Glutamate and GABA mediate suprachiasmatic nucleus inputs to spinal-projecting paraventricular neurons

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Abstract
We used patch-clamp recordings in slice preparations from Sprague-Dawley rats to evaluate responses of 20 spinal-projecting neurons in the dorsal paraventricular nucleus (PVN) to electrical stimulation in suprachiasmatic nucleus (SCN). Neurons containing a retrograde label transported from the thoracic (T1-T4) intermediolateral column displayed three intrinsic properties that collectively allowed distinction from neighboring parvocellular or magnocellular cells: a low-input resistance, a hyperpolarization-activated time-dependent inward rectification, and a low-threshold calcium conductance. Twelve of fifteen cells tested responded to electrical stimulation in SCN. All of 10 cells tested in media containing 2,3,-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium (5 μM) andd(−)-2-amino-5-phosphonopentanoic acid (20 μM) responded with constant latency (11.4 ± 0.7 ms) inhibitory postsynaptic potentials, able to follow 20- to 50-Hz stimulation and blockable with bicuculline (20 μM). By contrast, all eight cells tested in the presence of bicuculline demonstrated constant latency (9.8 ± 0.6 ms) excitatory postsynaptic potentials that followed at 20–50 Hz and featured both non-N-methyl-d-aspartate (NMDA) and NMDA receptor-mediated components. We conclude that both GABAergic and glutamatergic neurons in SCN project directly to spinal-projecting neurons in the dorsal PVN.