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Nonuniform alteration of dendritic development in the cerebral cortex following prenatal cocaine exposure.

Prenatal exposure to cocaine has the potential to modify normal brain development and result in behavioral dysfunction. We used a new animal model in which cocaine was administered intravenously during prenatal development in pregnant rabbits twice daily at low dosages. Analysis of brain development focused on two areas of the cerebral cortex, anterior cingulate and primary visual, in which dopamine afferents, a target of cocaine, are differentially distributed. All postnatal rabbits exposed to cocaine prenatally exhibited normal features of cortical organization, including thickness, lamination patterns, and cytoarchitectonic differentiation. General axonal and astroglial organization, assessed by neurofilament-H and glial fibrillary acidic protein immunostaining, also was unchanged in the cocaine-exposed animals. Analysis of dendritic organization was done using antibodies against microtubule-associated protein 2 (MAP2), which reveals mostly the larger apical shafts of cortical pyramidal cells. In the anterior cingulate cortex of adolescent rabbits exposed to cocaine in utero, there is a marked decrease in both dendritic bundling and typical long, straight MAP2-stained profiles. In normal animals, the long, bundled dendrites area readily traced in a single focal plane from layer III or V pyramidal cell somata to the pial surface in saline-treated animals. Instead, the drug-exposed animals contained many more short segments of MAP2-stained dendrites that could be viewed coursing in and out of the plane of focus in the sections. Apical dendrites in mature visual cortex appeared normal in the cocaine-exposed rabbits. Examination of MAP2 staining at various postnatal ages revealed that the dendritic changes expressed in the adolescent anterior cingulate cortex appeared less robust, but still evident at birth. By P10-14, dendritic modifications were similar to the adult. Counts of the number of MAP2-positive dendritic profiles crossing the layer II-III interface reached a nadir of 50% in the cocaine-exposed animals, indicative of a change in the organization of the apical dendrites compared to the control animals. Dendritic profiles of anterior cingulate neurons, filled by 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine percholate (Dil), confirmed that in the cocaine offspring, the dendrites coursed in an irregular, wavy manner from deep to superficial layers, suggestive of dendrites that were longer than normal, although cortical thickness was unchanged. The altered dendritic profiles also were seen in Golgi-impregnated neurons. The data indicate that prenatal exposure to cocaine can lead to specific alterations of neuronal growth that are long lasting. The lack of dendritic changes in visual cortex suggests that the drug does not modify development of cortical regions uniformly. This study also provides a new focus on the anterior cingulate cortex as a site in which aberrant structure-function relationships following prenatal cocaine exposure should be examined in both animal models and clinically.

Animals↗

PubMed1985

Role of cerebral cortex in voluntary movements. A review.

Findings from studies using electrical stimulation of cortex, recording from single neurons in awake animals, and measuring regional cerebral blood flow in humans have revealed some specific motor functions for several cerebral cortical areas. These areas include primary motor cortex, supplementary motor area, premotor area, parietal areas 5 and 7, and prefrontal area. Execution of movement is a function of the primary motor cortex, which translates program instructions for movement from other parts of the brain into signals. These signals encode variables of movement, such as the muscles to contract and the force and timing of their contraction. Long-latency reflex responses of muscles to stretch and cutaneous stimulation are also mediated by the motor cortex; other motor areas seem to perform higher order motor functions. The supplementary motor area controls input-output coupling in motor cortex and the programming of complex sequences of rapidly occurring discrete movements, such as playing the piano. The premotor area participates in the assembly of new motor programs. The parietal areas 5 and 7 are involved in directing attention to objects of interest in visual space and issuing commands for arm movements and eye movements to these objects. The prefrontal cortex performs cognitive functions, such as short-term memory of correct motor responses in delayed response tests.

Animals↗

PubMed2004

Eye movement control by the cerebral cortex.

