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

Abstract

SUMMARY1. 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.

Functional Connectivity of the Secondary Somatosensory Cortex of the Rat

“…Direct connections between VPL, S1, and S2 have been reported in mice, rats, cats, macaques, squirrel monkeys, and gray squirrels (Rowe and Sessle, 1968;Jones and Powell, 1969a;Manson, 1969;Jones, 1975;Spreafico et al, 1981;Fisher et al, 1983;Burton and Kopf, 1984;Carvell and Simons, 1987;Krubitzer and Kaas, 1987;Aldes, 1988;Stevens et al, 1993;Pierret et al, 2000). In the present study, both S1 and S2 were anterogradely labeled after BDA was injected into forepaw or hindpaw regions.…”

Thalamocortical Relationships in the Somatic Sensory System as Revealed by Silver Impregnation Techniques (Part 2 of 2)

“…Because S-I sends a very definite corticothalamic projection to these regions, nonreciprocality of connections seems to be a feature of the cortical-thalamic relationships existing in the somatic sensory system. This observation is at variance with the report that stim ulation of both S-I and S-II produced antidromic responses in PO [Rowe and Sessle, 1968].…”

Second Somatosensory Cortex and Related Areas

“…According to our results and those illustrated by Bentivoglio et al (1983), the labeled cells were located throughout central parts of VB that presumably also contained the relay cells to SI. Indeed, results from double-labeling experiments (Bentivoglio et al, 1983;Jones, 1975;Spreafico et al, 1981) and antidromic stimulation studies (Guillery et at., 1966;Manson, 1969;Rowe and Sessle, 1968) indicated that, at best, some proportion (-13-20%?) of VB cells projected to both SI and SI1.…”