Serotonin augments the cationic current Ih in central neurons

Area of Science:

• Neuroscience
• Neurophysiology
• Molecular Biology

Background:

• Serotonin (5-HT) is a neurotransmitter involved in various physiological processes.
• The nucleus prepositus hypoglossi (PH) plays a role in coordinating head and eye movements.
• Understanding neuronal excitability mechanisms is crucial for neuroscience research.

Purpose of the Study:

• To investigate the effects of serotonin (5-HT) on neurons in the rat brainstem nucleus prepositus hypoglossi (PH).
• To elucidate the ionic mechanisms underlying 5-HT-induced neuronal excitation in the PH.
• To determine the potential role of the Ih current in 5-HT's action.

Main Methods:

• In vitro electrophysiological recordings (depolarization, voltage clamp) were performed on rat PH neurons.
• The effects of 5-HT on neuronal input resistance and current flow were analyzed.
• Pharmacological agents, including CsCl and cAMP analogs, were used to probe the underlying mechanisms.

Main Results:

• Serotonin (5-HT) induced a slow depolarization and decreased input resistance in PH neurons.
• 5-HT evoked an inward current with properties consistent with the nonselective cation current, Ih.
• Forskolin, IBMX, and 8-bromo-cAMP mimicked the 5-HT-induced current, and CsCl blocked it.
• A 5-HT1 agonist also produced a similar inward current.

Conclusions:

• Serotonin (5-HT) excites PH neurons primarily by augmenting the Ih current.
• This augmentation likely occurs via stimulation of adenylate cyclase, suggesting a G-protein coupled receptor mechanism.
• The findings suggest that 5-HT regulation of Ih may be a widespread mechanism for controlling neuronal excitability.