PURPOSE OF REVIEW: This review focuses on eye movement control by the cerebral cortex, mainly in humans. Data have emerged based on the important contribution of recent techniques such as transcranial magnetic stimulation and functional magnetic resonance imaging, which provide complementary results to those of the classical lesion and electrical stimulation studies. RECENT FINDINGS: The location of the human frontal eye field and its role in pursuit eye movement control were recently detailed. Cumulative evidence for the role of the dorsolateral prefrontal cortex in unwanted reflexive saccade inhibition, short-term spatial memory and prediction suggests that this area controls decisional processes governing ocular motor behaviour. The organization of spatial memory in the dorsolateral prefrontal cortex (short-term), the parahippocampal cortex (medium-term) and the hippocampal formation (long-term) is also reviewed with the results of recent transcranial magnetic stimulation studies. The relatively complicated anatomy of the posterior parietal cortex in humans is briefly described followed by some additional results concerning the location of the parietal eye field - within the posterior half of the intraparietal sulcus - and its role in visuo-spatial integration and attention. The other areas involved in spatial attention are also examined in the light of several recent contributing reports. Lastly, there are also new functional magnetic resonance imaging findings concerning the posterior cingulate cortex, which appears to be mainly involved in the control of externally guided eye movements and attentional mechanisms. SUMMARY: Many new findings on the organization of saccades and pursuit eye movements at the cortical level have recently been reported. Furthermore, eye movements are increasingly used as a tool to elucidate relatively complex neuropsychological processes such as attention, spatial memory, motivation and decisional processes, and a considerable number of reports dealing with these questions have been observed.

Animals↗

PubMed2005

Pathology of the insular cortex in Alzheimer disease depends on cortical architecture.

The insular cortex plays important roles in a variety of regulatory mechanisms ranging from visceral control and sensation to covert judgments regarding inner well-being. The dementia of Alzheimer disease (AD) often includes behavioral dyscontrol and visceral dysfunction not observed in other diseases affecting cognition. This could be related to autonomic instability and to loss of the sense of self, and pathologic changes within the insula may play essential roles. The pattern of insular pathology of 17 patients with AD was examined and the severity of pathology was compared with that of the entorhinal cortex (EC), a region involved early in AD with reciprocal connections to the insula. Thioflavin S staining and Alz-50 immunostaining revealed that the insula carries a heavy burden of pathology in AD. Neurofibrillary tangles (NFTs) were largely confined to the deep layers of the cortex, whereas neuritic plaques (NPs) were distributed throughout the cellular layers and subcortical white matter. The density of NFTs, but not NPs, was highly correlated with the degree of EC pathology. However, NFTs were not seen in the insula until EC pathology reached a relatively advanced level. The density of insular NFTs varied according to architectonic type, with agranular cortex most affected, dysgranular cortex less affected, and granular cortex least affected. Thus, the insula is often involved in AD, and some of the behavioral abnormalities in AD may reflect insular pathology.

Aged↗

PubMed2006

Roles of the auditory cortex in discrimination learning by rats.

We investigated the roles of the auditory cortex in sound discrimination learning in Wistar rats. Absolute pitch or relative pitch can be used as discrimination cues in sound frequency discrimination. To clarify this, rats were trained to discriminate between rewarded (S+) and unrewarded (S-) test stimuli (S+ frequency>S- frequency). After learning was acquired by rats, performance was tested in a new test in which S+ frequency was constant but S+ frequency S- frequency but both frequencies were increased. If the discrimination cue of the first test was preserved in the new test, performance following change of testing procedures was expected to remain high. The measured performance suggested that rats used relative pitch in half octave discrimination (difference between S+ and S- frequencies, 0.5 octave), and absolute pitch in octave discrimination (difference between S+ and S- frequencies, 1.0 octave). Bilateral lesions in the auditory cortex had almost no effect on performance before procedure change. Furthermore, performance following procedure change was not affected by lesions in the auditory cortex when the discrimination cue was preserved. However, performance was impaired by lesions in the auditory cortex when a new discrimination cue was used following procedure change. Lesions in the auditory cortex also impaired multimodal discrimination between sound and sound plus light. The present findings suggest that the auditory cortex plays a role as a sensory interface of the higher cortices required for flexible learning and multimodal discrimination.

Acoustic Stimulation↗

PubMed1989

Long-term potentiation in the motor cortex.

Long-term potentiation (LTP) is a model for learning and memory processes. Tetanic stimulation of the sensory cortex produces LTP in motor cortical neurons, whereas tetanization of the ventrolateral nucleus of the thalamus, which also projects to the motor cortex, does not. However, after simultaneous high-frequency stimulation of both the sensory cortex and the ventrolateral nucleus of the thalamus, LTP of thalamic input to motor cortical neurons is induced. This associative LTP occurs only in neurons in the superficial layers of the motor cortex that receive monosynaptic input from both the sensory cortex and the ventrolateral nucleus of the thalamus. Associative LTP in the motor cortex may constitute a basis for the retention of motor skills.

Animals↗

PubMed2002

Localisation of the sensorimotor cortex during surgery for brain tumours: feasibility and waveform patterns of somatosensory evoked potentials.

