Nociceptive neurons in the rat caudal trigeminal nucleus respond to blood plasma perfusion of the subarachnoid space: the involvement of complement

The meninges of the brain are innervated by afferent nerve fibres containin g SP and CGRP, two typical peptides found in sensory neurons. These fibres project to the trigeminal nuclear complex and the cervical dorsal hem. Disc harge of the afferents may provide a physiological basis for some types of headaches. Considerable speculation surrounds the possible causes of mening eal afferent activation. Blood-borne substances released during subarachnoi d haemorrhage are one possibility and there is a possibility that these als o play a role in migraine. In the case of migraine, blood components, e.g. from platelets, cannot be excluded. To investigate the possible effects of platelets and plasma factors, the subarachnoid space of the rat was continu ously perfused with artificial cerebrospinal fluid during extracellular rec ordings from single units of the caudal trigeminal nucleus. Washed and conc entrated suspensions of adenosindiphosphate (ADP) activated platelets and p lasma, from which platelets had been removed - were introduced as a bolus i nto the continuous flow. Neurons in the caudal nucleus of the trigeminal co mplex receiving input from the meninges were stimulated. They did not respo nd to the activated platelet suspensions but showed intense responses to pl asma. Plasma completely lost its ability to excite trigeminal neurons after heat inactivation (30 min, 56 degrees C). It is concluded that the complem ent system may be involved in the excitatory nociceptive effect of platelet -poor plasma. (C) 1999 International Association for the Study of Pain. Pub lished by Elsevier Science B.V.