Latexin and calretinin together define a novel excitatory neuron subclass in the claustrum of the short-tailed fruit bat, Carollia perspicillata.

The claustrum is a telencephalic structure with inputs from and outputs to many other brain structures. This central arrangement has motivated research on the claustrum's role in cognition and highlights the need to understand its intrinsic connectivity. In the fruit bat, Carollia perspicillata, the large size of the claustrum offers access to its intrinsic structure. Previously, we defined the structure of the C. perspicillata claustrum with antibodies against latexin as an excitatory cell marker and against calcium-binding proteins as inhibitory cell markers. Using this immunohistochemical method, we have now identified an unexpected cell type with concurrent latexin and calretinin immunoreactivity. The calretinin(+) neurons of the claustrum, including those that coexpress GAD67 (another inhibitory cell marker) and those that coexpress latexin, are located in the claustral shell subregion. Neuronal latexin(+)/calretinin(+) somata are smaller than either latexin(-)/calretinin(+) or latexin(+)/calretinin(-) somata. Since latexin labels glutamatergic neurons in multiple brain areas and has never been found to colocalize with GAD, we conclude that the latexin(+)/calretinin(+) neurons in the claustral shell are excitatory. They represent one of three excitatory cell types that are identifiable in the claustral shell and demonstrate that calretinin can label both inhibitory and excitatory cells in the C. perspicillata claustrum.