Increases in Neuronal Activity in Rat Spinal Trigeminal Nucleus Following Changes in Barometric Pressure-Relevance for Weather-Associated Headaches?

Objective.- To determine whether controlled changes in barometric pressure activate rat spinal trigeminal neurons as a possible animal correlate of headaches. Background.- Changes in weather accompanied by changes in atmospheric pressure are suggested to trigger primary headaches. Mechanisms that increase neuronal activity in the rat spinal trigeminal nucleus may parallel those that contribute to the generation of headaches. Methods.- Urethane anesthetized rats were placed in a climatic chamber, in which the air pressure could be selectively manipulated. The parietal cranial dura mater and the spinal dura mater covering the medulla were exposed. Electrolyte-filled electrodes were introduced into the spinal trigeminal nucleus to record from neurons with receptive fields in facial areas and the cranial dura mater and/or the cornea and/or the temporal muscle. Arterial pressure and heart rate were monitored. The barometric pressure was lowered by 40 hPa during 8 minutes, kept at this level for 8 minutes and returned to the previous level. Results.- During lowering of the barometric pressure and the low pressure period a sample of neurons showed increased discharge rates. Group analysis revealed that it was the group of units with receptive fields in the cornea, but not in the dura mater or the temporal muscle, which was significantly activated when the animal was exposed to low atmospheric pressure. Exposure of the cranial dura and opening of the cisterna magna did not prevent an increase in activity. In another sample of units the activity recorded after infusion of the nitric oxide donor sodium nitroprusside did not change under low pressure exposure. Arterial pressure and heart rate changed slightly during barometric pressure changes. Conclusions.- We conclude that distinct neurons in the trigeminal nucleus caudalis, particularly with preferential afferent input from the eye, respond to lowering of atmospheric pressure. Similar mechanisms may contribute to the generation of headaches during changes in weather.