结果：将CTb单侧注入纹状体,同时将BDA注入同侧的前庭神经内侧核。在束旁核发现了CTb标记神经元和BDA标记轴突终末,BDA标记纤维和终末存在于外侧束旁核整个长度的背侧2／3区,而CTb标记神经元也存在于外侧束旁核背侧2／3区,2种标记相互重叠。电镜下可见标记终末与标记神经元形成非对称性的轴-体和轴-树突触。结论：由前庭神经内侧核发出的投射纤维在束旁核与投射至纹状体的束旁核神经元之间存在着非对称性的突触联系。     

Cortically projecting nucleus basalis neurons in rat are physiologically heterogeneous

The localization of serotonin and non-serotonin-containing cell bodies in the interpeduncular nucleus of the rat that project to the hippocampal formation was studied using the technique of retrograde tracing of Granular Blue and immunohistochemistry on the same sections. The results indicate that the caudal magnocellular subnucleus (pars dorsalis magnocellularis) and, to a lesser extent, the caudal part of the lateral subnucleus (par lateralis) of the interpeduncular nucleus send serotonin as well as non-serotonin fibers to the ventral hippocampus.     

Responses of cat motor cortex neurons to cortico-cortical and somatosensory inputs

Summary Intracellular techniques were used to investigate a cortico-cortical path from sensory cortex to motor cortex of cats. Cortico-cortical epsps were evoked in motor cortex neurons by microstimulation of area 3a. Epsps with latencies between 1.2 and 2.4 ms were identified as monosynaptic. These short latency cortico-cortical effects were recorded in layers II through VI of the motor cortex. Neurons with monosynaptic cortico-cortical epsps also received excitatory inputs from forelimb nerves, usually from both muscle and cutaneous afferent fibers. The epsps evoked from forelimb nerves in motor cortex neurons were preceded by neural activity in somatosensory cortex. Time delays between arrival of inputs in sensory cortex and in motor cortex were compared to the latencies of cortico-cortical epsps in the same motor cortex neurons. It was apparent that the timing was appropriate for the identified cortico-cortical path to have relayed some sensory inputs to motor cortex.Supported by the Medical Research Council of Canada (MT-7373, DG-186), the Harry Botterell Foundation for the Neurological Sciences, the Ontario Ministry of Health, and the Faculty of Medicine, Queen's UniversityRecipient of a Medical Research Council of Canada Studentship.Recipient of a Medical Research Council of Canada Fellowship