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PubMed1994

Isoflurane inhibits calcium currents in neocortical neurons.

We used voltage-clamp techniques to assess the effects of isoflurane anaesthesia in slices of sensorimotor cortex of guinea pigs and neonatal rats. Isoflurane (0.5-4%) depressed inward Ca(2+)-currents evoked by depolarizing commands from -50 mV. With additional blockade of K(+)-currents by internal Cs+, an early component of the sustained inward currents was a high voltage-activated current whereas the delayed component was an unclamped Ca(2+)-current; this was consistent with a simple compartmental model. Isoflurane decreased the magnitude of the high voltage-activated current.

Animals↗
PubMed1995

Direct measurement of fast axonal transport rates in corticospinal axons of the adult rat.

The bi-directional movement of proteins from the soma to the axon terminal is called axonal transport. Fast anterograde transport moves organelles and membrane-bound proteins distally. Fast transport rates were measured in corticospinal tract axons of male Sprague-Dawley rats by microinjection of tritiated proline into the sensorimotor cortex. Animals were killed after 3-5 h and the tract cut into 1 mm segments. A bimodal wave of radiolabeled proteins was evident, with the first peak at the spino-medullary junction and the second peak in cervical spinal segments. The fast transport rate was calculated at the leading edge of the distal wave, and found to be 303 +/- 44 mm/day.

Animals↗
PubMed1995

Analysis of neocortical grafts placed into focal ischemic lesions in adult rats.

This study investigated the viability of fetal neocortical block grafts transplanted into adult ischemic cortical lesions. Recipient rats sustained focal ischemic lesions by permanent occlusion of the middle cerebral artery 4-7 days prior to transplantation. Twenty days later, the animals were sacrificed and the brains examined using triphenyltetrazolium chloride, routine Nissl or acetylcholinesterase histochemistry. Ischemic infarctions were localized to the ipsilateral sensorimotor cortex and transplants were integrated with the host cerebral cortex or striatum. Cholinergic fibers were found crossing the host-transplant interface, presumably innervating the graft. This study demonstrates that fetal neocortical block grafts placed into adult focal ischemic lesions following permanent arterial occlusion can survive and establish connections with the host brain.

Acetylcholinesterase↗
PubMed1991

Short-latency excitatory postsynaptic potentials are evoked in primate spinothalamic tract neurons by corticospinal tract volleys.

The responses of 8 wide-dynamic-range (WDR) STT neurons to electrical stimulation of the sensorimotor cortex or the cerebral peduncle were recorded intracellularly in anesthetized monkeys. EPSPs and spikes were evoked in STT neurons with short latencies ranging from 0.4 to 5.3 msec after the corticospinal volley, indicating a monosynaptic connection in at least some STT neurons. Spatial and temporal summation seem necessary for the cortex to maintain an effective excitatory influence on STT neurons. It is postulated that the cortical facilitation of STT neurons helps them to acquire more nociceptive signals during behavioral tasks such as exploring a new object so that the brain can make decisions about whether to continue or to abandon a certain task. Possible implications for central pain states are discussed.

Animals↗
PubMed1995

Dextromethorphan suppresses both formalin-induced nociceptive behavior and the formalin-induced increase in spinal cord c-fos mRNA.

The injection of dilute formalin results in a stereotyped nociceptive behavioral response. Administration of dextromethorphan (s.c.) but not saline, 30 min prior to intraplantar formalin injection prevents this nociceptive response in a dose-dependent manner. In addition, intraplantar formalin reliably induces c-fos mRNA in the ipsilateral spinal dorsal horn as assessed with quantitative solution hybridization at 30 min postinjection. No change in c-fos mRNA was detected in the contralateral spinal dorsal horn, nucleus raphe magnus, periaqueductal grey, medial thalamus, or sensorimotor cortex. Pretreatment with dextromethorphan at 60 mg/kg s.c., 30 min prior to formalin resulted in a suppression of c-fos induction, so that c-fos mRNA levels in the ipsilateral spinal dorsal horn of animals receiving dextromethorphan prior to formalin did not differ from controls. These data indicate that dextromethorphan suppresses formalin nociceptive behavior and one of the biochemical consequences of formalin nociception, i.e., induction of c-fos mRNA.

