Vibrissae tactile stimulation: (14C) 2‐deoxyglucose uptake in rat brainstem, thalamus, and cortex

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Abstract
The right mystacial vibrissae of awake, adult rats were stroked at 4–6 times/second and brain regions which increased (14C) 2-deoxyglucose (2DG) uptake were mapped autoradiographically. The ventral parts of the ipsilateral spinal trigeminal nuclei pars caudalis (Sp5c), pars interpolaris (Sp5i), pars oralis (Sp5o), and the principal trigeminal sensory (Pr5) nuclei were activated. The lateral part of the ipsilateral facial (VII) nucleus (the region which innervates the vibrissae muscles) was also activated possibly via excitatory, trigeminal (Sp5c, Sp5i, Sp5o, Pr5) sensory afferents. A number of regions were activated contralateral to the sensory stimulus. Discrete patches of (14C) 2DG uptake occurred in deep layers of the superior colliculus (SCsgp). Dorsolateral and dorsomedial parts of the ventrobasal nucleus (VB), and posterior, dorsolateral parts of the reticular nucleus (R) of thalamus were activated, along with broad portions of the primary somatosensory cortex (SI) and second somatosensory cortex (SII). Though all layers of SI and SII cortex increased 2DG uptake, VB thalamic afferents to layers IV and Vc-Vla presumably accounted for the greater activation of these cortical layers during repetitive sensory stimulation of the vibrissae (RSSV). Activation of the above structures fits well with known anatomical data. However, the pattern of activation during RSSV was very different from that previously described during vibrissae motor cortex stimulation (VMIS). RSSV and VMIS both produced similar repetitive movements of all the mystacial vibrissae. However, only a few overlapping brain regions were activated during both RSSV and VMIS. These RSSV-VMIS overlap zones included Sp5o; rostral Sp5i; lateral VII; SCsgp; ventrobasal-posteromedial and ventrobasal-ventrolateral zones in thalamus; and a rostral region of SI probably anterior to the Woolsey vibrissae barrelfield in the dysgranular somatosensory (SI) cortex. Since RSSV and VMIS would both be expected to activate vibrissae proprioceptors, we have hypothesized that vibrissae proprioceptive input was processed in part in the RSSV-VMIS overlap zones. Convergence of motor-sensory inputs and other types of processing could have also occurred in these overlap zones.