Late onset muscle plasticity in the whisker pad of enucleated rats

Abstract

Blindness leads to a major reorganization of neural pathways associated with touch. Because incoming somatosensory information influences motor output, it is plausible that motor plasticity occurs in the blind. In this work, we evaluated this issue at the peripheral level in enucleated rats. Whisker muscles in enucleated rats 160 days of age or older showed increased cytochrome oxidase activity, capillary density, motor plate size, and amplitude of evoked field potentials as compared with their control counterparts. Such differences were not observed at ages 10 and 60 days, the capillary density was the exception being greater in the enucleated rat at the latter age. Interestingly, there was a trend to increased neurotrophin-3 concentrations in the whisker pads of enucleated rats throughout postnatal development. Our results show that neonatal enucleation leads to late onset plasticity of the whisker's motor system. blindness ͉ metabolic activity ͉ motor plasticity ͉ motor plate potentials ͉ skeletal muscle I n mammals, the loss of vision leads to a large scale sensory reorganization of the brain. Somatosensory and auditory areas enlarge whereas the former visual regions become activated by somatosensory and auditory information (1). These functional modifications are associated with the reorganization of their anatomical substrate (2, 3). The reorganized brain allows the blind to develop the somatosensory and auditory abilities that distinguish them from sighted subjects (4, 5).Somatosensory information calibrates motor output (5, 6-8). Hence, one might expect certain degree of motor plasticity in blind subjects. Accordingly, studies have shown incremental increases in the activity of glutamate dehydrogenase and in the size of neurons located in the motor cortex after visual deprivation (9). Magnetic resonance studies in blind humans have also documented a decreased functional connectivity to motor areas (9, 10), increments in the volume of cortical gray matter associated with sensory-motor cortices (11), and in the volume of the cortico-spinal tract (9). Whether motor plasticity in the blind extends to more peripheral levels is unknown.A good model system to test whether peripheral motor plasticity occurs in the blind is the sensory-motor system controlling whisking in rodents. Sensory information arising from the whiskers calibrates their movements (12) while motor activity modulates sensory information influx (13, 14). Our work was aimed at evaluating the morpho-functional plasticity ongoing in the intrinsic motor apparatus of the facial whiskers of neonatally enucleated rats. The time course and the possible relationship between the plastic response and neurotrophin-3 concentrations were analyzed. Our results document late onset morpho-functional plasticity in the intrinsic musculature of whisker follicles in rats enucleated at birth. The evidence we provide suggests that this plastic response is associated with increments in the concentrations of neurotrophin-3 in the whisker pad. Hence, blind individuals ...

Shifts in Developmental Timing, and Not Increased Levels of Experience-Dependent Neuronal Activity, Promote Barrel Expansion in the Primary Somatosensory Cortex of Rats Enucleated at Birth

“…Although previous work suggests that incremental increases in neuronal activity associated with enhanced somatosensory experience lead to S1 expansion in birth-enucleated rodents [9], [10], the present results weaken this notion. The observations that support our conclusions are: 1) The size and growth rate of whiskers in birth-enucleated rats are similar to those observed in control sighted rats; 2) The magnitude of barrel expansion was similar between young and adult rats enucleated at birth; 3) Unilateral dewhiskering at 168 h did not prevent barrel expansion in the deprived hemisphere nor did it produce barrel overgrowth in non-deprived hemispheres of birth-enucleated adult rats; 4) Neither enucleation after the period of barrel formation nor raising rats in complete darkness promoted barrel expansion; 5) Metabolic markers of neuronal activity (CyOx and 2DG) were comparable in the trigeminal ganglion and/or in non-expanded and expanded PMBSF barrels of control and birth-enucleated rats, respectively, at different ages; and 6) Barrel expansion in birth-enucleated rats took place before the onset of active whisking (PD12)[55]–[59], and before cortical-evoked activity [60]–[62].…”

Looking beyond Self-Protection: The Eyes Instruct Systemic Immune Tolerance Early in Life

“…BE rats [82]. These results suggest that, in the absence of eyes from early life, the rodent skin develops a condition characterized by a deregulated immune response that can be evidenced by sensitizing and challenging birth-enucleated rodents with OXA and/or DFBN.…”

“…Here, we found the epidermis thickened ( Figure 1 c–f and Figure 6 a,b; see also [ 81 ] for a similar result in rats) and some of the proinflammatory cytokines involved in regulating keratinocyte growth and differentiation (e.g., IL4, IL6 and IL17) upregulated two months after enucleation at birth. In a previous study, neurotrophin-3 was also found to be increased in the whisker muzzle of BE rats [ 82 ]. These results suggest that, in the absence of eyes from early life, the rodent skin develops a condition characterized by a deregulated immune response that can be evidenced by sensitizing and challenging birth-enucleated rodents with OXA and/or DFBN.…”