Contralateral Forepaw Stimulation Research Articles

The biological effect of contralateral forepaw stimulation in rat focal cerebral ischemia: a multispectral optical imaging study

Our group has already published the possible neuroprotective effect of contralateral forepaw stimulation in temporary focal ischemia in a study. However, the background is still unclear. In the present study we investigated the possible mechanism by monitoring focal ischemia with multispectral [laser speckle, imaging of intrinsic signals (OIS)] imaging. Sprague–Dawley rats were prepared using 1.2% isoflurane anesthesia. The middle cerebral artery was occluded by photothrombosis (4 mW) and the common carotid artery was ligated permanently. Physiological variables were constantly monitored during the experiment. A 6 × 6 mm area centered 3 mm posterior and 4 mm lateral to Bregma was thinned for laser speckle and OIS imaging. Nine circular regions of interests (0.3 mm in diameter) were evenly spaced on the speckle contrast image for the analysis of peri-infarct flow transients, blood flow, and metabolic changes. Both the sham (n = 7) and forepaw-stimulated animals (n = 7) underwent neurological examinations 24 h after ischemia at which point all animals were sacrificed and the infarct size was determined by triphenyltetrazolium chloride. The physiological variables were in normal range and the experimental protocol did not cause significant differences between groups. Both the neurological scores (sham: 3.6 ± 1.7, stimulated: 4.3 ± 1.4) and the infarct volume (sham: 124 ± 39 mm3, stimulated: 147 ± 47 mm3) did not show significant differences between groups. The forepaw stimulation did not increase the intra-ischemic flow neither over the penumbral or the peri-ischemic area. However, the hemoglobin transients related metabolic load (CMRO2) was significantly lower (p < 0.001) while the averaged number of hyperemic flow transients were significantly (p = 0.013) higher in the forepaw (sham: 3.5 ± 2.2, stimulated: 7.0 ± 2.3) stimulated animals.

Brain activity affects dynamic but not static autoregulation

A close correlation between neuronal activity and cerebral blood flow was documented (activation-flow coupling). The matter of an activity-related effect on autoregulation remains elusive. We modulated cortical activity by GABAergic inhibition in 10 pre-anestesized rats and compared effects on activation-flow coupling and autoregulation. Contralateral forepaw stimulation was used to assess activation-flow coupling. Somatosensory potentials as well as local flow velocity responses were recorded with surface electrodes and laser-Doppler flowmetry. Performing intermittent carotid compression we calculated from the laser-Doppler data the transient hyperemic response ratio as a parameter of dynamic cerebral autoregulation. Recovery of cerebral perfusion at the end of the compression phase served as an index of static autoregulation. Tests were performed at baseline and after four successive doses of midazolam (0.5 mg/kg), applied at 30 min intervals. Reversibility of the changes was evaluated by application of flumazenil (0.2 mg/kg). Resting flow velocity levels (162 ± 52 vs. 110 ± 62 U; p < 0.001), evoked potentials (N2-P1-amplitude; 13 ± 4 vs.6 ± 3 μV; p < 0.005), and resultant flow velocity responses (28 ± 12 vs. 4 ± 3%; p < 0.0001) decreased after the first dose of midazolam and then remained stable. A dose-dependent decrease was found for the transient hyperemic response ratio (28 ± 13 to 22 ± 14 to 15 ± 10 ( p < 0.05) to 9 ± 5% ( p < 0.025)) but not static autoregulation. After antagonism, all changes were reversible. Dynamic but not static cerebral autoregulation depends from neuronal activity and thus metabolic demand of neurons.

Neuron-to-astrocyte signaling is central to the dynamic control of brain microcirculation.

