Distribution of vesicular glutamate transporters in the brain of the turtle (Pseudemys scripta elegans)

The distribution of glutamatergic neurons has been extensively studied in mammalian and avian brains, but its distribution in a reptilian brain remains unknown. In the present study, the distribution of subpopulations of glutamatergic neurons in the turtle brain was examined by in situ hybridization using probes for vesicular glutamate transporter (VGLUT) 1-3. Strong VGLUT1 expression was observed in the telencephalic pallium; the mitral cells of the olfactory bulb, the medial, dorsomedial, dorsal, and lateral parts of the cerebral cortex, pallial thickening, and dorsal ventricular ridge; and also, in granule cells of the cerebellar cortex. Moderate to weak expression was found in the lateral and medial amygdaloid nuclei, the periventricular cellular layer of the optic tectum, and in some brainstem nuclei. VGLUT2 was weakly expressed in the telencephalon but was intensely expressed in the dorsal thalamic nuclei, magnocellular part of the isthmic nucleus, brainstem nuclei, and the rostral cervical segment of the spinal cord. The cerebellar cortex was devoid of VGLUT2 expression. The central amygdaloid nucleus did not express VGLUT1 or VGLUT2. VGLUT3 was localized in the parvocellular part of the isthmic nucleus, superior and inferior raphe nuclei, and cochlear nucleus. Our results indicate that the distribution of VGLUTs in the turtle brain is similar to that in the mammalian brain rather than that in the avian brain.