Coordinate Release of ATP and GABA at in Vitro Synapses of Lateral Hypothalamic Neurons

Autonomic and limbic information is integrated within the lateral hypothalamus (LH), and excitability of LH neurons is important in the control of feeding and behavioral arousal. Despite the prominent expression of P2X-type ATP receptors throughout the hypothalamus, the role of ATP in LH excitability is not known. Perforated-patch-clamp recordings of synaptically coupled neurons from both embryonic chick and postnatal mouse lateral hypothalamus in vitro reveal robust stimulus-evoked purinergic synaptic transmission. Suprathreshold activation elicits reliable and concurrent release of ATP with GABA. Tetrodotoxin-resistant P2X receptor-mediated events are readily observed at LH synapses from the embryonic chick, whereas GABA miniature postsynaptic currents (mPSCs) are recorded in innervated LH neurons from either embryonic chicks or postnatal mice. Two distinct mPSCs are recorded at ATP-GABA cosynapses; one has a monoexponential decay phase and is modulated by flunitrazepam, and the other has a decay phase that is best fit by a sum of two exponential functions (τ_fast and τ_slow), and only the τ _slow component is affected by flunitrazepam. Bicuculline does not completely inhibit all mPSCs. The remaining bicuculline-resistant mPSCs are blocked by suramin, and their decay phase is briefer than that of GABAergic mPSCs. Furthermore, at a holding potential intermediate for the reversal potentials of GABA_A and P2X receptors, little or no current is observed, consistent with concomitant release (and detection) of GABA and ATR Together, our data suggest that a subset of spontaneous and evoked PSCs arise from the concurrent activation of both GABA_A and P2X receptors.