The cellular mechanisms underlying functional hyperemia--the coupling of neuronal activation to cerebral blood vessel responses--are not yet known. Here we show in rat cortical slices that the dilation of arterioles triggered by neuronal activity is dependent on glutamate-mediated [Ca(2+)](i) oscillations in astrocytes. Inhibition of these Ca(2+) responses resulted in the impairment of activity-dependent vasodilation, whereas selective activation--by patch pipette--of single astrocytes that were in contact with arterioles triggered vessel relaxation. We also found that a cyclooxygenase product is centrally involved in this astrocyte-mediated control of arterioles. In vivo blockade of glutamate-mediated [Ca(2+)](i) elevations in astrocytes reduced the blood flow increase in the somatosensory cortex during contralateral forepaw stimulation. Taken together, our findings show that neuron-to-astrocyte signaling is a key mechanism in functional hyperemia.

Effects of DSP4 and dizolcipine on connectivity of solid E19 cortical grafts to ablated SmI region of adult rats; an in vivo electrophysiological study

The functional connectivity of an embryonic graft implanted into the lesioned somatosensory cortex and the effect of DSP4 (a selective noradrenergic neurotoxin to noradrenergic terminals) and dizolcipine (a non-competitive NMDA receptor antagonist), was studied electrophysiologically. The forepaw representational area of the rat primary somatosensory cortex was lesioned unilaterally and, 3–4 weeks later, tissue from the same region of E19 rat embryos was implanted into the cavity. At 7–9 months later, the rats were anaesthetized and single unit activity was recorded from the grafts in response to contralateral forepaw, ipsilateral hindpaw and contralateral hindpaw stimulation and compared with that obtained in control rats, in rats pretreated with dizolcipine immediately after lesioning and in rats given DSP4 24 h before transplantation. Neurones within the graft were integrated into the host brain and developed a pattern of representation similar to that of intact rats, but with a reduced proportion of neurones exhibiting short-latency response to contralateral forepaw stimulation and an increased proportion responding to stimulation of more than one paw. Pretreatment with dizolcipine did not increase short-latency responses to stimulation of contralateral forepaw stimulation however pretreatment with DSP4 reduced such responses and increased proportion of inhibitory responses. It was concluded that the noardrenergic system plays an important role in establishing host–graft connectivity. The importance of further pharmacological studies on host–graft connectivity and the relation of such connections to neural plasticity were discussed.

Sensory nerve crush and regeneration and the receptive fields and response properties of neurons in the primary somatosensory cerebral cortex of cats

Extracellular recordings were made of activity evoked in neurons of the forepaw focus of somatosensory cerebral cortex by electrical stimulation of each paw in control cats and cats that had undergone crush injury of all cutaneous sensory nerves to the contralateral forepaw 31 to 63 days previously. Neurons responding only to stimulation of the contralateral forepaw were classified as sa; neurons responding to stimulation of both forepaws were classified as sb; neurons responding to stimulation of both contralateral paws were classified as sc; and neurons responding to stimulation of at least three paws were classified as m. The ratio sa: sb: sc: m neurons was 46:3:0:0 in control cats and 104:15:3:26 in cats that had undergone nerve crush 1–2 months prior to study. sa neurons from experimental cats had depth distributions similar to those in controls and responded to contralateral forepaw stimulation with more spikes per discharge, longer latency, and higher threshold than sa neurons in control cats. m neurons from experimental cats were distributed deeper in the cortex than sa neurons, and, when compared to experimental sa neurons, they responded with longer latency and poorer frequency-following ability; however, the number of spikes per discharge and threshold were not significantly different. The appearance of wide-field neurons in this tissue may be explained in terms of strengthening of previously subthreshold inputs to neurons in the somatosensory system. If the neurons in sensory cortex play a requisite role in cutaneous sensations and if changes similar to those reported here occur and persist in human cortex after nerve crush, then “complete” recovery of sensation in such patients may occur against a background of changed cortical neuronal responsiveness.

The effects of focal epileptic activity on the somatosensory evoked potentials in the rat.

