Corticotropin releasing factor enhances survival of cultured GABAergic cerebellar neurons after exposure to a neurotoxin

Abstract

Corticotropin-releasing factor (CRF), in addition to its role as a hormone in the stress response, functions as a neuromodulator in the cerebellum, where it enhances both the spontaneous and amino acid induced firing rate of Purkinje cells. In the cerebellum, CRF and its two types of receptors (CRF-R 1 and CRF-R 2) are present during cerebellar development at ages that precede the onset of afferent ingrowth and synaptogenesis, suggesting a distinct role during early cerebellar development. The present study was undertaken to determine whether CRF enhances the survival of cerebellar neurons, in particular GABAergic neurons. Primary cultures of cerebellar neurons obtained from embryonic day 18 mice were composed primarily, but not exclusively, of GABAergic neurons. Although CRF-R 1 is present in most neurons in this culture system, when CRF was added to the medium, no significant change in neuronal survival was observed when compared to control cultures. It is possible that a role for CRF is not seen in growth-promoting culture medium at the plating density chosen for this study and may only be evident when the cells have been exposed to conditions that reduce the likelihood of survival, such as exposure to neurotoxins such as AraC. We propose that, because AraC increases the number of cleaved caspase-3 positive cells, indicating apoptosis, it is possible that a CRF effect involves an inhibition of the apoptotic pathway. Cultures treated with AraC had a decrease in the total number of GABAergic neurons and an increase in apoptotic cells as measured with the apoptotic marker cleaved caspase-3. Co-treatment with CRF rescued many GABAergic neurons. It is interesting to note that apoptotic cells do not exhibit GABA or c-fos positive immunolabeling. Thus, these data support the concept that CRF plays a neuroprotective role in the survival of GABAergic cerebellar neurons in culture after exposure to a neurotoxin.