The medial forebrain bundle of the rat. II. An autoradiographic study of the topography of the major descending and ascending components

Abstract

The medial forebrain bundle (MFB) is a complex fiber system that courses through and partly arises and partly terminates within the lateral preoptic and lateral hypothalamic areas. It consists mainly of thin fibers and may be comprised of as many as 50 descending and ascending components of varying lengths and of different origins and/or destinations (Nieuwenhuys et al., '82). With the aid of an an atlas of the MFB and the surrounding brain areas in the rat presented in the preceding paper (Nieuwenhuys et al., '82), the position and topographic relationships of some 21 components of the bundle have been analyzed in detail, in brains that had been prepared for autoradiography following injections of tritiated amino acids into a number of structures that are known to contribute fibers to the MFB. From this analysis it is clear that most of the labeled components occupy specific and rather constant positions within the MFB. For example, the ascending components are largely confined to the dorsal half of the bundle; those arising from the medial preoptic area and the various hypothalamic nuclei are distributed rather diffusely over much of the MFB; and the descending components that arise from the olfactory tubercle and the magnocellular preoptic nucleus are confined to restricted parts of the bundle. These findings indicate that the neurons which occupy different parts of the lateral hypothalamic area probably receive distinctive inputs, and to a first approximation these are likely to be determined principally by their position within the MFB.

In vivo comparison of the regulation of releasable dopamine in the caudate nucleus and the nucleus accumbens of the rat brain

“…Electrical stimulation of the MFB, a major pathway for many neuronal systems (Nieuwenhuys et al, 1982;Veening et al, 1982), should excite dopaminergic fibers in the mesolimbic and nigrostriatal systems. It is not surprising, then, that dopamine release should occur following stimulation of these fibers.…”

Intracranial Self-Stimulation to Evaluate Abuse Potential of Drugs

“…For example, ICSS promotes DA release in nucleus accumbens; it is enhanced by drugs that themselves increase extracellular DA levels in nucleus accumbens, and it is blocked by drugs that deplete DA or block DA receptors (Stellar and Stellar, 1985;Phillips et al, 1989;Fiorino et al, 1993;Wise, 1998;You et al, 2001;Cheer et al, 2005) [but see (Miliaressis et al, 1991;Kruk et al, 1998)]. Mesolimbic DA neurons constitute one subset of neurons that project through the MFB Veening et al, 1982), and optogenetic studies suggest that direct activation of these neurons is sufficient to maintain ICSS (You et al, 2001;Kim et al, 2012). However, electrical stimulation of the MFB or VTA is not thought to produce direct activation of mesolimbic DA neurons, in part because electrophysiological data summarized above suggest ICSS mediation by descending myelinated axons rather than by ascending unmyelinated axons like those from mesolimbic DA neurons.…”

Inhibitory Pathway for Female Sexual Behavior in Male Rat Brain: Effect of Medial Forebrain Bundle (MFB) Cuts.

“…Anatomical evidence suggests that the axons of the septum which leave from the ventrolateral side join to the MFB [9]. The preoptic area also sends the axons to the MFB.…”

“…The preoptic area also sends the axons to the MFB. The neural fibers from the septum and the preoptic area compose the medial part of the MFB [9,18]. The projections of the amygdala pass in the lateral part of the MFB.…”