Methods/results

The distribution of PACAP-38 and its receptors in the brain is only partly described in the literature. Here, we have performed a study to provide the more general picture of this system in rat brain in order to understand a putative role in primary headaches and partly in relation to the calcitonin gene-related peptide system. We observed a rich expression of PACAP-38 and PAC 1 receptor immunoreactivity in many regions throughout the cerebrum, cerebellum and brainstem. The expression pattern points to multiple functions, not least associated with pain and reactions to pain. The expression of VPAC 1 and VPAC 2 receptor immunoreactivity was very sparse. In several regions such as the cerebral cortex, trigeminal nucleus caudalis, hypothalamus and pons there was a close relation to calcitonin gene-related peptide expression.