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PubMedDate not supplied

Correlational association between changes in cell excitability and synaptic efficiency during posttetanic reorganizations in the cortex.

A positive linear association between the posttetanic changes in synaptic efficiency and the shifts in the cellular excitability observed at the same time was established using the method of calculation of the coefficient of correlation (CC) between the changes in the direct and synaptic components of the response of the pyramidal tract. The CC values found at the initial stages of the formation of the trace process decrease with time, and a significant correlational association between the changes in the components is absent by an hour after the tetanic stimulation. Such temporal specificity in the contingency of the mechanisms studied presupposes at a certain stage in the organization of the trace a communality of intracellular molecular substrate which determines the manifestation of these mechanisms. Correlation analysis carried out suggests that cortical plasticity is a complex dynamic system, the understanding of which requires not only the elucidation of the elementary cellular mechanisms forming it, but the study of the character of the interaction between them as well.

Animals↗

PubMed1980

Thyrotropin-releasing hormone has multiple actions in cortex.

The responses to application of TRH were examined on 38 identified neurons in sensory motor cortex of cat. Two pyramidal tract (PT) and 3 nonpyramidal tract (NPT) neurons were directly excited by TRH. Two other NPT neurons were inhibited by TRH. TRH potentiated the excitatory action of ACh on 4 of 12 PT neurons and 1 of 2 unidentified cells. None of these neurons showed a direct effect of TRH. TRH did not potentiate the response to Glu on 12 cells tested, even when the same cell showed TRH modulation of the ACh response. None of the NPT cells examined showed TRH modulation of the excitatory ACh response. These results demonstrate that TRH has multiple actions in mammalian cerebral cortex, but that these actions, such as the modulation of the ACh responses, appear to exist on discrete populations of neurons.

Acetylcholine↗

PubMed1983

Cortical motor neuron activity in the cat during classical conditioning with central stimulation as the CS and the US.

The neuronal basis of associative conditioning in the cat was investigated by pairing stimulation of thalamocortical pathways as the conditioned stimulus (CS) with antidromic activation of pericruciate pyramidal tract (PT) cells as the unconditioned stimulus in a differential classical conditioning paradigm. Contrary to expectations, based both on the available literature and on theoretical considerations (i.e., a pairing or activation hypothesis), thalamic stimulation was not an effective CS. The response of PT cells to thalamic stimulation did not change as a function of reinforcement with PT stimulation. These results led to a reconsideration of the hypothesis that the simple pairing of any two neural events is the essential mechanism underlying associative conditioning changes. The results did suggest that the combined activation of specific and nonspecific thalamic nuclei may be important in producing increases in responsiveness of PT neurons.

Animals↗

PubMedDate not supplied

[Correlation between the amplitude of action potentials and the rate of conduction along axons of the output cells of the sensomotor cortex].

Antidromic responses of neighbouring neurones in micro-areas of the sensorimotor cortex to the stimulation of fibers of the pyramidal tract as well as of the red nucleus and thalamic nuclei VPL and MGB, were studied in acute experiments on unanesthetized immobilized cats. Depending on the velocity of conduction along the axon, the neurones of all the categories were divided into fast and slow cells. When examining the two neuronal groups most differing in AP amplitude (N1 and N3), it was found that N1 neurones were mainly fast-conducting and N3 neurones-- slow-conducting. The conclusion is made that at multineuronal recording, each of the examined categories of the output neurones is characterized by positive correlation between AP amplitude and the axon conduction velocity and consequently, the size of the cell.

Animals↗

PubMed1983

Effects of neuropeptides on rat cortical neurons: laminar distribution and interaction with the effect of acetylcholine.

The effects of the microiontophoretic application of five different peptides (cholecystokinin octapeptide sulfated form, cholecystokinin octapeptide non-sulfated form, vasoactive intestinal polypeptide, angiotensin-II and substance P) on cortical neurons were studied in rats anaesthetized with urethane. Vertical electrode penetrations were made in the first somatic sensory cortex and the laminar position of the neurons determined by the reconstruction of the tracks based on extracellular dye deposits. The first type of effect observed was an excitation of some cortical neurons. These neurons were mostly found in infragranular layers, specially in layer Vb. Pyramidal tract neurons were more often excited by peptides than the cortical population taken as a whole. Substance P excited the largest percentage of neurons, followed by vasoactive intestinal polypeptide and cholecystokinin octapeptide sulfated form, whereas angiotensin II and cholecystokinin octapeptide non-sulfated form were the least potent in terms of frequency of neurons excited as well as of amplitude of the responses. The vast majority of the neurons excited by a peptide could also be excited by acetylcholine. A second and independent effect of peptides was observed: the neuronal excitation induced by acetylcholine could be depressed by the simultaneous application of peptide. This depressing effect was also the most frequently observed with substance P, followed by cholecystokinin and vasoactive intestinal polypeptide.

