Hypothalamic Kisspeptin Neurons as a Target for Whole-Cell Patch-Clamp Recordings

Summary

Here, we present a protocol to perform a whole-cell patch-clamp on brain slices containing kisspeptin neurons, the primary modulator of gonadotrophin-releasing hormone (GnRH) cells. By adding knowledge about kisspeptin neuron activity, this electrophysiological tool has served as the basis for significant advancements in the neuroendocrinology field over the last 20 years.

Abstract

Kisspeptins are essential for the maturation of the hypothalamic-pituitary-gonadal (HPG) axis and fertility. Hypothalamic kisspeptin neurons located in the anteroventral periventricular nucleus and rostral periventricular nucleus, as well as the arcuate nucleus of the hypothalamus, project to gonadotrophin-releasing hormone (GnRH) neurons, among other cells. Previous studies have demonstrated that kisspeptin signaling occurs through the Kiss1 receptor (Kiss1r), ultimately exciting GnRH neuron activity. In humans and experimental animal models, kisspeptins are sufficient for inducing GnRH secretion and, consequently, luteinizing hormone (LH) and follicle stimulant hormone (FSH) release. Since kisspeptins play an essential role in reproductive functions, researchers are working to assess how the intrinsic activity of hypothalamic kisspeptin neurons contributes to reproduction-related actions and identify the primary neurotransmitters/neuromodulators capable of changing these properties. The whole-cell patch-clamp technique has become a valuable tool for investigating kisspeptin neuron activity in rodent cells. This experimental technique allows researchers to record and measure spontaneous excitatory and inhibitory ionic currents, resting membrane potential, action potential firing, and other electrophysiological properties of cell membranes. In the present study, crucial aspects of the whole-cell patch-clamp technique, known as electrophysiological measurements that define hypothalamic kisspeptin neurons, and a discussion of relevant issues about the technique, are reviewed.

Introduction

Hodgkin and Huxley made the first intracellular record of an action potential described in several scientific studies. This recording was performed on the squid axon, which has a large diameter (~500 µm), allowing a microelectrode to be placed inside the axon. This work provided great possibilities for scientific research, later culminating in the creation of the voltage-clamp mode, which was used to study the ionic basis of action potential generation^{1,2,3,4,5,6....}

Protocol

All animal procedures were approved by the Institute of Biomedical Sciences Animals Ethics Committee at the University of São Paulo and were performed according to the ethical guidelines adopted by the Brazilian College of Animal Experimentation.

1. Preparation of solutions

1. Preparation of internal solution
   NOTE: The internal solution fills the patch-clamp micropipette and will contact the cell's interior (see an example in Figure 2). Internal solutions may vary depending on the type of activity to be measured³³.
   1. Choose the internal....

Results

To study the possible effects of human recombinant growth hormone (hGH) on the activity of hypothalamic kisspeptin neurons, we performed whole-cell patch-clamp recordings in brain slices and assessed whether this hormone causes acute changes in the activity of AVPV/PeN^Kisspeptin and ARH^kisspeptin neurons. Adult Kiss1-Cre/GFP female (diestrus-stage) and male mice³⁶ were used in this study. Gonad-intact animals were selected for the experiments, since the properties of the.......

Discussion

The development of the whole-cell patch-clamp technique had a significant impact on the scientific community, being considered of paramount importance for developing scientific research and enabling several discoveries. Its impact on science was enough to culminate in the Nobel Prize in Medicine in 1991, as this discovery opened the door to a better understanding of how ion channels function under physiological and pathological conditions, as well as the identification of potential targets for therapeutic agents

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Compounds for aCSF, internal and slicing solutions
ATP	Sigma Aldrich/various	A9187
CaCl2	Sigma Aldrich/various	C7902
D-(+)-Glucose	Sigma Aldrich/various	G7021
EGTA	Sigma Aldrich/various	O3777
HEPES	Sigma Aldrich/various	H3375
KCL	Sigma Aldrich/various	P5405
K-gluconate	Sigma Aldrich/various	G4500
KOH	Sigma Aldrich/various	P5958
MgCl2	Sigma Aldrich/various	M9272
MgSO4	Sigma Aldrich/various	230391
NaCl	Sigma Aldrich/various	S5886
NaH2PO4	Sigma Aldrich/various	S5011
NaHCO3	Sigma Aldrich/various	S5761
nitric acid	Sigma Aldrich/various	225711	CAUTION
Sucrose	Sigma Aldrich/various	S1888
Equipments
Air table	TMC	63-534
Amplifier	Molecular Devices	Multiclamp 700B
Computer	various	-
DIGIDATA 1440 LOW-NOISE DATA ACQUISITION SYSTEM	Molecular Devices	DD1440
Digital peristaltic pump	Ismatec	ISM833C
Faraday cage	TMC	81-333-03
Imaging Camera	Leica	DFC 365 FX
Micromanipulator	Sutter Instruments	Roe-200
Micropipette Puller	Narishige	PC-10
Microscope	Leica	DM6000 FS
Osteotome	Bonther equipamentos & Tecnologia/various	128
Recovery chamber	Warner Instruments/Harvard apparatus	-	can be made in-house
Recording chamber	Warner Instruments	640277
Spatula	Fisher Scientific /various	FISH-14-375-10; FISH-21-401-20
Vibratome	Leica	VT1000 S
Water Bath	Fisher Scientific /various	Isotemp
Software and systems
AxoScope 10 software	Molecular Devices	-	Commander Software
LAS X wide field system	Leica	-	Image acquisition and analysis
MultiClamp 700B	Molecular Devices	MULTICLAMP 700B	Commander Software
PCLAMP 10 SOFTWARE FOR WINDOWS	Molecular Devices	Pclamp 10 Standard
Tools
Ag/AgCl electrode, pellet, 1.0 mm	Warner Instruments	64-1309
Curved hemostatic forcep	various	-
cyanoacrylate glue	LOCTITE/various	-
Decapitation scissors	various	-
Filter paper	various	-
Glass capillaries (micropipette)	World Precision Instruments, Inc	TW150F-4
Iris scissors	Bonther equipamentos & Tecnologia/various	65-66
Pasteur glass pipette	Sigma Aldrich/various	CLS7095B9-1000EA
Petri dish	various	-
Polyethylene tubing	Warner Instruments	64-0756
Razor blade for brain dissection	TED PELLA	TEDP-121-1
Razor blade for the vibratome	TED PELLA	TEDP-121-9
Scissors	Bonther equipamentos & Tecnologia/various	71-72, 48,49;
silicone teat	various	-
Slice Anchor	Warner Instruments	64-0246
Syringe filters	Merck Millipore Ltda	SLGVR13SL	Millex-GV 0.22 μm
Tweezers	Bonther equipamentos & Tecnologia/various	131, 1518