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Abstract
Background
The gonadotropin releasing hormone (GnRH) neurons represent the final output cells of the neural network that controls fertility. Dopamine (DA) has been shown to control gonadotropin release in many species. However, the direct membrane effects of DA and the related receptors on GnRH neurons remain poorly understood. The purpose of this study was to investigate the direct actions of DA on GnRH neurons and the related receptors using brain slice electrophysiology.
Methods
Gramicidin-perforated patch clamp recordings were made from the GnRH neurons to examine the direct membrane effects of DA in GnRH-EGFP mut5 mice.
Results
DA induced hyperpolarization of the GnRH neurons, which was maintained in the presence of tetrodotoxin (TTX), a Na+ channel blocker, suggesting a direct, rather than indirect, action of DA on GnRH neurons. DA-induced hyperpolarizing effects were blocked by prazosin, an α1-adrenergic antagonist, and mimicked by phenylephrine (PE), an α1-adrenergic agonist.
Figures and Tables
Fig. 1
This trace shows the process of making pores. Usually, 5 to 20 minutes after gigaseal formation, gramicidin starts to make pores. When gramicidin starts to make pores, resting membrane potential (RMP) is decreased by making pores. When the RMP was stable, DA and other chemicals tested were applied. In perforated mode, access resistance between the pipette and cell was approximately 40 to 100 MΩ. The arrow indicates the point when the perforated mode becomes whole cell mode, and then the access resistance is lowered below 10 MΩ and shows overshooting of action potentials.
Fig. 2
Gramicidin perfroated-patch recordings showing the hyperpolarizing responses of GnRH neurons to dopamine (DA). A, GnRH neurons showed a hyperpolarizing response to 1 min exposure to 100 μM DA (74 day-old, RMP=-59 mV). B, DA-induced hyperpolarizing response was persisted in the presence of tetrodotoxin (TTX, 0.5 μM, 74 day-old, RMP=-59 mV).
Fig. 3
Hyperpolarizing effect of dopamine (DA) on GnRH neurons was mediated by α1 adrenergic receptor. A. DA (10 μM) hyperpolarized a GnRH neuron (48 day-old, RMP = -60 mV). B. DA-induced hyperpolarizing response was blocked by prazosin (Pra, 10 μM), an α1-adrenergic antagonist (70 day-old, RMP = -66 mV). C. DA-induced hyperpolarizing response was mimicked by phenylephrine (PE, 10 μM), an α1-adrenergic agonist (48 day-old, RMP = -60 mV).
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