Acetylcholine↗

PubMed1979

Operant control of precentral neurons in monkeys: evidence against open loop control.

Four normal monkeys were operantly conditioned to change the firing pattern of 111 precentral neurons from phasic to tonic using an operant paradigm which quantifies the control of single neurons. Two monkeys then had their contralateral pyramidal tract (PT) sectioned and one monkey had C5-7 ventral rhizotomies. Postlesion data were: (1) contralateral C1-2PT lesions did not encumber the monkeys' control of precentral PTNs: (2) contralateral C5-7 ventral rhizotomies completely abolished accurate control of precentral neurons which received proprioceptive feedback from flaccid arm regions. These results indicate that precentral neurons are operantly controlled through proprioceptive feedback from peripheral mechanoreceptors. The output of the mechanoreceptors is probably dependent upon discrete joint angles and/or muscle tension which is maintained through non-PT pathways. These data do not support the concept that precentral neurons are operantly controlled directly from a central; 'open loop', pathway.

Animals↗

PubMedDate not supplied

The correlation between changes in synaptic efficiency and cellular excitability during the development of a conditioned reflex analog.

The calculation of the coefficient of correlation between changes in the direct (D) and monosynaptic (I) components of the pyramidal tract (PT) response made it possible to establish the presence of a positive linear association between conditioned reflex changes in synaptic efficiency and the shifts in cellular excitability observed at the same time. The coincidence of the maximal strength of this association with the greatest increase in cellular excitability which is dependent on the activation of motivatiogenic structures points to the role of these subcortical structures in the launching of intracellular reactions which leads to the formation of the overall molecular substrate which underlies interaction of membrane and synaptic mechanisms. The preceding of the greatest enhancement of synaptic efficiency by the maximal manifestation of the interaction attests to the contribution of this process to the manifestation of the principal mechanism of the conditioned reflex (CR).

Animals↗

PubMed1986

[Self-sustaining rhythmic activity of the "peak-wave" type and responses of neuronal and glial cells of the sensomotor cortex of the cat].

In acute unanesthetized immobilized cats a sequence of fast hyperpolarization and long-lasting depolarization was found in pyramidal tract neurons of the sensorimotor cortex during tetanic stimulation (8-14/s for 10 s) of the ventro-postero-lateral nucleus of the thalamus. During long-lasting depolarization after cessation of stimulation self-sustained rhythmic paroxysmal depolarizing membrane potential shifts appeared which were terminated by long-lasting hyperpolarization. In glial cells only depolarization was observed during stimulation as well as during self-sustained "spike-and-wave" rhythmic activity. Hyperpolarization in glial cells appeared only after its termination in neurons. It is suggested that the long-lasting changes in the membrane potential of cortical elements may play a particular role in formation and cessation of "spike-and-wave" rhythmical activity.

Animals↗

PubMed1998

Ontogenesis of the sperm whale brain.

The development of the sperm whale brain (Physeter macrocephalus) was investigated in 12 embryos and early fetuses to obtain a better understanding of the morphological and physiological adaptations in this most exotic cetacean concerning locomotion, deep diving, and orientation. In male adult sperm whales, the average absolute brain mass and the relative size of the telencephalic hemisphere are the largest within the mammalia, whereas the ratio of the brain mass to the total body mass is one of the smallest. In the early sperm whale fetus, the rostral part of the olfactory system (olfactory nerves and bulbs) is lost, whereas the nervus terminalis seems to persist. Several components of the limbic system show signs of regression (hippocampus, fornix, mamillary body). In contrast, some components of the auditory system (trapezoid body, inferior colliculus) show marked enlargement in the early fetal period, thereby reflecting their dominant position in the adult. The cerebellum and pons grow slower than in most smaller toothed whales. The pyramidal tract develops poorly (reduction of the limbs), whereas marked growth of the striatum and inferior olive may be related to the animal's locomotion via trunk and tail. In the early fetal period, the trigeminal, vestibulocochlear, and facial nerves are the dominant cranial nerves (besides the vagus nerve). Whereas the number of axons in the vestibulocochlear nerve is high in adult, toothed whales and their diameters are considerable, the trigeminal nerve of the sperm whale may be the thickest of all cranial nerves and has the largest number of axons (innervation of the huge forehead region). A similar situation seems to exist for the facial nerve: It innervates the blowhole musculature that surrounds the very large spermaceti organ and melon (generation and emission of sonar clicks).

Animals↗

PubMedDate not supplied

[Duration of trace processes in the neocortex of rabbits].

