CUTANEOUS VASOMOTION CONTROL BY MEDIAN MEDULLARY RAPHE NEURONS

Aim: Median Medullary Raphe (MMR) neurons are thought to be sympathetic premotor neurons controlling cutaneous vasomotion. Experiments designed to test this hypothesis have been so far performed in the animal under general anaesthesia. Aim of this study was to explore the role of RMM neurons in the free behaving animal. Methods: Male CD Sprague-Dawley rat were used. Animals were implanted under general anaesthesia with: i) electrodes for EEG, EMG and EKG recording; ii) a catheter in the femoral artery to telemetric record arterial pressure (AP); iii) a hypothalamic thermistor to record deep brain temperature; iv) a microcannula in RMM. Following 7 days of recovery, experiments were performed in a termoregulated, sound-attenuated recording box, equipped with a thermocam to measure cutaneous temperature. After 2 hours of baseline recording, all animals received in RMM, according to a group balanced sequence, 100 nl of the following solutions: i) 1 mM GABA-A antagonist bicuculline methiodide b) 1 mM GABA-A agonist muscimol c) isotonic saline (NaCl 0.9%). Results: The administration of muscimol evoked a rapid cutaneous vasodilation followed by a deep hypothermia. This confirmed the observations in the anaesthetized animal. In contrast to the findings from the anaesthetized animal, also bicuculline administration induced a fast increase in cutaneous blood flow, but brain temperature did not significantly change. Conclusion: These data suggest that RMM control on cutaneous vasomotion is, in the free behaving rat, more complex than that inferred from the results obtained under general anaesthesia.