Distinct Firing Properties of Vasoactive Intestinal Peptide-Expressing Neurons in the Suprachiasmatic Nucleus

Dec 30, 2015Journal of biological rhythms

Unique Activity Patterns of Vasoactive Intestinal Peptide Neurons in the Brain's Biological Clock

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Abstract

VIP neurons exhibit higher firing rates of 3.1 ± 0.2 Hz during the day compared to non-VIP neurons' 1.8 ± 0.2 Hz.

VIP neurons are spontaneously active both day and night, showing distinct firing properties compared to non-VIP neurons.
Firing rates are consistently higher in VIP neurons than in non-VIP neurons, regardless of the time of day.
Action potential durations are shorter in VIP neurons than in non-VIP neurons throughout the light-dark cycle.
VIP neurons have larger afterhyperpolarization amplitudes compared to non-VIP neurons both during the day and at night.
Day/night differences in action potential durations and afterhyperpolarization amplitudes suggest rhythmic changes in ionic conductances in both neuron types.

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The suprachiasmatic nucleus (SCN) regulates daily rhythms in physiology and behavior. Previous studies suggest a critical role for neurons expressing vasoactive intestinal peptide (VIP) in coordinating rhythmicity and synchronization in the SCN. Here we examined the firing properties of VIP-expressing SCN neurons in acute brain slices. Active and passive membrane properties were measured in VIP and in non-VIP neurons during the day and at night. Current-clamp recordings revealed that both VIP and non-VIP neurons were spontaneously active, with higher firing rates during the day than at night. Average firing frequencies, however, were higher in VIP neurons (3.1 ± 0.2 Hz, day and 2.4 ± 0.2 Hz, night) than in non-VIP neurons (1.8 ± 0.2 Hz, day and 0.9 ± 0.2 Hz, night), both day and night. The waveforms of individual action potentials in VIP and non-VIP neurons were also distinct. Action potential durations (APD50) were shorter in VIP neurons (3.6 ± 0.1 ms, day and 2.9 ± 0.1 ms, night) than in non-VIP neurons (4.4 ± 0.3 ms, day and 3.5 ± 0.2 ms, night) throughout the light-dark cycle. In addition, afterhyperpolarization (AHP) amplitudes were larger in VIP neurons (21 ± 0.8 mV, day and 24.9 ± 0.9 mV, night) than in non-VIP neurons (17.2 ± 1.1 mV, day and 20.5 ± 1.2 mV, night) during the day and at night. Furthermore, significant day/night differences were observed in APD50 and AHP amplitudes in both VIP and non-VIP SCN neurons, consistent with rhythmic changes in ionic conductances that contribute to shaping the firing properties of both cell types. The higher day and night firing rates of VIP neurons likely contribute to synchronizing electrical activity in the SCN.

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Distinct Firing Properties of Vasoactive Intestinal Peptide-Expressing Neurons in the Suprachiasmatic Nucleus

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