Calretinin (CR) is a calcium binding protein that is found in subpopulations of brain neurons such as the substantia nigra (SN) and cortex. Because CR has been linked to neuroprotective functions in the SN, we decided to treat mesencephalic cultures with L-DOPA, the precursor to the neurotransmitter dopamine, and a drug used to treat Parkinson's disease. We found that many TH-containing neurons were very sensitive to L-DOPA in culture and over 60% were lost after treatment. When CR was colocalized with TH in dopaminergic neurons, these neurons were immune to the deleterious effects of L-DOPA. We wished to examine whether this sparing of CR-containing neurons in the mesencephalon was found in other embryonic primary neuronal cultures. We developed a new dissection procedure to isolate a diencephalic area rich in CR neurons and examined both diencephalic and cortical CR-containing neurons for resistance to excitatory amino acids. We found no evidence for sparing in either subpopulation. In addition, when we used a calcium ionophore to elevate cytosolic calcium concentrations, we found no evidence for resistance in CR-containing cortical neurons. While CR has consistently been found in spared neurons of the mesencephalon, we have concluded that the presence of CR in a neuron is not sufficient to protect it against either excitatory amino acid toxicity or calcium overload.
