Pattern of distribution of serotonergic fibers to the thalamus of the rat.
It is well established that serotonergic (5-hydroxytryptamine, 5-HT) fibers, mainly originating from the dorsal and median raphe nuclei of the brainstem, distribute throughout the forebrain, most heavily to 'limbic' forebrain structures. Few reports have examined the distribution of 5-HT fibers to the thalamus and none to our knowledge using immunoprocedures for the detection of the serotonin transporter (SERT)-a very sensitive marker for 5-HT fibers. Using immunohistochemical methods for SERT, we examined the pattern of distribution of 5-HT fibers to the thalamus in the rat. We show that serotonergic fibers are heavily concentrated in midline, intralaminar and association nuclei of the thalamus, and with the exception of the lateral geniculate complex, weakly distributed to principal nuclei of thalamus. Specifically, we demonstrate that 5-HT fibers are densely concentrated in the anteroventral, anteromedial and interanteromedial nuclei of the anterior thalamus, the paraventricular, rhomboid and reuniens nuclei of the midline thalamus, the central medial and central lateral nuclei of the intralaminar thalamus, the intermediodorsal nucleus, the lateral dorsal nucleus, and the dorsal and ventral lateral geniculate nuclei and intergeniculate leaflet of the LGN complex. Less densely innervated sites include the mediodorsal, paracentral, parafascicular, lateral posterior and submedial nuclei of thalamus. Remaining regions of the thalamus, largely consisting of principal nuclei, contained few 5-HT fibers. This pattern of 5-HT innervation indicates that serotonin/ serotonergic fibers mainly affect thalamic nuclei with connections to 'non-principal' or limbic regions of the cortex (or forebrain). This suggests that serotonergic fibers to the thalamus may exert a significant influence on affective and cognitive functions, possibly complementing the actions of 5-HT fibers to other parts of the brain involved in emotional and cognitive behaviors.
Vertes
Robert P
RP
Center for Complex Systems and Brain Sciences, Florida Atlantic University, Boca Raton, FL 33431, USA. vertes@ccs.fau.edu
Linley
Stephanie B
SB
Hoover
Walter B
WB
D000818:Animals; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D007124:Immunoenzyme Techniques; D008297:Male; D009412:Nerve Fibers / Q000378:metabolism*; D009434:Neural Pathways / Q000166:cytology* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D013787:Thalamic Nuclei / Q000166:cytology* / Q000378:metabolism
D016601:RNA-Binding Proteins; C482440:Sert1 protein, rat; D012701:Serotonin