Projections from the amygdaloid complex to the claustrum and the endopiriform nucleus: A Phaseolus vulgaris leucoagglutinin study in the rat

Abstract

The claustrum and the endopiriform nucleus contribute to the spread of epileptiform activity from the amygdala to other brain areas. Data of the distribution of pathways underlying the information flow between these regions are, however, incomplete and controversial. To investigate the projections from the amygdala to the claustrum and the endopiriform nucleus, we injected the anterograde tracer Phaseolus vulgaris leucoagglutinin into various divisions of the amygdaloid complex, including the lateral, basal, accessory basal, central, anterior cortical and posterior cortical nuclei, the periamygdaloid cortex, and the amygdalohippocampal area in the rat. Analysis of immunohistochemically processed sections reveal that the heaviest projections to the claustrum originate in the magnocellular division of the basal nucleus. The projection is moderate in density and mainly terminates in the dorsal aspect of the anterior part of the claustrum. Light projections from the parvicellular and intermediate divisions of the basal nucleus terminate in the same region, whereas light projections from the accessory basal nucleus and the lateral division of the amygdalohippocampal area innervate the caudal part of the claustrum. The most substantial projections from the amygdala to the endopiriform nucleus originate in the lateral division of the amygdalohippocampal area. These projections terminate in the central and caudal parts of the endopiriform nucleus. Lighter projections originate in the anterior and posterior cortical nuclei, the periamygdaloid cortex, the medial division of the amygdalohippocampal area, and the accessory basal nucleus. These data provide an anatomic basis for recent functional studies demonstrating that the claustrum and the endopiriform nucleus are strategically located to synchronize and spread epileptiform activity from the amygdala to the other brain regions. These topographically organized pathways also provide a route by means of which the claustrum and the endopiriform nucleus have access to inputs from the amygdaloid networks that process emotionally significant information.

Expression ofDbx1,Neurogenin 2,Semaphorin 5A,Cadherin 8, andEmx1distinguish ventral and lateral pallial histogenetic divisions in the developing mouse claustroamygdaloid complex

“…Notably, neurons of this nucleus do not extend their dendrites into superficial strata of the insular cortex and are separated from it by the white matter of the capsula extrema, which makes them unlike the neurons of deep cortical layers (Ramón y Cajal, 1911). Considering in addition the independent organization and connections of the claustrum in the adult (Majak et al, 2002), we agree with previous authors who saw it as an independent nucleus topologically deep to the insula (de Vries, 1910;Filimonoff, 1966). Our data on Cad8 expression also show that the claustrum proper is related topologically to the insula and dorsal part of the piriform cortex, but is distinct from them.…”

“…In the claustral complex, some differences are also observed between LP versus VP derivatives regarding cortical connections. Thus, the claustrum proper is extensively and reciprocally connected with the cerebral cortex, including motor and somatosensory areas (Clascá et al, 1992;Dinopoulos et al, 1992;Majak et al, 2002). In contrast, the ventromedial claustrum and endopiriform nucleus show very few connections with the isocortex (Dinopoulos et al, 1992).…”

Differential modes of termination of amygdalothalamic and amygdalocortical projections in the monkey

“…Together, these differences strongly suggest that, as in rats, the AC and AT pathways originate from separate populations, although there are obviously multiple opportunities for convergence and interaction. For example, the amygdala and OFC both project to the claustrum (Majak et al, 2002) and to the nucleus accumbens (Russchen et al, 1985;Friedman et al, 2002;Price, 2003); and these broader connectivity loops may be supposed to play a fundamental role in amygdala associative functions.…”

Projections of the paraventricular and paratenial nuclei of the dorsal midline thalamus in the rat

“…BLA is an integral part of the "prelimbic circuit." BLA has strong links with PL (Sesack et al, 1989;McDonald, 1987McDonald, , 1991McDonald et al, 1996;Conde et al, 1995;Vertes, 2004;Gabbott et al, 2006;Hoover and Vertes, 2007), as well as with other parts of the circuit including the hippocampus, ACC, claustrum, and the insular cortex (McDonald, 1987;Brog et al, 1993;Petrovich et al, 1996;Pikkarainen et al, 1999;Majak et al, 2002).…”