Ej. Vanbockstaele et al., TOPOGRAPHY OF SEROTONIN NEURONS IN THE DORSAL RAPHE NUCLEUS THAT SENDAXON COLLATERALS TO THE RAT PREFRONTAL CORTEX AND NUCLEUS-ACCUMBENS, Brain research, 624(1-2), 1993, pp. 188-198
Diverse physiological actions have been reported for 5-hydroxytryptami
ne (5-HT, serotonin) in the medial prefrontal cortex (MPFC) and the nu
cleus accumbens (Acb) suggesting that the 5-HT innervation of these fo
rebrain areas may be derived from different populations of neurons. We
examined this possibility by mapping the distribution of 5-HT-immunor
eactive (ir) and non-5-HT-ir neurons containing retrograde labeling fo
llowing injections of different tracers into both these target regions
. The analysis was focused in the dorsal raphe nucleus (DRN) of the mi
dbrain, since 5-HT pathways to the MPFC and Acb primarily originate fr
om this area. Volume microinjections of the fluorescent retrograde tra
cer, Fluoro-Gold (FG), were placed into the MPFC and microinjections o
f cholera toxin B subunit coupled to 15 nm gold particles (CT-Au) were
placed into the Acb of the same animal. Sections through the DRN cont
aining retrogradely labeled neurons were further processed for immunof
luorescent localization of 5-HT using a rhodamine marker. Neurons retr
ogradely labeled from the Acb were greater in number overall than thos
e projecting to the MPFC. In addition, Acb-projecting neurons extended
into the lateral wings of the DRN, whereas MPFC-projecting neurons we
re more restricted to the midline. Both groups of retrogradely labeled
neurons, however, were more numerous in the caudal aspect of the dors
al raphe nucleus and were scattered amongst 5-HT immunoreactive perika
rya. Of 783+/-69 CT-Au labeled cells, 15% also contained the FG label
and 11% contained FG and 5-HT immunoreactivity. Of 613+/-48 FG labeled
cells, 24% also contained the CT-Au label and 21% were also immunorea
ctive to 5-HT. The results suggest a more prominent input to the Acb f
rom both 5-HT-ir and non-5-HT-ir neurons in the caudal aspect of the D
RN and further indicate that while most 5-HT-ir and non-5-HT-ir neuron
s project differentially to both forebrain regions, a few cells also s
how collateralization to the MPFC and Acb. Such collateralization of s
ingle serotonergic neurons to divergent targets may integrate cognitiv
e and motor activities in response to pharmacological manipulations of
ascending serotonergic pathways.