Carnosine-like immunoreactivity in astrocytes of the glial tubes and in newly-generated cells within the tangential part of the rostral migratory stream of rodents.

In the nervous system, the aminoacylhistidine dipeptide carnosine (beta-alanyl-L-histidine) has been shown to be expressed in the olfactory receptor neurons and in brain astrocytes. Using immunocytochemical techniques, we report here a dense carnosine-like immunoreactivity in the subependymal layer of the rodent forebrain. Since the subependymal layer involves two distinct compartments (astrocytic cells forming glial tubes and newly-generated cells of the rostral migratory stream, here organized to form chains contained within the glial tubes [Brannon Thomas L. et al. (1996) Glia 17, 1-14; Jancovski A. and Sotelo C. (1996) J. comp. Neurol. 258, 112-124; Lois C. et al (1996) Science 271, 978-981; Peretto P. et al. (1997) Brain Res. Bull. 42, 9-21]), we investigated in detail the cellular distribution of carnosine-like immunoreactivity in this area. By using double labelling techniques with antisera raised against carnosine and specific markers of glial tubes or chains of migrating cells, we show that carnosine-like immunoreactivity is associated with both the compartments. On the other hand, unlike markers of the rostral migratory stream, carnosine-like immunoreactivity was not observed in isolated, migrating cells located outside the subependymal layer, which spread through the olfactory bulb in a radially-oriented manner. This suggests that carnosine is transiently expressed by cells of the rostral migratory stream when moving in the tangentially-oriented part of the migration route. Moreover, we investigated the distribution of carnosine-like immunoreactivity in the postnatal rat forebrain and found that it is detectable in the subependymal layer only starting from the third postnatal week, although it is well known that the dipeptide is present in the olfactory receptor neurons since the embryonic day 16 [Biffo S. et al. (1992) J. chem Neuroanat. 5, 5162]. Taken together, these results show that camosine, other than abundantly present in astrocytes of the glial tubes, is associated to the tangential part of the rostral migratory stream.