Projections of VIP/PHI neurons of the interstitial nucleus of Cajal in the rat.

Neurons expressing VIP/PHI precursor mRNA have been localized in the interstitial nucleus of Cajal. Unilateral surgical cut through the medial forebrain bundle failed to influence VIP/PHI mRNA expression in the Cajal nucleus while brainstem hemisection or unilateral transection of the medial longitudinal fascicle reduced it markedly, ipsilateral to the knife cuts. Thus, in contrast to forebrain projecting VIP neurons in the rostral periaqueductal gray, VIP/PHI neurons in the Cajal nucleus project downwards, to the lower brainstem.