Ex Vivo Preparations of the Intact Vomeronasal Organ and Accessory Olfactory Bulb

Summary

The mouse accessory olfactory bulb (AOB) has been difficult to study in the context of sensory coding. Here, we demonstrate a dissection that produces an ex vivo preparation in which AOB neurons remain functionally connected to their peripheral inputs, facilitating research into information processing of mouse pheromones and kairomones.

Abstract

The mouse accessory olfactory system (AOS) is a specialized sensory pathway for detecting nonvolatile social odors, pheromones, and kairomones. The first neural circuit in the AOS pathway, called the accessory olfactory bulb (AOB), plays an important role in establishing sex-typical behaviors such as territorial aggression and mating. This small (<1 mm³) circuit possesses the capacity to distinguish unique behavioral states, such as sex, strain, and stress from chemosensory cues in the secretions and excretions of conspecifics. While the compact organization of this system presents unique opportunities for recording from large portions of the circuit simultaneously, investigation of sensory processing in the AOB remains challenging, largely due to its experimentally disadvantageous location in the brain. Here, we demonstrate a multi-stage dissection that removes the intact AOB inside a single hemisphere of the anterior mouse skull, leaving connections to both the peripheral vomeronasal sensory neurons (VSNs) and local neuronal circuitry intact. The procedure exposes the AOB surface to direct visual inspection, facilitating electrophysiological and optical recordings from AOB circuit elements in the absence of anesthetics. Upon inserting a thin cannula into the vomeronasal organ (VNO), which houses the VSNs, one can directly expose the periphery to social odors and pheromones while recording downstream activity in the AOB. This procedure enables controlled inquiries into AOS information processing, which can shed light on mechanisms linking pheromone exposure to changes in behavior.

Introduction

Sensory processing in the mammalian brain typically spans multiple reciprocally-connected neuronal circuits, each of which extracts particular features from sensory input. In sensory pathways, early information processing is vital for normal perception and behavior. In the accessory olfactory system (AOS), the accessory olfactory bulb (AOB) is the principal neural circuit linking the sensory periphery to downstream structures that dictate hormonal balance^1,2, aggression³, and arousal⁴. As such, information processing within this circuit is strongly linked to changes in animal behavior.

The accessory olfactor....

Protocol

All experiments were carried out in accordance with protocols approved by the UT Southwestern Institutional Animal Care and Use Committee, and were chosen so as to minimize stress, discomfort, and pain experienced by the experimental animals.

1. Dissection Chamber

A custom dissection chamber and small, thin plastic plank are required for best results (Figure 1). Construct or obtain such a chamber in advance of attempting this protocol.

2. Dissection Solutions

1. Prepare 1 L of standard artificial cerebrospinal fluid (aCSF) for use in Steps 3.22-5.4. Add NaCl 125....

Results

Achieving success with this preparation takes extensive practice, and has several steps at which it can fail. One should expect to require many attempts before achieving success. The custom dissection chamber is required for successful completion of this protocol, and should be obtained prior to starting the later stages of the dissection. The chamber design presented in Figure 1 is sufficient for this purpose, and can be made of relatively inexpensive plastics with minimal machining demands. If one lack.......

Discussion

The VNO-AOB ex vivo preparation described in this protocol is a useful alternative to anesthetized in vivo^5-7 and acute live slice¹⁷ experiments of AOB function. Unlike acute AOB slice experiments, which also expose circuit elements for electrophysiological and optical recordings, this preparation retains all sensory afferents and intra-AOB connections. Although this can also be said of anesthetized in vivo approaches, the presence of anesthetics necessarily alter.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Straight Scissors	Fine Science Tools	14002-14
Fine Scissors-Straight	Fine Science Tools	14060-10
Fine Scissors-Curved	Fine Science Tools	14061-10
Adson Forceps	Fine Science Tools	11006-12
#3 Scalpel Handle	Fine Science Tools	10003-12
#11 Scalpel Blades	Fisher Scientific	3120030
Straight Carbon Steel Razor Blades	Fisher Scientific	12-640
35 mm Petri Dish	Fisher Scientific	08-772-21
Dissection Chamber	Custom	N/A	See Figure 1
Delrin plastic plank 0.6 cm x 1.5 cm x 0.1 cm	Custom	N/A
Dow Corning Silicon Vacuum grease	Fisher Scientific	146355D
#5 Forceps, Student	Fine Science Tools	91150-20
#5 Forceps, Biologie Tip	Fine Science Tools	11295-10
#5 Forceps, Student	Fine Science Tools	91150-20
Vannas Spring Scissors	Fine Science Tools	15000-08
1/16" Male Luer	Cole-Parmer	EW-45505-00
1/16" Tubing	Fisher Scientific	14-171-129
Two ton epoxy	Grainger	5E157
ValveBank Pressurized Perfusion Kit	AutoMate Scientific	09-16
ValveLink digital/manual controller	AutoMate Scientific	01-18
NaCl	Sigma-Aldrich	various
KCl	Sigma-Aldrich	various
CaCl2 dihydrate	Sigma-Aldrich	various
MgCl2 hexahydrate	Sigma-Aldrich	various
NaHCO3	Sigma-Aldrich	various
NaH2PO4	Sigma-Aldrich	various
myo-inositol	Sigma-Aldrich	various
Na-pyruvate	Sigma-Aldrich	various
Na-ascorbate	Sigma-Aldrich	various
HEPES buffer	Sigma-Aldrich	various
Glucose	Sigma-Aldrich	various