Primary afferent input to and receptive field properties of cells in rat lumbar area X.
In this study we examined the primary afferent input to rat area X of Rexed, and characterized sensory receptive fields (RFs) of the cells therein. This poorly understood area contains primary afferent fibres, some of which are arranged into a compact bundle beneath the central canal. Anterograde transport of the B fragment of cholera toxin (CTB) from the sciatic nerve showed a strictly ipsilateral projection to segments in L4 and L5 but both ipsi- and contralateral projections in L6 and more caudal segments. The response of cells in area X to mechanical cutaneous stimuli was recorded through extracellular microelectrodes in decerebrate, decerebrate-spinal, and urethane-anaesthetised preparations. The lateral edge of area X was marked by an abrupt change in the RFs: Lateral to area X in the dorsal horn, they were strictly unilateral and relatively small. At a mean of 90 microm from the midline, there was an abrupt expansion of the RFs to cover at least the entire ipsilateral dermatome. Within area X, 70% of the cells' RFs extended across the midline to include contralateral skin. In 35% of cells recorded in rats with intact spinal cords, the RF extended rostrally onto the forelimb. In a small number of cells, the RF included ear pinnae and nose. The precise function of area X cells remains unknown; although they have been shown to be involved in visceral reflexes, the fact that they receive convergent input from a wide variety of tissues and from local and remote body parts implies a more generalized, integrative function.
Sensory Function Group, Centre for Neuroscience Research, Guy's, King's and St. Thomas' School of Biomedical Sciences, King's College London, Guy's Campus, SE1 1UL London, United Kingdom.
Patrick D
PD
Wall
Bradley J
BJ
Kerr
Matt S
MS
Ramer
D000344:Afferent Pathways / Q000502:physiology; D000818:Animals; D003655:Decerebrate State; D004431:Ear, External / Q000502:physiology; D005552:Forelimb / Q000502:physiology; D008159:Lumbar Vertebrae; D008297:Male; D009412:Nerve Fibers / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D009666:Nose / Q000502:physiology; D051381:Rats / Q000502:physiology*; D017207:Rats, Sprague-Dawley; D012677:Sensation / Q000502:physiology; D012879:Skin Physiological Phenomena; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*