Co-expression of GAD67 and Choline Acetyltransferase in Neurones in the Mouse Spinal Cord and Medulla Oblongata

GABAergic and cholinergic interneurones play an important role in modulating activity of neuronal circuits within the spinal cord and medulla oblongata. This study investigates the spatial distribution of co-localisation of the synthesising enzymes for ACh/GABA in the spinal cord and medulla oblongata. Immunohistochemistry, retrograde neuronal tracing and juxtacellular labelling were employed in combination with mice in which a green fluorescent protein (GFP) is expressed under the control of the promoter of the GABA synthesising enzyme, glutamic acid decarboxylase 67 (GAD67-GFP mice). Within the cervical, thoracic and lumbar spinal cord the majority of GAD67-GFP neurones co-localising with the ACh synthesising enzyme choline acetyltransferase (ChAT) were observed in lamina X. Located primarily ventral to the central canal, they were neither motoneurones nor preganglionic neurones since they were negative for Fluorogold transported retrogradely following intraperitoneal injections. On application of juxtacellular labelling to neurones in spinal cord slices from young mice, the processes of the ChAT/GAD67-GFP neurone were located in lamina X. Investigations into synaptic inputs indicated that ChAT/GAD67-GFP neurones in lamina X received inputs from terminals immunoreactive for vesicular glutamate transporter 1, vesicular glutamate transporter 2, glycine transporter 2 and GAD67. Co-expression of ChAT/GAD67-GFP was also observed in the medulla oblongata in the nucleus of tractus solitarius, area postrema and reticular formation. Although the function of these ChAT/GAD67-GFP neurones is currently unknown, this study has furthered knowledge regarding their morphology, location, possible projections and inputs.