Animals↗
PubMed1984

Neural substrates of two different rhythmical vibrissal movements in the rat.

Normal rats show two types of rhythmical vibrissal movement, one synchronized precisely with alpha waves (about 9 Hz) of the thalamocortical system, and the other often synchronized with theta waves (about 7 Hz) of the septohippocampal system. The alpha-synchronized vibrissal movements appear while the rat stands still with a slow respiratory pattern, and are of small amplitude (a fine tremor). The theta-synchronized vibrissal movements appear during exploratory sniffing behavior, and are of large amplitude. Thus, a group of facial motoneurons which constitute the final common pathway for vibrissal movement apparently receive input convergently from these two neural systems. In the present study, we observed the following: (1) the two types of movement rarely, if ever, appeared simultaneously and the same was true of the two brain wave patterns. Topographically, the predominant appearance of the alpha waves was in the frontal (sensorimotor) cortex, whereas that of the theta waves was in the occipital cortex and hippocampus. (2) Bilateral ablation of either the entire neocortex or just its anterior (but not posterior) half eliminated the vibrissal alpha-tremor movement while leaving vibrissal theta-sniffing movement normal. In anterior decorticate rats, the tremor movements started to recover by 1-4 months, and were abolished again by the removal of the remaining posterior cortex. (3) Lesions of the medial septum or the fornix eliminated hippocampal theta waves, but had no effect on vibrissal sniffing movement or alpha wave-vibrissal tremor. (4) Cerebellectomy and, to a lesser extent, pharmacological lesions of the inferior olive slowed, but did not block, alpha waves. In addition, vibrissal tremor movement became intermittent and less vigorous. The same manipulations, however, did not affect theta wave-vibrissal sniffing movement. (5) Harmaline (30 mg/kg, i.p.) did not induce alpha-tremor, which, in combination with the results with cerebellectomy and inferior olive lesions, indicates that alpha-tremor is generated by a neural mechanism that is different from that for harmaline-induced generalized tremor of 10 Hz. These findings confirmed that there exist two patterns of synchrony between vibrissal movement and rhythmical brain activity in the rat, i.e. alpha wave-vibrissal tremor movement and theta wave-vibrissal sniffing movement, and suggest that the two patterns reflect a rhythmical mode of functioning of two different neural systems, probably the thalamocortical and the septohippocampal system, respectively.

Animals↗
PubMed1987

Effects of altered visual input upon the development of the visual and somatosensory representations in the hamster's superior colliculus.

The right superior colliculus and right eye were ablated in hamsters within 12 h of birth and the visual and somatosensory representations in the remaining (left) superior colliculus were evaluated using standard single unit recording and receptive field mapping techniques when the animals reached adulthood (at least 3 months of age). In a number of the hamsters used for recording, injections of [3H]leucine were made into the left eye 6-10 days prior to the terminal experiment. This was done to insure that the neonatal lesions did, in fact, produce the extensive recrossing of retinal fibers demonstrated by others who have employed this preparation. All of the hamsters which received [3H]leucine injections prior to the recording experiment exhibited a markedly expanded ipsilateral retinocollicular projection and retinal axons which recrossed the midline at the level of the tectum. The recording experiments showed further that this projection resulted in a visual map which was generally mirror symmetric to that in normal hamsters. There were, however, numerous irregularities and discontinuities in this representation and, in a few hamsters, it appeared almost completely disorganized. There were also a number of abnormalities in the somatosensory representation in the deep tectal laminae of the neonatally brain damaged hamsters. There was a substantial increase in the number of cells with receptive fields that extended onto the ipsilateral side of the body, neurons with split receptive fields were recorded and there were changes in the magnification of different portions of the body surface. These alterations did not, however, change the organization of the somatosensory map in a manner which brought it into alignment with the visual representation in the superficial laminae. Nevertheless, additional recording experiments in animals subjected to enucleation of both eyes and ablation of the superficial laminae of one superior colliculus did indicate that the existence of the aberrant retinal projection was a necessary condition for the somatosensory abnormalities which we observed. Additional anterograde and retrograde tracing experiments demonstrated only one abnormality in the organization of the somatosensory afferent input to the remaining colliculus. In 75% of the brain damaged hamsters, there was a weak crossed projection from the sensorimotor cortex that was never observed in normal animals. Ablation of this cortex at the time of the recording experiment did not, however, reduce the incidence of abnormal somatosensory receptive fields in these hamsters.

