Afterhyperpolarization mechanisms in cat sympathetic preganglionic neuron in vitro

Area of Science:

• Neuroscience
• Cellular Physiology
• Autonomic Nervous System

Background:

• Sympathetic preganglionic neurons (SPNs) are crucial for regulating autonomic functions.
• Action potentials in neurons are followed by afterhyperpolarizations (AHPs) that influence firing rate.
• The ionic mechanisms underlying AHPs in SPNs are not fully elucidated.

Purpose of the Study:

• To characterize the biophysical properties of the afterhyperpolarization (AHP) in cat sympathetic preganglionic neurons (SPNs).
• To investigate the ionic conductances responsible for the fast (F-AHP) and slow (S-AHP) components of the AHP.
• To determine the role of the AHP in regulating SPN excitability and synaptic input efficacy.

Main Methods:

• Intracellular recordings from SPNs in an in vitro slice preparation of the cat spinal cord.
• Induction of action potentials via antidromic stimulation or direct current injection.
• Pharmacological manipulation using calcium channel blockers (cobalt), potassium channel blockers (tetraethylammonium, cesium), and tetrodotoxin (TTX).
• Analysis of AHP amplitude, duration, voltage-dependence, and reversal potential under varying extracellular potassium concentrations.

Main Results:

• A long-lasting AHP (2.8 ± 0.3 s) with distinct fast and slow components was observed following single spikes in SPNs.
• Both F-AHP and S-AHP components were associated with increased membrane conductance and were voltage-dependent.
• The S-AHP was sensitive to calcium channel blockers, suggesting a role for calcium-activated potassium channels.
• The F-AHP showed characteristics consistent with voltage-gated potassium channels and reversed polarity at negative membrane potentials.
• The AHP persisted in the presence of TTX and was associated with a decrease in synaptic input efficacy.

Conclusions:

• The AHP in SPNs comprises two distinct components, likely mediated by different potassium conductances.
• A calcium-activated potassium conductance contributes to the slow component (S-AHP).
• The fast component (F-AHP) is likely mediated by voltage-gated potassium channels.
• The AHP plays a significant role in regulating the firing rate and synaptic integration of SPNs.