Calretinin in the thalamic reticular nucleus of the rat: Distribution and relationship with ipsilateral and contralateral efferents

Abstract

In order to investigate the existence of anatomical subdivisions within the thalamic reticular nucleus (Rt), the distribution of reticular neurons expressing the calcium binding protein calretinin was investigated in the rat by means of immunocytochemistry. Calretinin immunoreactive (Cr-ir) neurons were mainly distributed in the lateral and ventral regions, and along the medial border of the Rt rostral pole. Caudal to the rostral pole, many neurons were Cr-ir in the more dorsal part of the rostral two-thirds (the "dorsal cap") of the Rt. Fewer Cr-ir neurons were present more caudally along the lateral and medial borders, and in the caudalmost part of the nucleus, related to the acoustic thalamus. The distribution of Cr-ir neurons in the rostral Rt was compared with that of neurons projecting to the ipsilateral and contralateral anterior, intralaminar, midline, and mediodorsal nuclei, or to the contralateral rostral Rt. The retrograde transport of Fluorogold revealed a remarkably precise topography of the rostral Rt: different reticular areas were found to project to different thalamic nuclei, or to different rostrocaudal or mediolateral portions of the same thalamic nucleus, with a limited degree of overlap. The double-labeling experiments demonstrated that the reticular neurons projecting to the ipsilateral anterodorsal, midline, mediodorsal, and anterior intralaminar nuclei frequently expressed calretinin; by contrast, the majority of the reticular commissural neurons did not express the protein, with the exception of neurons projecting to the contralateral mediodorsal and midline nuclei. The ipsilaterally projecting calretinin-positive neurons were frequently located along the medial edge of the rostral pole and in the dorsal cap of the nucleus, segregated from the commissural calretinin-negative neurons. The combined analysis of calretinin expression patterns and tract tracing data provided further insight in the anatomical organization of the thalamic reticular nucleus, suggesting a different neurophysiological role for the ipsilaterally vs. the contralaterally projecting reticular neurons in the modulation of the synaptic activity of the dorsal thalamus.

Parvalbumin and GABA in the developing somatosensory thalamus of the rat: an immunocytochemical ultrastructural correlation

“…An inhomogeneous distribution of PVir (this study ;Mitrofanis 1992) and GABAir (A. Amadeo, personal communication) neurons was however observed in the rostral pole of RT at light microscopy, where a peculiar neurochemical content was also described in other studies (Arai et al 1994;Lizier et al 1997). As regards the somatosensory sector of RT, the ultrastructural finding of scarce PVir/GABAir terminals during development indicates that recurrent collaterals are rare in this area, thus confirming previous ultrastructural results (De Biasi et al 1996;.…”

Chondroitin sulfate proteoglycans in the rat thalamus: expression during postnatal development and correlation with calcium-binding proteins in adults

“…This nucleus belongs to the ventral thalamus and consists of a population of projecting gamma-aminobutyric-acid-ergic cells (De Biasi et al 1986) that provide an inhibitory innervation to all nuclei of the dorsal thalamus (Steriade et al 1997). The vast majority of Rt neurons express parvalbumin and, to a lesser extent, calretinin and calbindin (Celio 1990;Winsky et al 1992;Arai et al 1994;Lizier et al 1997). The present data demonstrate that the strongest labeling of the perineuronal nets and of the intervening neuropil matches the distribution of calretinin-positive neurons.…”

“…Moreover, a strong pericellular staining is associated with neurons distributed along the medial edge of the whole nucleus. These marginal neurons, although belonging to functionally different sectors, share a number of features, such as their morphology (Spreafico et al 1991), their preferential expression of calretinin (Lizier et al 1997;present study), and their distinctive expression of neurofilament subunits and adhesive molecules (A. Amadeo, personal communication), and may represent a subpopulation with distinct, although as yet unknown, functional properties. Interestingly, in the rat, neurons of the inner tier of the somatosensitive, visual, and acustic sectors of the Rt nucleus are connected with higher order thalamic nuclei and with secondary cortical areas (Guillery et al 1998).…”

“…Previous studies (Celio 1990;Arai et al 1994;Winsky et al 1992;Lizier et al 1997) have shown that most neurons of Rt contain parvalbumin, whereas calretinin and calbindin have a more restricted distribution.…”

“…In the present investigation, we have used immunocytochemical and immunoblotting techniques to study the expression of CSPGs in the thalamus of the rat during postnatal development. Moreover, with double-labeling techniques, we have investigated the distribution of perineuronal nets in adult thalamus in relation to the expression of the calcium-binding proteins that identify functionally distinct populations of neurons (Celio 1990;Arai et al 1994;Winsky et al 1992;Lizier et al 1997). …”