Corticocuneate projections are altered after spinal cord dorsal column lesions in New World monkeys

Abstract

Recovery of responses to cutaneous stimuli in the area 3b hand cortex of monkeys after dorsal column lesions (DCLs) in the cervical spinal cord relies on neural rewiring in the cuneate nucleus (Cu) over time. To examine whether the corticocuneate projections are modified during recoveries after the DCL, we injected cholera toxin subunit B into the hand representation in Cu to label the cortical neurons after various recovery times, and related results to the recovery of neural responses in the affected area 3b hand cortex. In normal New World monkeys, labeled neurons were predominately distributed in the hand regions of contralateral areas 3b, 3a, 1 and 2, parietal ventral (PV), secondary somatosensory cortex (S2), and primary motor cortex (M1), with similar distributions in the ipsilateral cortex in significantly smaller numbers. In monkeys with short-term recoveries, the area 3b hand neurons were unresponsive or responded weakly to touch on the hand, while the cortical labeling pattern was largely unchanged. After longer recoveries, the area 3b hand neurons remained unresponsive, or responded to touch on the hand or somatotopically abnormal parts, depending on the lesion extent. The distributions of cortical labeled neurons were much more widespread than the normal pattern in both hemispheres, especially when lesions were incomplete. The proportion of labeled neurons in the contralateral area 3b hand cortex was not correlated with the functional reactivation in the area 3b hand cortex. Overall, our findings indicated that corticocuneate inputs increase during the functional recovery, but their functional role is uncertain.

Finger somatotopy is preserved after tetraplegia but deteriorates over time

“…Research in non-human primate models of chronic and complete cervical SCI has shown that the S1 hand area becomes largely unresponsive to tactile hand stimulation after the injury (Jain et al, 2008;Kambi et al, 2014;Liao et al, 2021). The surviving fingerrelated activity became disorganised such that a few somatotopically appropriate sites but also other somatotopically nonmatched sites were activated (Liao et al, 2021). Seminal nonhuman primate research has further demonstrated that SCI leads to extensive cortical reorganisation in S1, such that tactile stimulation of cortically adjacent body parts (e.g., of the face) activated the deprived brain territory (e.g., of the hand; Halder et al, 2018;Jain et al, 2008;Kambi et al, 2014).…”

“…Research in non-human primate models of chronic and complete cervical SCI has shown that the S1 hand area becomes largely unresponsive to tactile hand stimulation after the injury ( Jain et al, 2008 ; Kambi et al, 2014 ; Liao et al, 2021 ). The surviving finger-related activity became disorganised such that a few somatotopically appropriate sites but also other somatotopically non-matched sites were activated ( Liao et al, 2021 ). Seminal non-human primate research has further demonstrated that SCI leads to extensive cortical reorganisation in S1, such that tactile stimulation of cortically adjacent body parts (e.g.…”

Regressive changes in sizes of somatosensory cuneate nucleus after sensory loss in primates

“…Numerous studies have demonstrated how the somatosensory system undergoes functional recovery after sensory loss by unmasking or forming new connections ( 15 , 19 , 31 – 37 ; see ref. 26 for review).…”

“…Detailed microelectrode maps of the large representation of hand and arm in the primary somatosensory cortex (3b) revealed the changes in somatotopy most clearly. Descending inputs from the sensorimotor cortex to the Cu ( 19 ), along with the remaining second-order dorsal column afferents, may facilitate the reactivation although their roles are mainly modulatory ( 20 ).…”

The postnatal development of retinal projections in strepsirrhine galagos (Otolemur garnettii)

“…Other series were processed stains for Nissl, cytochrome oxidase (CO; Wong‐Riley, 1979), vesicular glutamate transporter 2 (VGLUT2), or parvalbumin (PV) that revealed the architectonic features of brain structures. See details in previous publications (Liao et al., 2021; Turner et al., 2020).…”