Journal of Neuroscience, Vol 12, 4188-4194, Copyright © 1992 by Society for Neuroscience
Excitatory amino acid-mediated responses and synaptic potentials in medial pontine reticular formation neurons of the rat in vitro
DR Stevens, RW McCarley and RW Greene
Harvard Medical School, Massachusetts.
Neurons of the medial pontine reticular formation (mPRF) are involved in
the execution of numerous behaviors including initiation of locomotion, eye
movements, startle responses, and rapid eye movement sleep phenomena.
Approximately half of the afferent projections to mPRF neurons come from
within the reticular formation (Shammah-Lagnado et al., 1987). In spite of
the importance of reticulo-reticular connections, virtually nothing is
known about transmitters mediating these synapses. In order to identify a
candidate excitatory neurotransmitter, the actions of excitatory amino
acids (EAAs) on the membrane properties of mPRF neurons recorded in rat
brainstem slices in vitro were studied. Standard intracellular recording
methods, including single-electrode voltage clamp, were used to examine the
postsynaptic actions of EAAs. We also tested whether EAA antagonists block
EPSPs evoked by stimulation of the contralateral reticular formation in the
slices. mPRF neurons responded to both non-NMDA and NMDA agonists. NMDA-
induced conductances were voltage dependent and depressed by physiological
concentrations of magnesium. Stimulation of the contralateral reticular
formation elicited EPSPs that were depressed by the general EAA antagonist
kynurenate. Evoked EPSPs were partially depressed by
6,7-dinitroquinoxaline-2,3-dione. The evoked EPSP was further reduced by
the NMDA antagonist (+/-)-2-amino-5- phosphonopentanoic acid in some cases.
These results suggest that excitatory reticulo-reticular neurotransmission
is mediated by an EAA. Both non-NMDA and NMDA receptors contribute to EAA
neurotransmission in the mPRF formation and play an integral role in
reticular formation function.