Heterogeneity of Intrinsic and Synaptic Properties of Neurons in the Ventral and Dorsal Parts of the Ventral Nucleus of the Lateral Lemniscus

Dec 5, 2015Frontiers in neural circuits

Differences in Natural and Signal-Related Properties of Neurons in the Lower and Upper Parts of the Sound Processing Nucleus

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Abstract

Neurons in the ventral nucleus of the lateral lemniscus (VNLL) show different firing patterns and excitatory input characteristics compared to dorsal VNLL neurons.

Ventral VNLL neurons exhibit an onset-type firing pattern with minimal hyperpolarization-activated current (Ih).
Stimulation of inputs to the ventral VNLL results in a strong, all-or-none excitatory response, akin to responses at Calyx of Held synapses.
Dorsal VNLL neurons display a mix of onset-type and sustained firing, with larger Ih and high levels of the HCN1 channel subunit.
Both types of dorsal neurons receive weaker and slower excitatory inputs compared to ventral neurons.
Neurons in both dorsal and ventral regions are suggested to be inhibitory, as they are depolarized by light stimulation in a specific mouse model.

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The ventral nucleus of the lateral lemniscus (VNLL) provides a major inhibitory projection to the inferior colliculus (IC). Neurons in the VNLL respond with various firing patterns and different temporal precision to acoustic stimulation. The present study investigates the underlying intrinsic and synaptic properties of various cell types in different regions of the VNLL, using in vitro electrophysiological recordings from acute brain slices of mice and immunohistochemistry. We show that the biophysical membrane properties and excitatory input characteristics differed between dorsal and ventral VNLL neurons. Neurons in the ventral VNLL displayed an onset-type firing pattern and little hyperpolarization-activated current (Ih). Stimulation of lemniscal inputs evoked a large all-or-none excitatory response similar to Calyx of Held synapses in neurons in the lateral part of the ventral VNLL. Neurons that were located within the fiber tract of the lateral lemniscus, received several and weak excitatory input fibers. In the dorsal VNLL onset-type and sustained firing neurons were intermingled. These neurons showed large Ih and were strongly immunopositive for the hyperpolarization-activated cyclic nucleotide-gated channel 1 (HCN1) subunit. Both neuron types received several excitatory inputs that were weaker and slower compared to ventrolateral VNLL neurons. Using a mouse model that expresses channelrhodopsin under the promotor of the vesicular GABA transporter (VGAT) suggests that dorsal and ventral neurons were inhibitory since they were all depolarized by light stimulation. The diverse membrane and input properties in dorsal and ventral VNLL neurons suggest differential roles of these neurons for sound processing.

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Heterogeneity of Intrinsic and Synaptic Properties of Neurons in the Ventral and Dorsal Parts of the Ventral Nucleus of the Lateral Lemniscus

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