Fig. 10.     A: PHA-L injection site in the dorsal raphe nucleus. The same section stained for serotonin (5-HT) (A') reveals that many of the labeled neurons contain serotonin. B: A cholinergic neuron from the dorsal aspect of the HDB (arrow in D) is approached by PHA-L fibers with varicosities. C: Serotonin axon with varicosities in juxtaposition to cholinergic neurons in the same area of intact animal. Note the similar pattern of axonal arborization with respect to cholinergic neurons in B and C. Scale; A, A', and D = 100µm; B and C = 10µm. Abbrev. ac = anterior commissure; Aq = aqueductus cerebri; FStr = fundus striati; mlf = medial longitudinal fascicle.