Responses of neurons of the parietal association cortex of the cat to acoustic stimulation before and after suppression of the auditory cortex in the cat

The aim of this work was to study the influence of auditory cortex suppression in cat on response patterns of the parietal associative cortex neurons responding to different frequency tones. Suppression was performed by two methods: bilateral isolation and application of 6% nembutal solution on the cortex surface. Frequency-thresholds curves were plotted for all neurons studied. Prior to suppression the majority (84%) of studied neurons had one or two characteristic frequencies. After suppression the percentage of such cells fell to 63% of all responding neurons. Frequency range to which neurons could respond was altered as well. Normally almost all neurons tested could respond to a wide spectrum of presented frequencies. After suppression 69% of neurons did not respond to tones above 8-10 kHz. This may indicate that mainly information about high frequency tones is transmitted via the auditory cortex. The possibility that associative thalamic nuclei are the main source of acoustic information for parietal associative cortex neurons is discussed.     

Responses of neurons in the Clare-Bishop cortical association area of the cat cerebral cortex to photic stimulation

In acute experiments on cats with protrigeminal section immobilized by flaxedil the electrical activity of single neurons in associative visual cortex of Clare-Bishop was investigated by the extracellular registration of their spike activity. 95.5% of investigated neurons responding to natural stimulation (light spots) were sensitive to the movement of stimulus through the receptive field. Nearly 55% of neurons exhibited selective responses to the direction of stimulus movement. Some neurones responded only when the stimulus was crossing the border points of receptive field. Nearly 85.3% of neurons responded to the flashing spot with "on", "on-off" and "off" reactions, and also to the stimulation by diffuse flashes. Receptive fields of neurons in the Clare-Bishop area were of strip-like form with longitudinal axis in horizontal orientation. Presented observations allow concluding that the Clare-Bishop cortical association area plays an essential role in the central processing of visual information.     

GABA-B-related activity in processing of transcallosal response in cat motor cortex

GABA-ergic characteristics of transcallosal (TC) responses were studied with specific antagonists of both GABA-A and GABA-B receptor subtypes. We used a paired-pulse paradigm to get insight into the role of GABA in interhemispheric interactions between motor cortices. 3-Amino-2-(4-chlorophenyl)-propylphosphonic acid (phaclofen) and 3-aminopropyl-diethoxymethyl-phosphinic acid (CGP 35348) were used as GABA-B antagonists and bicuculline methiodide (BMI) was used to block the GABA-A receptor. Although both GABA-A and GABA-B antagonists increased spike discharge upon transcallosal stimulation, in both pyramidal tract and non-pyramidal tract neurons, they had different effects on the responses to the first and second stimuli of paired-pulse stimulation (200 msec interval). Although the inhibition seen with the second stimulus was greatly attenuated by antagonists of the GABA-B receptor, it was maintained in the presence of the GABA-A antagonist. These finding support a presynaptic regulation of callosal transmission by GABA-B receptors in the callosal synapse of the cat motor cortex.     

Two groups of corticofugal neurons identified with the pontine stimulation in the cat parietal association cortex: an intracellular HRP study

A classification of the parietal corticofugal neurons was performed in cats under Nembutal anesthesia. Eighty-eight neurons were identified with antidromic activation by the pontine stimulation. Thirteen neurons were furthermore identified with intracellular HRP staining. In these neurons, we found the close correlation between morphological features and conduction velocities. The faster conducting group of the neurons had relatively large somata, sparsely spinous apical dendrites, tap root basal dendrites and wide apical dendritic fields. The slower group had small somata and numerous dendritic spines.     

Effects of claustral stimulation on the properties of visual cortex neurons in the cat

To assess the possible role of the claustrum in visual processing, extracellular unit recordings were made in the striate cortex of cats during claustral stimulation. The results showed that electrical stimulation of the dorsocaudal portion of the claustrum produced a decrease in the spontaneous activity and optimal firing characteristics of visual cortical cells.     

