Bilateral eye enucleation at birth (BE) leads to an expansion of the primary somatosensory cortex (S1) in rat pups. Although increased growth of the somatosensory thalamo-cortical afferents (STCAs) in part explains S1 expansion, timing mechanisms governing S1 formation are also involved. In this work, we begin the search of a developmental clock by intending to document the existence of putative clock neurons in the somatosensory thalamus (VPM) and S1 based upon changes of spontaneous spike amplitude; a biophysical property sensitive to circadian regulation; the latter known to be shifted by enucleation. In addition, we also evaluated whether STCAs growth rate and segregation timing were modified, as parameters the clock might time. We found that spontaneous spike amplitude transiently, but significantly, increased or decreased in VPM and S1 neurons of BE rat pups, respectively, as compared to their control counterparts. The growth rate and segregation timing of STCAs was, however, unaffected by BE. These results support the existence of a developmental clock that ticks differently in the VPM and S1 after BE. This observation, together with the fact that STCAs growth rate and segregation timing is unchanged, suggests that S1 expansion in BE rats may in part be controlled at the cortical level.
Keywords: ACSF, artificial cerebrospinal fluid; AChE, acetylcholinesterase; BE, birth-enucleated; Barrel formation; Blind; CP, cortical plate; DAPI, 4′,6-diamidino-2-phenylindole; Developmental clock; Developmental timing; DiI, 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine Perchlorate; PD, postnatal day; S, sighted; S1, primary somatosensory cortex; SEM, standard error of the mean; STCAs, somatosensory thalamo-cortical afferents; Somatosensory cortex specification; Spontaneous activity; VPM, ventral posteromedial nucleus; τd, decay time constant.
© 2019 The Authors.