CALRETININ IMMUNOREACTIVITY IN THE DEVELOPING THALAMUS OF THE RAT - AMARKER OF EARLY GENERATED THALAMIC CELLS

The present work was aimed to study the immunocytochemical localizatio n of the calcium-binding protein, calretinin, in the rat thalamus from embryonic day 14 to the third postnatal week. In the adult rat thalam us, calretinin immunoreactivity is intensely expressed in some intrala minar and midline nuclei, as well as in selected regions of the reticu lar nucleus. At embryonic day 14, calretinin was expressed by immature and migrating neurons and fibres laterally to the neuroepithelium of the diencephalic vesicle in the region identified as reticular neuroep ithelium. At embryonic day 16, immunoreactive neurons were present in the primordium of the reticular nucleus and in the region of the retic ular thalamic migration. where neurons showed the morphology of migrat ory cells. At the end of embryonic development and in the first postna tal week, calretinin-positive neurons were observed in selected region of the reticular nucleus and it was intensely expressed in some intra laminar and midline nuclei. Bands of immunopositive fibres were also o bserved crossing the thalamus. During the second postnatal week, the i mmunolabelling in the reuniens, rhomboid, paraventricular and central medial thalamic nuclei remains very intense while a decrease of immuno reactivity in mediodorsal, centrolateral and laterodorsal nuclei was o bserved. The immunostaining of fibres, particularly evident in the per inatal period, progressively decreased and it was no longer visible by the end of the second postnatal week when the distribution and intens ity of calretinin immunostaining was similar to that observed in the a dult rat thalamus. The present findings indicate that the immunolocali zation of calretinin can be used to identify subsets of thalamic neuro nal population during pre-and postnatal maturation allowing also the d etection of the migratory pattern of early generated reticular thalami c neurons. (C) 1998 IBRO. Published by Elsevier Science Ltd.