?30 25.30 pA). our understanding of the specific mechanisms through which muscarinic agonists are likely to modulate neuronal excitability in the hilar network, and further uncover a mechanism that could plausibly promote endocannabinoid mediated signaling in vivo. A mossy cell was held at a membrane potential of ?60 mV and a 500 ms depolarizing pulse was applied to evoke a train of action potentials. After the depolarization the cell immediately returned to ?60 mV. Following application of 5 M muscarine an ADP was induced following the depolarizing current which could last for several seconds. The ADP could be blocked by 5 M atropine, a mAChR antagonist. After application of muscarine, unlike mossy cells, there was no ADP. An ADP could still not be produced with a larger somatic current injection. Summary plot showing the average area of ADP following the depolarizing pulse. The three bars left of the hash marks summarize the results of experiments in hilar mossy cells, while the three bars to the right of the hash marks are from hilar interneurons. *p<0.05 compared to baseline. **p<0.05 compared to muscarine. Higher stim was tested in 7 of 10 non-mossy hilar neurons. By contrast, across 10 non-mossy hilar neurons examined in an identical fashion, 50% were depolarized by 5 mV in response to muscarine (average Cytidine V: 10.2 1.7 mV), while the other 50 Cytidine % were unaffected (average V: 0.6 0.6 mV). Interestingly, however, VPS33B all 10 non-mossy hilar neurons examined lacked a muscarinic ADP in response to both moderate (192 28.4 pA) and large (429 42.1 pA) depolarizing pulses (Fig. 1B, control: 2.23 1.70 mV*s; muscarine: 1.93 0.86 mV*s; n=10, p > 0.05, and higher stim: 1.83 1.02 mV*s, n=7, p > 0.05). There was no difference between non-mossy hilar neurons that were depolarized by muscarine and those that were not in terms of whole cell capacitance (109.88 20.64 pF vs. 137.63 22.63 pF), input resistance (213.97 37.10 M vs. 156.08 14.75 M), or holding current at ?60 mV (?34.00 5.10 pA vs. ?30 25.30 pA). Similarly, while there was some variability among non-mossy hilar neurons in firing pattern in response to depolarization, in degree of afterhyperpolarization observed after an action potential, and in sag currents observed in response to a hyperpolarizing pulse, none of these features were clearly related to the propensity to be depolarized by bath application of muscarine. Thus significant additional anatomical and immunohistochemical work would be necessary to further sub-divide non-mossy hilar cells based on susceptibility to mAChR mediated depolarization. Instead, for the remainder of this manuscript, we focused our attention on further characterizing the strong muscarinic ADP that was uniquely observed in hilar mossy cells. 2.2. ADP depends on a calcium activated nonselective cation channel As a first step, we asked whether induction of a muscarinic ADP in hilar mossy cells was consistent with opening (as opposed to closing) of Cytidine an ionic conductance. Hyperpolarizing actions of ?40 pA for 500 ms were applied before, during, and after the ADP in the presence of 1 M TTX (see below for TTX experiments) to prevent action potentials from contaminating the measurements (Fig. 2A). During the ADP there was a significant reduction in the change in voltage produced by the hyperpolarizing step, which returned to baseline levels after the ADP (Fig. 2C; pre-ADP: ?7.72 0.49 mV; ADP: ?3.33 0.24 mV; Cytidine post-ADP: ?7.30 1.07 mV, n=4, p<0.05). Although other voltage dependent conductances may contribute to this observation, these data are consistent with the hypothesis that activation of the ADP is usually.