Perinatal delta9-tetrahydrocannabinol exposure augmented the magnitude of motor inhibition caused by GABA(B), but not GABA(A), receptor agonists in adult rats

Effects of Cannabinoid Exposure during Neurodevelopment on Future Effects of Drugs of Abuse: A Preclinical Perspective

The endocannabinoid system plays a central role in the earliest stages of embryonic, postnatal and adolescent neurodevelopment. Aberrant activity of this system at key developmental phases has been shown to affect neural development. The aim of this review is to synthesise and analyse preclinical insights within rodent populations, focusing on the effects that perinatal (embryonic, gestational and early postnatal developmental stages) and adolescent (postnatal day 21–60) cannabinoid exposure impose across time on the subsequent activity of various drugs of abuse. Results in rodents show that exposure to cannabinoids during the perinatal and adolescent period can lead to multifaceted behavioural and molecular changes. In the perinatal period, significant effects of Δ⁹-THC exposure on subsequent opiate and amphetamine reward-related behaviours were observed primarily in male rodents. These effects were not extended to include cocaine or alcohol. In adolescence, various cannabinoid agonists were used experimentally. This array of cannabinoids demonstrated consistent effects on opioids across sex. In contrast, no significant effects were observed regarding the future activity of amphetamines and cocaine. However, these studies focused primarily on male rodents. In conclusion, numerous gaps and limitations are apparent in the current body of research. The sparsity of studies analysing the perinatal period must be addressed. Future research within both periods must also focus on delineating sex-specific effects, moving away from a male-centric focus. Studies should also aim to utilise more clinically relevant cannabinoid treatments.

The Impact of Early Life Exposure to Cannabis: The Role of the Endocannabinoid System

Cannabis use during pregnancy has continued to rise, particularly in developed countries, as a result of the trend towards legalization and lack of consistent, evidence-based knowledge on the matter. While there is conflicting data regarding whether cannabis use during pregnancy leads to adverse outcomes such as stillbirth, preterm birth, low birthweight, or increased admission to neonatal intensive care units, investigations into long-term effects on the offspring’s health are limited. Historically, studies have focused on the neurobehavioral effects of prenatal cannabis exposure on the offspring. The effects of cannabis on other physiological aspects of the developing fetus have received less attention. Importantly, our knowledge about cannabinoid signaling in the placenta is also limited. The endocannabinoid system (ECS) is present at early stages of development and represents a potential target for exogenous cannabinoids in utero. The ECS is expressed in a broad range of tissues and influences a spectrum of cellular functions. The aim of this review is to explore the current evidence surrounding the effects of prenatal exposure to cannabinoids and the role of the ECS in the placenta and the developing fetus.

Persistent proteomic changes in glutamatergic and GABAergic signaling in the amygdala of adolescent rats exposed to chlorpyrifos as juveniles

Chlorpyrifos (CPF) remains one of the most widely used organophosphorus insecticides (OPs) despite the concerns about its developmental neurotoxicity. Developmental exposure to CPF has long-lasting negative impacts, including abnormal emotional behaviors. These negative impacts are observed at exposure levels do not cause inhibition of acetylcholinesterase, the canonical target of OPs. Exposure to CPF at these levels inhibits the endocannabinoid metabolizing enzyme fatty acid amide hydrolase (FAAH) but it is not clear what the persistent effects of this inhibition are. To investigate this, male rat pups were exposed orally to either corn oil, 0.75 mg/kg CPF, or 0.02 mg/kg PF-04457845 (PF; a specific inhibitor of FAAH) daily from postnatal day 10 (PND10) - PND16. This dosage of CPF does not inhibit brain cholinesterase activity but inhibits FAAH activity. On PND38 (adolescence), the protein expression in the amygdala was determined using a label-free shotgun proteomic approach. The analysis of control vs CPF and control vs PF led to the identification of 44 and 142 differentially regulated proteins, respectively. Gene ontology enrichment analysis revealed that most of the proteins with altered expression in both CPF and PF treatment groups were localized in the synapse-related regions, such as presynaptic membrane, postsynaptic density, and synaptic vesicle. The different biological processes affected by both treatment groups included persistent synaptic potentiation, glutamate receptor signaling, protein phosphorylation, and chemical synaptic transmission. These results also indicated disturbances in the balance between glutamatergic (↓ Glutamate AMPA receptor 2, ↓ Excitatory amino acid transporter 2, and ↑ vesicular glutamate transporter 2) and GABAergic signaling (↑ GABA transporter 3 and ↑ glutamate decarboxylase 2). This imbalance could play a role in the abnormal emotional behavior that we have previously reported. These results suggest that there is a similar pattern of expression between CPF and PF, and both these chemicals can persistently alter emotional behavior as a consequence of inhibition of FAAH.

