A 14-day period of hindpaw sensory deprivation enhances the responsiveness of rat cortical neurons

• Published in: Neuroscience Vol. 121; no. 2; pp. 433 - 439
• Main Authors: Dupont, E, Canu, M.-H, Falempin, M
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-01-2003; Elsevier
• Subjects: Action Potentials - physiology; Animals; Biological and medical sciences; cortical activity; Electric Stimulation; Electrophysiology; Evoked Potentials, Somatosensory; extracellular recording; Fundamental and applied biological sciences. Psychology; Hindlimb - innervation; Hindlimb - physiology; hindlimb unloading; Hypokinesia - physiopathology; Male; Mechanoreceptors; Neural Pathways; neuronal plasticity; Neurons - classification; Neurons - physiology; Rats; Rats, Wistar; Reaction Time; Sensory Deprivation - physiology; Sensory Thresholds - physiology; Skin - innervation; Skin - physiopathology; somatosensory cortex; Somatosensory Cortex - cytology; Somatosensory Cortex - physiopathology; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Space life sciences; Time; Vertebrates: nervous system and sense organs; extracellular recording; HH; C; ACh; GAD; cortical activity; SmI; neuronal plasticity; SP/Stim; PSTH; hindlimb unloading; SP count; somatosensory cortex; RFs; Hindlimb; Rat; Rodentia; Central nervous system; Electrophysiology; Encephalon; Somatosensory cortex; Vertebrata; Sensory deprivation; Mammalia; Somesthetic pathway; Plasticity
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(03)00494-9

Hypodynamia-hypokinesia (HH) is a model of hindpaw sensory deprivation. It is obtained by unloading of the hindquarters during 14 days. In this situation, the feet are not in contact with the ground and as a consequence, the cutaneous receptors are not activated; the sensory input to the primary somatosensory cortex (SmI) is thus reduced. In a previous study, we have shown that HH induced a cortical reorganisation of the hindlimb representation. The understanding of the mechanisms involved in cortical map plasticity requires a close examination of the changes in response properties of cortical neurons during HH. The aim of the present study was thus to study the characteristics of neurons recorded from granular and infragranular layers in hindlimb representation of SmI. A total of 289 cortical neurons were recorded (158 from control rats and 131 from HH rats) in pentobarbital-anaesthetized rats. Cutaneous threshold, cutaneous receptive fields, spontaneous activity (discharge rate and instantaneous frequency) and activity evoked by air-jet stimulation (response latency and duration, amplitude) were analysed.
The present study suggests that activity-dependent changes occur in the cortex. The duration of the spike waveform presented two populations of spikes: thin-spike cells (<1 ms, supposed to be inhibitory interneurons) and regular cells (>1 ms). Thin-spike cells were less frequently encountered in HH than in control rats. The analysis of regular cells revealed that after HH (1) spontaneous activity was unchanged and (2) cortical somatosensory neurons were more responsive: the cutaneous threshold was reduced and the response magnitude increased. Taken together, these results suggest a down-regulation of GABAergic function.