Organization of serotoninergic projections from the raphé nuclei to the anterior thalamic nuclei in the rat: a combined retrograde tracing and 5-HT immunohistochemical study.
We combined retrograde transport of horseradish peroxidase (HRP) with 5-hydroxytryptamine (5-HT) immunohistochemistry to study serotoninergic projections to the anterior thalamic nuclei (ATN) of the rat. Small iontophoretic injections of HRP into the anterodorsal thalamic nucleus resulted in double-labelled neurons predominantly in the ventromedial and also in the ventrolateral part of the ipsilateral dorsal raphé (DR). A smaller number of double-labelled neurons was also found in the dorsomedial part of the nucleus, predominantly ipsilaterally, and in the median raphé nucleus (MnR), close to the midline. After injection into the medial subdivision of the anteroventral thalamic nucleus, the pattern of labelling in DR and MnR was similar to that detected following injections into the anterodorsal thalamic nucleus. However, injection into the posterior subdivision of the anteroventral thalamic nucleus resulted in bilateral retrograde labelling of a few 5-HT-containing neurons in the dorsolateral part of the DR. Labelling in the ventromedial, ventrolateral and dorsomedial regions of DR and MnR was similar to that detected after injections into the medial subdivision of the anteroventral thalamic nucleus. After all injections into the ATN, double-labelled cells were found throughout the rostrocaudal extent of MnR and throughout the rostral two-thirds of DR. The caudal extension of DR was devoid of double-labelled cells. Although double-labelled cells were observed bilaterally in the dorsolateral part of the DR, the projection from DR to ATN was predominantly ipsilateral. These results show that there is an internal organization within DR such that subnuclei of the DR can be defined on the basis of their efferent projections to specific subdivisions of the ATN.
Gonzalo-Ruiz
A
A
Department of Anatomy, School of Physiotherapy, Soria, Spain.
Lieberman
A R
AR
Sanz-Anquela
J M
JM
D000344:Afferent Pathways; D000818:Animals; D001692:Biological Transport; D001931:Brain Mapping; D006735:Horseradish Peroxidase / Q000493:pharmacokinetics; D007150:Immunohistochemistry; D008297:Male; D011903:Raphe Nuclei / Q000033:anatomy & histology / Q000737:chemistry*; D051381:Rats; D012701:Serotonin / Q000032:analysis*; D013787:Thalamic Nuclei / Q000033:anatomy & histology / Q000737:chemistry*
D012701:Serotonin; D006735:Horseradish Peroxidase