Bulbospinal systems (BS) originate from various regions of the brainstem and influence spinal neurons by classical synaptic and modulatory mechanisms. Our aim was to determine the brainstem locations of cells of origin of BS pathways passing through the medial longitudinal fasciculus (MLF) and the caudal ventrolateral medulla (CVLM). We also examined the transmitter content of spinal terminations of the CVLM pathway. Six adult rats received Fluorogold (FG) injections to the right intermediate gray matter of the lumbar cord (L1–L2) and the b-subunit of cholera toxin (CTb) was injected either into the MLF or the right CVLM (3 animals each). Double-labeled cells were identified within brainstem structures with confocal microscopy and mapped onto brainstem diagrams. An additional 3 rats were injected with CTb in the CVLM to label axon terminals in the lumbar spinal cord. Double-labeled cells projecting via the MLF or CVLM were found principally in reticular regions of the medulla and pons but small numbers of cells were also located within the midbrain. CVLM projections to the lumbar cord were almost exclusively ipsilateral and concentrated within the intermediate gray matter. Most (62%) of terminals were immunoreactive for the vesicular glutamate transporter 2 while 23% contained the vesicular GABA transporter. The inhibitory subpopulation was glycinergic, GABAergic or contained both transmitters. The proportions of excitatory and inhibitory axons projecting via the CVLM to the lumbar cord are similar to those projecting via the MLF. Unlike the MLF pathway, CVLM projections are predominantly ipsilateral and concentrated within intermediate gray but do not extend into motor nuclei or laminia VIII. Terminations of the CVLM pathway are located in a region of the gray matter that is rich in premotor interneurons; thus its primary function may be to coordinate activity of premotor networks.

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28 sEPTEmBER 1985 865 zine successfully reduced the incidence of dysphoric reactions it might also antagonise the antiemetic effect of nabilone. The incidences of other side effects were similar in both treatment arms; sedation and dryness of the mouth occurred most commonly and generally were not too troublesome. Indeed, we suspect that with moderately emetogenic cytotoxic regimens5 the occurrence of these side effects could be reduced by using a lower dose of nabilone (1 mg twice daily) without necessarily compromising the control of emesis. Nabilone and prochlorperazine are a good oral antiemetic combination suitable for use with outpatient chemotherapy, but because they are associated with a small incidence of adverse effects on the central nervous system the first course of treatnent should be given under inpatient supervision.We thank Eli Lilly for financial support and Miss A Penrice, our secretary.

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