The somatosensory intercollicular nucleus of the cat's mesencephalon.

Abstract

SUMMARY1. Unitary, neural activity was sampled with tungsten electrodes in the mesencephalic, intercollicular region of cats anaesthetized with chloralose. The units' stereotaxic co-ordinates 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.

Distinct cell groups in the lumbosacral cord of the cat project to different areas in the periaqueductal gray

“…In contrast, somatosensory input from large areas of the skin and perhaps IA fierents from muscles of the hindlimbs and back seems to be conveyed from the lower lumbar cord to the lateral part of the lateral PAG and adjacent tegmentum. The latter region overlaps well with the location of the so-called intercollicular nucleus Norrsell, 1985, 1986;Blomqvist et al, 1990). Some units in the intercollicular nucleus receive exclusively somatosensory input, i.e., light tactile cutaneous stimuli from mainly the contralateral body Norrsell, 1985, 1986).…”

Characterization of inducible cyclooxygenase in rat brain

“…Of particular interest are projections to parts of the auditory associative thalamus, which are thought to be involved in the assignment of emotional significance to auditory stimuli (Calford and Aitkin, 1983;Kudo et al, 1984;LeDoux et al, 1991). Single-unit recordings in this nucleus have revealed the presence of cells responding to polymodal (auditory, visual, and proprioceptive) sensory input (Blomqvist et al, 1990).…”

Distribution of brainstem projections from spinal lamina I neurons in the cat and the monkey

“…The IN receives dense topographic input from the major ascending somatosensory pathways, the dorsal column nuclei, the lateral cervical nucleus, and the spinal cord (Flink et al, 1983;Wiberg and Blomqvist, 1984;Wiberg et al, 1987). It contains low-threshold neurons with receptive fields of varying sizes (Blomqvist et al, 1990); nociceptive responses have not been recorded. The role of the IN is unknown but presumably could be involved in tectal alerting and orientation functions or, perhaps, in providing somatosensory input to the adjacent PAG.…”