Projections between the interpeduncular nucleus and basal forebrain in the rat as demonstrated by the anterograde and retrograde transport of WGA-HRP

Abstract

The distribution of anterogradely-labeled fibers and retrogradely-labeled cell bodies in the interpeduncular nucleus (IPN) was mapped after injections of wheat-germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into various structures of the basal forebrain in adult rats. WGA-HRP injections into the medial septum/vertical limb of the diagonal band nucleus resulted in: 1) dense anterograde labeling in the rostral, intermediate, and central subnuclei; and 2) retrograde labeling in the apical and central subnuclei. Injections into the lateral septum produced: 1) no anterograde labeling in the IPN; and 2) retrograde labeling which was dense in the apical subnucleus, moderate in the central and lateral subnuclei, and light in the intermediate subnucleus. Injections into the horizontal limb of the diagonal band nucleus resulted in: 1) anterograde labeling which was most pronounced in the central, rostral, and intermediate subnuclei; and 2) retrograde labeling which was strongest in the apical, central, and lateral subnuclei. After injections into the substantia innominata-magnocellular preoptic nucleus, there was: 1) dense anterograde labeling in the rostral and central subnuclei and moderate anterograde labeling in the intermediate subnucleus; and 2) essentially no retrograde cell labeling in the IPN. These findings demonstrate that the IPN receives inputs from, and projects to specific portions of the basal forebrain. The rostral and central subnuclei are the primary targets of inputs from the basal forebrain to the IPN, and the apical subnucleus is the primary source of IPN projections to the basal forebrain.

Efferent connections of septal nuclei of the domestic chick (Gallus domesticus): An anterograde pathway tracing study with a bearing on functional circuits

“…This projection may be equivalent to the observed avian septal projection on TO and perhaps also to CPi. In mammals, SM and DBB send efferents to different subdivisions of the interpeduncular nucleus (Hamill and Jacobowitz, 1984;Vertes and Fass, 1988). No such connections were observed in the present study.…”

“…Efferents from DBB also terminate in VTA (Meibach and Siegel, 1977a;Krayniak et al, 1980). The dorsal tegmental nucleus and the interpeduncular nucleus receive afferents from the septum and DBB (Krayniak et al, 1980;Hamill and Jacobowitz, 1984;Liu et al, 1984;Vertes and Fass, 1988).…”

Functional topography of midbrain and pontine serotonergic systems: implications for synaptic regulation of serotonergic circuits

“…The septum and IPN appear to have reciprocal connections via acetylcholinergic (Woolf and Butcher 1985) and serotonergic axons, respectively. The IPN as a whole is a major target of cholinergic innervation from the vertical and horizontal limbs of the nucleus of the diagonal band and magnocellular preoptic area, and the dorsolateral tegmental nucleus, as well as a few cells from the medial septum, substantia innominata, nucleus basalis, and the pedunculopontine tegmental nucleus (Shibata et al 1986;Vertes and Fass 1988;Woolf and Butcher 1985). Consistent with a pattern of extensive raphe-raphe projections, the MnR is a major source of afferents to the IPA (Shibata et al 1986).…”

“…Instead, the IPA is the major source of IPN projections to the basal forebrain and hippocampus. Neurons within the IPA, similar to those in the adjacent MnR nucleus, project via the medial forebrain bundle to the supramammillary region, the medial and lateral hypothalamus, vertical and horizontal limbs of the nucleus of the diagonal band, and the medial and lateral septal nuclei, and project via the fornix to the hippocampus (Groenewegen et al 1986;Imai et al 1986b;Vertes and Fass 1988). In the case of projections to the septum/nucleus of the diagonal band and hippocampus, these have been confirmed to include serotonergic projections, some of which are collateral projections to both nuclei (Montone et al 1988).…”

Modulation of hippocampal theta oscillations and spatial memory by relaxin-3 neurons of the nucleus incertus

“…It is also well established that hippocampal theta rhythm is dependent on the integrity of an ascending pathway originating from the brainstem reticular formation and that the RPO is an effective theta-generating nucleus of the brainstem (Nuñez et al 1991;Vertes et al 1993). The RPO, however, does not have direct projections to the MS and other subcortical pacemaker regions (Vertes and Fass 1988). Recent evidence suggests that brainstemgenerated theta rhythm occurs through a multisynaptic pathway via the NI (Nuñez et al 2006;Teruel-Marti et al 2008), which has strong connectivity with the MS, SuM, and interpeduncular nuclei, and with the hippocampus itself (Goto et al 2001;Olucha-Bordonau et al 2003); and lesion or muscimol inactivation of the NI abolishes RPO-stimulated theta activity (Nuñez et al 2006).…”