Afferent Pathways↗
PubMed1987

Dendritic and somatic appendages of identified rubrospinal neurons of the cat.

Giant neurons of the red nucleus of the cat were stained intracellularly with horseradish peroxidase and examined using light microscopy, electron microscopy of thin sections, and high voltage electron microscopy of thick sections (2-5 microns). Special attention was paid to the arrangement of dendritic spines and other appendages relative to the distribution of synaptic contacts from known sources. In the region of the neuron known to receive synaptic contacts from the nucleus interpositus of the cerebellum (soma and proximal 200-300 microns of dendrites), the dendrites were relatively unbranched, and free of long spines or complex appendages. The surface of the neurons in this region was covered with a dense layer of short thin appendages that invaginated or penetrated between the synaptic terminals that cover this part of the cells. The small spines received synapses of the types associated both with the cerebellar afferent fibers and with the local inhibitory interneurons. These same terminals made synaptic contacts directly onto the surface of the neurons and onto the lateral surfaces of the spines, suggesting that the spines may serve primarily to increase the available synaptic surface area. The more distal portion of the dendritic field, where cerebellar afferents do not make synaptic contacts, exhibited a dramatically different appearance. The dendrites were much more branched, and exhibited many and varied dendritic appendages. The appendages were of three general types. One was a large protrusion with a cup-shaped head that formed the principal postsynaptic component of a glomerular arrangement also involving an axon terminal and usually a presynaptic dendrite. A second was a long thin filiform process that usually occurred around the glomeruli. This appendage was occasionally postsynaptic. The third was a spherical appendage containing many lysosomal organelles resembling residual bodies. The glomerular dendritic protrusions were very common in the distal portion of the dendritic field, numbering at least 1000 per cell. At least some of the glomeruli are specialized for receipt of synaptic input from the corticorubral pathway, since lesions of sensorimotor cortex resulted in degeneration of the central synaptic terminal in some glomeruli on horseradish peroxidase-injected rubrospinal neurons. These specializations of dendritic structure may contribute to the differences in excitatory postsynaptic potential wave shape between cortical and cerebellar inputs, and they may play a role in the changes in the cortical excitatory postsynaptic potential that develop after lesions of cerebellar inputs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Substantia nigra influences on the reticulospinal neurons: an electrophysiological and ionophoretic study in cats and rats.

The influences exerted by the substantia nigra on reticulospinal neurons and the nature of the synaptic transmitter subserving these projections have been studied in adult cats and rats. Nigral stimulation evokes discharge changes in a significant number of reticulospinal cells (32.4% in cats and 39.1% in rats) on both ipsi- and contralateral sides. The responses were short-latency inhibitions (69.5% in cats and 76.5% in rats), short-latency excitations (22.2% in cats and 23.6% in rats) and in the remaining few cases long-latency excitations. Short-latency excitations, quite similar to the nigra-induced ones, were the predominant response pattern (95.2% in cats and 96.9% in rats) elicited on reticulospinal cells following stimulation of cerebral peduncle. The stimulation of substantia nigra in rats submitted to chronic ablation of sensorimotor cortex elicited only inhibitory responses while stimulation of nigral area in rats with intranigral injection of kainic acid was still capable of evoking short-latency excitations but not short-latency inhibitions. Therefore, the former can be ascribed to activation of corticoreticular fibers running in the cerebral peduncle whereas the latter can be considered as depending on activation of nigral efferents. The nigra-influenced cells were both 'fast' and 'slow' reticulospinal neurons and resulted mainly located in most rostral regions of reticular formation. Ionophoretic application of GABA suppressed the spontaneous firing of reticulospinal cells while no effect was observed following application of dopamine. The nigra-induced inhibitions were abolished by GABA-antagonist bicuculline and not by dopamine-antagonist fluphenazine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Effects of intracellular calcium chelation on voltage-dependent and calcium-dependent currents in cat neocortical neurons.

