Cholera toxin B (CTB) the non-toxic subunit of the toxin produced by Vibrio cholerae labels motor, sensory and autonomic preganglionic neurones in the CNS when administered systemically1. Heat-labile enterotoxin B (LTB) is a homologous protein produced by Escherichia coli with similar binding affinity. This work aims to develop these toxin subunits as a means to deliver other proteins into these neurones to influence their function. The labelling of the CNS by LTB was evaluated via two routes of systemic administration. Unanaesthetised GAD67-GFP mice were injected I.P. with 2000 μg (n=4), 1000 μg (n=4), or 500 μg (n=4) of LTB dissolved in 100 μl of 0.1 M PBS. For I.V. injections mice were anaesthetised with isoflurane and 500 μg (n=2), 250 μg (n=3), or 125 μg (n=3) of LTB dissolved in 50 μl of 0.1 M PBS was administered to the right jugular vein. Either 3 days (I.P.) or 5 days (I.V.) following injections, mice were anaesthetised with 80 mg/kg pentibarbitol I.P. and transcardially perfused with 4% paraformaldehyde. Brain and spinal cord were sectioned at 50 μm on a vibrating microtome. LTB immunoreactivity was detected in motor neurones in the brainstem and ventral horn of the spinal cord in all treatments. The highest doses for both routes also labelled autonomic preganglionic neurones and primary afferents in the brainstem and dorsal horn of the spinal cord. These results provided rationale for delivery of proteins to these neurones via conjugation to CTB/LTB. However, to enable smaller amounts to be used for test purposes it was determined that intramuscular tongue injections of 50 μg (n=2) of LTB dissolved in 5 μl of 0.1 M PBS effectively labelled the hypoglossal nucleus. Parvalbumin is a calcium buffer that is not expressed in most motor neurones. It is hypothesised that introducing parvalbumin into the cells could provide protection against excitotoxicity involving increases in calcium, for example as may occur in amyotrophic lateral sclerosis2 . A fusion protein of CTB and parvalbumin (CTBparv) was created to be expressed using a bacterial system. Tongue injections of 100 μg (n=2) of CTBparv in 5 μl 50 mM HEPES successfully labelled the hypoglossal nucleus as revealed by immunoreactivity to both CTB and parvalbumin. Control mice injected with 100 μg CTB in 5 μl of 0.1 M PBS had CTB labelled hypoglossal neurones with no parvalbumin immunoreactivity. These data indicate that CTB/LTB can be used to target motor neurones, as well as autonomic preganglionic fibres and primary afferents when administered I.P. or I.V. It is possible to conjugate a protein of interest to the toxin subunit, with the fusion protein maintaining its binding affinity to GM1 to allow entrance into neurones. Further experiments will seek to determine the sub-cellular localisation and functionality of the parvalbumin within the neurones.