Cannabinoid Exposure via Lactation in Rats Disrupts Perinatal Programming of the Gamma-Aminobutyric Acid Trajectory and Select Early-Life Behaviors

BACKGROUND

Cannabis usage is increasing with its widespread legalization. Cannabis use by mothers during lactation transfers active cannabinoids to the developing offspring during this critical period and alters postnatal neurodevelopment. A key neurodevelopmental landmark is the excitatory to inhibitory gamma-aminobutyric acid (GABA) switch caused by reciprocal changes in expression ratios of the K+/Cl- transporters potassium-chloride cotransporter 2 (KCC2) and sodium-potassium-chloride transporter (NKCC1).

METHODS

Rat dams were treated with Δ9-tetrahydrocannabinol or a synthetic cannabinoid during the first 10 days of postnatal development, and experiments were then conducted in the offspring exposed to these drugs via lactation. The network influence of GABA transmission was analyzed using cell-attached recordings. KCC2 and NKCC1 levels were determined using Western blot and quantitative polymerase chain reaction analyses. Ultrasonic vocalization and homing behavioral experiments were carried out at relevant time points.

RESULTS

Treating rat dams with cannabinoids during early lactation retards transcriptional upregulation and expression of KCC2, thereby delaying the GABA switch in pups of both sexes. This perturbed trajectory was corrected by the NKCC1 antagonist bumetanide and accompanied by alterations in ultrasonic vocalization without changes in homing behavior. Neurobehavioral deficits were prevented by CB1 receptor antagonism during maternal exposure, showing that the CB1 receptor underlies the cannabinoid-induced alterations.

CONCLUSIONS

These results reveal how perinatal cannabinoid exposure retards an early milestone of development, delaying the trajectory of GABA's polarity transition and altering early-life communication.

GABAB Receptors and Drug Addiction: Psychostimulants and Other Drugs of Abuse

Metabotropic GABA_B receptors (GABA_BRs) mediate slow inhibition and modulate synaptic plasticity throughout the brain. Dysfunction of GABA_BRs has been associated with psychiatric illnesses and addiction. Drugs of abuse alter GABA_B receptor (GABA_BR) signaling in multiple brain regions, which partly contributes to the development of drug addiction. Recently, GABA_BR ligands and positive allosteric modulators (PAMs) have been shown to attenuate the initial rewarding effect of addictive substances, inhibit seeking and taking of these drugs, and in some cases, ameliorate drug withdrawal symptoms. The majority of the anti-addiction effects seen with GABA_BR modulation can be localized to ventral tegmental area (VTA) dopamine neurons, which receive complex inhibitory and excitatory inputs that are modified by drugs of abuse. Preclinical research suggests that GABA_BR PAMs are emerging as promising candidates for the treatment of drug addiction. Clinical studies on drug dependence have shown positive results with GABA_BR ligands but more are needed, and compounds with better pharmacokinetics and fewer side effects are critically needed.

Prenatal cannabinoid exposure and altered neurotransmission

Marijuana is one of the most commonly used illicit drugs worldwide. In addition, use of synthetic cannabinoids is increasing, especially among adolescents and young adults. Although human studies have shown that the use of marijuana during pregnancy leads to adverse behavioral effects, such as deficiencies in attention and executive function in affected offspring, the rate of marijuana use among pregnant women is steadily increasing. Various aspects of human behavior including emotion, learning, and memory are dependent on complex interactions between multiple neurotransmitter systems that are especially vulnerable to alterations during the developmental period. Thus, exploration of neurotransmitter changes in response to prenatal cannabinoid exposure is crucial to develop an understanding of how homeostatic imbalance and various long-term neurobehavioral deficits manifest following the abuse of marijuana or other synthetic cannabinoids during pregnancy. Current literature confirms that vast alterations to neurotransmitter systems are present following prenatal cannabinoid exposure, and many of these alterations within the brain are region specific, time-dependent, and sexually dimorphic. In this review, we aim to provide a summary of observed changes to various neurotransmitter systems following cannabinoid exposure during pregnancy and to draw possible correlations to reported behavioral alterations in affected offspring.

