Enhanced anxiety-like behavior induced by chronic neuropathic pain and related parvalbumin-positive neurons in male rats.

Anxiety commonly co-occurs with and exacerbates pain, but the interaction between pain progression and anxiety, and its underlying mechanisms remain unclear. Inhibitory interneurons play a crucial role in maintaining normal central nervous system function and are suggested to be involved in pain-induced anxiety. This study aimed to elucidate the time-dependent effects of neuropathic pain on the developmental anxiety-like behaviors and related inhibitory interneurons; parvalbumin (PV)- and cholecystokinin (CCK)-positive neurons in corticolimbic regions. Using an 8-week-old male Wistar rat model with partial sciatic nerve ligation (pSNL), anxiety-like behaviors were biweekly assessed post-surgery through open field (OF) and elevated plus maze (EPM) tests. From 4 weeks post-surgery, pSNL rats exhibited reduced OF center time, rearing, and initial activity, along with diminished EPM open-arm activities (time spent, head dips, movement, and rearing), which correlated with the paw withdrawal threshold. These effects were absent at 2 weeks post-surgery. At 8 weeks post-surgery, specific behaviors (decreased total rearing and increased inactive time in EPM) were observed in the pSNL group. Immunohistochemistry revealed changes in PV- and CCK-positive neurons in specific corticolimbic subregions of pSNL rats at 8 weeks post-surgery. Notably, PV-positive neuron densities in the basolateral amygdaloid complex (BLC) and hippocampal cornu ammonis areas 1 and 2 correlated with anxiety-like behavioral parameters. PV-positive neurons in the BLC of pSNL rats were predominantly changed in large-cell subtypes and were less activated. These findings indicate that anxiety-like behaviors emerge in the late phase of neuropathic pain and relate to PV-positive neurons in corticolimbic regions of pSNL rats.

Regional activity and effective connectivity within the frontoparietal network during precision walking with visual cueing: an fNIRS study.

Precision walking (PW) incorporates precise step adjustments into regular walking patterns to navigate challenging surroundings. However, the brain processes involved in PW control, which encompass cortical regions and interregional interactions, are not fully understood. This study aimed to investigate the changes in regional activity and effective connectivity within the frontoparietal network associated with PW. Functional near-infrared spectroscopy data were recorded from adult subjects during treadmill walking tasks, including normal walking (NOR) and PW with visual cues, wherein the intercue distance was either fixed (FIX) or randomly varied (VAR) across steps. The superior parietal lobule (SPL), dorsal premotor area (PMd), supplementary motor area (SMA), and dorsolateral prefrontal cortex (dlPFC) were specifically targeted. The results revealed higher activities in SMA and left PMd, as well as left-to-right SPL connectivity, in VAR than in FIX. Activities in SMA and right dlPFC, along with dlPFC-to-SPL connectivity, were higher in VAR than in NOR. Overall, these findings provide insights into the roles of different brain regions and connectivity patterns within the frontoparietal network in facilitating gait control during PW, providing a useful baseline for further investigations into brain networks involved in locomotion.