Stereotaxic Mapping of the Monoamine Pathways in the Rat Brain*

TLDR

The study maps ascending monoamine pathways in the rat brain using fluorescent labeling after lesions, revealing that 5‑HT pathways share a distribution similar to the ventral noradrenergic pathway. The authors aim to detail the course of the nigro‑striatal and meso‑limbic dopamine pathways. They delineate pathway anatomy with frontal brain section drawings and determine origins and terminations by analyzing anterograde and retrograde degeneration following precise lesions. Ascending noradrenergic pathways split into dorsal and ventral bundles; the dorsal bundle, originating in the locus coeruleus, innervates cortex and hippocampus, while the ventral bundle supplies medulla, pons, mesencephalon, and diencephalon, and lesions of the locus coeruleus eliminate cortical terminals, underscoring its global influence.

Abstract

Abstract The ascending monoamine pathways in the rat brain are demonstrated by the pile up of fluorescent material occurring in the axons after various types of lesions. The anatomy of the pathways is outlined in drawings of frontal sections of the brain and the origin and termination of several pathways is determined by studying the anterograde and retrograde degeneration occurring after well localised lesions. It is possible to separate the ascending NA pathways into a dorsal and a ventral bundle of axons. The dorsal bundle innervates the cortex and the hippocampus and the ventral bundle supplies NA nerve terminals to the medulla, the pons, the mesencephalon and the diencephalon. The dorsal bundle is found to originate in the locus coeruleus. Lesions of this nucleus abolish the nerve terminals in all cortical areas and in several other areas of the brain indicating a unique role for the locus coeruleus in influencing the activity of the entire brain. The 5‐HT pathways have a distribution similar to the ventral NA pathyway. The course of the nigro‐striatal and the meso‐limbic DA pathways is presented in detail.