Intranasal Administration of CNS Therapeutics to Awake Mice

Summary

A method to intranasally administer drugs to awake mice for the purpose of targeting the brain is described. This method allows for repeat dosing over long periods using intranasal administration of drug without anesthesia, and nose-to-brain delivery with minimal systemic exposure.

Abstract

Intranasal administration is a method of delivering therapeutic agents to the central nervous system (CNS). It is non-invasive and allows large molecules that do not cross the blood-brain barrier access to the CNS. Drugs are directly targeted to the CNS with intranasal delivery, reducing systemic exposure and thus unwanted systemic side effects¹. Delivery from the nose to the CNS occurs within minutes along both the olfactory and trigeminal neural pathways via an extracellular route and does not require drug to bind to any receptor or axonal transport². Intranasal delivery is a widely publicized method and is currently being used in human clinical trials³.

Intranasal delivery of drugs in animal models allows for initial evaluation of pharmacokinetic distribution and efficacy. With mice, it is possible to administer drugs to awake (non-anesthetized) animals on a regular basis using a specialized intranasal grip. Awake delivery is beneficial because it allows for long-term chronic dosing without anesthesia, it takes less time than with anesthesia, and can be learned and done by many people so that teams of technicians can dose large numbers of mice in short periods. Efficacy of therapeutics administered intranasally in this way to mice has been demonstrated in a number of studies including insulin in diabetic mouse models ^4-6 and deferoxamine in Alzheimer's mouse models. ^7,8

The intranasal grip for mice can be learned, but is not easy and requires practice, skill, and a precise grip to effectively deliver drug to the brain and avoid drainage to the lung and stomach. Mice are restrained by hand using a modified scruff in the non-dominant hand with the neck held parallel to the floor, while drug is delivered with a pipettor using the dominant hand. It usually takes 3-4 weeks of acclimating to handling before mice can be held with this grip without a stress response. We have prepared this JoVE video to make this intranasal delivery technique more accessible.

Protocol

1. Acclimation to Handling for Intranasal Dosing to Awake Mice

Introduction

Mice must be acclimated to handling for a period of two-four weeks before the onset of intranasal dosing. Acclimation to handling is important, as it helps ensure a correct body position for maximum effectiveness of awake intranasal drug delivery. In addition, mice that have not been properly accustomed to this process can have a severe anxiety reaction after dosing. Mice should spend about 2-3 days on each of nine steps before progressing to the next step, depending upon the animal's comfort to handling. The mouse's stress level shoul....

Results

There are several ways to determine the efficacy of drug delivery. The first is to intranasally administer a dye, such as India ink or methylene blue and to visualize the dye after euthanasia of the animal within the olfactory epithelium and after the brain is removed, entering the CNS through the cribriform plate. The second is to measure the drug delivered either by using a radio-labeled tag or using ELISA detection of the unlabeled molecule. A good example of drug distribution in the CNS after administration t.......

Discussion

This method shows how mice can be given regular doses of intranasal drug to target the brain without the use of anesthesia. Intranasal drug can be delivered to large groups of mice for extended periods of time with minimal effort. A single group of up to 20 mice can be intranasally treated by a single person in less than one hour. A vast array of molecules, ranging from small iron chelators to growth factors to mesenchymal stem cells, have been demonstrated to rapidly target the CNS and have shown efficacy in rodents mod.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
P20 pipettor set at 6 μl
Gel loading pipette tips
Timer
Waste receptacle for tips
Dosing sheet for notes
Pen
Drug and vehicle
Container to hold drug vials
Animals to be dosed
Spare gloves
Paper towels to wipe urine
Table 3. Materials Needed