Changes in the synaptic vesicles of cat motor cortex axon terminals upon stimulation]

The relation of the synaptic vesicle size to the distance between the vesicle and the synapse active zone was studied in the axon terminals at the motor cortex neuron spines and dendrites of resting cats (under moderate barbiturate anesthesia) and after prolonged repetitive stimulation of the somatosensory SII area. Thes sizes of the vesicles belonging to any of the three strata observed in the terminal section profile under the electron microscope were registered as a decrementing variation sequence. The predominance of small vesicles in stratum I adjoining to the synapse active zone was found by means of the statistical analysis (symbol criterion and criterion chi2), both in the control and experimental material. A significant gradient of the vesicle size diminution from peripheral stratum III to stratum I as well as vesicle size decrease both in stratum I and intermediate stratum II in comparison with the control developed after the cortico-cortical projection stimulation. The functional role of this phenomenon is discussed.     

Cholinergic neurons in the basal forebrain of the cat have direct projections to the sensorimotor cortex

Previous studies showed that projections from the cells in the substantia innominata to the sensorimotor cortex exist in the monkey and rat and that this group of cortical afferent fibers utilizes acetylcholine as a neurotransmitter. Because similar studies have not been made in the cat, the following study was undertaken to analyze the extent and distribution of this projection from the basal forebrain. Horseradish peroxidase (HRP) injections were made into the anterior and posterior sigmoid gyri 24 h before, and diisopropyl fluorophosphate was injected intramuscularly 3 h before the anesthetized cats were perfused. Brain sections from these cats were incubated in solutions to simultaneously detect retrogradely transported HRP and acetylcholinesterase (AChE) reaction product within the somata. The cell bodies that contained reaction product for both HRP and AChE were mostly large (25 to 30 μm) and multipolar. These double-labeled cells were located in (i) the nucleus of the diagonal band in rostral sections, (ii) the globus pallidus, entopeduncular nucleus, and substantia innominata at the level of the anterior commissure, and (iii) the lateral hypothalamus in the most caudal sections. Many of these sites corresponded to that for the basal nucleus of Meynert, an aggregation of large multipolar neurons scattered throughout the basal forebrain. Although the presence of AChE within a cell does not define a cholinergic neuron, recent studies indicated that its presence is a requirement for this neurotransmitter. These data together with biochemical and immunocytochemical data indicate that a cholinergic projection to the sensorimotor cortex of cats arises from the basal forebrain. This pathway may play a vital role in memory and cognition.     

Synaptic processes in neurons of the cat pericruciate cortex evoked by pyramidal tract stimulation]

The influences of pyramidal tract stimulation on the activity of neurons in the pericruciate cortex were investigated on 423 neurons (81 neurons were studied intracellularly and 342--extracellularly), 78 of them having background activity. Pyramidal stimulation is shown to evoke not only antidromic spikes (0.5-16.0 ms latency) in the pyramidal cells, but also lateral and recurrent PSPs in the pyramidal and unidentified units of all cortical layers. IPSPs were observed in 46.7% of the investigated neurons, EPSPs--in 21.0%, mixed responces--in 26.0%. The latency of IPSPs was 1.5-14.0 ms, their amplitude ranged from 1.3 to 17.0 mV, the duration of the rising phase varied from 4 to 18 ms and the whole duration was 18-120 ms reaching sometimes 250-500 ms. In 30% of cases it was possible to divide the IPSPs into two phases: a fast one with a duration of 10-20 ms and a slow one. The latency of IPSPs was 2.6-19.0 ms, their amplitude--1.0--7.8 mV and duration--from 10.0 to 50.0 ms. The antidromic discharge in the pyramidal tract inhibited the background activity for 200-400 ms in 51.2% of spontaneously active units; acceleration was observed in 19.5% and mixed effect in 7.4% of units. The participation of pyramidal axonal collaterals and cortical interneurons in generation of the described processes is discussed.     

