Long-term Potentiation of Perforant Pathway-dentate Gyrus Synapse in Freely Behaving Mice

Summary

Transgenic and knockout mouse models of neurological diseases are useful for studying the role of genes in normal and abnormal neurophysiology. This article describes methodologies which can be used to study long-term potentiation, a cellular mechanism which may underlie learning and memory, in transgenic and knockout freely behaving mouse models of neuropathology.

Abstract

Studies of long-term potentiation of synaptic efficacy, an activity-dependent synaptic phenomenon having properties that make it attractive as a potential cellular mechanism underlying learning and information storage, have long been used to elucidate the physiology of various neuronal circuits in the hippocampus, amygdala, and other limbic and cortical structures. With this in mind, transgenic mouse models of neurological diseases represent useful platforms to conduct long-term potentiation (LTP) studies to develop a greater understanding of the role of genes in normal and abnormal synaptic communication in neuronal networks involved in learning, emotion and information processing. This article describes methodologies for reliably inducing LTP in the freely behaving mouse. These methodologies can be used in studies of transgenic and knockout freely behaving mouse models of neurodegenerative diseases.

Introduction

The development of technology to manipulate genes has produced transgenic and knockout mouse models of almost every neurodegenerative and neurological diseases. This has necessitated translation of electrophysiological research techniques previously used in larger rodent species to the mouse animal model. One such neurophysiological investigation technique is the use long-term potentiation (LTP) to test the efficacy of synaptic connections within neuronal networks involved in various neuropathological disorders. This protocol describes techniques for reliable electrophysiological investigation of LTP in freely behaving mice. The advantage of this protocol over others ....

Protocol

This protocol is appropriate for mice of 3 and 18 months of age and approximate body weight of 30-50 g). Mice can be obtained from The Jackson Laboratory (Bar Harbor, ME). All surgical and experimental protocols were approved by the Trinity College Animal Care and Use Committee and were in accordance with the NIH Guide for the Care and Use of Laboratory Animals.

1. Animal Preparation and Surgical Procedures

1. Prepare anesthesia cocktail containing ketamine (25 mg/ml), xylazine (2.5 mg/ml) and acepromazine (0.5 mg/ml). Inject 1 ml/kg body weight in the lower right quadrant of the abdomen supplemented by 0.2 ml/kg injections every 45 min thereafter....

Results

Table 1 shows the coordinates for DG and mPP as used in this protocol. Figure 1A shows the markings for the target structures on the skull; also shown are the location of the ground and reference electrodes. Figure 1B illustrates representative evoked response traces both pre- and posttetanization in the same animal. Note that the posttetanization evoked response is larger than the pretetanization response which is indicative of LTP induction². Figure .......

Discussion

In this protocol, we have demonstrated a reliable and simple method for studying LTP in DG in freely behaving mice. While many studies of LTP in awake rats have been performed^3,4, very few have been conducted in awake mice primarily due to the technical complexity posed by the limited cranial real estate in mice and the weight of electrode headstages relative to the average weight of mice⁵. The few studies that have demonstrated LTP in DG in freely behaving mice utilized either microdrive electrode .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Ketamine (100 mg/ml)	Henry Schein	10177
Xylazine (20 mg/ml)	Henry Schein	33197
Acepromazine (10 mg/ml)	Henry Schein	2177
Dental acrylic powder	Lang Dental Manufacturing Co.	1330CLR
Dental acrylic liquid	Lang Dental Manufacturing Co.	1306CLR
Tungsten wire (0.127 mm)	World Precision Instruments	TGW0515
Stainless Steel Hypodermic Tubing (0.286 mm)	World Precision Instruments	832400
Flunixin (50 mg/ml)	Henry Schein	14165
Epoxilyte	Superior Essex	EP 6001-M
Stainless steel wire insert (0.2 mm)	World Precision Instruments	792900
Stereotaxic frame apparatus	Kopf Instruments	Model 902
Ear cuffs (ear cups)	Kopf Instruments	Model 921
Electrophysiological stimulator	Astro-Med, Inc.	S88
Digital oscilloscope	B K Precision Corp.	2542
Current isolation unit	Astro-Med, Inc.	PSIU-6
Differential amplifier	World Precision Instruments, Inc.	DAM-50
Commutator	Plastics One	SLC6
Dental drill	Stoelting	58650