Abstract 866, Date 1:00 pm, Sunday, February 20, 2005 (24 hours)
Session : D9: Auditory Brainstem: Molecular Aspects
     Distribution of the Vesicular Glutamate Transporters VGluT1 and VGluT2 in Central Auditory Nuclei
Rafael Luj‡n, Joaquin Soriano, Elena Caminos, Carmen Diaz, Juan Ramon Martinez Gal‡n, Jose M. Juiz
     Glutamate is the major central excitatory neurotransmitter, including the auditory pathway. Identification of auditory neurons releasing glutamate is important to understand the functional organization of neuronal circuits involved in auditory processing. Such identification has been hampered by the lack of markers with sufficient specificity to label neurons and neuronal elements, particularly synaptic endings, involved in excitatory glutamatergic neurotransmission. Antibodies to glutamate, metabolic precursors, and synthetic or degradative enzymes are limited in that they label glutamatergic and non-glutamatergic neuronal populations. We analyzed the immunocytochemical distribution of the vesicular glutamate transporters VGluT1 and VGluT2 in central auditory nuclei. Wistar rats were perfused transcardially with 2 to 4% paraformaldehyde. Brain stem sections containing different auditory nuclei were incubated with anti-VGluT1 or anti-VGluT2 polyclonal antibodies and immunoreactivity was detected either with immunoperoxidase or immunofluorescence methods. VGluT1 immunoreactivity was abundant and intense in the cochlear nucleus and superior olivary complex. Immunolabeling was present in structures resembling axonal endings, a finding confirmed using double labeling experiments with anti-synaptophysin antibodies. In the anteroventral cochlear nucleus and medial nucleus of the trapezoid body, many labeled endings had the usual morphology associated with endbulbs and chalyces of Held, embracing or decorating unlabeled cell bodies. Other VGluT1 labelled structures had a more bouton-like appearance. With respect to VGluT2, this transporter seemed to be less abundant than VGluT1 and followed a different distribution pattern. Thus, VGluT2 is present in bouton-like structures of the cochlear nucleus and superior olivary complex. Some regions and layers of the dorsal cochlear nucleus were particularly enriched in VGluT2 immunolabeling. These findings strongly suggest that VGluTs are specifically concentrated in excitatory synaptic endings. Differences in the distribution of VGluT1 and VGluT2 indicate that there may be molecular and functional differences among populations of excitatory endings in auditory brain stem nuclei, which require further study. Supported by grants PAI-03-015 (Consejeria de Ciencia y Tecnolog’a, JCCM) and BFI2003-0914-CO2-02 (Ministerio de Ciencia y Tecnolog’a), Spain.