Long-lasting alterations of hippocampal GABAergic neurotransmission in adult rats following perinatal Δ9-THC exposure

The long-lasting effects of gestational cannabinoids exposure on the adult brain of the offspring are still controversial. It has already been shown that pre- or perinatal cannabinoids exposure induces learning and memory disruption in rat adult offspring, associated with permanent alterations of cortical glutamatergic neurotransmission and cognitive deficits. In the present study, the risk of long-term consequences induced by perinatal exposure to cannabinoids on rat hippocampal GABAergic system of the offspring, has been explored. To this purpose, pregnant rats were treated daily with Delta⁹-tetrahydrocannabinol (Δ⁹-THC; 5mg/kg) or its vehicle. Perinatal exposure to Δ⁹-THC induced a significant reduction (p<0.05) in basal and K⁺-evoked [³H]-GABA outflow of 90-day-old rat hippocampal slices. These effects were associated with a reduction of hippocampal [³H]-GABA uptake compared to vehicle exposed group. Perinatal exposure to Δ⁹-THC induced a significant reduction of CB1 receptor binding (B_max) in the hippocampus of 90-day-old rats. However, a pharmacological challenge with either Δ⁹-THC (0.1μM) or WIN55,212-2 (2μM), similarly reduced K⁺-evoked [³H]-GABA outflow in both experimental groups. These reductions were significantly blocked by adding the selective CB1 receptor antagonist SR141716A. These findings suggest that maternal exposure to cannabinoids induces long-term alterations of hippocampal GABAergic system. Interestingly, previous behavioral studies demonstrated that, under the same experimental conditions as in the present study, perinatal cannabinoids exposure induced cognitive impairments in adult rats, thus resembling some effects observed in humans. Although it is difficult and sometimes misleading to extrapolate findings obtained from animal models to humans, the possibility that an alteration of hippocampus aminoacidergic transmission might underlie, at least in part, some of the cognitive deficits affecting the offspring of marijuana users, is supported.

Effect of cannabis on glutamate signalling in the brain: A systematic review of human and animal evidence

Use of cannabis or delta-9-tetrahydrocannabinol (Δ9-THC), its main psychoactive ingredient, is associated with psychotic symptoms or disorder. However, the neurochemical mechanism that may underlie this psychotomimetic effect is poorly understood. Although dopaminergic dysfunction is generally recognized as the final common pathway in psychosis, evidence of the effects of Δ9-THC or cannabis use on dopaminergic measures in the brain is equivocal. In fact, it is thought that cannabis or Δ9-THC may not act on dopamine firing directly but indirectly by altering glutamate neurotransmission. Here we systematically review all studies examining acute and chronic effects of cannabis or Δ9-THC on glutamate signalling in both animals and man. Limited research carried out in humans tends to support the evidence that chronic cannabis use reduces levels of glutamate-derived metabolites in both cortical and subcortical brain areas. Research in animals tends to consistently suggest that Δ9-THC depresses glutamate synaptic transmission via CB1 receptor activation, affecting glutamate release, inhibiting receptors and transporters function, reducing enzyme activity, and disrupting glutamate synaptic plasticity after prolonged exposure.

