Ascending Monoamine Neurons to the Telencephalon and Diencephalon

Abstract

By means of sensitive and specific methods for histochemical and biochemical determination of dopamine (DA), noradrenaline (NA) and 5‐hydroxytryptamine (5‐HT) we have succeeded in demonstrating and mapping out a number of ascending monoamine neuron systems from the lower brain stem by studying the anterograde and retrograde changes that occur in these neurons after various types of brain lesions. In this way it has been possible to discover: 1) a large, uncrossed nigro‐neostriatal DA neuron system; 2) a DA neuron system, arising from cell‐bodies in the mesen‐cephalon, ascending uncrossed in the medial forebrain bundle close to the nigro‐neostriatal DA fibres, and innervating e.g. the tuberculum olfactorium and nuc. accumbens; 3) ascending NA neuron systems with cell‐bodies situated mainly in the medulla oblongata and pons (locus coeruleus, formatio reticularis), and axons running uncrossed mainly in the medial forebrain bundle, innervating e.g. the limbic forebrain structures, the neocortex and the hypothalamus; 4) ascending 5‐HT' neurons with cell‐bodies situated mainly in the raphe nuclei of the mesencephalon (nuc. raphe dorsalis, nuc. raphe medianus), and axons running uncrossed mainly in the medial forebrain bundle, innervating e.g. the limbic forebrain structures and the hypothalamus. The effects observed on the amine levels of the neurons represent intraneuronal and not transsynaptic changes.

Cross-hemispheric dopamine projections have functional significance

“…The magnitude and frequency of dopamine transients increase in response to drugs of abuse (12,13), which is thought to contribute to their reinforcing properties (14). Although numerous studies have summarized the function of dopamine circuits in reward-based behaviors (15,16) and motor control (17)(18)(19), anatomic descriptions of dopamine projections are conflicting (20)(21)(22)(23). Recent evidence suggests that some dopamine neurons project contralateral to their origin (22,23), contradictory to the uncrossed dopamine system described previously (20,21).…”

Actions of 5‐hydroxytryptamine and 5‐HT1A receptor ligands on rat dorso‐lateral septal neurones in vitro

“…In limbic areas innervated by raphe 5-hydroxytryptaminergic neurones (Anden et al, 1966;Ungerstedt, 1971;Azmitia & Segal, 1978) there is a high density of 5-HTIA receptors (Gozlan et al, 1983;Kdhler, 1984;Pazos & Palacios, 1985), the activation of which inhibits neuronal firing (VanderMaelen & Aghajanian, 1983;Sprouse & Aghajanian, 1988). However, the actions of proposed agonists and antagonists at 5-HTA receptors in these areas is non-uniform and the underlying mechanisms are, at present, far from clear.…”

HIT and brain reward function: A case of mistaken identity (theory)

“…Some took the distribution of DA in the brain to indicate a function unique to this previously-overlooked neurotransmitter (Carlsson, 1959). Advancements in histochemical methods allowed researchers to trace the brain pathways of catecholamine neurons within a decade, leading to the discovery of a nigro-neostriatal DA neuron system, and DA pathways projecting from the substantia nigra pars compacta and the ventral tegmental area (Dahlstrom & Fuxe, 1965;Anden et al 1966;Hornykiewicz, 1966).…”