A: histologically identified microdialysis probe and microinjection placements from brain stem coronal slices stained with neutral red. Black rectangles, placement of microdialysis membranes used in microdialysis collection. Open rectangles, placement of microdialysis membranes used in microperfusion experiments. +, Placement of muscimol microinjections. IC, inferior colliculus; CP, cerebral pedunclc; LDT, laterodorsal tegmental nucleus: BC, brachium conjunctivum: PAG. periaqueductal gray, MLF, medial longitudinal fasciculus; BP. brachium pontis; FTC, central tegmental field; PI, AP0, anterior-posterior stereotaxic planes. B: photomicrograph of a microinjection site (dark lesioned area) on midline of the ventral PAG. C: photomicrograph of area outlined in B, demonstrating placement of microinjection within a population of neurons immunopositive for 5-hydroxytryptamine.