Bouton renewal patterns in rat hindlimb cortex after thoracic dorsal funicular lesions

Abstract

The transneuronal effect of bilateral, dorsal funicular lesions (T 12) on the frequency of boutons on cells in layer IV of hindlimb cortex was studied. Adult rats were utilized 1, 2, 3, 7, 14, 30, 45, 60, 90, or 120 days postoperative (DPO), and tissue was processed for the light microscopic visualization of silver-impregnated boutons (Rasmussen method). Bouton counts were taken on soma, or along 5- and 10-micrometers segments or proximal dendrite branching from soma. The soma diameter also was measured on those neurons chosen for bouton counts on the circumference of the soma. Statistically significant, increased afferentation on soma and proximal dendrite occurred during the first postlesion week relative to longer survival times; bouton counts on the proximal dendrite showed a trend (not statistically significant) toward increases above normal. These data mirror similar, consistent increases in bouton counts reported in thalamic ventroposterolateral nucleus of these same cases. At 14 DPO, bouton counts on the soma decreased below normal (P less than 0.005) and, except at 60 DPO, remained so through 120 DPO (P less than 0.025). Bouton counts on the proximal dendrite also decreased below normal at 14 DPO (P less than 0.005), thereafter exhibiting either periodic (along 5-micrometers) or extended (along 10-micrometers) periods in significant decreases from normal. Correlations in lesioned cases between the number of boutons on the soma and either bouton counts on proximal dendrite or soma diameter were positive and statistically significant (P less than 0.005 in all correlations). Possible anterograde (via the dorsal column-medial lemniscal system) and/or retrograde (via the corticospinal tract) transneuronal mediation of these effects in hindlimb cortex is discussed.

Development and Maintenance of Somatotopic Maps of the Skin: A Mosaic Hypothesis Based on Peripheral and Central Contiguities (Part 2 of 2)

“…Current observations are consistent with the pos sibility that anatomical changes in this fringe include changes in the terminal trees of thalamocortical fi bers. In addition, it is possible that changes in dendri tic trees of cortical cells are also involved [Granchrow and Bernstein, 1981;Woolsey, 1979, 1981;Ryugo et al, 1975;Steffen and Van der Loos, 1980]. Although most observations on the hindpaw system come from cortex, the evidence from the vibrissal sys tem suggests similar changes occur at subcortical levels as well.…”

Cortical Reorganization of Sensorimotor Systems and the Role of Intracortical Circuits After Spinal Cord Injury

“…Spinal cord injury disrupts cortical networks with effects on corticospinal dendrites. Both injured and non-injured layer 5b neurons in hindlimb cortical areas begin to show a reduction in dendritic spines within the first week after thoracic spinal cord injury [102][103][104][105]. This reduction in spines proceeds over a time scale ranging from days to months, with continuous remodeling of the dendritic spines in the hindlimb representation after thoracic injury.…”