Examination of Age-Related Cholinergic Activity during Nicotine Exposure and Withdrawal

1
Examination of Age-Related Cholinergic Activity
during Nicotine Exposure and Withdrawal
The University of Texas at El Paso

• Luis M Carcoba, M.D, Ph.D.
• University of Texas at El Paso
• Department of Psychology
• CHARLES R. DREW UNIVERSITY OF MEDICINE AND
  SCIENCE
• 9th Drug Abuse Research Symposium
• September 12, 2014

2
Introduction (Adolescents
Tobacco Use)

• Although the prevalence of smoking among the
  general population has generally decreased over
  recent years, there has been a steady rise in the
  rate of smoking behavior among adolescents.
• Adolescents are particularly vulnerable to
  tobacco abuse, and they are more likely to
  initiate tobacco use and continue to use tobacco
  products as adults. As a result, they are at
  greater risk of smoking-related diseases caused
  by long-term tobacco use.
• Studies have demonstrated that adolescent rodents
  display fewer physical symptoms of nicotine
  withdrawal as compared with adult rats (ODell et
  al. 2006 Shram et al. 2008) and mice (Kota et
  al. 2007).
• Also, the rewarding effects of nicotine are
  enhanced during the adolescent period of
  development (Torres et al., 2008).

3
Introduction (Nicotine
Withdrawal Syndrome)

• It is well-accepted that relapse to smoking
  behavior is due, in large part, to negative
  reinforcement processes that maintain smoking
  behavior and relapse behavior in order to avoid
  the negative consequences of withdrawal.
• Current treatment strategies focus on alleviating
  withdrawal. However, the role of withdrawal in
  smoking behavior during adolescence is presently
  unclear.

4

What We Know ? There are more than 4,000
chemicals found in the smoke of tobacco products.
Of these, nicotine, first identified in the early
1800s, is the primary reinforcing component of
tobacco.
5
What We Know ?
Koob GF (2005). The neurocircuitry of addiction
implications for treatment. Clin Neurosci Res 5
89101.
6
Role of ACh in NAcc

• The behavioral mechanisms of nicotine are
  mediated, in large part, in the nucleus accumbens
  (NAcc), a terminal region of mesolimbic pathway
  where dopamine levels are increased following
  nicotine administration and decreased during
  withdrawal from this drug (Corrigall, 1991, 1992
  Mansvelder and McGehee, 2002 Watkins et al.,
  2000).

7
Role of ACh in NAcc

• The nucleus accumbens (NAcc) has been implicated
  in modulating the reinforcing properties of drugs
  of abuse playing a role in the aversive aspects
  of drug withdrawal as reported during diazepam
  and morphine withdrawal.

8
Role of ACh in NAcc

• Recent work in our laboratory focused on
  developmental differences to nicotine withdrawal
  demonstrated that adolescent rats exhibit lesser
  withdrawal-associated deficits in NAcc dopamine
  as compared to nicotine-dependent adults
  (Natividad et al., 2010).

9
Role of ACh in NAcc

• Our initial studies focused on NAcc dopamine were
  a logical first step towards understanding the
  mechanisms of nicotine withdrawal given the
  importance of dopamine in mediating the
  behavioral effects of nicotine.
• However, the mechanisms of nicotine withdrawal
  also appear to involve cholinergic transmission
  in the NAcc, since nicotine withdrawal produces
  increased ACh levels in this brain region of
  adult rats experiencing nicotine withdrawal (Rada
  et al., 2001).
• Given the potential role of cholinergic systems
  in mediating age differences to withdrawal, the
  present study compared ACh levels in the NAcc of
  adolescent and adult rats during precipitated
  withdrawal.

10
Methods

• Rats were divided in three groups
• Adolescents
• (PND 2830)
• Adults
• (PND 6075)
• Pre Exposed
• (PND 95)

• Study Design
• Pump Implant
• Probe Implant
• Assess Nacc ACh during Withdrawal

11
Nicotine Withdrawal in Rats

• Study Design
• Pump Implant
• Probe Implant
• Assess Nacc ACh during Withdrawal

• To measure ACh activity rats were prepared with
  osmotic pumps delivering an equivalent nicotine
  dose in these age groups

Dependence Induction Administration of
nicotine via subcutaneous osmotic pumps for 7-14
days Withdrawal Spontaneous withdrawal
Removal of nicotine pump Precipitated
withdrawal Administration of the nicotinic
antagonist mecamylamine
12
Nicotine Withdrawal in Rats

• Study Design
• Pump Implant
• Probe Implant
• Assess Nacc ACh during Withdrawal

• Following 13 days of nicotine exposure, rats were
  implanted with microdialysis probes in the NAcc.

Bregma 1.70 mm (Paxinos and Watson, 1998).
13
Nicotine Withdrawal in Rats

• Study Design
• Pump Implant
• Probe Implant
• Assess Nacc ACh during Withdrawal

• Following 13 days of nicotine exposure, rats were
  implanted with microdialysis probes in the NAcc.

14
Nicotine Withdrawal in Rats

• Study Design
• Pump Implant
• Probe Implant
• Assess Nacc ACh during Withdrawal

• Next day, dialysis samples were collected during
  baseline and following systemic administration of
  the nicotinic-receptor antagonist mecamylamine.
  ACh was quantified from 10-µl samples injected
  into a HPLC system

15
Baseline levels of ACH are higher in adolescent
rats
16
Extracellular Levels Ach (mM)
17
Extracellular Levels Ach (mM)
18
Extracellular Levels Ach (mM)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
Conclusions

• Age Differences
• Baseline levels of ACh were higher in adolescent
  versus adult rats.
• During withdrawal, both groups displayed similar
  levels of ACh. This suggests that behavioral
  differences observed in nicotine exposed animals
  are not ACh-mediated.
• Pre-exposure to Nicotine Effects
• Baseline levels of ACh were slightly increased
  by adolescent nicotine
  exposure.
• During withdrawal, the increases in ACh levels
  observed in naïve adults were blunted by
  adolescent nicotine exposure.

23
Questions ?
24
Acknowledgments Collaborators Dr. Laura E
ODell Dr. James Orfila Dr. ODell Lab Financial
Support from -Vulnerability Issues in Drug
Abuse (VIDA) Program -Research Incentive funds
from UTEP -National Institute on Drug Abuse
(R01-DA-021274)