Prenatal Cannabis Exposure Increases Heroin Seeking with Allostatic Changes in Limbic Enkephalin Systems in Adulthood M.Sabrina Spano, Maria Ellgren,

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