TABLE 2.

Morphological Rating of HLA-DR-Positive Microglia in the Contralateral and Ipsilateral Midbrain 3 Months After Unilateral MPTP Infusion in Young, Middle-Aged, and Old-Aged Monkeys

Age group	Animal no.	Age (years)	Regions
			vtSN		dtSN		VTA
			C	I	C	I	C	I
Young	6965	8	−	++	−	++	−	++
	6966	8	−	+	−	+	−	++
	7009	8	−	++	−	+	−	+
	7086	10	−	+++	−	+++	−	+++
Middle	6339	14	+	++	−	++	−	+
	6327	17	++	++	+	++	+	++
	6337	17	+	+++	+	+++	+	++
	7010	17	+	+	+	+	+	+
	7014	17	−	++	−	+	−	+
Old	6254	27	+	++	+	++	+	++
	6237	28	++	+++	+	+	+	++
	6553	30	++	+++	+	++	+	++
	6725	30	+	+++	+	++	+	++
	6724	31	+++	+++	+	++	+	++

C, contralateral midbrain; I, ipsilateral midbrain; (−) resting microglia with little to no cytoplasmic immunoreactivity and few lightly stained fine fibers; (+) numerous hyperramified microglia, characterized by increased cytoplasmic immunoreactivity and numerous highly branched fibers with moderate levels of staining, but no or few microglia with morphologies of advanced activation; (++) numerous hyperramified microglia and fully activated microglia, characterized by shortened thicker processes, increased cell body size, and strong immunoreactivity, in addition to the emergence of multicellular clusters; (+++) vast majority of microglia are in advanced stages of activation, which includes macrophage-like morphology and numerous multicellular clusters.