Changes of pyramidal tract (PT) response after short tetanization, similar to natural stimulation conditions, were analysed in unanaesthetized and nonimmobilized rabbits. PT response recording revealed a long-term (1 h and more) potentiation of monosynaptic neocortical reactions. Predominant better expressed and more preserved increase of synaptic (N) component provides evidence to the conjecture that the basic mechanism of the long-term potentiation consists in the rise of efficiency of excitatory synaptic connections. Less protracted and differently directed changes of D-component permit to consider that excitability change of neurones may be only an additional mechanism of the long-term potentiation. Such features of neocortical long-term potentiation were revealed as its low-frequency depression (at test stimuli repetition) and its spontaneous restoration after depression.

Animals↗

PubMed1989

[An increase in the excitability of the cortical neurons during reinforcing stimulation of the lateral hypothalamus].

Pyramidal tract response (PTR) was recorded from unanaesthetized rabbits. The following three experimental paradigms were used which imitated behavioural conditioning procedures: pairing of direct stimulation of two cortical points; similar pairing conjoint with stimulation of additional reinforcing the lateral hypothalamus (LH); LH stimulation in response to increased PTR in a manner similar to instrumental conditioning procedure. An increase in the monosynaptic wave was the most common result for all three paradigms. The direct wave increase was significantly larger for the second and third experimental paradigms in comparison with the first one. In general the data obtained suggest that an increase in the synaptic efficacy is the major mechanism of behavioural conditioning, while changes in the membrane excitability reflect a participation of motivational components of reinforcement resulted from the LH activation.

Animals↗

PubMed1981

Corticospinal and corticorubral projections from the supplementary motor area in the monkey.

Neurons that were antidromically invaded from either pyramidal tract (PT) stimulation or red nucleus (RN) stimulation were studied in the anterior portion of the supplementary motor cortex of anaesthetized rhesus monkeys. The conduction velocity of 58 PT neurons ranged from 11 to 63 m/sec while those of the 29 RN neurons ranged from 10 to 38 m/sec. None of the neurons were found to be antidromically invaded from both stimulation sites. Thus, the corticorubral projection from the SMA does not appear to consist primarily of PT axon collaterals. There appeared to be a trend towards spatial segregation of the PT and RN neurons in the monkey cortex, the RN neurons tended to be located nearer the pial surface than the PT neurons, which tend to have somata nearer the subcortical white matter.

Animals↗

PubMed1989

Claustral influence on ipsi- and contralateral motor cortical areas, in the cat.

The electrophysiological relationships between the claustrum and the contralateral motor areas of the cerebral cortex were studied in anaesthetized cats. The extracellular unitary activity of 207 pyramidal tract neurons (PTNs) was recorded from area 4 (125 cells) and area 6 (82 cells). Single shock activation of the contralateral claustrum affected 26% of the total tested PTNs, causing long lasting inhibition (44 PTNs) or long lasting inhibition preceded by early excitation (10 PTNs). Forty-three neurons of the 54 were also influenced by ipsilateral claustrum stimulation. Surgical removal of motor and insular cortices ipsilateral to the stimulated claustrum did not modify claustrum inhibition on contralateral PTNs, whereas section of the corpus callosum abolished this effect, suggesting the existence of a direct claustro-contralateral motor cortex pathway passing through the corpus callosum. These results support the hypothesis that the claustrum may exert a bilateral control on motor coordination.

Animals↗

PubMed1998

[Induction of rhythmical activity in digastric muscles in an in vitro brainstem preparation from adult mice].

In this study, it was attempted to induce masticatory movements in an in vitro brainstem-spinal cord preparation isolated together with the orofacial structure from adult mice. The preparation was perfused intra-arterially with an artificial cerebrospinal fluid (ACSF) containing dextran through a cannula fixed to the descending aorta, and was placed in a bath perfused with the ACSF. Repetitive electrical stimulation of the medullary pyramidal tract (MPT) induced rhythmic EMG activities in the digastric muscle (3.8-7.2 Hz). Bath and intra-arterial application of kynurenic acid (KYN) or D, L-2-amino-5-phosphonovaleric acid (APV) suppressed the rhythm. During application of KYN, the rhythmic EMG activity in the digastric muscle could not be induced, even though the intensity of stimulation was raised. On the other hand, during application of APV, stimulation at a higher intensity induced rhythmic EMG activities with a lower frequency and a smaller amplitude. The results showed that glutamate is involved in induction of the rhythmic EMG activities by stimulation of the MPT, and that excitatory effects via the N-methyl-D-aspaltic acid receptor is not indispensable for its induction.

2-Amino-5-phosphonovalerate↗

PubMed1995

Fronto-parietal control of electrodermal activity in the cat.