Long-term consequences of perinatal and adolescent cannabinoid exposure on neural and psychological processes

Marihuana is the most widely consumed illicit drug, even among adolescents and pregnant women. Given the critical developmental processes that occur in the adolescent and fetal nervous system, marihuana consumption during these stages may have permanent consequences on several brain functions in later adult life. Here, we review what is currently known about the long-term consequences of perinatal and adolescent cannabinoid exposure. The most consistent findings point to long-term impairments in cognitive function that are associated with structural alterations and disturbed synaptic plasticity. In addition, several neurochemical modifications are also evident after prenatal or adolescent cannabinoid exposure, especially in the endocannabinoid, glutamatergic, dopaminergic and opioidergic systems. Important sexual dimorphisms are also evident in terms of the long-lasting effects of cannabinoid consumption during pregnancy and adolescence, and cannabinoids possibly have a protective effect in adolescents who have suffered traumatic life challenges, such as maternal separation or intense stress. Finally, we suggest some future research directions that may encourage further advances in this exciting field.

Epigenetic Regulation of Immunological Alterations Following Prenatal Exposure to Marijuana Cannabinoids and its Long Term Consequences in Offspring

Use of marijuana during pregnancy is fairly commonplace and can be expected increase in frequency as more states legalize its recreational use. The cannabinoids present in marijuana have been shown to be immunosuppressive, yet the effect of prenatal exposure to cannabinoids on the immune system of the developing fetus, its long term consequences during adult stage of life, and transgenerational effects have not been well characterized. Confounding factors such as co-existing drug use make the impact of cannabis use on progeny inherently difficult to study in a human population. Data from various animal models suggests that in utero exposure to cannabinoids results in profound T cell dysfunction and a greatly reduced immune response to viral antigens. Furthermore, evidence from animal studies indicates that the immunosuppressive effects of cannabinoids can be mediated through epigenetic mechanisms such as altered microRNA, DNA methylation and histone modification profiles. Such studies support the hypothesis that that parental or prenatal exposure to cannabis can trigger epigenetic changes that could have significant immunological consequences for offspring as well as long term transgenerational effects.

Low level chlorpyrifos exposure increases anandamide accumulation in juvenile rat brain in the absence of brain cholinesterase inhibition

The prevailing dogma is that chlorpyrifos (CPF) mediates its toxicity through inhibition of cholinesterase (ChE). However, in recent years, the toxicological effects of developmental CPF exposure have been attributed to an unknown non-cholinergic mechanism of action. We hypothesize that the endocannabinoid system may be an important target because of its vital role in nervous system development. We have previously reported that repeated exposure to CPF results in greater inhibition of fatty acid amide hydrolase (FAAH), the enzyme that metabolizes the endocannabinoid anandamide (AEA), than inhibition of either forebrain ChE or monoacylglycerol lipase (MAGL), the enzyme that metabolizes the endocannabinoid 2-arachidonylglycerol (2-AG). This exposure resulted in the accumulation of 2-AG and AEA in the forebrain of juvenile rats; however, even at the lowest dosage level used (1.0mg/kg), forebrain ChE inhibition was still present. Thus, it is not clear if FAAH activity would be inhibited at dosage levels that do not inhibit ChE. To determine this, 10 day old rat pups were exposed daily for 7 days to either corn oil or 0.5mg/kg CPF by oral gavage. At 4 and 12h post-exposure on the last day of administration, the activities of serum ChE and carboxylesterase (CES) and forebrain ChE, MAGL, and FAAH were determined as well as the forebrain AEA and 2-AG levels. Significant inhibition of serum ChE and CES was present at both 4 and 12h. There was no significant inhibition of the activities of forebrain ChE or MAGL and no significant change in the amount of 2-AG at either time point. On the other hand, while no statistically significant effects were observed at 4h, FAAH activity was significantly inhibited at 12h resulting in a significant accumulation of AEA. Although it is not clear if this level of accumulation impacts brain maturation, this study demonstrates that developmental CPF exposure at a level that does not inhibit brain ChE can alter components of endocannabinoid signaling.

