Influence de la température sur les mouvements précoces chez l’opossum Monodelphis domestica
Changes in external temperature are detected by nerve fibres located in the skin and mucosae that express thermosensitive receptors. In mammals, thermosensation is mostly studied in mature animals and little is known about its development. We use the newborn opossum as a model of study to asses if thermosensation is functional at early stages of development, using in vitro preparations of brainstem and spinal cord where both facial skin and forelimbs (FL) were kept. Like other marsupials, newborn opossums are very immature at birth, but must climb on the mother’s belly to find a teat where they attach. Stimulations consisted of puff ejections of liquids at cold, neutral and hot temperatures directed towards the face, and FL responses were observed visually under a microscope or triceps activity was recorded in electromyography. Cold temperatures always induced FL or muscular responses, but neutral and hot temperatures were less potent to do so. Sections of the trigeminal nerve and spinal cord showed that thermal responses are at least partially mediated through the trigeminal nerve. Facial skin removal abolished FL responses to hot and neutral stimulation, but only decreased those to cold temperature. Immunohistochemistry and RT-PCR suggest that TRPM8, the main receptor involved in cold sensation in adult mammals, is not expressed in opossum at birth. Overall the present study demonstrates that the newborn opossum is sensitive to temperature, but mostly to cold and that this sensation is not mediated by TRPM8.
Thermosensation TRPM8 Trigeminal system Development Motor behaviors