Characteristics of projections from primary sensory cortex to motorsensory cortex in cats (original) (raw)
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Distribution and properties of commissural and other neurons in cat sensorimotor cortex
The Journal of Comparative Neurology, 1975
Commissural, cortico-cortical and corticocaudate neurons have been investigated in the primary sensorimotor cortex of the cat, using antidromic stimulation techniques, and histological identification of recording sites. These neurons are to be found in all cortical laminae except the first; commissural and cortico-cortical neumns were found to be commonest in laminae 111 and VI, whilst corticocaudate neurons were most abundant on the border between laminae I11 and V, in motor areas. In sensory areas topographically identified as representing distal parts of limbs, commissural neurons are very rare, confirming neuroanatomical studies on the origin and termination of callosal fibres. The intracerebral neuronal Projections investigated in this study had slow conduction velocities (less than 1 m/sec, up to about 10 m/sec). It was found that projections from area 6, whether commissural, cortico-caudate, or corticopeduncular have slower conduction velocities than their counterparts from area 4. It is suggested that this is related to the type of motor control in which these two areas are involved (slowly-responding postural movements, as opposed to more rapid distal limb movements). No neurons were found which had both commissural (or corticocortical), and cortico-fugal projections.
Journal of Comparative Neurology, 2004
Experiments were carried out on the second somatic sensory area (SII) of cats to study (1) the laminar distribution of axon terminals from the ipsilateral first somatic sensory cortex (SI); and (2) the topographical relations between their terminal field and the callosal neurons projecting to the contralateral homotopic cortex. To label simultaneously in SII both ipsilateral cortical afferents and callosal cells, cats were given iontophoretic injections of Phaseolus vulgaris-leucoagglutinin (PHA-L) in the forepaw zone of ipsilateral SI, and pressure injections of horseradish peroxidase (HRP) in the same zone of contralateral SII. The possibility that ipsilateral cortical axon terminals synape callosal neurons was investigated with the electron microscope by combining lesion-induced degeneration with retrograde HRP labelling.Fibers and terminations immunolabelled with PHA-L from ipsilateral SI were distributed in SII in a typical patchy pattern and were mostly concentrated in supragranular layers. Labelled fibers formed a very dense plexus in layer III and ramified densely also in layers I and II. Labelled axon terminals were both en passant and single-stalked boutons. Counts of 8,303 PHA-L-labelled terminals of either type showed that 82.40% were in supragranular layers. The highest concentration was in layer III (43.99%), followed by layers II (30.22%) and I (8.09%). The remaining terminals were distributed among layers IV (6.96%), V (4.93%), and VI (5.68%). The same region of SII containing anterogradely labelled axons and terminals also contained numerous neurons retrogradely labelled with HRP from contralateral SII. Callosal projection neurons were pyramidal, dwelt mainly in layer III, and were distributed tangentially in periodic patches. Patches of anterograde and retrograde labelling either interdigitated or overlapped both areally and laminarly. In the zones of overlap, numerous PHA-L-labelled axon terminals were seen in close apposition to HRP-labelled pyramidal cell dendrites. Combined HRP-electron microscopic degeneration experiments showed that in SII axon terminals from ipsilateral SI form asymmetric synapses with HRP-labelled dendrites and dendriticc spines pertaining to callosal projection neurons.These results are discussed in relation to the layering and function of the SI to SII projection, and to the evidence that SII neurons projecting to the homotopic area of the contralateral hemisphere have direct access to the sensory information transmitted from ipsilateral SI. © 1994 Wiley-Liss, Inc.
Homotypical ipsilateral cortical projections between somatosensory areas I and II in the cat
Neuroscience, 1985
In 11 cats, small quantities of horseradish peroxidase conjugated to wheat germ agglutinin were placed into cortical zones of somatosensory area I representing the distal digits (n = 3), distal toes (n = 2), toes and digits (n = 1), proximal forelimb (n = 1), proximal hindlimb (n = 1), trunk (n = 2), and the face and nose (n = 1). Reconstruction of the pattern of retrograde labeling in somatosensory area II revealed dense, heavily labeled patches of cells in regions that were precisely homotypical to the injection site as determined by electrophysiological recordings. This dense, homotypical patch of labeled cells was usually surrounded by a less densely populated fringe of labeled cells that bordered, but did not appear to enter, heterotypical zones. In two animals, however, some retrogradely labeled cells were found in the cortex representing somatotopic zones adjacent to the sites injected with horseradish peroxidase. These results indicated that somatosensory area II primarily sends homotypical projections to somatosensory area I. In a few cases, however, some retrogradely labeled cells may represent either homo-or heterotypical projections depending on how receptive field sizes and the areal extent of labeling in somatosensory areas I and II are interpreted.