OBJECTIVE: Intraoperative localisation of the sensorimotor cortex using the phase reversal of somatosensory evoked potentials (SEPs) is an essential tool for surgery in and around the perirolandic gyri, but unsuccessful and perplexing results have been reported. This study examines the effect of tumour masses on the waveform characteristics and feasibility of SEP compared with functional neuronavigation and electrical motor cortex mapping. METHODS: In 230 patients with tumours of the sensorimotor region the SEP phase reversal of N20-P20 was recorded from the exposed cortex using a subdural grid or strip electrode. In one subgroup of 80 patients functional neuronavigation was performed with motor and sensory magnetic source imaging and in one subgroup of 40 patients the motor cortex hand area was localised by electrical stimulation mapping. RESULTS: The intraoperative SEP method was successful in 92% of all patients, it could be shown that the success rate rather depended on the location of the lesion than on preoperative neurological deficits. In 13% of the patients with postcentral tumours no N20-P20 phase reversal was recorded but characteristic polyphasic and high amplitude waves at 25 ms and later made the identification of the postcentral gyrus possible nevertheless. Electrical mapping of the motor cortex took up to 30 minutes until a clear result was obtained. It was successful in 37 patients, but failed in three patients with precentral and central lesions. Functional neuronavigation indicating the tumour margins and the motor and sensory evoked fields was possible in all patients. CONCLUSION: The SEP phase reversal of N20-P20 is a simple and reliable technique, but the success rate is much lower in large central and postcentral tumours. With the use of polyphasic late waveforms the sensorimotor cortex may be localised. By contrast with motor electrical mapping it is less time consuming. Functional neuronavigation is a desirable tool for both preoperative surgical planning and intraoperative use during surgery on perirolandic tumours, but compensation for brain shift, accuracy, and cost effectiveness are still a matter for discussion.

Adolescent↗

PubMed1998

Dorsal premotor cortex and conditional movement selection: A PET functional mapping study.

Positron emission tomography (PET) brain mapping was used to investigate whether or not human dorsal premotor cortex is involved in selecting motor acts based on arbitrary visual stimuli. Normal subjects performed four movement selection tasks. A manipulandum with three graspable stations was used. An imperative visual cue (LEDs illuminated in random order) indicated which station to grasp next with no instructional delay period. In a power task, a large aperture power grip was used for all trials, irrespective of the LED color. In a precision task, a pincer grasp of thumb and index finger was used. In a conditional task, the type of grasp (power or precision) was randomly determined by LED color. Comparison of the conditional selection task versus the average of the power and precision tasks revealed increased blood flow in left dorsal premotor cortex and superior parietal lobule. The average rate of producing the different grasp types and transport to the manipulandum stations was equivalent across this comparison, minimizing the contribution of movement attributes such as planning the individual movements (as distinct from planning associated with use of instructional stimuli), kinematics, or direction of target or limb movement. A comparison of all three movement tasks versus a rest task identified movement related activity involving a large area of central, precentral and postcentral cortex. In the region of the precentral sulcus movement related activity was located immediately caudal to the area activated during selection. The results establish a role for human dorsal premotor cortex and superior parietal cortex in selecting stimulus guided movements and suggest functional segregation within dorsal premotor cortex.

Adult↗

PubMed2006

Motor cortex rTMS restores defective intracortical inhibition in chronic neuropathic pain.

OBJECTIVE: To assess cortical excitability changes in patients with chronic neuropathic pain at baseline and after repetitive transcranial magnetic stimulation (rTMS) of the motor cortex. METHODS: In 22 patients with unilateral hand pain of various neurologic origins and 22 age-matched healthy controls, we studied the following parameters of cortical excitability: motor threshold at rest, motor evoked potential amplitude ratio at two intensities, cortical silent period (CSP), and intracortical inhibition (ICI) and intracortical facilitation. We compared these parameters between healthy subjects and patients at baseline. We also studied excitability changes in the motor cortex corresponding to the painful hand of patients after active or sham rTMS of this cortical region at 1 or 10 Hz. RESULTS: At baseline, CSP was shortened for the both hemispheres of patients vs healthy subjects, in correlation with pain score, while ICI was reduced only for the motor cortex corresponding to the painful hand. Regarding rTMS effects, the single significant change was ICI increase in the motor cortex corresponding to the painful hand, after active 10-Hz rTMS, in correlation with pain relief. CONCLUSION: Chronic neuropathic pain was associated with motor cortex disinhibition, suggesting impaired GABAergic neurotransmission related to some aspects of pain or to underlying sensory or motor disturbances. The analgesic effects produced by motor cortex stimulation could result, at least partly, from the restoration of defective intracortical inhibitory processes.