The cortical somatosensory evoked potential (SEP) of the rat, evoked by contralateral forepaw stimulation, consisted of early (P 1 and N 1) and the late components (P 2 and N 2). Microelectrode recording yielded evoked unitary responses of short latencies in the range of the early components and responses of longer latencies in the range of P 2. During the development of focal epilepsy after topical application of penicillin, the late components of SEP were enhanced and the enhanced late negativity corresponded to a surface negative cortical spike. The prominent enlargement of later components was associated with prolonged, often recurrent discharges of long latency unitary responses and with enlarged local field potentials. Early components of SEP remained relatively unaffected and so did unitary responses with short latencies. Epileptic spike-conditioned SEPs in the cuneate nucleus, thalamic sensory relay nucleus and sensory cortex were depressed from 100 ns (cuneate nucleus) to about 300 ms (thalamus and cortex) subsequent to spike discharge. Transmission in the cuneate nucleus was least affected. Thalamic and cortical early components of SEP had similar time courses of recovery, which differed markedly from hat of cortical late components. Our findings suggest that two different neuronal activities generate different components of SEP and are differentially involved in the epileptic activities, which results in the different amplitude recovery following spontaneous epileptic spike discharges.

Effects of topical application of diphenylhydantoin on gross evoked responses and single-neuron activity in pericruciate and precoronal cerebral cortex of the domestic cat

Surface gross potentials and extracellular single-neuron responses evoked by stimulation of each of the four paws were recorded in the forepaw region of precoronal (field 3b), postcruciate, and precruciate (both field 4γ) tissues before and after topical application of diphenylhydantoin (DPH) to the surface recording site. When applied in crystalline form in any but the most minute amount, spreading cortical depression was induced. When applied in saline solution at 1 to 2 mg/ml, the primary gross response evoked by contralateral forepaw stimulation was markedly enhanced at the site of application, whatever the site. Occasionally, the primary response amplitude was briefly reduced, but it recovered within 2 min and then became enhanced for 15 to 90 min. By analogy with the “strychnine spike,” this greatly enhanced response is termed a “DPH spike.” At both pericruciate sites, DPH spikes developed from the small surface responses evoked by stimulation of the “off-focus” paws (ipsilateral forepaw and the two hind paws), as well as from the primary response evoked by contralateral forepaw stimulation. Single-neuron responsiveness to contralateral forepaw stimulation increased gradually as the DPH spike increased, and decreased as it decreased. Some neurons became responsive to off-focus paw stimulation when off-focus DPH spikes appeared. At the precoronal site, no off-focus DPH spikes appeared and no off-focus responsiveness developed on single neurons. In a few instances, an increase in the number of unit spikes per discharge occurred only during the first few responses to a 1 s iterative stimulus train, the responses returning to the pretreatment condition for the remainder of the stimulus train. Reinstituting the 1 s stimulus train after 5 to 10 min rest produced a similar transient enhancement of the neuron response. Thus, at a critical local concentration, this clinically anticonvulsant drug enhances the responsiveness of cerebral cortex to afferent input. Except for the transient enhancement of responsiveness seen on a few neurons, the effect is similar to, but weaker than, that produced by topical strychnine or bicuculline.

Wide-field conditioning effects on small-field neurons in the posterior sigmoid gyrus of domestic cats

Single neurons were isolated in four different recording sites in sensorimotor cortex of the domestic cat, all sites being topographically related to the contralateral forepaw. Conditioning-testing interactions were made on 409 small-field neurons, the testing input being the contralateral forepaw (also the ipsilateral forepaw in the case of bilateral-field neurons) and the conditioning input being any paw that was ineffective in exciting the neuron. About 29% of the neurons showed inhibitory interactions and 23% showed facilitatory interactions. Of these, about 5.5% showed both effects, according to the conditioning site. Nearly 54% of the neurons failed to show any interaction effects. Most of the latter were isolated in the two posterior recording sites, located in somatosensory area I; the interaction effects were found predominantly in the two anterior recording sites, located in agranular tissue. Neurons that responded only to contralateral forepaw stimulation ( sa neurons) and showed facilitatory interactions from the other three paws had response properties characteristic of neurons that respond to all four paws ( m neurons). The sa neurons that showed inhibitory interactions from the other three paws did not differ significantly in response properties from those that showed no interaction effects. These findings are relevant to current criteria for the classification of sensorimotor cortex neurons and lead to remarks on the possible thalamic routes that mediate the interaction effects.