Large neurons from layer V in a slice preparation of cat sensorimotor cortex were impaled with microelectrodes containing KCl plus different concentrations of the Ca2+ chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (BAPTA) or two of its derivatives. Impalement with electrodes containing high BAPTA (200 mM) quickly abolished Ca(2+)-dependent afterhyperpolarizations. Spike parameters were normal, but the usual time- and voltage-dependent rectification of subthreshold membrane potential was absent. Normally, this rectification results from activation of two voltage-gated currents, the persistent sodium current (INaP) and the hyperpolarizing inward rectifier current (Ih). Both of these currents were absent during voltage clamp with high BAPTA microelectrodes. Impalement with electrodes containing low BAPTA (2 mM) or derivatives caused a different effect. Injection of a 1-s current pulse evoked phasic firing instead of the tonic firing seen normally. Both the amplitude and the duration of the Ca(2+)-dependent afterhypolarization that followed repetitive firing were much greater than normal. The effectiveness of BAPTA derivatives in altering afterhyperpolarizations and firing properties were similar to their effectiveness in chelating Ca2+. It is assumed that the BAPTA effects result from reduction of intracellular Ca2+ concentration. Results with high BAPTA suggest that (i) both INaP and Ih require a minimal intracellular calcium concentration for normal expression, and that (ii) these voltage-gated currents may be modulated by changes in intracellular calcium concentration. Results with low BAPTA suggest that a small reduction of intracellular calcium concentration preferentially enhances a slow, Ca(2+)-dependent K+ current which then dominates the firing properties of the cell. The transformed firing properties resemble those of hippocampal pyramidal neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The effect of cortical lesion on systemic penicillin epilepsy in rats.

There is a certain recovery of function following brain damage, due to neuronal plasticity. The experiments were performed in order to investigate the effects of cortical lesion on seizural activity in rats induced by systemic application of penicillin. The sensorimotor cortex was unilaterally removed in the lesioned animals, while the control animals were only sham operated or non-operated (before implantation of the electrodes). Seizural activity was recorded by means of electroencephalograms before and after penicillin treatment (1,000,000 I.U./kg, i.p). Testing of penicillin started at least 30 days after cortical lesion. Seizural activity was characterized by spike and wave complexes accompanied by vigilance reduction and sometimes by mild myoclonic jerks in both control and lesioned animals. The early period (about 2 h after penicillin administration) with appearance of the spike-wave discharges with relative increase of the mean total electroencephalogram powers as well as the succeeding period 2.5-5.5 h after penicillin administration) with maximum number of spike-wave discharges did not differ in the electroencephalogram of the control and lesioned animals. The late period of penicillin effect (from 6-11 h after penicillin administration) with frequent spike-wave discharges and still large mean total electroencephalogram powers was observed only in lesioned animals. It is concluded that a cortical lesion destabilizes the brain function in the rat model of epilepsy induced by parenteral administration of penicillin.

Animals↗
PubMed1992

Ketamine blocks cortical epileptic afterdischarges but not paired-pulse and frequency potentiation.

Cortical epileptiform afterdischarges (spike-and-wave rhythm) induced by low-frequency stimulation of the sensorimotor cortex were dose-dependently shortened by ketamine (10, 20 and 40 mg/kg, i.p.). Myoclonic jerking during stimulation was unaffected by ketamine whereas the same motor pattern accompanying afterdischarges was markedly suppressed by this drug. Paired-pulse as well as frequency potentiation of the cortical interhemispheric (transcallosal) responses were not significantly altered by the 40 mg/kg dose of ketamine. The two simple potentiation phenomena studied probably did not play a role in initiation of cortical epileptic afterdischarges.

