Abstract
Retrograde tracing with choleratoxin B, injected into the nucleus accumbens (Ac) and bed nucleus of stria terminalis, lateral part (BSTL), yielded labeled perikarya in a ring-shaped area of arcopallium, including dorsal and hilar subdivisions, with a wedge-shaped node of dense accumulation in the amygdalopiriform area (APir). Also, the position of source neurons for this arcopallio-subpallial pathway was verified by anterograde tracing. Three subregions of arcopallium (amygdalopiriform, dorsal, hilar) were injected with dextran (10 kDa), and fibers and terminal fields were detected in Ac, BSTL and extended amygdala (EA). Most abundant projections to Ac arose from APir. The study enabled precise description of the main output fiber streams: the dorsal stream follows the dorsal border of arcopallium and, continuing in the ventral amygdalofugal tract, it traverses the EA and the BSTL before reaching the Ac. The ventral stream of fibers enters the EA along the ventral subpallial border and terminates in the basal nucleus and ventral pallidum. The course of the pathway was reconstructed in 3D. Retrogradely labeled arcopallial neurons were devoid of DARPP-32. DARPP-32 was present in the Ac but not the BSTL. No colocalization between the calcium binding proteins calbindin, parvalbumin and calretinin, and retrogradely labeled neurons was detected, despite a considerable territorial overlap. This finding further supports the excitatory nature of the arcopallial-accumbens pathway. Conjoint and convergent amygdalar input to EA, including BSTL, as well as to Ac subregions likely transmits fear and aggression related signals to both viscerolimbic (EA) and learned reward- and motivation-related (Ac) ventrobasal forebrain regions.
Highlights
The ventrobasal forebrain nuclei, including the nucleus accumbens (Ac), bed nucleus of stria terminalis, lateral part (BSTL) and other components of extended amygdala (EA), ventral pallidum (VP) and cholinergic cell groups have been implicated in the initiation and reinforcement of movements, motivation and emotion, reward and aversion (Alheid et al 1995; Alheid and Heimer 1988; de Olmos et al 2004; Li and Sakaguchi 1997)
Retrograde tracing with choleratoxin B, injected into the nucleus accumbens (Ac) and bed nucleus of stria terminalis, lateral part (BSTL), yielded labeled perikarya in a ring-shaped area of arcopallium, including dorsal and hilar subdivisions, with a wedge-shaped node of dense accumulation in the amygdalopiriform area (APir)
We found that axons arising from the APir follow two pathways: (1) medially along the dorsal border of the arcopallium (Fig. 2d0, d02, d03) to reach the vaf (Fig. 2d01) with terminal endings subsequently identified in the BSTL (Fig. 2d, d2, compare with Fig. 2a) or (2) a ventral course, passing through the ventrobasal part of EA (Fig. 2d, d1), and invading the nucleus basalis and olfactory tubercle
Summary
The ventrobasal forebrain nuclei, including the nucleus accumbens (Ac), bed nucleus of stria terminalis, lateral part (BSTL) and other components of extended amygdala (EA), ventral pallidum (VP) and cholinergic cell groups (such as the basal nucleus of Meynert) have been implicated in the initiation and reinforcement of movements, motivation and emotion, reward and aversion (Alheid et al 1995; Alheid and Heimer 1988; de Olmos et al 2004; Li and Sakaguchi 1997) These regions are extensively connected with the amygdala, whose involvement in emotional responses is well established (Phelps and LeDoux 2005; Swanson 2000). This may serve as justification for a comparative approach in the investigation of neural mechanisms, such as motivation of elementary actions, which have been conserved throughout vertebral evolution in both mammals and Sauropsida (diverging over 200 million years ago)
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