LOSS OF GLUTAMATE IMMUNOREACTIVITY FROM MOUSE 1ST SOMATOSENSORY (SI) CORTEX FOLLOWING NEONATAL VIBRISSAL LESION

Whisker follicles were surgically ablated (lesioned) on two entire row s (B and C) of the left snout of two groups of Swiss mice, in the firs t 2 days after birth (neonatally lesioned) with the animals being allo wed to survive for 4 weeks. In the second group at 8 weeks of age (adu lts), the whisker follicles of rows B and C were similarly lesioned an d a survival period of 3 days allowed. Glutamate-immunoreactivity (Glu -IR) was examined in tangential sections of the first somatosensory (S I) 'barrel' cortex of these two groups (at which time it was also conf irmed that the follicles had not regrown). In the neonatally lesioned mice, barrel rows B and C were more poorly defined in the right (exper imental) hemisphere sections and a semi-quantitative study showed that there was a decrease in Glu-IR cell number (up to 41%) in rows B and C of the right hemisphere compared to the spared barrel rows (A and D) . The loss appears to occur over almost the entire area of each depriv ed barrel rather than being confined to the sides or hollows. In contr ast to neonatally lesioned animals, the barrels of the adult-lesioned mice appeared intact and visually similar in both the experimental (ri ght) and control hemispheres (left). The only notable change in Glu-IR observed in the adult-lesioned animals was a decrease of 38% in the n umber of Glu-IR cells in the sides between the two deafferented rows o f barrels (B and C), compared to the cell number between the unaffecte d barrels (D and E), a change also seen in the neonatally lesioned mic e. Since this effect was visible in adult animals only 3 days after le sion of vibrissae, when no other changes were found, it would appear t hat this site - the furthest removed in the barrels from sources of no rmal afferentation - is the first to exhibit neural plasticity.