Mechanical frequency and stimulation-site-related differences in vibrotactile detection capacity along the lip vermilion in young adults.

Accurate clinical assessment of the infraorbital and mental branch of the trigeminal nerve is aided by an appreciation of the variations in sensitivity that may exist along the surface of the perioral region under examination. The purpose of this investigation was to map the mediolateral spatial and frequency variations in vibrotactile detection capacity to inputs delivered to the upper lip (UL) and lower lip (LL) vermilion. Mechanical vibrotactile inputs at frequencies of 5, 10, 50, and 150 Hz were delivered to three locations on the vermilion of the UL and LL: midsagittally and laterally (left and right) at a point halfway between the midsagittal plane and the oral angle. An adapted staircase tracking method was used to converge upon a threshold value for each test frequency at each stimulation site. The results indicated that midsagittal vermilion sites were significantly more sensitive to our range of vibrotactile inputs compared to lateral vermilion locations. In addition, no significant differences in sensitivity as a function of laterality or between the UL and LL vermilion sites were noted. Greater midline sensitivity to vibrotactile stimulation suggests that receptive fields at this location may be of greater density and/or demonstrate greater overlap compared to lateral vermilion sites.

Src activation in the induction of long-term potentiation in CA1 hippocampal neurons.

Long-term potentiation (LTP) is an activity-dependent strengthening of synaptic efficacy that is considered to be a model of learning and memory. Protein tyrosine phosphorylation is necessary to induce LTP. Here, induction of LTP in CA1 pyramidal cells of rats was prevented by blocking the tyrosine kinase Src, and Src activity was increased by stimulation producing LTP. Directly activating Src in the postsynaptic neuron enhanced excitatory synaptic responses, occluding LTP. Src-induced enhancement of alpha-amino-3-hydroxy-5-methylisoxazolepropionic acid (AMPA) receptor-mediated synaptic responses required raised intracellular Ca2+ and N-methyl-D-aspartate (NMDA) receptors. Thus, Src activation is necessary and sufficient for inducing LTP and may function by up-regulating NMDA receptors.