Reactions of neostriatal neurons to direct electric stimulation of the optic tract and to photic stimulation in the alert cat

Responses of 98 cells in the head and body of caudate nucleus to direct electric stimulation of the optic tract and to visual stimuli were recorded extracellularly in awake chronic cats. 34.6 and 36.2% of the studied cells, respectively, have responded to these types of stimulation. Long-latency (over 40 ms for optic tract and over 80 ms for visual stimulations) excitatory responses prevailed in both cases. Small number of units responded to optic tract stimulation with short (5-14 ms) latencies. Eight of 58 tested cells were activated by both electric and visual stimuli. In this case, responses of the same cells could differ (relatively to the type of applied stimulus) either in pattern or sign. These data are discussed relative to the possible pathways for transfer of the visual information to non-specific brain structures.     

Effects of claustrum stimulation on spontaneous bioelectrical activity of motor cortex neurons in the cat

Electrophysiologic interactions between claustrum and motor cortex neurons were investigated in the cat. A total of 136 neurons was recorded from the motor cortex in area 4 (90 cells) and in area 6 (46 cells). Ninety-eight of the total neurons were identified as pyramidal tract neurons (PTNs). Stimulation of the claustrum by single shocks or by trains of stimuli imposed on the tested PTNs a pure long-lasting inhibition, or a long-lasting inhibition preceded by a short early activation, or no effect. No functional localization of the effects of claustrum activation were found within the motor areas. The observed results are consistent with the hypothesis that the claustrum may play a role in movement organization.     

Effects of stimulation of the dorsocaudal claustrum on activities of striate cortex neurons in the cat

In the cat striate cortex, single electrical shocks applied to the dorsocausal claustrum (CLdc) elicited bimodal excitatory responses with about 12 and 26 ms latencies. About one-fourth of the cortical cells observed had CLdc-induced inhibitions with onset latencies longer than the excitations. On cortical field responses to geniculate stimulation, CLdc conditioning shocks exerted early facilitatory and late inhibitory effects which were shown to be not transmitted through the mesencephalic reticular formation.     

Influence of cerebral cortex stimulation upon cough-like spasmodic expiratory response (SER) and cough in the cat

In 27 pentobarbitalized cats, the influence of electrical stimulation of the cerebral cortex upon the spasmodic expiratory response (SER) was studied and compared with cortical influences on coughing induced by stimulation of the superior laryngeal nerve (sup. laryngeal N.). This cortical influence was evoked by electrical stimulation of the cortical nucleus of amygdala (Aco), and was very similar to coughing accompanying changes in emotional behavior and was depressed more effectively by psychotropics than by centrally acting antitussives like codeine.When anterior cingulate gyrus (ant. cingulate G.) or orbital gyrus (orbital G.) were stimulated simultaneously with Aco or sup. laryngeal N., weak stimulation was sufficient to inhibit SER, while stronger stimuli were needed for the suppression of cough. If the same cortical regions were stimulated after initiation of SER or cough, SER was markedly suppressed but cough little affected. Production of SER was facilitated by simultaneous stimulation of the piriform lobe (piriform L.) or olfactory tract (olfactory T.), whereas cough production was facilitated by simultaneous stimulation of the suprasylvian gyrus. These results suggest that SER and coughing are differently controlled by the cerebral cortex, and that SER is modulated by the limbic cortex, in particular, by ant. cingulate G., orbital G. and piriform L. The mechanism of modulation for SER is discussed.     

Transcranial direct current stimulation and the visual cortex

Neuroplastic changes are defined as enduring changes in the organization of the central nervous system, such as the strength of connections, representational patterns, or neuronal properties, either morphological or functional. In recent years, new tools have emerged to induce and manipulate ongoing neuroplastic changes by external stimulation, either by modification of synchronized neuronal activity or modulation of the spontaneous firing rate. The first is performed by transcranial magnetic stimulation (TMS), the latter by direct current stimulation (tDCS). tDCS as a tool aims to induce prolonged neuronal excitability and activity alterations in the human brain via alterations of the neuronal membrane potential and results in prolonged synaptic efficacy changes. Apart from its impressive persistent excitability effects, it is a non-invasive method and can be applied painlessly. Most likely that up- or downregulation of different cortical areas by tDCS will open a new branch in the area of visual psychophysics.