Article Figures & Data
Figures
- Figure 1.
Diverse activity states of MHb neurons. MHb neurons displayed diverse activity states at baseline. The majority of neurons exhibited tonic AP firing (A), whereas others were silent (B), displayed DLAMOs (C), fired AP doublets at depolarized membrane potentials (D), or bursted at a hyperpolarized membrane potential (E). F, Percent of MHb neurons that displayed different activity states at baseline. G, Average resting membrane potential of different cell states; *p < 0.05 versus silent. Hyp., hyperpolarized.
- Figure 2.
Depolarization from hyperpolarized membrane potentials triggered burst firing in a subset of MHb neurons. A, Step depolarization triggered burst firing from a resting Vm of −63 mV. With constant current injection to a Vm of −58 mV, step depolarization triggered initial burst firing followed by tonic firing. With constant current injection to a Vm of −52 mV, step depolarization triggered solely tonic firing. B, Ramp depolarization from a Vm <−60 mV triggered initial burst firing in 30 of 152 MHb neurons (19.7%). Tonic firing was observed as the Vm depolarized above approximately −55 mV. C, Bursting was observed when the Vm was −68 mV before ramp depolarization but was abolished with constant current injection to −57 or −53 mV before the ramp.
- Figure 3.
Hyperpolarization triggered burst firing in a subset of MHb neurons. A, Ramp hyperpolarization in a tonic firing neuron with a resting Vm of −40 mV converted tonic firing to burst firing. B, Progressively longer hyperpolarizing current injections triggered rebound burst firing in an MHb neuron. C, Progressively greater hyperpolarizing current injections triggered rebound burst firing in an MHb neuron. D, A 1.5-s-long hyperpolarizing current injection triggered rebound burst firing in an MHb neuron. E, Baseline state of MHb neurons that displayed burst firing from a hyperpolarized Vm (<−60 mV).
- Figure 4.
Cav3.1 is expressed in the MHb. RNAscope in situ hybridization demonstrated that mRNA for Cav3.1 is expressed in the MHb, in particular its lateral aspect. Both Tac1+ and ChAT+ neurons express Cav3.1 mRNA.
- Figure 5.
T-type channel expression in the MHb. A, RNAscope in situ hybridization for Cav3.1, Cav3.2, and Cav3.3 mRNA in the MHb with Tac1 and ChAT. B, Expression of Cav3.1 is significantly greater than Cav3.2 and Cav3.3 expression, and Cav3.3 expression is significantly greater than Cav3.2 in the MHb; ***p < 0.001. C, Cav3.1 expression is significantly greater in the lateral MHb than the medial MHb; ***p < 0.001.
- Figure 6.
Location of neurons that bursted from a hyperpolarized membrane potential. Neurons that bursted from a Vm <−60 mV were predominantly located in the lateral and central MHb. Map includes neurons that bursted to ramp depolarization and/or to step hyperpolarization.
- Figure 7.
The selective T-type channel antagonist Z944 blocked ramp depolarization-induced burst firing from hyperpolarized membrane potentials. A, Representative traces demonstrating the effect of Z944 to block ramp-induced burst firing from a hyperpolarized Vm. B, The number of bursts per ramp was significantly reduced following Z944 perfusion; **p < 0.01.
- Figure 8.
The selective T-type channel antagonist Z944 blocked rebound burst firing. Representative traces demonstrating the effect of Z944 to block rebound burst firing following 1.5-s (A) or 100-ms (D) hyperpolarization. The number of bursts and rebound AP frequency were significantly reduced following 1.5-s (B, C) or 100-ms (E, F) hyperpolarization after Z944 perfusion; *p < 0.05, **p < 0.01.
- Figure 9.
Voltage-gated Ca2+ currents in MHb neurons. A, top, Representative currents induced by step depolarization from −90 mV to progressively more depolarized test potentials in the absence of Z944. Bottom, Voltage dependence of activation for voltage-gated Ca2+ currents before and after Z944 perfusion. B, top, Representative currents evoked by step depolarization to −50 mV after different initial test potentials. Bottom, Voltage dependence of inactivation for voltage-gated Ca2+ currents.
- Figure 10.
AP doublet firing at depolarized membrane potentials is not T-type channel mediated. A, AP doublet firing at depolarized membrane potentials could be enhanced by low-level ramp depolarization. B, Hyperpolarization caused a transition to tonic firing in depolarized AP doublet firing neurons, which returned to AP doublet firing on subsequent spontaneous depolarization. C, Depolarized AP doublet firing was not blocked by perfusion of Z944.
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