Olfactory Hallucinations without Clinical Motor Activity: A Comparison of Unirhinal with Birhinal Phantosmia

Olfactory hallucinations without subsequent myoclonic activity have not been well characterized or understood. Herein we describe, in a retrospective study, two major forms of olfactory hallucinations labeled phantosmias: one, unirhinal, the other, birhinal. To describe these disorders we performed several procedures to elucidate similarities and differences between these processes. From 1272, patients evaluated for taste and smell dysfunction at The Taste and Smell Clinic, Washington, DC with clinical history, neurological and otolaryngological examinations, evaluations of taste and smell function, EEG and neuroradiological studies 40 exhibited cyclic unirhinal phantosmia (CUP) usually without hyposmia whereas 88 exhibited non-cyclic birhinal phantosmia with associated symptomology (BPAS) with hyposmia. Patients with CUP developed phantosmia spontaneously or after laughing, coughing or shouting initially with spontaneous inhibition and subsequently with Valsalva maneuvers, sleep or nasal water inhalation; they had frequent EEG changes usually ipsilateral sharp waves. Patients with BPAS developed phantosmia secondary to several clinical events usually after hyposmia onset with few EEG changes; their phantosmia could not be initiated or inhibited by any physiological maneuver. CUP is uncommonly encountered and represents a newly defined clinical syndrome. BPAS is commonly encountered, has been observed previously but has not been clearly defined. Mechanisms responsible for phantosmia in each group were related to decreased gamma-aminobutyric acid (GABA) activity in specific brain regions. Treatment which activated brain GABA inhibited phantosmia in both groups.

Dose-response effect between cannabis use and psychosis liability in a non-clinical population: evidence from a snowball sample

This study aimed to explore the associations between daily cannabis use and the specific profiles of subclinical symptoms in a non-clinical population obtained through snowball sampling, taking into account alcohol use, other drug use, social exclusion and age at onset of cannabis use. We included 85 daily cannabis users and 100 non-daily cannabis users. Both the case and the control populations were identified by snowball sampling. Daily cannabis use was associated with more alcohol intake and other drug use, as well as with early onset in the use of cannabis. Daily cannabis use appeared to exert a dose-response effect on first-rank symptoms, mania symptoms and auditory hallucinations, even after adjusting for sex, age, other drug use, social exclusion and age at onset of cannabis use. The paranoid dimension was only associated with the heaviest consumption of cannabis. Initial age of cannabis use modified the effects of daily cannabis use on the first-rank and voices experiences. Daily cannabis use was associated with significantly more first-rank and voices experiences among those subjects who started to use cannabis before 17 years of age. Our study supports the association of psychotic experiences with cannabis use even among non-psychotic subjects.

Altering endocannabinoid neurotransmission at critical developmental ages: impact on rodent emotionality and cognitive performance

The endocannabinoid system shows functional activity from early stages of brain development: it plays an important role in fundamental developmental processes such as cell proliferation, migration, and differentiation, thus shaping brain organization during pre- and postnatal life. Cannabis sativa preparations are among the illicit drugs most commonly used by young people, including pregnant women. The developing brain can be therefore exposed to cannabis preparations during two critical periods: first, in offspring of cannabis-using mothers through perinatal and/or prenatal exposure; second, in adolescent cannabis users during neural maturation. In the last decade, it has become clear that the endocannabinoid system critically modulates memory processing and emotional responses. Therefore, it is well possible that developmental exposure to cannabinoid compounds induces enduring changes in behaviors and neural processes belonging to the cognitive and emotional domains. We address this issue by focusing on rodent studies, in order to provide a framework for understanding the impact of cannabinoid exposure on the developing brain.

Prenatal tetrahydrocannabinol (THC) alters cognitive function and amphetamine response from weaning to adulthood in the rat

Research suggests that not only is marijuana use prevalent among women of reproductive age, but a significant number of women continue to use marijuana and its derivatives throughout pregnancy. Many studies have shown, in both humans and animals, that marijuana exposure during adolescence and adulthood is detrimental to normal cognition and memory. In this study, we examined the effects of daily intravenous injections of 0.15 mg/kg Δ(9)-tetrahydrocannabinol (THC), given to pregnant dams throughout gestation, on cognitive function in the offspring. Offspring were exposed to three tests: a passive avoidance test at postnatal day (PND) 22, an active place avoidance test at PND 45, and an attention task at PND 60, which assessed learning and long-term memory, spatial working memory and prediction, and attention, respectively. Other offspring were also given a 1mg/kg amphetamine challenge at PND 60. Passive avoidance testing showed that prenatal THC had no effect on acquisition but interfered with consolidation during retention testing. The active place avoidance task showed no treatment-related effects on acquisition but a significant treatment effect was observed in reversal performance in males. The attention task showed that a smaller percentage of THC-exposed rats completed the test, although the failure rate of both groups was quite high. Finally, THC exposed animals, both male and female, showed a dampened locomotor response to amphetamine, but females were more active than males overall. These results suggest that prenatal THC exposure has effects on certain aspects of cognitive function in rats from weaning to adulthood. These effects suggest that prenatal marijuana exposure could also alter cognitive function in humans and therefore have an impact on school performance and dampen responses to psychostimulants as well.