Somatic sensory projections to the pretectum in the cat
Brain Research, 1978
It is well known that part of the pretectum receives direct input from the retina6,19 and projects to diencephalic structures which have visual functions6,14,15. Very little is known, however, about pretectal regions which do not appear to be connected to the visual system. The present work demonstrates that, in the cat, some of these regions receive extensive input from the dorsal column nuclei and the somatic sensory portions of the cerebral cortex. Such projections have been mentioned briefly in the rat by other investigators22,31.
The Journal of Physiology, 1984
1. Previous studies of input on to spinocervical tract neurones have been extended by investigating the post-synaptic actions of non-cutaneous afferent fibres and of descending tracts on to these neurones, using intracellular recording. In particular, actions of group II muscle, joint and Pacinian afferent fibres and rubro-and corticospinal tract fibres were investigated. 2. Group II muscle afferent fibres evoked excitation and inhibition at a minimal latency compatible with a disynaptic linkage. Increasing the stimulus strength to include group III afferent fibres enhanced these post-synaptic actions only modestly. Inhibition was evoked less frequently and/or required trains of stimuli. 3. Weak stimulation of the interosseous nerve evoked short latency (disynaptic) inhibition or excitation, the latter less frequently. Post-synaptic potentials evoked below threshold for group III afferent fibres of the interosseous nerve are attributed to the actions of Pacinian corpuscles. 4. Low threshold joint afferent fibres evoked excitation at short latency. Higher threshold joint afferent fibres usually evoked inhibition at longer latency, although high threshold excitation was sometimes observed. 5. Stimulation of the pyramidal tract evoked constant latency, unitary e.p.s.p.s which followed high frequencies. The evidence suggests that such e.p.s.p.s are evoked monosynaptically. Polysynaptic excitation and inhibition were also observed. 6. No convincing evidence could be found of actions evoked directly by the rubrospinal tract, although actions mediated via other descending systems could be induced from the red nucleus. 7. A large degree of convergence was seen from different peripheral and descending systems on to individual neurones.
The somatosensory intercollicular nucleus of the cat's mesencephalon
The Journal of Physiology, 1990
1. Unitary, neural activity was sampled with tungsten electrodes in the mesencephalic, intercollicular region of cats anaesthetized with chloralose. The units' stereotaxic coordinates were noted and they were tested for activation by adequate tactile, visual and acoustic stimuli as well as electrical nerve stimulation. The units' geometrical gradations were afterwards translated into morphological terms by means of unbiased, cytoarchitectonic identifications of those structures which had been penetrated by the electrodes. 2. The primary objectives were the conventional, somatosensory units, which had reliable, low-threshold, tactile receptive fields and could not be activated by the two other types of adequate stimulation. There were 139 such units from a total sample of 495. 3. These somatosensory units were found to occupy many of the region's structures, notably the intercollicular nucleus (INC), the nucleus of the brachium of the inferior colliculus, the stratum griseum intermedium and the stratum griseum profundum of the superior colliculus. INC was the only structure which had an exclusively somatosensory input. 4. The units of INC had tactile receptive fields varying between one and several hundred square centimetres. Convergence of afferent input from outside these fields could sometimes be demonstrated by nerve stimulation. The latencies of activation from the contralateral sciatic nerve were, on average, shorter for units of INC than for the somatosensory units of the other intercollicular structures, and INC units could also follow higher stimulation frequencies. 5. The findings support the assumption that INC may constitute a distinct mesencephalic centre for somatosensory function.
Brain Research, 1986
The terminal areas and the cells of origin of the projection from the sensory trigeminal nuclei to the mesencephalon were investigated, using the method of anterograde and retrograde transport of horseradish peroxidase or wheat germ agglutinin-horseradish peroxidase conjugate. Injection of tracer into the nucleus interpolaris or nucleus oralis (in the latter cases with involvement of the nucleus principalis) resulted in dense anterograde labeling in the deep and intermediate gray layers of the contralateral superior colliculus, extending throughout the rostrocaudal extent of the colliculus with the exception of its caudalmost part, which was not labeled. Minor projections to the intercollicular nucleus, posterior pretectal nucleus and nucleus of Darkschewitsch were found. Injection of tracer into the nucleus caudalis yielded a completely different result; terminal labeling in the midbrain was now present only in the periaqueductal gray matter, in its rostral and middle parts. The retrograde labeling observed after injection of tracer into the midbrain terminal areas showed that the cells of origin were located mainly in the alaminar spinal trigeminal nucleus, and the highest density of labeled neurons was found in the rostral part (subnucleus y) of the nucleus oralis. The retrograde labeling in the nucleus principalis was very sparse and almost exclusively involved peripherally located neurons. In the nucleus caudalis the overwhelming majority of the retrogradely labeled neurons were situated in its marginal layer. The functional implications of the above observations are discussed in relation to the findings in previous studies of the projections from the dorsal column nuclei and spinal cord to the midbrain. The combined results suggest that the trigeminal projections to the superior colliculus may be involved in the mechanisms of orientational behavior. The observation that the projection to the periaqueductal gray matter originates in the marginal layer suggests that it transmits information related to noxious stimuli.