EFFECTS OF UNILATERAL DEAFENING ON THE COCHLEAR NUCLEUS OF THE GUINEA-PIG AT DIFFERENT AGES

Developmental changes in spherical cell sizes were measured in the ven tral cochlear nucleus (VCN) in normal guinea pigs aged 2 days and 2, 7 and 12 weeks to establish the time course of postnatal neuronal growt h, as a baseline for our experimental work. A continued growth of sphe rical cell size was observed in the VCN up to 7 weeks postnatally. Ani mals were unilaterally deafened by cochlear perfusion with kanamycin s ulphate at ages 1 and 6 weeks. After 6 weeks survival the spherical ce lls were measured in the VCNs of both sides. Unilateral deafferentatio n at both ages caused an ipsilateral reduction in spherical cell size, neurons of the younger group being smaller than in the older. On the contralateral side these cells in the older group were larger than age -matched controls while in the younger group there was no difference c ompared with age-matched controls. These findings suggest that the res ults of deafferentation are age-dependent, and may indicate an ability of the neural circuitry to adapt to the loss of sensory input on the other side.d