Calcium-binding proteins as markers of layer-I projecting vs. deep layer-projecting thalamocortical neurons: a double-labeling analysis in the rat.
The thalamus contains two main populations of projection neurons that selectively innervate different elements of the cortical microcircuit: the well-known "specific" or "core" (C-type) cells that innervate cortical layer IV, and, the "matrix" (M-type) cells that innervate layer I. Observations in different mammal species suggest that this may be a conserved, basic organizational principle of thalamocortical networks. Fragmentary observations in primate sensory nuclei suggest that M-type and C-type cells might be distinguished by their selective expression of calcium binding-proteins. In adult rats, we tested this proposal in a systematic manner throughout the thalamus. Applying Fast-Blue (FB) to a large swath of the pial surface in the lateral aspect of the cerebral hemisphere we labeled a large part of the M-type cell populations in the thalamus and subsequently examined FB co-localization with calbindin or parvalbumin immunoreactivity in thalamic neuron somata. FB-labeled cells were present in large numbers in the ventromedial, interanteromedial, posterior, lateral posterior and medial geniculate nuclei. Distribution of the FB-labeled neuron somata was roughly coextensive with that of the calbindin immunolabeled somata, while parvalbumin immunoreactive somata were virtually absent from dorsal thalamus. Co-localization of FB and calbindin immunolabeling ranged from >95% in the ventromedial and interanteromedial nuclei, to 30% in the dorsal lateral geniculate. Moreover, in the ventromedial and interanteromedial nuclei nearly all of the calbindin-immunoreactive neurons were also labeled with FB. In most other nuclei, however, a major population of M-type cells cannot be identified with calbindin immunolabeling. Consistent with studies in primates and carnivores, present data show that in rats M-type cells are numerous and widely distributed across the rat thalamus; however, calbindin is expressed only by a fraction, albeit a large one, of these cells.
Rubio-Garrido
P
P
Department of Anatomy and Neuroscience, Autonoma University School of Medicine, Avenida Arzobispo Morcillo s/n, Madrid, E-28029, Spain.
Pérez-de-Manzo
F
F
Clascá
F
F
D000578:Amidines; D000818:Animals; D064026:Calbindins; D002540:Cerebral Cortex / Q000166:cytology*; D005260:Female; D009434:Neural Pathways / Q000166:cytology; D009474:Neurons / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*; D013788:Thalamus / Q000166:cytology*
D000578:Amidines; D064026:Calbindins; D064030:S100 Calcium Binding Protein G; C031455:diamidino compound 253-50