Table 2.

d -Amphetamine activation of ERK1/2 in Drd1a- and Drd2-expressing striatal neurons

Striatal region	pERK-immunoreactive/Drd1a-GFP+	pERK-immunoreactive/Drd1a-GFP−	Drd1a-GFP+ (%)	pERK-immunoreactive/Drd1a-GFP+	pERK-immunoreactive/Drd1a-GFP−	Drd2-GFP+ (%)
Dorsal lateral	4.5	0.25	95	0.25	7.25	3.3
Dorsal medial	12.5	1	93	1.0	15.75	6.0
Accumbens	35.2	3.25	92	7	63.75	9.6

Counts of phospho-ERK1/2-immunoreactive (pERK-immunoreactive) striatal neurons in different regions after d -amphetamine (10 mg/kg) in Drd1a-GFP and Drd2-GFP transgenic mice. Cell counts are the average numbers of pERK1/2-immunoreactive cells that colocalize with GFP-IR in a 100 μm² area in each region. For each region, the percentage of pERK-immunoreactive cells is calculated by summing pERK-immunoreactive-positive cells, which are either GFP positive (GFP⁺) or GFP negative (GFP⁻). Although the average number of pERK-immunoreactive cells varies from few in the dorsolateral striatum to many in the nucleus accumbens, >90% colocalize with GFP in Drd1a-GFP mice, whereas <10% colocalize with GFP in Drd2-GFP mice. These data indicate that >90% of striatal neurons in which ERK1/2 is activated after d -amphetamine treatment express the Drd1a receptor.