Transcript Examination of Cholinergic Activity during Nicotine

The University of Texas at El Paso
Examination of Age-Related Cholinergic
Activity during Nicotine Exposure and
Withdrawal
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
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 (O’Dell 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).
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.
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.
What We Know ?
Koob GF (2005). The neurocircuitry of addiction: implications for treatment.
Clin Neurosci Res 5: 89–101.
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).
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.
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).
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.
Methods
• Rats were divided in three groups:
Control
– Adolescents
(PND 28–30)
– Adults
(PND 60–75)
– Pre Exposed
(PND 95)
Nicotine Treated
Study Design:
• Pump Implant
Control
• Probe Implant
Nicotine Treated
Nicotine----Saline
Nicotine----Nicotine
• Assess Nacc ACh
during Withdrawal
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
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).”
Nicotine Withdrawal in Rats
•
Following 13 days of nicotine exposure,
rats were implanted with microdialysis
probes in the NAcc.
Study Design:
• Pump Implant
• Probe Implant
• Assess Nacc ACh
during Withdrawal
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
Baseline levels of ACH are higher in adolescent rats
5
Adults
Average Baseline ACh [μM]
Adolescents
Pre-Exposed
4
*
3
*
*
2
1
0
Control Nicotine
Treated
Control
Nicotine
1
Treated
Control Nicotine
Treated
Extracellular Levels Ach (mM)
Extracellular Levels Ach (mM)
Extracellular Levels Ach (mM)
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.
Acknowledgments
Collaborators:
Dr. Laura E O’Dell
Dr. James Orfila
Dr. O’Dell Lab
Financial Support from:
-Vulnerability Issues in Drug Abuse (VIDA) Program
-Research Incentive funds from UTEP
-National Institute on Drug Abuse (R01-DA-021274)