Miniscope Recording Calcium Signals at Hippocampus of Mice Navigating an Odor Plume

Summary

This protocol investigates the brain-behavior relationship in hippocampal CA1 in mice navigating an odor plume. We provide a step-by-step protocol, including surgery to access imaging of the hippocampus, behavioral training, miniscope GCaMP6f recording and processing of the brain, and behavioral data to decode the mouse position from ROI neural activity.

Abstract

Mice navigate an odor plume with a complex spatiotemporal structure in the dark to find the source of odorants. This article describes a protocol to monitor behavior and record Ca²⁺ transients in dorsal CA1 stratum pyramidale neurons in the hippocampus (dCA1) in mice navigating an odor plume in a 50 cm x 50 cm x 25 cm odor arena. An epifluorescence miniscope focused through a gradient-index (GRIN) lens imaged Ca²⁺ transients in dCA1 neurons expressing the calcium sensor GCaMP6f in Thy1-GCaMP6f mice. The paper describes the behavioral protocol to train the mice to perform this odor plume navigation task in an automated odor arena. The methods include a step-by-step procedure for the surgery for GRIN lens implantation and baseplate placement for imaging GCaMP6f in CA1. The article provides information on real-time tracking of the mouse position to automate the start of the trials and delivery of a water reward. In addition, the protocol includes information on using an interface board to synchronize metadata describing the automation of the odor navigation task and frame times for the miniscope and a digital camera tracking mouse position. Moreover, the methods delineate the pipeline used to process GCaMP6f fluorescence movies by motion correction using the NorMCorre algorithm followed by identification of regions of interest with EXTRACT. Finally, the paper describes an artificial neural network approach to decode spatial paths from CA1 neural ensemble activity to predict mouse navigation of the odor plume.

Introduction

Although significant progress has been made in understanding neural circuits involved in olfactory navigation in head-fixed mice^1,2,3 and navigation strategies in freely moving mice^4,5,6,7,8, the role of neural circuits in ethologically relevant freely moving navigation of turbulent odor plumes is still unknown. This article describes monitoring neural activity by imaging Ca²⁺ transients in ce....

Protocol

Studies were carried out in 3-6-month-old male and femaleThy1-GCaMP6f transgenic mice²³. All experimental protocols were approved by the Institutional Animal Care and Use Committee of the University of Colorado Anschutz Medical Campus in accordance with National Institutes of Health guidelines. The surgical procedures for GRIN lens implantation (Section 1) and the baseplate placement (Section 2) were adapted from previous works^9,24,

Discussion

This protocol meticulously outlines the steps to record place-cells and odor-responsive cells in the dCA1 area of the hippocampus of mice navigating an odor plume. The critical steps in the protocol include stereotaxic surgery, placement of the miniscope baseplate, construction of the odor area, checking the plume in the odor arena, behavioral training, miniscope recording of the freely moving mouse, data preprocessing, and data analysis. Additionally, the protocol explains the process of decoding the mouse trajectory fr.......

Materials

Name	Company	Catalog Number	Comments
Arduino Micro	Arduino	Micro
Biocompatible Methacrylate Resin	Parkell	S380	C&B-Metabond Adhesive Luting Cement
Data Acquisition System (DAQ)	Labmaker	NA	DAQ for UCLA Miniscope V4
Decoding Brain Signals Software	CU Anschutz		https://github.com/restrepd/drgMiniscope
Dental Drill	Osada	LHP-6	AZ210015
Dental Drill Box	Osada	XL-230	30000 rotations per minute
Digital stereotaxic instrument	Stoelting	51730D	Mouse Stereotaxic Instument, #51904 Digital Manipulator Arm, 3-Axes, Add-On, LEFT
Drill Bit	FST Fine Science Tools	19007-05	Tip diameter 0.5 mm
Fast Digital Camera	Edmund Optics	BFS-U3-63S4C	FLIR Blackfly S
Focal Lens	Edmund Optics	C-Series	3.5 mm
GRIN lens	Inscopix	1050-004595	1 mm diameter and 4 mm length
GRIN lens Holder	UCLA		http://miniscope.org/index.php/Surgery_Protocol
Liquid Tissue Adhesive	3M	1469C	Vetbond Tissue Adhesive
Low-Flow Anesthesia System for Mice	Kent Scientific Corporation	SomnoSuite	https://www.kentscientific.com/products/somnosuite/
Low Toxicity Silicone Adhesive	WPI – World Precision Instruments	Kwik-sil
miniPID Controller	ASI – Aurora Scientific Inc.	Model 200B	Fast-Response Miniature Photo-Ionization Detector
Miniscope V4 Holder	UCLA	NA	https://github.com/Aharoni-Lab/Miniscope-v4/tree/master/Miniscope-v4-Holder
Miniscope V4	Labmaker	NA	https://www.labmaker.org/products/miniscope-v4
Miniscope Base Plate V2	Labmaker	NA	https://www.labmaker.org/products/miniscope-v4-base-plates-variant-2-pack-of-10
Miniscope DAQ-QT software	UCLA		https://github.com/Aharoni-Lab/Miniscope-DAQ-QT-Software/wiki
Motion Correction Software	CU Anschutz		https://github.com/restrepd/drgMiniscope
Odor Arena Hardware	Custom Made	3D Model	https://www.dropbox.com/scl/fo/lwtpqysnpzis32mhrx3cd/ADomsxyhxu42sqDmTBl2O6k?rlkey=b3l4809eradundt5l3iz0gq74& dl=0
Odor Arena Software	CUAnschutz		https://github.com/wryanw/odorarena
Odorant Isoamyl Acetate	Aldrich Chemical Co	06422AX	Diluted at 1% in odorless mineral oil
RHD USB Interface Board	Intan Technologies	C3100	Product discontinued. Alternatively use another equivalent board.
ROI Extraction Software	CU Anschutz		https://github.com/restrepd/drgMiniscope
Sutter Micromanipulator	Sutter Instrument Company	MP-285
Synchronization Software	CU Anschutz		https://github.com/fsimoesdesouza/Synchronization
Thy1-GCaMP6f mice	Jackson Laboratory	IMSR_JAX 028281	C57BL/6J-Tg(Thy1-GCaMP6f)GP5.12Dkim/J)