Effects of topical bicuculline on primary evoked responses in pericruciate and precoronal cortex of the domestic cat

The effects of topical application of bicuculline crystals to the anterior and posterior sigmoid gyri of the cerebral cortex were examined, using surface gross potential and single-neuron recording. Recordings were taken at the forepaw foci of precoronal tissue in field 3b, postcruciate tissue in field 4γ and precruciate tissue in field 4γ. Bicuculline enhanced the amplitude of the primary response evoked by contralateral forepaw stimulation an average of 400% in precoronal tissue, 250% in postcruciate tissue, and 200% in precruciate tissue. The effect built up over a 30- to 45-min period, maintained that state for 2 to 3 hr and then gradually disappeared, lasting a total of 5 to 6 hr. When spontaneous bicuculline spikes appeared, an event of similar configuration could be evoked in pericruciate tissue, usually with a variable latency, following stimulation of any off-focus paw. Single-neuron discharges that occurred during the surface-recorded bicuculline spikes were clearly enhanced. Iterative stimulation at 3/sec resulted in the bicuculline effect occurring only on alternate trials, the gross potential configuration and amplitude returning to the pretreatment control condition on the other alternate trials. Single-neuron discharge likewise alternated with the changing gross potentials. It is argued that bicuculline acts in a manner similar to strychnine, increasing the excitability of a process intermediate to, and/or independent of, the mechanism producing the postsynaptic potentials of the normal primary response. It is further argued that blockage of inhibition does not offer an adequate explanation of the observed effects.

Facilitatory and inhibitory modulation of wide-field neuron activity in postcruciate cerebral cortex of the domestic cat

A large sample of single neurons was gathered from the forepaw topographic focus in cytoarchitectonic field 4γ of the posterior sigmoid gyrus. Sufficient data were gathered on 596 m (wide-field) neurons to perform a quantitative analysis via the model of sa (small-field) neuron modulation of neighboring m neurons, with the aid of the property of coadunate behavior among the m neurons. A method is shown whereby the sign and magnitude of the net modulation can be calculated for each individual m neuron following stimulation of the contralateral forepaw. Using the coadunate property of m neurons to forecast an expected response latency for each individual m neuron following contralateral forepaw stimulation, the ratio of the observed to expected response latencies is then used to order the m neurons along an excitability modulation axis. This ordering is shown to impose a high degree of order onto all other measured neuron response properties, in a manner consistent with the idea of facilitatory and inhibitory modulation by local sa neurons. The tenability of the model is thereby enhanced.

Intracortical transmission of specific evoked activity across the cerebral cortex

The intracortical transmission of abnormally generated activity, like spreading depression and the direct cortical response, across the cortex is well known. In the experiments described here, the tangential transmission of a more normal type of cortical activity, the short latency response evoked by contralateral forepaw stimulation, was investigated. No evidence for tangential transmission was found from surface recordings. Various methods, such as passing polarizing currents, intravenous injection and topical application of strychnine, were used to alter the state of cortical excitation in order to induce a change in tangential transmission; none was found. The boundaries of the contralateral forepaw receiving area (CRA) appeared to be rigid, since the responses could not be induced beyond the perimeter by these manipulations of the cortex. Evoked responses in the centre of the CRA were shown to be unaffected by the excitation state of the cortex 2 mm or more away. The data support the hypothesis that the neural activity represented by the short latency surface evoked response is not transmitted laterally across the cortex and does not appear to be influenced by activity, beyond a range of about 2 mm or possibly less. The effectiveness of the methods used to alter cortical excitation, and to detect a spread of the evoked activity are discussed.