Animals↗
PubMed1993

Time course, localization and pharmacological modulation of immediate early inducible genes, brain-derived neurotrophic factor and trkB messenger RNAs in the rat brain following photochemical stroke.

A focal, unilateral thrombotic stroke was produced in the rat sensorimotor cortex. The time course of expression and localization of the immediate early inducible genes: c-fos, c-jun, zif268; nerve growth factor, brain-derived neurotrophic factor and the related tyrosine kinase high-affinity receptor (trkB) messenger RNAs were studied by in situ hybridization. The levels of messenger RNAs for c-fos, zif268, brain-derived neurotrophic factor (but not nerve growth factor) and trkB were consistently increased in cortex ipsilaterally to the lesion, while c-jun messenger RNA content was only slightly increased. The brain-derived neurotrophic factor messenger RNA was increased from 2 to 18 h following the stroke, mainly in cells having a normal morphological appearance. The trkB messenger RNA displayed temporal and spatial increases similar to brain-derived neurotrophic factor messenger RNA. The time course and pattern of expression of immediate early inducible gene and trophic factor messenger RNAs did not clearly support a causal relationship between these two families of factors. The observed messenger RNA increases were greatly attenuated by the non-competitive N-methyl-D-aspartate-sensitive glutamate receptor antagonist (+)-5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imine , but substantially unaffected by the non-N-methyl-D-aspartate receptor antagonist 2,3-dihydroxy-6-nitrosulphanoylbenzoquinoxaline. The results suggest a major contribution of N-methyl-D-aspartate-sensitive glutamate receptor activation to the transcriptionally directed events subsequent to stroke. Future studies should clarify the contribution of these processes to either the progression of neuronal degeneration or the establishment of protective compensatory responses.

Animals↗
PubMed1988

Behavioral changes and structural defects in rats irradiated in utero.

Pregnant rats were irradiated with whole-body doses (0.25-1.25 Gy) of Cs-137 gamma-rays on gestational day 15, or with 1.0 Gy on gestational days 11, 13, 15, or 17. Postnatal growth (body weight) and several preweaning behaviors (righting reflex, negative geotaxis, reflex suspension, modified open field activity, spatial maze exploration, continuous corridor activity, and gait) of the offspring were monitored prior to sacrifice on post-parturition day 28. Brain (sensorimotor cortex) and pituitary tissues were processed for histological evaluation and morphometric analysis. For most behavioral endpoints, there were dose-dependent changes produced by irradiation on gestational day 15, with one endpoint (continuous corridor activity) demonstrating changes after 0.25 Gy that were significantly different from control values. The data indicate that the most sensitive organ showing radiation-induced alterations changes from the pituitary at gestational day 11 to the primitive cortex of the brain at days 13 to 17 with a peak of sensitivity at day 15. These results demonstrate that a spectrum of related functional and morphological deficits can be produced by even low-dose in utero irradiation, with the specific endpoint showing the greatest change being determined by the specific day of gestation on which irradiation occurs. Extrapolating from these experimental data with rats to the human situation, it is recommended that care be taken, when possible, to avoid exposure of the fetus, even after the early stages of organogenesis.

Animals↗
PubMedDate not supplied

Unilateral cortical spreading depression in the rat: effects on feeding, drinking and other behaviors.

The effects of unilateral cortical spreading depression (CSD) on feeding, drinking and other behaviors were studied in rats. CSD waves were elicited by a microinjection of KC1 solution through an implanted cannula. The animal's behavior and slow potential changes (SPC) accompanying CSD were then simultaneously monitored for 20 min. Intensive face grooming was observed while the CSD wave-front propagated across the sensorimotor cortex. Animals commenced their first feeding or drinking shortly after the invasion of the negative SPC into the frontal cortex of Krieg's area 6 and 10 [14] had reached its maximum height. A two-way switching effect between the first feeding or drinking and quiescence (freezing) and a close relationship between their onsets were observed. The results are discussed specifically in relation to cortico-hypothalamic pathways.

