TRIGEMINAL INPUTS TO RETICULOSPINAL NEURONS IN LAMPREYS ARE MEDIATED BY EXCITATORY AND INHIBITORY AMINO-ACIDS

Reticulospinal (RS) neurones integrate sensory inputs from several mod alities to generate appropriate motor commands for maintaining body or ientation and initiation of locomotion in lampreys. As in other verteb rates, trigeminal afferents convey sensory inputs from the head region . The in vitro brainstem/spinal cord preparation of the lamprey was us ed for characterizing trigeminal inputs to RS neurones as well as the transmitter systems involved. The trigeminal nerve on each side was el ectrically stimulated and synaptic responses, which consisted of mixed excitation and inhibition, were recorded intracellularly in the middl e and posterior rhombencephalic reticular nuclei. The EPSPs were media ted by activation of lpha-amino-3-hydroxy-5-methyl-4-isoxazolepropioni c acid (AMPA)/kainate receptors. An increase in the late phase of the excitatory response occurred when Mg2+ ions were removed from the Ring er's solution. This effect was antagonized by 2-amino-5-phosphonopenta noate (2-AP5) or reversed by restoring Mg2+ ions to the perfusate sugg esting the activation of N-methyl-D-aspartate (NMDA) receptors. IPSPs were mediated by glycine. These findings are similar to those reported for other types of sensory inputs conveyed to RS neurones, where exci tatory and inhibitory amino acid transmission is also involved.