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Biomedical subjects

M J Rowe

Publications and source records attributed to M J Rowe.

104 records · Page 6Linked to original sources
PubMed1968

Somatic afferent input to posterior thalamic neurones and their axon projection to the cerebral cortex in the cat.

1. A technique of reversible block of synaptic transmission through the dorsal column nuclei and the trigeminal nucleus caudalis (n. caudalis) has been employed to assess the somatic afferent input to individual posterior thalamic neurones in the cat. The axon projection to the cerebral cortex of these neurones has been identified by antidromic activation following cortical stimulation.2. Unitary responses in the nucleus ventralis posterolateralis (VPL) evoked by cutaneous stimulation were abolished or depressed following block of transmission in the dorsal column nuclei. Block in n. caudalis, however, depressed unitary responses in nucleus ventralis posteromedialis (VPM) evoked by facial skin stimulation in less than 10% of cells.3. A more complex source of the somatic input to the posterior nuclear region of the thalamus (PO) was found. It was most commonly noted that PO unitary activity evoked by cutaneous stimulation of the face was unaffected by block of synaptic transmission in n. caudalis. No uniform effect was observed on unitary responses in PO evoked by limb stimulation when transmission in the dorsal column nuclei was blocked.4. Antidromic activation from the cerebral cortex was seen in 69% of ventrobasal neurones. Most cells (66%) had ;antidromic cortical fields' restricted to a region consisting of a third to a half of the specific somatic projection areas. In 10% of cells evidence was obtained for discontinuous cortical ;antidromic fields' suggesting subcortical bifurcation of the projecting axon.5. An axon projection to the cortex was found in 35% of PO cells, about half of which projected only to specific somatic projection areas. Evidence for subcortical branching of the axon was obtained for seven PO cells.

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Parallel organization of somatosensory cortical areas I and II for tactile processing.

1. The two principal tactile processing areas in the cerebral cortex, somatosensory areas I and II, receive direct projections from the thalamus and, as well, are linked through intracortical reciprocal connections. Tactile information may therefore be conveyed to SII, for example, over either a direct path from the thalamus or an indirect, or serial, path from the thalamus via SI. 2. Reports in recent years that tactile responsiveness within the hand area of SII was abolished by surgical ablation of the hand area of the postcentral, or SI area of the cortex in the macaque and marmoset monkeys indicated that a serial processing scheme may operate at least in primates. However, as the surgical ablation is clearly irreversible and precludes examination of individual SII neurons in both the control and test circumstances, that is, when SI is intact and when it is inactivated, we have examined in the cat, the rabbit and the marmoset monkey the behaviour of SII neurons before, during and after the selective, rapidly-reversible inactivation of SI by means of localized cooling. 3. The results demonstrate that in the cat and rabbit, SII responsiveness is never abolished and infrequently affected by SI inactivation and that tactile inputs to SII therefore traverse a direct path from thalamus, organized in parallel with that to SI. In the marmoset (Callithrix jacchus), in contrast to earlier studies based on ablation of SI we found that with reversible inactivation of SI, SII responsiveness was unaffected in 25% of neurons and, although reduced in the remainder, was rarely abolished (< 10% of SII neurons). 4. The results indicate that there is substantial direct thalamic input to SII, even in this simian primate, and therefore necessitate revision of the hypothesis that tactile processing at the thalamocortical level in simian primates is based on a strict serial scheme in which tactile information is conveyed from the thalamus to SI and thence to SII.

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PubMedDate not supplied

Mechanosensory perception: are there contributions from bone-associated receptors?

1. The identity of the receptors and afferent nerve fibres that mediate the sense of touch varies somewhat with body location. Those that have been most intensively characterized are associated with the distal glabrous skin of the limbs and, in primates, mediate the sense of touch in the fingertips and palms. In this glabrous skin region, there appear to be three or four principal classes of tactile sensory nerves that fall into two broad groups. One group, the so-called slowly adapting (SA) receptors and afferent fibres, is responsive to static mechanical displacement of skin tissues and is made up of two classes, the type I (SAI) fibres that innervate Merkel receptors and the type II (SAII) fibres that innervate Ruffini endings. The second broad group displays a pure dynamic sensitivity to tactile stimuli and also falls into two principal classes, the rapidly adapting (RA) tactile fibres that are associated with Meissner corpuscle receptors and the Pacinian corpuscle (PC)-associated class of tactile afferent fibres. 2. In other regions of the skin, such as the hairy skin of the arms, legs and trunk, there are similar functional classes of tactile sensory nerves, although the receptor endings differ somewhat from those of the glabrous skin. 3. Receptors in close association with the long bones of the limbs include groups of Pacinian corpuscles distributed along the interosseous membranes. These are highly sensitive to dynamic forms of mechanical stimuli, in particular vibrotactile disturbances. However, despite their close association with bone, these receptors probably cannot be legitimately considered 'osseoreceptors'. 4. Both the periosteum and the bone marrow are richly supplied by nerve fibres. However, much evidence indicates that these are largely or entirely in the fine-diameter category of nerve fibres, whose roles may be confined to either nociception or to the efferent autonomic regulation of bone-associated blood vessels. 5. In conclusion, it remains uncertain whether any aspects of our innocuous touch or kinaesthetic senses, in either the limbs or in orofacial regions, can be ascribed to 'osseoreceptors' located in the periosteum or within the bone marrow itself.

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