Characterization of Cholinergic Receptor Agonists Nicotine and Arecoline Using Drug Discrimination

By: Kelly Bresnahan

On-Site Supervisor: James Woods, Ph.D.

Department of PharmacologyUniversity of Michigan

Faculty Supervisor:Laura Furge, Ph.D

Clinical Significance• Why do we care about

smoking cessation?

• Aren’t there already drugs on the market?

Why Do We Care About Smoking Cessation?

• Tobacco smoking is the 3rd most addictive drug behind heroin and cocaine

•Partly due to the discriminative stimulus property of nicotine

Aren’t There Already Drugs on the Market to Aid in Smoking

Cessation?

Drugs/Therapies Already on the Market

Drugs/Therapies Already on the Market

*

Drugs/Therapies Already on the Market

*

Drugs/Therapies Already on the Market

*

Approach: Drug Discrimination• Used male

Sprague-Dawley rats

• No previous drug experience

**All studies were carried out in accordance with the Guide for Care and Use of Laboratory Animals

** All experimental protocols were approved by the University of Michigan’s Committee on the Use and Care of Animals

What is Drug Discrimination?• Procedure where subjects recognize a

drug state and respond accordingly to receive reinforcement13

• Uses operant conditioning- a form of learning where individual’s behavior is modified by it’s consequences

• Subjects must distinguish between training drug and vehicle (two-key) or two training drugs and a vehicle (three-key)

Has This Punch Been Spiked?!?

Why Pair Nicotine with Arecoline?• Both are Acetylcholine

(ACh) receptor agonists

Preliminary Training• Trained to a fixed

ratio (FR) 10 schedule

• Response on any aperture resulted in reinforcement

• Reinforcement: 10 s access to vanilla Ensure® or one sugar pellet

Discrimination Training/TestingTraining:• “Correct” apertures

are assigned depending on the pretreatment drug given

• Correct responses result in reinforcement

Testing:• Response on either

(any) aperture results in reinforcement

Aperture Assignments†Subject Left Middle RightD88 Nicotine Arecoline** SalineD89 Nicotine** Saline ArecolineD90 Arecoline Saline** NicotineD91 Saline* Nicotine Arecoline**D92 Saline** Arecoline NicotineD93 Arecoline Nicotine** Saline

† Apertures were assigned in order to reduce bias and were as follows: 1) each aperture had approximately 33% of subjects assigned to vehicle (saline), nicotine, and arecoline; 2) 33% of rats had vehicle-associated, nicotine-associated, or arecoline-associated assigned to their most preferred aperture.

* Middle preferred aperture** Most preferred aperture No asterisk indicates least preferred aperture(s)

Discrimination Training/TestingTraining:• “Correct” apertures

are assigned depending on the pretreatment drug given

• Correct responses result in reinforcement

Testing:• Response on either

(any) aperture results in reinforcement

Nicotine-TrainedA

B

A

B

Arecoline-Trained

Nicotine-TrainedA

B

A

B

Arecoline-Trained

0.32 mg/kg 1.0 mg/kg

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

THERE ARE SOME ANOMALIES

But wait one second…

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

Nicotine-Trained Arecoline-Trained

B

A

B

A

B

AA

B

n=2

Potential Solution: Three-Key Discrimination

Pros• Uses three “keys”

instead of two• Compares nicotine

and arecoline to saline

• May explain anomalies in the two-key studies

Potential Solution: Three-Key Discrimination

Pros• Uses three “keys”

instead of two• Compares nicotine

and arecoline to saline

• May explain anomalies in the two-key studies

Cons• Takes much longer

to train rats

Learning Ability

Take-Home Points• Varenicline (Chantix) is

a partial agonist of nicotine- which explains how it is an effective smoking cessation aid

• Nicotine does not bind to muscarinic receptors, but arecoline may bind to nicotinic receptors at high doses

• The three-key discrimination paradigm is underway and showing promising results

Future Directions• Repeat two-key

studies with nicotine using subjects able to respond to 1.0 mg/kg arecoline

• Introduce potential nicotinic antagonist in hopes of developing a smoking cessation aid.

Acknowledgements• Principle Investigator: Dr. James Woods • On-Site Supervisor: Jessica Priebe• SIP Advisor: Dr. Furge• SIP Review Team: Mara, Dagan, and Josh• Presentation Team: Ben, Kenny, Jesyca,

Lynza, Josh, and Eric• Chemistry department

References1. http://www.cartoonstock.com/directory/n/nonsmoking_cages.asp2. Nutt, D.; King, L. A.; Saulsbury, W.; Blakemore, C. (2007). "Development of a rational scale

to assess the harm of drugs of potential misuse". The Lancet  369 (9566): 1047-10533. http://www.quitsmokingpress.com/does-nicotine-patch-work/4. http://drugline.org/drug/medicament/16288/5. Sdf http://ecigarettereviewsite.net/going-cold-turkey-or-using-e-cigarettes-to-quit-smoking/ 6. http://www.luuux.com/node/2338502 (fake cigarette)7. http://www.nrtdirect.co.uk/niquitin-lozenge-mint-4mg-36-pack (lozenge)8. http://www.wired.com/medtech/drugs/news/2008/03/chantix (chantix)9. http://www.healthmake.org/mental-disorders/ (wellbutrin)10. http://doctorsofphysicaltherapy.wordpress.com/2013/01/16/i-am-who-i-am/(solo therapy)11. http://www.health.com/health/condition-article/0,,20213727,00.html(group therapy)12. http://www.swaebr.org/resources.html(animal testing pic)13. Pickens, R. Behavioral pharmacology: a brief history. Adv. in Behav. Pharm. 1977, 1, 229-

253. 14. http://www.vibe.com/photo-gallery/guide-summer-travel-essentials-drinks-gadgets/?

page=1615. http://store.perspicuity.com/view_photo.php?set_albumName=Products&id=Press16. http://www.nature.com/nprot/journal/v1/n3/fig_tab/nprot.2006.167_F1.html17. http://www.lawyersandsettlements.com

Questions?