2019 Volume 56 Issue 2 Pages 80-87
The arterial pressure reflexly increases in response to noxious mechanical stimulation (pinching) of the unilateral hindpaw in anesthetized rats. The pressor reflex is mediated via the supraspinal structure; however, the precise brain mechanisms have not been elucidated. Since approximately 90% of the projection neurons from spinallamina I terminate in the contralateral side of the lateral parabrachial nucleus (LPBN), the present study aimed to clarify the involvement of the LPBN in the pressor reflex responses to pinching of the hindpaw in anesthetized rats. Arterial pressure was recorded via a catheter inserted into the carotid artery. Muscimol, a widely used neuronal inhibitor, was nanoinjected into the unilateral LPBN. Pinching was applied with a surgical clamp at a force of 3-5 kg to the unilateral hindpaw for 20 s. Administration of muscimol into the LPBN had no influence on the tonic arterial pressure. On the other hand, the pressor responses to pinching of the hindpaw contralateral to the site of the muscimol injection were significantly attenuated after the administration of muscimol. The pressor responses to pinching of the hindpaw ipsilateral to the site of the muscimol injection were slightly attenuated, but the attenuation was not statistically significant. The present results demonstrate that the LPBN is involved in the pressor reflex responses elicited by pinching of the contralateral hindpaw.