Effect of strychnine on single neurons of the pericruciate cerebral cortex

The effects of topically applied strychnine sulfate on cerebral neurons were investigated in chloralose-anesthetized, paralyzed cats. Single neurons in both the postcruciate and precruciate forepaw foci were recorded before and after strychnine application. Direct effects on sa neurons in postcruciate and sa and sb neurons in precruciate cortex included an increase in the frequency and duration of discharge and a decrease in threshold to skin stimulation, whereas response latency remained unchanged. All postcruciate m neurons and some precruciate m neurons increased their discharge in response to contralateral forepaw stimulation, without changing their discharges to stimulation of the other paws. This implies an indirect effect of strychnine through the known facilitation from sa neurons. On the other hand, the discharges of many precruciate m neurons to stimulation of each of the four paws increased and response thresholds decreased after strychnine application, undoubtedly due to the direct action of the alkaloid. The effects of topically applied strychnine appear within 1 min, peak 7–14 min later, plateau for 10–20 min and then slowly subside. Possible reasons for the difference between postcruciate and precruciate cortex are discussed. Strychnine action ascribable entirely to alteration in hyperpolarizing responses is ruled out, and possible alternative mechanisms are discussed.

Population and modality characteristics of neurons in the coronal region of somatosensory area I of the cat

By extracellular microelectrode techniques, neurons were isolated within the forepaw receiving area of primary somatosensory area I of the cat, just medial to the caudal end of the coronal sulcus. The response properties of 278 neurons were studied from several aspects, including: (a) modality specificity; (b) location and extent of receptive field; (c) responsiveness to direct electrical stimulation of the skin; (d) ability to follow iterative electrical stimulation; and (e) locus of isolation within the cortical tissue. Eighty-two per cent of the neurons responded to touch but not hair stimulation; only 6% were classed as hair sensitive. The receptive fields were uniformly small, the largest identified being 8 cm 2, and were located mainly on the distal parts of the forelimb. All these neurons responded to electrical stimulation of the skin, and all tested responded to direct electrical stimulation of the cuneate nucleus. A population analysis revealed that the greatest amount of neuron activity following stimulation of the contralateral forepaw occurred 0.6–0.9 mm below the pial surface, 11–13 msec after the stimulus. The population pattern of response to direct stimulation of the cuneate nucleus was identical to that following contralateral forepaw stimulation—merely shifted 5.2 msec earlier in time. The positive phase of the surface recorded primary evoked response occurred during this peak activity. It is concluded that the afferent input to this region of the cortex comes entirely by way of the dorsal column-medial lemniscus system, for no other afferent influence was found necessary to explain the response pattern. The population response pattern is compared with that from the postcruciate cortex and found to be strikingly different. However, the coronal neuron population displayed an affinity to one particular subset of neurons isolated in more rostral and medial cortex.

Response properties of neurons in the pericruciate cortex of the cat following electrical stimulation of the appendages

In chloralose-anesthetized cats activity was recorded extracellularly from single neurons isolated in two circumscribed regions of the anterior cerebral hemisphere, one just rostral and the other just caudal to the lateral tip of the cruciate sulcus. Each neuron was classed as either PT or non-PT, depending upon whether or not its axon coursed through the medullary pyramids. The discharge patterns of each neuron were measured following electrical stimulation of the central footpad of each appendage. If the neuron responded to contralateral forepaw stimulation but failed to respond to stimulation of any other appendage, it was classed as an s neuron; if it responded to stimulation of the contralateral forepaw and at least one other appendage, it was classed as an m neuron. PT, s neurons constituted a negligible fraction of the total sample. Both the depth within the cortex and the temporal pattern of discharge of non-PT, s neurons differed markedly from that of m neurons. PT, m and non-PT, m neurons were identical in behavior and are believed to have similar functional significance. The population response of m neurons to stimulation of the ipsilateral forepaw was the same as that following stimulation of the contralateral forepaw—merely delayed a few milliseconds. It is thus concluded that the non-PT, s neurons, which discharge before m neurons, do not drive the m neurons. The s neurons, which do not follow as high input frequencies as do m neurons, are thought to be a functionally distinct population of neurons which inhabits the external granular layers of the cortex. Their activity is closely associated with the surface positive phase of the concomitant primary evoked response. It is suggested on the basis of these experiments that the cortical input is directly linked to the cortical output.