Adult↗

PubMed1987

Cortical and subcortical afferent connections of the squirrel monkey's (lateral) premotor cortex: evidence for visual cortical afferents.

The afferent connections of the squirrel monkey's lateral premotor cortex were investigated with the horseradish peroxidase (HRP) technique. Seven monkeys received small, unilateral injections of HRP spaced between the most dorsal and the most lateral region of the premotor cortex. Results are based on six brains, all of which showed a considerable number of labeled neurons both cortically and subcortically. At the cortical level, labeled cells were found both ipsi- and contralateral to the injection site. Heavy labeling occurred in the fields surrounding the prefrontal, central, and precentral cortex, while the temporal regions usually innervated the premotor cortex with a moderate number of cells, and the parietal fields with only a minor number. Surprisingly, in all brains, but especially in those with the more lateral injections, we also found a considerable number of afferents originating from occipital fields, including a few neurons from the striate cortex. Subcortically, a few labeled cells were seen in basal forebrain regions, the amygdala, and the claustrum; a considerable number of thalamic nuclei and also some hypothalamic nuclei contained labeled cells; and within the brainstem, labeling was found most consistently in the locus ceruleus and in the tegmental fields. It is concluded that the (lateral) premotor cortex is involved in sensorimotor integration to a higher degree than has been recognized up to now.

Afferent Pathways↗

PubMed1990

Changes in choline acetyltransferase activity and high-affinity choline uptake, but not in acetylcholinesterase activity and muscarinic cholinergic receptors, in rat somatosensory cortex after sciatic nerve injury.

Selected cholinergic markers (choline acetyltransferase, acetylcholinesterase, muscarinic acetylcholine receptor, high-affinity choline uptake) were studied in the hindlimb representation areas of the rat somatosensory cortex and within the visual cortex 1 to 63 days after unilateral transection of the sciatic nerve. In the contralateral somatosensory cortex, peripheral deafferentation resulted in a significant reduction of choline acetyltransferase activity (by 15%) 3 days after sciatic nerve injury, and in a significant reduction of high-affinity choline uptake (by 30%) 1 day after nerve transection, in comparison to untreated control rats. Investigations in individual cortical layers revealed that the decrease of both choline acetyltransferase activity and high-affinity choline uptake sites was mainly due to reductions in cortical layer V. Acetylcholinesterase activity and [3H]quinuclidinyl benzilate binding to muscarinic acetylcholine receptors were not affected by unilateral transection of the sciatic nerve. In the ipsilateral somatosensory cortex, as well as in the visual cortex at both cortical hemispheres, no significant changes in the cholinergic parameters studied could be detected. The data indicate that peripheral deafferentation of the somatosensory cortex results in a transient change of presynaptic cholinergic parameters within the affected somatosensory area as early as 1 to 3 days after the lesion; thus, they emphasize the involvement of cholinergic mechanisms in cortical reorganizational events.

Acetylcholinesterase↗

PubMed2002

Anatomical evidence of multimodal integration in primate striate cortex.

The primary visual cortex (area 17 or V1) is not thought to receive input from nonvisual extrastriate cortical areas. However, this has yet to be shown to be the case using sensitive tracers in the part of area 17 subserving the peripheral visual field. Here we show using retrograde tracers that peripheral area 17 subserving the visual field at an eccentricity of 10-20 degrees receives projections from the core and parabelt areas of the auditory cortex as well as from the polysensory area of the temporal lobe (STP). The relative strength of these projections was calculated for each injection by computing the proportions of retrogradely labeled neurons located in the auditory and STP areas with respect to number of labeled neurons constituting the established projection from the superior temporal sulci (STS) motion complex (middle temporal area, medial superior temporal, fundus of the superior temporal area). In peripheral area V1 the projection from auditory cortex corresponds to 9.5% of that of the STS motion complex and STP to 35% of that from the STS motion complex. Compared to peripheral area 17, central and paracentral area 17 showed considerably weaker inputs from auditory cortex (0.2-0.8%) but slightly more from STP cortex (3.5-6.1%). The present results show that the connectivity of area 17 is eccentricity dependent. Direct projections from auditory and STP cortex to peripheral area 17 have important consequences for higher visual functions of area 17, including multimodal integration at early stages of the visual cortical pathway.

Animals↗

PubMed1999

Topographic organization of human visual areas in the absence of input from primary cortex.