The aim of this work was to investigate the direct involvement of the fronto-parietal cortex in the control of spinal autonomic centers eliciting electrodermal activity (EDA). This autonomic response, linked with the activity of sweat glands, was recorded as skin potential responses (SPRs) from forepaws in the cat. Animals were paralyzed by gallamine and SPRs were obtained under halothane anaesthesia. For each animal, a transection of the medulla sparing only pyramidal tracts was carried out. SPRs were elicited by direct electrical stimulation of pericruciate and posterior parietal cortical areas before and after such a transection. Results showed that in intact preparations, stimulation of the pericruciate cortex evoked SPRs at lower thresholds than the posterior parietal cortex. After the bulbar transection, only the stimulation of pericruciate areas still elicited SPRs at low intensities. Results are interpreted as indicating that fronto-parietal control of EDA is probably mediated by a double descending system: one involving corticoreticulospinal pathways and a direct corticospinal one. We hypothesized that the somatic motor cortex initiates descending programs to autonomic centers at bulbar and spinal levels, and that these centers are involved in autonomic adjustments to somatomotor movements.

Anesthesia↗

PubMed1979

[Impulse reactions of cortico-spinal neurons to stimulation of the lateral hypothalamus].

In anesthetized cats, evoked responses of pyramidal tract (PT) cells to lateral hypothalamus (LH) stimulation were studied in pericruciate cortex. The PT cells responded to hypothalamic stimulation with latencies ranging from 1.6 to 52.5 msec and were situated between 0.75 and 2.5 mm below the pial surface. Orthodromic spikes of PT neurons occurred more readily during stimulation of caudal part of the LH. PT neurons activated by the LH stimulation were also tested with electro-skin stimulation of limbs: 75% of the neurons responded to stimulation of several limbs and had large bilateral receptive fields, 15%--to one contralateral limb stimulation and had small contralateral receptive fields. The time of involvement of PT cells in the responses to hypothalamic or somesthetic signal had no correlation with the type of these neurons according to their axonal conduction velocity.

Animals↗

PubMed1975

Input-output relations of the red nucleus in the cat.

In unanesthetized cats, microstimulation within the red nucleus produces contraction of single muscles of the contralateral limbs and face. Separate zones may activate different muscles. Forelimb muscles were primarily activated from areas in the dorsomedial quadrants of the red nucleus whereas hindlimb muscles were predominantly activated from the ventorlateral quadrants. With stimulus currents of 10 muA there was considerable overlap in the effective zones activating different muscles. In the majority of cases the minimal threshold was under 10 muA when stimilating with a 50-msec pulse train. Current thresholds for electromypgraphic changes in the muscles varied inversely with pulse frequency and train duration. When long stimulus trains were applied to the red nucleus, the resulting muscle contraction was sustained for the duration of the stimulus. These motor effects did not depend upon the motor cortex or pyramidal tract but were mediated by a tract in contralateral dorsal quadrants of the spinal cord which was likely to be the rubrospinal tract. Units within the red nucleus typically had wide cutaneous receptive fields and responded to deep pressure and joint rotation in one or more limbs. Usually the focus driving the cell most briskly was located in one of the contralateral limbs and corresponded to the limb where muscle contraction was elicited by microstimulation with the same electrode. It is concluded that the red nucleus includes overlapping efferent neuronal colonies controlling individual muscles irrespective of their functional class. This property is shared by the motor cortex and suggests that these two structures may complement each other in the control of movement. The more diffuse activation of rubral than cortical neurons by natural stimuli suggests that rubral activity may not be as tightly linked as that of the motor cortex to specific peripheral input.

Animals↗

PubMed1987

Application of autoradiographic analysis of 2-deoxyglucose in the study of locomotion.

Trace amounts of [14C]2-deoxyglucose (2-DG) were used to detect regions of the brainstem involved in forelimb stepping in thalamic and low spinal cats. Under ether anesthesia, cats were transected at the stereotaxic A12 level and T10 segment. Two hours later, 50 microCi/kg of 2-DG was infused i.v. and one of 4 procedures was followed: 3 cats stepped on a motor-drive treadmill (Stepping), 3 were kept in a stationary standing position (Rigidity), 2 were anesthetized with sodium pentobarbital (Anesthetized), and 2 were stimulated in the mesencephalic locomotor region (MLR-induced). Absolute optical densities of the autoradiograms corresponding to identified anatomical structures of the brainstem were generally in the following order: Stepping greater than Anesthetized greater than MLR-induced greater than Rigidity. The 2-DG uptake relative to the pyramidal tract (2-DG ratio) also was compared for each of the 4 experimental procedures. In the Stepping cats, the 2-DG ratio was highest in the vestibular nuclei, periaqueductal gray, red nucleus and thalamic nuclei. In the Rigid cats, the 2-DG ratio was highest in the medial vestibular nucleus and subthalamic and thalamic nucleus. These findings suggest that the 2-DG tracer method can be useful in associating neural structures with specific kinds of motor functions within a cat. This is particularly true when using the relative activities of different neural structures and in comparing specific neural structures across cats under different experimental conditions when the amount of 2-DG infused is standardized and the optical densities of the autoradiograms are calibrated to a specific level of 2-DG.

Animals↗