Activation of proprioceptors in neck muscles has a sympatho-excitatory effect (Kuwagata et al. 1991). However, the pathways mediating these actions have not been elucidated. The intermedius nucleus of the medulla (InM) is ideally placed to participate in these autonomic responses to stimulation of neck muscle afferents – it sends monosynaptic projections to the nucleus of the solitary tract (Dallas et al. 2005) and receives inputs from neck muscle proprioceptors (Neuhuber & Zenker, 1989). We are investigating the anatomical organisation of the InM and here report initial findings on the neurochemistry of the GABAergic neurones in this nucleus. Immunohistochemistry was conducted on tissue from mice expressing GFP under the control of the glutamic acid decarboxylase 65 promoter (GAD65-GFP; De Marchis et al. 2004) or glutamic acid 67 GFP knock in mice (GAD67-GFP; (Tamamaki et al. 2003). Adult mice were anaesthetised via an I.P (60 mg/kg) injection of Sagatal and perfused transcardially with 4% paraformaldehyde (in 0.1M phosphate buffer, pH 7.4), the medulla oblongata removed, post fixed overnight and sectioned at 30µm using a vibrating microtome. Preliminary studies revealed that the InM is rich in neurones immunoreactive for neuronal nitric oxide synthase (nNOS) as well as the calcium binding proteins parvalbumin and calretinin. The extent of co-localisation of these markers with GFP in GAD65-GFP or GAD67-GFP mice, or GAD67 immunoreactivity (GAD67-IR) is summarised in Table 1. Although investigated, the calcium binding protein calbindin was not present within the InM. These results show that nNOS is only found to co-localise with neurones expressing the GAD65 reporter gene, parvalbumin is found in the cells expressing the GAD67 reporter gene, and calretinin is found within the GAD67 immunoreactive population. These findings suggest that the GABAergic neurones in the InM are likely to be a heterogenous population.