Cannabis use at a young age is associated with psychotic experiences

BACKGROUND

Cannabis use is associated with psychosis and a range of subclinical psychiatric symptoms. The strength of this association depends on dosage and age at first use. The current study investigates whether level of cannabis exposure and starting age are associated with specific profiles of subclinical symptoms.

METHOD

We collected cross-sectional data from a young adult population sample by administering an online version of the Community Assessment of Psychic Experiences (CAPE). Cannabis exposure was quantified as the amount of Euros spent on cannabis per week and the age of initial cannabis use. The primary outcome measure was the odds ratio (OR) to belong to the highest 10% of scores on the total CAPE and the positive-, negative- and depressive symptom dimensions.

RESULTS

In 17 698 adolescents (mean age 21.6, s.d.=4.2 years), cannabis use at age 12 years or younger was strongly associated with a top 10% score on psychotic experiences [OR 3.1, 95% confidence interval (CI) 2.1-4.3] and to a lesser degree with negative symptoms (OR 1.7, 95% CI 1.1-2.5). The OR of heavy users (>€25/week) for negative symptoms was 3.4 (95% CI 2.9-4.1), for psychotic experiences 3.0 (95% CI 2.4-3.6), and for depressive symptoms 2.8 (95% CI 2.3-3.3).

CONCLUSIONS

Early start of cannabis use is strongly associated with subclinical psychotic symptoms and to a lesser degree with negative symptoms, while smoking high amounts of cannabis is associated with increased levels of all three symptom dimensions: psychotic, negative and depressive. These results support the hypothesis that the impact of cannabis use is age specific.

Effect of developmental chlorpyrifos exposure, on endocannabinoid metabolizing enzymes, in the brain of juvenile rats

The endogenous cannabinoids 2-arachidonoylglycerol (2-AG) and arachidonoyl ethanolamide (AEA or anandamide) play vital roles during nervous system development including regulating axonal guidance and synaptogenesis. The enzymatic degradation of 2-AG and AEA is highly susceptible to inhibition by organophosphate compounds in vitro. Furthermore, acute in vivo exposure of adult animals to the agricultural insecticide chlorpyrifos (CPS) caused moderate inhibition of both 2-AG and AEA hydrolysis. However, the effects of repeated exposure to lower levels of CPS, especially during development, on endocannabinoid metabolism in the brain is not known. To examine this, rat pups were orally exposed daily from postnatal days 10-16 to either 1.0, 2.5, or 5.0 mg/kg CPS. Body weight gain was reduced by 5.0 mg/kg on all days of treatment whereas 2.5 mg/kg reduced the weight gain only on the last two days of treatment. At 4-h postexposure on day 16, forebrain cholinesterase (ChE) activity and hydrolysis of 2-AG and AEA were inhibited in a dose-related manner, and the extent of inhibition from highest to lowest level was AEA hydrolysis > ChE activity > 2-AG hydrolysis. The extent of inhibition of AEA hydrolysis was approximately twice than that of ChE activity with AEA hydrolysis being virtually eliminated by 2.5 and 5.0 mg/kg and 1.0 mg/kg causing 40% inhibition. The sensitivity of AEA hydrolysis, compared with canonical targets such as ChE activity, suggests a potential alternative developmental target for CPS. Inhibition of AEA hydrolysis could result in accumulation of endocannabinoids, which could alter normal endocannabinoid transmission during brain maturation.

