Neurogenesis in the Caudate Nucleus of the Adult Rabbit
Journal of Neuroscience
Stem cells with the potential to give rise to new neurons reside in different regions of the adult rodents CNS, but in vivo only the hippocampal dentate gyrus and the subventricular zone-olfactory bulb system are neurogenic under physiological condition. Comparative analyses have shown that vast species differences exist in the way the mammalian brain is organized and in its neurogenic capacity. Accordingly, we have demonstrated recently that, in the adult rabbit brain, striking structural
... ing structural plasticity persists in several cortical and subcortical areas. Here, by using markers for immature and mature neuronal and glial cell types, endogenous and exogenously administered cell-proliferation markers, intraventricular cell tracer injections coupled to confocal analysis, three-dimensional reconstructions, and in vitro tissue cultures, we demonstrate the existence of newly formed neurons in the caudate nucleus of normal, untreated, adult rabbit. Our results suggest that neurogenesis in the caudate nucleus is a phenomenon independent from that occurring in the adjacent subventricular zone, mostly attributable to the activity of clusters of proliferating cells located within the parenchyma of this nucleus. These clusters originate chains of neuroblasts that ultimately differentiate into mature neurons, which represent only a small percentage of the total neuronal precursors. These results indicate that striatum of rabbit represents a favorable environment for genesis rather than survival of newly formed neurons. Experiments were conducted in accordance with current European Union and Italian law, under authorization of the Italian Ministry of Health number 66/99-A. All experiments were designed to minimize the numbers of animals used and their discomfort. Twenty-four sexually mature female (3.5-4 kg body weight; Charles River, Milan, Italy) New Zealand White HY/CR rabbits (Orictolagus cuniculus) were intraperitoneally injected with 5-bromo-2Ј-deoxyuridine (BrdU; Sigma, Steinheim, Germany) (40 mg/kg body weight in 0.1 M Tris). Seven rabbits were killed 2 h after a single BrdU injection. Seventeen rabbits received one daily injection of BrdU for 5 consecutive days and were killed 2 h (n ϭ 5), 10 d (n ϭ 3), 30 d (n ϭ 5), and 60 d (n ϭ 4) after the last injection. Animals were deeply anesthetized with a ketamine/xylazine solution (100 and 33 mg/kg body weight, respectively) and transcardially perfused with icecold saline solution (0.9% NaCl), followed by a freshly prepared solution of 4% paraformaldehyde (PFA) plus 2% picric acid in 0.1 M sodium phosphate buffer, pH 7.4. Brains were then postfixed overnight, cryoprotected, frozen at Ϫ80°C, and cryostat (25 and 40 m) sectioned in series.