Recently, there has been evidence for considerable plasticity in primary sensory areas of adult cortex. In this study, we asked to what extent topographical maps in human extrastriate areas reorganize after damage to a portion of primary visual (striate) cortex, V1. Functional magnetic resonance imaging signals were measured in a subject (G.Y.) with a large calcarine lesion that includes most of primary visual cortex but spares the foveal representation. When foveal stimulation was present, intact cortex in the lesioned occipital lobe exhibited conventional retinotopic organization. Several visual areas could be identified (V1, V2, V3, V3 accessory, and V4 ventral). However, when stimuli were restricted to the blind portion of the visual field, responses were found primarily in dorsal extrastriate areas. Furthermore, cortex that had formerly shown normal topography now represented only the visual field around the lower vertical meridian. Several possible sources for this reorganized activity are considered, including transcallosal connections, direct subcortical projections to extrastriate cortex, and residual inputs from V1 near the margin of the lesion. A scheme is described to explain how the reorganized signals could occur based on changes in the local neural connections.

Adult↗

PubMed2000

Regulation of rat cortex function by D1 dopamine receptors in the striatum.

Interactions between the basal ganglia and the cerebral cortex are critical for normal goal-directed behavior. In the present study, we used immediate-early genes (c-fos, zif 268) as functional markers to investigated how basal ganglia output altered by stimulation/blockade of D1 dopamine receptors in the striatum affects cortical function. Systemic administration of the mixed D1/D2 receptor agonist apomorphine (3 mg/kg) increased immediate-early gene expression in the striatum and throughout most of the cortex. Unilateral intrastriatal infusion of the selective D1 receptor antagonist SCH-23390 (0.5-10 microg) blocked this response bilaterally in striatum and cortex in a dose-dependent manner. Even apparently regionally restricted blockade of striatal D1 receptors attenuated gene expression throughout striatum and cortex in both hemispheres. Intrastriatal administration of the D1 antagonist inhibited apomorphine-induced sniffing/whisking, whereas other motor behaviors were unaffected. To determine whether such changes in cortical gene expression could reflect altered cortical function, we examined the effects of blocking striatal D1 receptors on whisker stimulation-evoked immediate-early gene expression in the sensorimotor cortex. Apomorphine increased sensory stimulation-evoked gene expression in the barrel cortex, and intrastriatal infusion of SCH-23390 attenuated this effect. These results suggest that stimulation of D1 dopamine receptors in the striatum exerts a widespread facilitatory effect on cortical function.

Animals↗

PubMed1992

Growth of the rat somatic sensory cortex and its constituent parts during postnatal development.

We have compared the size and arrangement of the primary somatic sensory cortex (SI) and its constituent parts in juvenile (1 week old) and mature (10-12 weeks old) rats using succinic dehydrogenase histochemistry and digital image analysis. Our goal was to determine whether some regions of the maturing cortex grow more than others. To this end, we examined (1) the growth of barrels and the surrounding (interbarrel) cortex, (2) the growth of the major somatic representations within SI, and (3) the overall growth of SI compared to the neocortex as a whole. With respect to the first of these issues, SI barrels and barrel-like structures grow more than the intervening cortex. The growth of these elements varies according to region: barrels in the head representation more than double in size, whereas the barrel-like structures in the paw representations increase by only about half this amount. The growth of the major somatic representations within SI is also heterogeneous, the representation of the head enlarging to a greater extent than the representations of the paws. Thus, the ratio of the total area of head representation to the combined paw representation is 15% greater in adults than in juveniles. Finally, the primary somatic sensory cortex grows to a somewhat greater extent than the neocortex as a whole. These observations demonstrate that postnatal cortical growth is not uniform; it varies among cortical barrels and the immediately surrounding (interbarrel) cortex, among the representations of different body parts, and between SI and the rest of the neocortex. As an explanation of this differential growth, we suggest that the neuropil of metabolically (and/or electrically) more active cortical regions grows to a greater extent during maturation than that of less active regions.

Aging↗

PubMed1986

Long-range focal collateralization of axons arising from corticocortical cells in monkey sensory-motor cortex.

