Seasonal differences in ventricular proliferation of adult Gallotia galloti lizards.

Lizards present neuronal production throughout the telencephalon in their adult state, both naturally and after experimentally induced brain lesions. As in birds, lizards present seasonal behavioural variations. In birds, such variations have been shown to alter neuronal production. In birds and mammals, lack of stimuli or exposure to stress interferes with adult neurogenetic capacity. The effect of this type of study has not been performed with lizards. In the present study we used bromodeoxyuridine to label dividing cells in the ventricular walls of Gallotia galloti lizards during all four seasons and we investigated the effect of captivity on such proliferation. We found that G. galloti presented a particular distribution that differed from that previously described in other reptiles with respect to regions of greater or lesser proliferative rate. In addition, proliferative rate varied seasonally, with greater production of cells in Spring and low production in Autumn and Winter. Proliferative rate was significantly lower throughout the telencephalon and during all seasons in those lizards kept in captivity as compared with wild animals, even though photoperiod and temperature were similar to natural conditions. Our results indicate that cell production in lizards is species-dependent, varies with seasons and is significantly reduced in captive animals.

Study of adult neurogenesis in the Gallotia galloti lizard during different seasons.

In a previous study we found a seasonal distribution of cell proliferation (the first stage of adult neurogenesis) in the telencephalic ventricular walls of the adult Gallotia galloti lizard. The aim of the present work was to determine the influence of seasonality on the subsequent migration of the resulting immature neurons. We used wild animals injected with bromodeoxyuridine and kept in captivity within 30 days. To confirm the neuronal identity of these cells, we used double immunohistochemical 5-bromo-2'-deoxyuridine (BrdU) and doublecortin (DCX, an early neuronal marker) labeling, as well as autoradiography after the administration of methyl-[³H]thymidine ([³H]T). We found that: (1) the rate of cell division and/or migration from the ventricular walls varied with the season, especially in regions related with olfaction. (2) Immature neuron-like cells appeared to migrate in an apparently radial and tangential way towards different parts of the telencephalic parenchyma. (3) We did not observe ultrastructurally mature neurons until at least 90 days later, a period considerably greater than that reported for other species of vertebrates in similar studies.

A Nissl, Golgi-Kopsch and ultrastructural study of the Gallotia galloti red nucleus.

The object of this study was to understand the different types of morphological neurons of the Gallotia galloti red nucleus using quantitative and qualitative analysis, under the aspects of optical (Nissl and Golgi-Kopsch) and electronic microscopy. The results from this study and considering the size, the distribution of NISSL bodies and the dendritic arborization, we have identified three neuronal types: ellipsoidal or ovoid (15 microns), triangular (15-35 microns) and polygonal (20-50 microns). In general the polygonal neurons contain a cytoplasm with abundant organelles, well developed Nissl bodies, perinuclear Golgi complex, numerous mitochondria, an ovoid nucleus and multiple dendrites. The triangular neurons have a similar structure, although the dendritic model is less ramified than that of the polygonal and the ellipsoidal neurons contain a smaller cytoplasm with less dendritic ramification. The contact with spines is not very frequent but can be observed in somas and dendrites. The neuronal population is heterogeneous and therefore neither the magnocellular part nor the other parvicellular were observed separately, but a mixture of both.