Developmental consequences of perinatal cannabis exposure: behavioral and neuroendocrine effects in adult rodents

RATIONALE

Cannabis is the most commonly used illicit drug among pregnant women. Since the endocannabinoid system plays a crucial role in brain development, maternal exposure to cannabis derivatives might result in long-lasting neurobehavioral abnormalities in the exposed offspring. It is difficult to detect these effects, and their underlying neurobiological mechanisms, in clinical cohorts, because of their intrinsic methodological and interpretative issues.

OBJECTIVES

The present paper reviews relevant rodent studies examining the long-term behavioral consequences of exposure to cannabinoid compounds during pregnancy and/or lactation.

RESULTS

Maternal exposure to even low doses of cannabinoid compounds results in atypical locomotor activity, cognitive impairments, altered emotional behavior, and enhanced sensitivity to drugs of abuse in the adult rodent offspring. Some of the observed behavioral abnormalities might be related to alterations in stress hormone levels induced by maternal cannabis exposure.

CONCLUSIONS

There is increasing evidence from animal studies showing that cannabinoid drugs are neuroteratogens which induce enduring neurobehavioral abnormalities in the exposed offspring. Several preclinical findings reviewed in this paper are in line with clinical studies reporting hyperactivity, cognitive impairments and altered emotionality in humans exposed in utero to cannabis. Conversely, genetic, environmental and social factors could also influence the neurobiological effects of early cannabis exposure in humans.

Maternal exposure to the CB1 cannabinoid agonist WIN 55212-2 produces robust changes in motor function and intrinsic electrophysiological properties of cerebellar Purkinje neurons in rat offspring

The cerebellum, which controls coordinated and rapid movements, is a potential target for the deleterious effects of drugs of abuse including cannabis (i.e. marijuana, cannabinoids). Prenatal exposure to cannabinoids has been documented to cause abnormalities in motor and cognitive development, but the exact mechanism of this effect at the cellular level has not been fully elucidated. Previous studies indicate that cannabinoids are capable of modulating synaptic neurotransmission. In addition to altering synaptic activity, cannabinoid exposure may also change intrinsic neuronal properties. In the present study several different approaches including behavioral assays, extracellular field potential recordings and whole-cell patch clamp recordings, were used to address whether maternal exposure to the CB1 cannabinoid receptor agonist WIN 55-212-2 (WIN) affects the intrinsic electrophysiological properties of Purkinje neurons. WIN treatment of pregnant rats produced a significant decrease in the rearing frequency, total distance moved and mobility of the offspring, but significantly increased the time of the righting reflex, the grooming frequency and immobility. Neuromotor function, as assessed in the grip test and balance beam test, was also significantly impaired in prenatally WIN-treated group. Prenatal exposure to WIN increased the amplitude of population spikes (PS) recorded from the cerebellar Purkinje cell layer of offspring following synaptic blockage. WIN treatment of pregnant rats also profoundly affected the intrinsic properties of Purkinje neurons in offspring. This treatment increased the firing regularity, firing frequency, amplitude of afterhyperpolarization (AHP), the peak amplitude of action potential and the first spike latency, but decreased significantly the time to peak and duration of action potentials, the instantaneous firing frequency, the rate of rebound action potential and the voltage "sag" ratio. These results raise the possibility that maternal exposure to cannabinoids may profoundly affect the intrinsic membrane properties of cerebellar Purkinje neurons of offspring by altering the membrane excitability through modulation of intrinsic ion channels.

GABA(A) receptor density is altered by cannabinoid treatment in the hippocampus of adult but not adolescent rats

