The trigeminal subnucleus caudalis (SpVc) plays a crucial role in relaying inputs from the primary nociceptive afferents within the orofacial area to higher brain centers. In the SpVc, the central endings of most of primary afferents are located and release excitatory neurotransmitters and neuropeptide such as glutamate, substance P and calcitonin-gene related peptide (CGRP) in response to noxcious stimuli, which can lead excitation in the second-order nociceptive neurons (Sessle et al., 2000). We showed previously that GABAergic neurons densely distributed in the SpVc using the glutamic acid decarboxylase (GAD) 67-green fluorescence protein (GFP) knock-in neonatal mice (Kuwana et al., 2006). In the present study, we investigated the electrophysiological characteristics of GABAergic and non-GABAergic neurons, and the relationship between localization of CGRP receptors (calcitonin receptor-like receptor, CRLR) and GABAergic neurons in the SpVc of GAD67-GFP knock-in mice. The mouse was deeply anesthetized with diethyl ether and the brainstem was isolated. We recorded activities of GFP-positive (GABAergic, n=20) and GFP-negative (non-GABAergic, n=33) neurons by whole-cell patch clamp technique in the sagittal slice of brainstem attaching the trigeminal nerve rootlet. Electrical stimulations to the trigeminal nerve rootlet evoked excitatory postsynaptic potentials (EPSPs) in most of cells from both groups (20 GFP-positive and in 31 GFP-negative neurons). On the other hand, inhibitory postsynaptic potentials (IPSPs) were not frequently evoked especially in GFP positve neurons (3 in GFP-positive and 13 in GFP-negative neurons). In morphological study, most GFP-positive neurons had multipolar-shaped somata (n=8/10) while GFP-negative neurons had bipolar (n=5/10) or triangular (n=5/10) somata. However, there is no difference in the size of neurons between groups. These data show that GABAergic neurons characterized by multipolar-shaped somata in the SpVc received exclusively excitatory postsynaptic inputs in response to electrical stimulation. Furthermore, we investigated the localization of CRLR by immunohistochemical technique in the SpVc. The CRLR-immunoreactions appeared in about 30% of GFP-positive neurons and some GFP-negative neurons of the SpVc, suggesting that the CRLR-immunoreactive neurons are second-order of nociceptive neurons in the SpVc. Therefore, we conclude that the excitatory synaptic input to GABAergic neuron may be induced by glutamate and CGRP because the primary afferent terminals containing glutamate form synapses with the dendrites of GABA neurons (Iliakis et al., 1996).