Animals↗
PubMed1983

Glutamate uptake, glutamate decarboxylase and choline acetyltransferase in subcortical areas after sensorimotor cortical ablations in the cat.

High affinity glutamate uptake (HAGU), glutamate decarboxylase (GAD) and choline acetyltransferase (CAT) activities were measured from subcortical nuclei in the cat brain after ipsilateral ablation of the sensorimotor cortex. Results showed a drop in HAGU in all the structures assayed except the subthalamic nucleus. These changes in HAGU are generally accompanied by a decrease in GAD while CAT is unaffected. However, in the red nucleus the drop in HAGU is concomitant to an increase in GAD and CAT. In the subthalamic nucleus HAGU and CAT are increased while GAD is decreased. These results are consistent with the concept that most corticofugal fibres to subcortical structures use glutamate as their neurotransmitter. Results concerning GAD suggest that GABAergic subcortical neurons are under a cortical influence. This influence seems to be weak on cholinergic neurons.

Animals↗
PubMed1989

Cortical projection of giant neostriatal neurons in the cat. Light and electron microscopic horseradish peroxidase study.

Following voluminous injections of horseradish peroxidase (HRP) in various neocortical fields, a small number of labeled large neurons are observed ipsilaterally in the putamen, striatal ponticuli, caudate nucleus, and nucleus accumbens septi. The bulk of the corticopetal cells are found in the putamen and in the striatal ponticuli. A more significant number of labeled neurons is encountered following injections in auditory and sensorimotor cortex, followed by the prefrontal and premotor cortex; very few cells project to the visual cortex. Ultrastructurally, the large HRP-labeled neurons display an eccentrically located, indented nucleus, abundant granular endoplasmic reticulum forming Nissl bodies, well developed Golgi zones, and numerous dense bodies. The simultaneous demonstration of retrogradely transported HRP and acetylcholinesterase (AChE) suggest that the large neurons are presumably cholinergic. These results provide evidence that at least some of the giant striatal neurons are efferent cells. The coincidence of cytological, histochemical, and hodological criteria invite the speculation that the giant corticopetal neostriatal neurons might be related to the magnocellular cholinergic groups of the basal forebrain (especially the Ch4 group).

Animals↗
PubMed1992

Quantitative histochemical changes in enzymes involved in energy metabolism in the rat brain during postnatal development. II. Glucose-6-phosphate dehydrogenase and beta-hydroxybutyrate dehydrogenase.

The postnatal maturation of glucose-6-phosphate and beta-hydroxybutyrate dehydrogenase activity was assessed by histochemistry in rats at eight postnatal stages, P0, P5, P10, P14, P17, P21, P35 and the adult stage. Enzyme activities were revealed on cryostat brain sections with nitroblue tetrazolium. Both enzyme activities were low and homogeneous at birth, and increased to reach a peak in all areas studied, at P17 for beta-hydroxybutyrate dehydrogenase and at P21 for glucose-6-phosphate dehydrogenase. Then, glucose-6-phosphate dehydrogenase activity decreased regularly by 20-49% from P21 to adult stage, except in cerebellar white matter where activity did not change after P21. beta-hydroxybutyrate dehydrogenase activity decreased regularly from P17 to adult stage in globus pallidus, hippocampus, thalamus, brainstem, genu of corpus callosum and cerebellar white matter. It sensorimotor cortex, medial geniculate body, caudate nucleus, hypothalamus and inferior colliculus, beta-hydroxybutyrate dehydrogenase activity stayed stable between P17 and P35 and decreased thereafter to adult levels. Finally, in parietal, auditory and cerebellar cortices, beta-hydroxybutyrate dehydrogenase activity either stayed stable or slightly increased after P17. The present study shows that there is a quite good correlation between postnatal changes in cerebral glucose-6-phosphate and beta-hydroxybutyrate dehydrogenase activities and the importance of pentose phosphate pathway and ketone body utilization in the developing brain. Our results also reflect the regional heterogeneity of beta-hydroxybutyrate utilization in the adult rat brain, translating into a remaining high activity of beta-hydroxybutyrate dehydrogenase in cerebral cortex.

Aging↗