Small extracellular injections of HRP were placed into a stratum of corticocortical axons situated immediately deep to area 3b of the monkey somatic sensory cortex. This stratum had previously been demonstrated to contain corticocortical fibers linking the cytoarchitectonic fields of the somatic sensory cortex to one another and certain of them to the motor cortex. This method resulted in extremely successful filling of pyramidal cells, their axons, collateral axon branches, and terminations in areas 3b, 1, and 2 posterior to the injection and in areas 3a and 4 anterior to it. The major finding was that cells with somata situated in any one of these fields and with principal axons traversing the injection site have long collaterals, primarily in layers III and V, which can extend throughout their own cytoarchitectonic field and into one or more other fields. In these fields they give off focused, columnlike concentrations of terminal boutons, which can be separated from one another by 800 micron or more. The anterogradely labeled, primary corticocortical fibers, traced forwards into areas 3a and 4, have virtually identical focal terminations. These findings indicate that interareal connectivity in the sensory-motor cortex can be effected by the axon branches of single cells rather than by separate groups of cells, and this may form a basis for the convergence of place and modality information on single cells in the sensorimotor cortex, a convergence that is not seen in the thalamic input to this cortex.

Animals↗

PubMed1988

Neuronal populations stained with the monoclonal antibody Cat-301 in the mammalian cerebral cortex and thalamus.

The monoclonal antibody Cat-301 was used to examine neurons in the cerebral cortex and dorsal thalamus of several mammalian species, including Old World monkeys, cats, bush babies, guinea pigs, and rats. In each species, subpopulations of cortical and thalamic neurons are stained along the surfaces of their somata and proximal dendrites. Cat-301-positive cortical neurons include specific groups of pyramidal cells (e.g., corticospinal but not corticobulbar or callosal neurons in the monkey sensory-motor areas) and certain GABA-immunoreactive nonpyramidal cells. In the thalamus, the relay neurons projecting to the cortex and not the intrinsic neurons are stained. The Cat-301-positive neurons are nonhomogeneously distributed in the cat and monkey cortex and thalamus. In the cortex, they are densely packed in 2 bands that in most areas include layers III and V, but that in primary sensory areas include layers IV and VI. Because the density of stained neurons, their distribution, and the intensity of their staining vary among cortical areas, the borders between neighboring areas can often be detected by the differences in Cat-301 staining. Broader, regional differences are also readily apparent, for areas in the parietal and occipital lobes contain large numbers of intensely stained cells, but most areas in the frontal and temporal lobes contain fewer, more lightly stained neurons. The same broad differences are seen within the thalamus: only those nuclei reciprocally connected with intensely stained cortical areas contain large numbers of Cat-301-positive neurons. Differences among species include variations in cell density and distribution when a given cortical area or thalamic nucleus is compared between cats and monkeys. Greater differences are seen among the other species. Immunoreactive neurons in the cerebral cortex are sparse and lightly stained in guinea pigs, are restricted to the hippocampal formation in rats, and are very rare and isolated in bush babies. Similarly, Cat-301-positive thalamic neurons are restricted to only one or 2 nuclei in the guinea pig and rat and are extremely rare in the bush baby. Cat-301 stains organized groups of neurons in the cat and monkey cortex and thalamus. In addition to the laminar organization of stained cells in all cortical areas (see above), the Cat-301-positive neurons of monkey areas 17 and 18 are grouped into radial arrays. In area 17, clusters of stained cells are present in layers above and below layer IVC. These clusters lie at the centers of ocular dominance columns, within patches stained for cytochrome oxidase (CO). Most of these cells are also GABA-immunoreactive.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1978

Developing role of sensorimotor cortex and pyramidal tract neurons in contact placing in kittens.

Unilateral or bilateral removal of kitten sensorimotor (SM) cortex prior to the fourth postnatal week was followed by recovery of contact placing (CP) to stimulation of any of the four forepaw cutaneous fields. However, immediately after a removal under ethyl chloride, CP was depressed contralaterally, especially to lateral stimulation (lateral CP). When the operated kitten aged to 5--9 weeks, the likelihood of CP secondarily declined contralateral to the SM cortical extirpation, but was restored by administration of d-amphetamine. An initial extirpation after the fifth postnatal week was followed by a severe deficit in CP. 2. Cooling the SM cortex, internal capsule or bulbar pyramid during the 2nd and 3rd week was followed by reversible, contralateral loss of lateral CP, extension of the forelimb and, later, by reduced movements. Lateral CPs were often hypermetric prior to loss. By contrast, cooling SM cortex in the first week was usually ineffective. Thus, during the 2nd week, lateral CP developed a dependence on SM cortex, and in particular on PT neurons. 3. After a delay usually of 1 or more min, cooling the SM cortex reduced the resting discharge of individual neurons in buried motor cortex; the antidromic conduction time in PT neurons was significantly increased and the spike height was reduced.

Animals↗