Microglia, astrocytes, and macrophages react differentially to central andperipheral lesions in the developing and mature rat whisker-to-barrel pathway: A study using immunohistochemistry for Lipocortin1, phosphotyrosine, S100 beta, and mannose receptors

Adult and neonatal rats were subjected to transection of the left infraorbi tal nerve or ablation of the left parietal cortex. The ensuing glial reacti on in the whisker-to barrel pathway was studied with immunohistochemistry f or Lipocortin1- (LC1+), phosphotyrosine-(PY+), S100 beta- (S100 beta+), and mannose receptor- (MR+) immunoreactive microglia, astrocytes, and macropha ges. Four days after infraorbital nerve transection in adult rats, LC1+ and PY+ microglia were prominently increased in the trigeminal sensory brain-s tem nuclei on the deafferented side compared with the intact side. Changes were negligible at the second synapse of the pathway, i.e., the thalamic ve ntroposterior medial nucleus. Cortical ablation in adults led to an increas e in microglia in the ipsilateral ventroposterior medial nucleus that recip rocally connects with the ablated cortex. Moreover, microglial reactions oc curred in the contralateral trigeminal sensory brainstem nuclei in which co rticofugal projections from the ablated cortex terminate. S100 beta+ astroc ytes, in contrast, appeared unaltered after both types of lesion in adults. In neonates, LC1+, PYS, and S100 beta+ cells did not have the adult morpho logy of microglia or astrocytes. Four days after nerve transection, LC1+ an d PY+ cells were sparse and remained unchanged. In contrast, S100 beta+ cel ls substantially increased in the deafferented trigeminal brain-stem nuclei . Four days after cortical ablation in neonates, LC1+, PY+, and S100 betacells had accumulated in the deprived thalamus. In contrast to adults, many of these cells were MR+ macrophages. In the deprived brain-stem, only S100 beta+ cells increased and none were macrophages. Therefore, macrophages do not appear to stem from microglia, and neonatal LC1+, PY+, and S100 betacells may possess functions different from those in adults. (C) 2001 Academ ic Press.