The dorsal raphe nucleus through its extensive efferents has been implicated in a
great variety of physiological and behavioural functions. However, little is know
about its afferents. Therefore, to identify the systems likely to influence the activity
of serotonergic neurons of the dorsal raphe nucleus, we re-examined the forebrain
afferents to the dorsal raphe nucleus using cholera toxin b subunit and Phaseolus
vulgaris-leucoagglutinin as retrograde or anterograde tracers. With small cholera
toxin b subunit injection sites, we further determined the specific afferents to the
ventral and dorsal parts of the central dorsal raphe nucleus, the rostral dorsal raphe
nucleus and the lateral wings. In agreement with previous studies, we observed a large
number of retrogradely-labelled cells in the lateral habenula following injections
in all subdivisions of the dorsal raphe nucleus. In addition, depending on the subdivision
of the dorsal raphe nucleus injected, we observed a small to large number of retrogradely-labelled
cells in the orbital, cingulate, infralimbic, dorsal peduncular, and insular cortice,
a moderate or substantial number in the ventral pallidum and a small to substantial
number in the claustrum. In addition, we observed a substantial to large number of
cells in the medial and lateral preoptic areas and the medial preoptic nucleus after
cholera toxin b subunit injections in the dorsal raphe nucleus excepting for those
located in the ventral part of the central dorsal raphe nucleus, after which we found
a moderate number of retrogradely-labelled cells. Following cholera toxin b subunit
injections in the dorsal part of the central dorsal raphe nucleus, a large number
of retrogradely-labelled cells was seen in the lateral, ventral and medial parts of
the bed nucleus of the stria terminalis whereas only a small to moderate number was
visualized after injections in the other dorsal raphe nucleus subdivisions. In addition,
respectively, a substantial and a moderate number of retrogradely-labelled cells was
distributed in the zona incerta and the subincertal nucleus following all tracer injections
in the dorsal raphe nucleus. A large number of retrogradely-labelled cells was also
visualized in the lateral, dorsal and posterior hypothalamic areas and the perifornical
nucleus after cholera toxin b subunit injections in the dorsal part of the central
raphe nucleus and to a lesser extent following injections in the other subdivisions.
We further observed a substantial to large number of retrogradely-labelled cells in
the tuber cinereum and the medial tuberal nucleus following cholera toxin b subunit
injections in the dorsal part of the central dorsal raphe nucleus or the lateral wings
and a small to moderate number after injections in the two other dorsal raphe nucleus
subdivisions. A moderate or substantial number of labelled cells was also seen in
the ventromedial hypothalamic area and the arcuate nucleus following cholera toxin
injections in the dorsal part of the central dorsal raphe nucleus and the lateral
wings and an occasional or small number with injection sites located in the other
subdivisions. Finally, we observed, respectively, a moderate and a substantial number
of retrogradely-labelled cells in the central nucleus of the amygdala following tracer
injections in the ventral or dorsal parts of the central dorsal raphe nucleus and
a small number after injections in the other subnuclei. In agreement with these retrograde
data, we visualized anterogradely-labelled fibres heterogeneously distributed in the
dorsal raphe nucleus following Phaseolus vulgaris-leucoagglutinin injections in the
lateral orbital or infralimbic cortice, the lateral preoptic area, the perifornical
nucleus, the lateral or posterior hypothalamic areas, the zona incerta, the subincertal
nucleus or the medial tuberal nucleus. (ABSTRACT TRUNCATED)