Intracranial Pharmacotherapy and Pain Assays in Rodents

Summary

Here we present a protocol to perform intracranial pharmacological experiments followed by pain behavior assays in rodents. This protocol allows researchers to deliver molecular and cellular targets in the brain, for pharmacologic agents in the treatment of pain.

Abstract

Pain is a salient sensory experience with affective and cognitive dimensions. However, central mechanisms for pain remain poorly understood, hindering the development of effective therapeutics. Intracranial pharmacology presents an important tool for understanding the molecular and cellular mechanisms of pain in the brain, as well as for novel treatments. Here we present a protocol that integrates intracranial pharmacology with pain behavior testing. Specifically, we show how to infuse analgesic drugs into a select brain region, which may be responsible for pain modulation. Furthermore, to determine the effect of the candidate drug in the central nerve system, pain assays are performed after intracranial treatment. Our results demonstrate that intracranial administration of analgesic drugs in a targeted region can provide relief of pain in rodents. Thus, our protocol successfully demonstrates that intracranial pharmacology, combined with pain behavior testing, can be a powerful tool for the study of pain mechanisms in the brain.

Introduction

The central nervous system is known to play a key role in pain regulation. For example, glutamate signaling in the brain has a regulatory role in the context of pain^1,2. Hence, there is a need to study cellular and molecular signaling pathways in the brain with respect to pain. In addition, there is a need to understand if molecular targets in specific brain regions can be modified to treat pain. Current studies of pain in the brain rely on in vitro studies of electrophysiology in combination with systemic (intraperitoneal) delivery of pharmacological agents. In vitro studies have obvious def....

Protocol

All procedures in this study were approved by the New York University School of Medicine Institutional Animal Care and Use Committee (IACUC) as consistent with the National Institute of Health (NIH) Guide for the Care and Use of Laboratory Animals.

1. Stereotaxic Cannula Implantation

1. Use 10-12 week old male Sprague-Dawley rats.
2. As previously described, anesthetize animals with 1.5-2% isoflurane^1,3,5. Once the animal becomes unresponsive to a strong pinch with sharp forceps, perform the surgery. Be sure to autoclave all instrum....

Results

As an example, we infused an AMPAkine into the PFC via cannulas (Figure 1). We also infused morphine systemically to assess the synergistic analgesic effects between AMPAkines and morphine. These results show that AMPAkines and morphine have an additive analgesic effect. It also shows that intracranial injections have the power to discover, at least in part, a mechanism for drug activation in the context of pain.

Discussion

In this study, we have demonstrated that intracranial pharmacology is a powerful tool to study pain mechanisms and has potential as a therapeutic delivery system. In our protocol, we delivered AMPAkines directly into the PFC and found that by enhancing glutamate signaling in the PFC, AMPAkines provided pain relief. We were able to demonstrate this through the use of intracranial injections combined with intraperitoneal injections, with subsequent pain assays. Based on the evidence of pain-relieving effects, when AMPAkine.......

Materials

Name	Company	Catalog Number	Comments
Sterotaxic Cannula	PlasticsOne	8I26GA8MMKIT
Digital Syringe	Hamilton	8440
AMPAkine	Sigma Aldrich	C-271
Dimethyl Sulfoxide	Sigma Aldrich	D4540
Hargreaves Apparatus	Ugo Basile	37370
Male Sprague-Dawley rats	Taconic Farms	NTac:SD
Sterile Surgical gloves	Dynarex	6535