Variability of peripheral representation in ventrobasal thalamic nuclei of the cat: Effects of chloralose treatment

• Published in: Experimental neurology Vol. 60; no. 3; pp. 469 - 483
• Main Authors: Haimann, Claudia, Margnelli, Marco, Sotgiu, Maria Luisa
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.01.1978
• Subjects: Afferent Pathways - drug effects; Afferent Pathways - physiology; Animals; Cats; Chloralose - pharmacology; Electric Stimulation; Peripheral Nerves - physiology; Sensation - physiology; Spinal Cord - physiology; Thalamic Nuclei - drug effects; Thalamic Nuclei - physiology; PRF; VPL
• ISSN: 0014-4886; 1090-2430
• DOI: 10.1016/0014-4886(78)90004-3

The effects of the intravenous administration of α-chloralose on the static and dynamic properties of 20 highly specific somatosensory neurons isolated within the forepaw focus of the thalamic ventralis posterolateralis (VPL) nucleus of locally anesthetized cats were studied. Observations were made (extracellular recording) before, during, and after injection. Nine units of the sample were identified as thalamocortical relay cells. Spontaneous activity, activity during tonic afferent drive maintained by weak peripheral stimuli, responsiveness to stimulation of the dorsal column and dorsolateral funiculus, and location and extent of peripheral receptive fields were examined. In none of the sample units did the drug bring to light aspecific properties such as those previously described in sizable proportions of the cell populations sampled from the VPL nucleus of cats anesthetized with chloralose or subjected to surgical interventions which lower the amount of the ascending or corticofugal influx to the thalamus. After the treatment, eight units (six of which were identified as thalamocortical relay cells) exhibited continuous or (in two cases) discontinuous enlargements of their peripheral receptive fields, which, however, remained rather small compared to the aspecific fields. The effects are tentatively explained by hypothesizing the “unmasking” of a convergent specific input, directed only to a fraction of thalamocortical relay cells and normally blocked by afferent or corticofugal inhibition. It is suggested that the unmasked input could be mediated by the spinocervicothalamic pathway.