A physiological study of brainstem and peripheral inputs to trigeminal motoneurons in lampreys

The inputs to trigeminal motoneurons from sensory afferents and rhombenceph alic premotor regions were studied in isolated brainstem preparations of ad ult lampreys (Petromyzon marinus). Stimulation of both trigeminal nerves, c ontralateral nucleus motorius nervi trigemini, nucleus sensibilis nervi tri gemini and ipsilateral rostral reticular formation elicited large-amplitude excitatory postsynaptic potentials with short latencies. These were signif icantly attenuated by adding 6-cyano-7-nitroquinoxaline-2,3-dione (10 mu M) and 2-amino-5-phosphonopentanoate (200 mu M) to the bath, suggesting parti cipation of both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate and N -methyl-D-aspartate receptors. The inputs from ipsilateral trigeminal affer ents included a di- or oligosynaptic glycinereic inhibition. Sustained rhyt hmical membrane potential oscillations were observed in 52% of the recorded cells upon stimulation of trigeminal afferents or the contralateral nucleu s sensibilis nervi trigemini. Two types of rhythm were obtained: (i) low-fr equency oscillations (0.1-0.5 Hz), with peak-to-peak amplitudes between 8.5 and 17 mV; and (ii) higher frequency oscillations (1.0-2.8 Hz) with smalle r amplitudes (1.8-5.1 mV). The two types of trigeminal rhythm could occur i ndependently of fictive locomotion and fictive breathing. In a decerebrate semi-intact preparation, slow rhythmical trigeminal motoneuron potential os cillations were also evoked by stimulation of the oral disc. This study shows that trigeminal motoneurons receive excitatory synaptic in puts from several brainstem sites, and that membrane potential oscillations can be triggered upon stimulation of trigeminal afferents or the nucleus s ensibilis nervi trigemini. We suggest that these oscillations recorded in v itro may represent the centrally generated components that underlie rhythmi cal feeding in lampreys. (C) 1999 IBRO. Published by Elsevier Science Ltd.