Post on 27-Dec-2015
Prenatal Cannabis Exposure Increases Heroin Seeking with Allostatic Changes in Limbic
Enkephalin Systems in Adulthood
M.Sabrina Spano, Maria Ellgren, X. Wang, Yasmin L. Hurd
• THC exposure in prenatal development:– Higher rates of fetal distress– Growth retardation
• Transferred from mother to offspring via placental blood during gestation and via maternal milk during lactation
• CB1 receptors mediate neural actions of cannabinoids & emerge early in development– synaptogenesis, proliferation and migration of
neuronal cells
• Clinical studies indicate in utero exposure is associated – impulsive behavior, cognitive impairment,
psychiatric disorders (schizophrenia, anxiety) in later life
• Kandel 03 suggested potential for cannabis to increase the risk of consumption of other drugs of abuse
• hypothesized that long lasting neurobiological changes in neuronal systems linked with limbic function might be affected by in utero THC exposure– Gateway….?
Opioids
• Endogenous opioid system shares neuroanatomical and neurochemical characteristics with the cannabinoid system; tightly linked
• 3 families– Enkephalin from preproenkephalin (PENK)– Dynorphin from preprodynorphin– Endorphin from proopiomelanocortin (POMC)
• Cannabinoids stimulate release of enkephalin in the NAc and VTA– NAc is part of the mesocorticolimbic circuit– VTA is origin of DA mesocorticolimbic circuit
• PENK widely dist. (NAc, amygdala, PFC)
• Previous human studies show sig. impairment of PENK and meso-limbic DA genes in association with in utero CB exposure– Enduring effects into adulthood?– Influence adult behavior relative to addiction
disorders?
• In rats, perinatal THC exposure alters opioid gene expression, opioid receptor binding and morphine self-administration – Differs between males and females
• treated with THC through gestation & entire lactation period– Dams treated with THC orally, different
pharmacokinetic property than alternate routes of ingestion e.g. smoking, iv
Methods
Fear Leads to Anger---Anger Leads to StressStress Leads to Doobies—Doobies lead to Twinkies
Test animals
• Female Long-Evans rats
• Reversed light/dark cycle
• Permanent right jugular catheter for IV
• Following surgery were mated with a male to induce pregnancy
Admin of drug
• Drug exposure limited to prenatal period– Gestational day5 to post-natal day 2– Corresponds with mid-gestation period in
humans ~ week 20
• THC given IV to better mimic the pharmacokinetics of smoking cannabis in pregnant human females– THC injected .15mg/kg daily
During Drug Treatment
• Maternal weight gain, gestational length and fetal weights were recorded
• PND 2 pups from both groups cross fostered; some brains taken at this time
• PND 21 males weaned; housed 4/cage • PND 55 iv catheter implanted
– Housed individually, 7 day recovery • These are the test animals
– More brains taken PND 62 prior to behav studies
Heroin Self Admin
• Active lever press = 15ug/kg in 85 l fluid
• Fixed Ratio 1, 10s timeout, 3 hour sessions during dark cycle
• After 6 days, dose increased to 30 g/kg
• Baseline= <15% change in # bar presses for 3 consecutive days
• During training food=20g/day– Ad libitum after stable response reached
Dose Response
• Between session dose response test
• Rats now receive either higher 60,100g or lower 7.5, 15 g doses– Self admin as normal for 3 days, order of
presentation was random
• Following test, back to 30g maintenance for 5 more days
Food Stress
• Food deprived for 24 hours
• Response measured following day
Extinction and Reinstatement
• First week of extinction = saline
• Following days = no fluid injected
• Decrease in bar presses of 85% baseline for 3 days = extinction
• Priming: – saline – heroin 0.25 mg/kg sc 10 min prior
– CB1 antagonist 3 mg/kg ip + heroin
Results
• No significant change between groups in– % weight gain in pregnant dams– Gestational length– Pup length at PND 2– Pup weight– Weight between groups at PND 62
• Start of heroin self adminstration training
15 g/kg/infusion 30 g/kg/infusion
• No self admin at 15 g/kg dose
• Both THC and Vehicle groups self admin at 30 g/kg dose
• THC animals show shorter latency to first active response 34 ± 0.84s vs 115 ± 0.91s
Dose Response Test
• Dose-dependant decrease in responding with increasing heroin dose
• THC animals show higher responding at lower doses (7.5 & 15 g/kg)
• No diff in responding at 30, 60 or 100 g doses between groups
Response after Stress Test
• THC animals respond to food deprivation stress with more active lever presses
Extinction, Priming, SR Treatment
• THC group responded to active bar more during first day of extinction (more than maintenance, more than vehicle group)
• Heroin priming reinstated active bar presses– THC group responded to active bar sig more
than they had during maintenance
• SR treatment abolished priming induced reinstatment
Locomotion Response
• THC group showed less locomotion during acquisition and maintenance phases– No diff during extinction phase
• Differences are due to heroin intake
CB1 and Opioid Receptor G-Protein Coupling
• Agonist-stimulated GTPS binding
• No change in or CB1 binding at PND2
• In adults, prenatal THC exposure significantly associated with – decreased opioid binding in NAc shell– Increased binding in SN
– No change in CB1 receptor coupling
1=NAc shell, 2=NAc core, 3=CP, 4=VTA, 5=SN
PENK mRNA Expression
• Prenatal THC Exposure decreased PENK mRNA expression in NAc at PND2– No reliable measurements from amygdala
• No change in preprodynorphin which is colocalized in the NAc
• HOWEVER…• Prenatal THC exposure increased PENK mRNA
in Adults at PND 62 in– NAc core and shell– Central and medial amygdala nuclei
• Compensation?
1=NAc shell2=NAc core3=CP4=m.amy5=c.amy
IncreasedPENK mRNA incAmy
Discussion
• Hyperactivity of the mesocorticolimbic enkephalinergic system in adult animals may be due to the blunted PENK gene expression during early development
Self Administration
• No diff in self admin of heroin between groups in adulthood– THC group showed
• Shorter latency to first active lever press• Higher response to lower doses of heroin• Increased response following food stress• Higher level of seeking during extinction
• Suggests long term vulnerability in the motivation to self-administer heroin
Relapse!
• Following 21 days of drug extinction– Heroin primed THC group responded with
higher number of bar presses than maintenance (increased seeking)
– CB1 antagonist SR141716A completely blocked heroin primed relapse in both groups
– Cross talk between opioid and cannabinoid systems
opioid receptor binding
• THC group show less OR binding in NAc – Key region in reward processing– also modulates locomotion
• THC group showed less loco when on heroin
• Similar toOR deficient animals
Take-Home Message
• THC administered during prenatal period significant affects PENK mRNA expression during prenatal period and adulthood
• Alterations of the opioid system last into adulthood and enhance vulnerability to opiate-seeking behavior