Cortical representation of first and second pain sensation in humans

Single painful stimuli evoke two successive and qualitatively distinct sensations referred to as first and second pain sensation. Peripherally, the neural basis of this phenomenon is a dual pathway for pain with Aδ and C fibers mediating first and second pain, respectively. Yet, the differential cortical correlates of both sensations are largely unknown. We therefore used magnetoencephalography to record and directly compare first and second pain-related cortical responses to cutaneous laser stimuli in humans. Our results show that brief painful stimuli evoke sustained cortical activity corresponding to sustained pain perception comprising early first pain-related and late second pain-related components. Cortical activity was located in primary (S1) and secondary (S2) somatosensory cortices and anterior cingulate cortex. Time courses of activations disclosed that first pain was particularly related to activation of S1 whereas second pain was closely related to anterior cingulate cortex activation. Both sensations were associated with S2 activation. These results correspond to the different perceptual characteristics of both sensations and probably reflect different biological functions of first and second pain. First pain signals threat and provides precise sensory information for an immediate withdrawal, whereas second pain attracts longer-lasting attention and motivates behavioral responses to limit further injury and optimize recovery

Comparative genomic analysis of Lactobacillus rhamnosus GG reveals pili containing a human- mucus binding protein

To unravel the biological function of the widely used probiotic bacterium Lactobacillus rhamnosus GG, we compared its 3.0-Mbp genome sequence with the similarly sized genome of L. rhamnosus LC705, an adjunct starter culture exhibiting reduced binding to mucus. Both genomes demonstrated high sequence identity and synteny. However, for both strains, genomic islands, 5 in GG and 4 in LC705, punctuated the colinearity. A significant number of strain-specific genes were predicted in these islands (80 in GG and 72 in LC705). The GG-specific islands included genes coding for bacteriophage components, sugar metabolism and transport, and exopolysaccharide biosynthesis. One island only found in L. rhamnosus GG contained genes for 3 secreted LPXTG-like pilins (spaCBA) and a pilin-dedicated sortase. Using anti-SpaC antibodies, the physical presence of cell wall-bound pili was confirmed by immunoblotting. Immunogold electron microscopy showed that the SpaC pilin is located at the pilus tip but also sporadically throughout the structure. Moreover, the adherence of strain GG to human intestinal mucus was blocked by SpaC antiserum and abolished in a mutant carrying an inactivated spaC gene. Similarly, binding to mucus was demonstrated for the purified SpaC protein. We conclude that the presence of SpaC is essential for the mucus interaction of L. rhamnosus GG and likely explains its ability to persist in the human intestinal tract longer than LC705 during an intervention trial. The presence of mucus-binding pili on the surface of a nonpathogenic Gram-positive bacterial strain reveals a previously undescribed mechanism for the interaction of selected probiotic lactobacilli with host tissues