Stereotaxic mapping of the monoamine pathways in the rat brain

Catecholamine-containing neurones and electrical self-stimulation. 1. A review of some data

SYNOPSIS Experimental data on the location in the brain of electrode sites supporting electrical self-stimulation are reviewed. All previous studies are in agreement that the behaviour is most easily elicited from lateral hypothalamic sites corresponding approximately to the fibre pathways known as the ‘medial forebrain bundle’. Some brainstem electrode sites will support self-stimulation. Experiments are summarized which indicate that there is a correlation between the sites of electrode tips positive for self-stimulation and the location of catecholamine-containing neurones in two regions: (1) in the region of the dopamine-containing cells in the ventral mesencephalon (cell-body groups A9 and AIO of Dahlstr¨m and Fuxe, 1964), and (2) in the region of the noradrenaline-containing cells of the locus coeruleus (A6 group). These two cell-body groups give rise to axons which pass through the medial forebrain bundle to form terminal systems with a widespread distribution in the prosencephalon. The hypothesis is advanced that electrical self-stimulation results in the majority of cases from activation of one or both of these catecholamine-containing systems.

The use of dopamine -hydroxylase as a marker for the central noradrenergic nervous system in rat brain

Improvements in the method for localization of dopamine-beta-hydroxylase by immunofluorescence allow the observation of noradrenergic-cell bodies, non-terminal fibers, and axon terminals in the rat brain. The distribution of the hydroxylase correlated well with the results obtained by localization of norepinephrine. Dopamine-beta-hydroxylase was not observed in dopaminergic neurons or terminals, indicating that these cells do not have the capacity to synthesize norepinephrine. The use of the hydroxylase as a marker, however, has made it possible to visualize noradrenergic nerve terminals on small arteries in the brain parenchyma that have not been described by catecholamine-fluorescence histochemistry. The source of the terminals on small arteries appears to be central noradrenergic neurons rather than the peripheral sympathetic nervous system. Dopamine-beta-hydroxylase generally was not observed in the large arteries of the brain parenchyma. These observations suggest that cerebral microcirculation is regulated by central noradrenergic neurons.