Acute reductions in GABAA receptor binding in layer IV of adult primate somatosensory cortex after peripheral nerve injury

The reactivation of somatosensory cortex and behavioral recovery after sensory loss in mature primates

“…We have previously suggested that dorsal column lesions are often incomplete, and that preserved but subthreshold dorsal column inputs to the cuneate nucleus gain strength by forming more synapses on more neurons as the result of reduced competition for synaptic space (Rasmusson and Northgrave, 1997; Xu and Wall, 1997; Darian-Smith, 2004; Darian-Smith and Ciferri, 2006). Similar changes likely occur at the levels of the ventroposterior nucleus and somatosensory cortex (Garraghty et al, 1991, 2006; Rasmusson, 1996; Wellman et al, 2002). Under conditions of extreme loss of afferents to the cuneate nucleus, we had evidence that even afferents from the adjacent trigeminal complex for the face could sprout and grow to innervate the cuneate nucleus (Jain et al, 2000), providing relays to the hand subnucleus of the contralateral ventroposterior nucleus and then to the hand territory of primary somatosensory cortex.…”

“…Other reactivations with greater changes in the receptive field locations of central neurons occurred over hours to weeks, such as the reactivation of cortical neurons previously activated from the glabrous skin of the hand by touch on the back of the hand after sectioning of the median nerve to the glabrous skin of digits 1–3 (Merzenich et al, 1983a,b). Such rapid reactivations may largely result from the potentiation of previously existing subthreshold inputs, especially in the cuneate nucleus representing the hand in the lower brainstem, by homeostatic mechanisms (Garraghty et al, 1991; Turrigiano, 1999; Wellman et al, 2002), and possibly by new axon growth over short distances (Darian-Smith and Gilbert, 1994; Jain et al, 2000; Darian-Smith, 2004; Hickmott and Steen, 2005; Cheetham et al, 2008; Yamahachi et al, 2009; Marik et al, 2010, 2014). Other reactivations that follow the loss or denervation of the forelimb, including invasion by inputs from the face (Pons et al, 1991; Jain et al, 1997, 2000; Wu and Kaas, 1999; Florence et al, 2000), may take many months to emerge (Jain et al, 1997), and depend on longer distances of new axon growth at subcortical and cortical levels (Florence et al, 1998; Jain et al, 2000).…”

AMPA and GABAA/B receptor subunit expression in the cuneate nucleus of adult squirrel monkeys during peripheral nerve regeneration

“…Developmental plasticity happens considerably faster (hours/days) than more prolonged forms of adult plasticity (weeks/months). Rapid shifts in subunit expression occur during the critical period of brainstem nuclei development [eg 34, 35] and a rapid decrease in cortical GABA A R expression occurs within hours of nerve injury in adults [60]. Our studies suggest that shifts in specific subclasses of receptor phenotype (eg increased homomeric, decreased heteromeric) can be hidden by autoradiography techniques that quantify net changes in receptors [26].…”

“…Continued remapping demonstrated the reinstatement of the original peripheral inputs as the median nerve regenerated down the intact neural sheath. These studies have provided useful platforms to study the mechanisms of adult neural plasticity [7, 8, 20, 21, 22, 23, 26, 49, 60]. …”

Nursing-Induced Somatosensory Cortex Plasticity: Temporally Decoupled Changes in Neuronal Receptive Field Properties Are Accompanied by Modifications in Activity-Dependent Protein Expression

“…These findings corroborate studies showing that GABAergic inhibition is also regulated in an experience-dependent manner. For example, whisker trimming or nerve transection were found to reduce GAD immunostaining or GABA A receptor binding within layer IV of the deprived cortical zone (Akhtar and Land, 1991;Land et al, 1995;Wellman et al, 2002). Prolonged stimulation of a set of whiskers increases GAD immunoreactivity in layer IV of the corresponding region of the barrel cortex (Welker et al, 1989b).…”