title: Intracellular horseradish peroxidase labeling of rapidly firing dorsal raphe projection neurons.
abstract: The class of rapidly firing neurons in the dorsal raphe of the rat was examined using extracellular recording and intracellular injection of horseradish peroxidase. Rapidly firing neurons (termed F-cells in this report) continue to fire at high spontaneous rates during intracellular recording. This and their brief (ca. 1 ms) and symmetrical action potentials distinguish them from the slowly firing, presumably serotonergic neurons in dorsal raphe. Intracellular labeling with horseradish peroxidase reveals that F-cells have small (10-15 microns) spherical, multipolar or piriform somata. Somatic spines are sparse or entirely absent. The general form of the dendritic tree is radiant and poorly branching. However, the dendrites of F-cells take two forms, with both forms being present on the same neuron so that besides having a complement of poorly branching dendrites, each F-cell has at least one dendrite with a slightly tufted branching pattern: a short primary dendrite gives rise to 3 or 4 secondary branches. The axons of F-cells project from the nucleus. They align themselves along the trajectories of known dorsal raphe efferent pathways, coursing laterally and ventrorostrally beyond the bounds of the nucleus. Morphometric measurements of retrogradely labeled dorsal raphe projection neurons provide additional evidence that small projection neurons exist.
mesh_terms: D000200:Action Potentials; D000818:Animals; D001369:Axons; D003712:Dendrites; D007091:Image Processing, Computer-Assisted; D008297:Male; D011903:Raphe Nuclei / Q000166:cytology* / Q000502:physiology; D051381:Rats; D012701:Serotonin / Q000502:physiology; D009435:Synaptic Transmission
chemical_list: D012701:Serotonin