Cannabinoids are known to induce transient psychotic symptoms and cognitive dysfunction in healthy individuals and contribute to trigger schizophrenia in vulnerable individuals, particularly during adolescence. Converging preclinical evidence suggests important interactions between cannabinoid and GABAergic systems. In the present study, we compared the effects of cannabinoid treatment on GABA(A) receptor binding in the brain of adolescent and adult rats. Adolescent (5 weeks old) and adult (10 weeks old) rats were treated with the synthetic cannabinoid HU210 (25, 50 or 100 microg/kg/day) or vehicle for 1, 4 or 14 days. Rats were sacrificed 24 h after the last injection and GABA(A) receptor density was measured in several brain regions using [(35)S]TBPS and in vitro autoradiography. Adolescent rats had higher numbers of GABA(A) receptors compared to adults. A 24% increase of binding in adult rats treated with 100 microg/kg HU210 for 14 days compared to controls was observed in the CA1 region of the hippocampus (16.1 versus 12.9 fmol/mg tissue equivalent, t=2.720, p<0.05). HU210 did not affect GABA(A) receptors in adolescent rats in any treatment regimen and in adult rats treated with HU210 for 1 or 4 days. These data suggest that long-term, high-dose treatment with HU210 increases GABA(A) receptors in the hippocampus of adult rats, changes that may interfere with associated hippocampal cognitive functions such as learning and memory. In addition, our results suggest that the adolescent brain does not display the same compensatory mechanisms that are activated in the adult brain following cannabinoid treatment.

Neurobiological consequences of maternal cannabis on human fetal development and its neuropsychiatric outcome

Despite the high prevalence of marijuana use among pregnant women and adolescents, the impact of cannabis on the developing brain is still not well understood. However, growing evidence supports that the endocannabinoid system plays a major role in CNS patterning in structures relevant for mood, cognition, and reward, such as the mesocorticolimbic system. It is thus clear that exposure to cannabis during early ontogeny is not benign and potential compensatory mechanisms that might be expected to occur during neurodevelopment appear insufficient to eliminate vulnerability to neuropsychiatric disorders in certain individuals. Both human longitudinal cohort studies and animal models strongly emphasize the long-term influence of prenatal cannabinoid exposure on behavior and mental health. This review provides an overview of the endocannabinoid system and examines the neurobiological consequences of cannabis exposure in pregnancy and early life by addressing its impact on the development of neurotransmitters systems relevant to neuropsychiatric disorders and its association with these disorders later in life. It posits that studying in utero cannabis exposure in association with genetic mutations of neural systems that have strong relationships to endocannabinoid function, such as the dopamine, opioid, glutamate, and GABA, might help to identify individuals at risk. Such data could add to existing knowledge to guide public health platform in regard to the use of cannabis and its derivatives during pregnancy.

The type 1 cannabinoid receptor is highly expressed in embryonic cortical projection neurons and negatively regulates neurite growth in vitro

In the rodent and human embryonic brains, the cerebral cortex and hippocampus transiently express high levels of type 1 cannabinoid receptors (CB(1)Rs), at a developmental stage when these areas are composed mainly of glutamatergic neurons. However, the precise cellular and subcellular localization of CB(1)R expression as well as effects of CB(1)R modulation in this cell population remain largely unknown. We report that, starting from embryonic day 12.5, CB(1)Rs are strongly expressed in both reelin-expressing Cajal-Retzius cells and newly differentiated postmitotic glutamatergic neurons of the mouse telencephalon. CB(1)R protein is localized first to somato-dendritic endosomes and at later developmental stages it localizes mostly to developing axons. In young axons, CB(1)Rs are localized both to the axolemma and to large, often multivesicular endosomes. Acute maternal injection of agonist CP-55940 results in the relocation of receptors from axons to somato-dendritic endosomes, indicating the functional competence of embryonic CB(1)Rs. The adult phenotype of CB(1)R expression is established around postnatal day 5. By using pharmacological and mutational modulation of CB(1)R activity in isolated cultured rat hippocampal neurons, we also show that basal activation of CB(1)R acts as a negative regulatory signal for dendritogenesis, dendritic and axonal outgrowth, and branching. Together, the overall negative regulatory role in neurite development suggests that embryonic CB(1)R signaling may participate in the correct establishment of neuronal connectivity and suggests a possible mechanism for the development of reported glutamatergic dysfunction in the offspring following maternal cannabis consumption.

The pharmacology of the endocannabinoid system: functional and structural interactions with other neurotransmitter systems and their repercussions in behavioral addiction

Addiction is a chronic, recurring and complex disorder. It is characterized by anomalous behaviors that are linked to permanent or long-lasting neurobiological alterations. Furthermore, the endocannabinoid system has a crucial role in mediating neurotransmitter release as one of the main neuromodulators of the mammalian central nervous system. The purpose of the present review is to instruct readers about the functional and structural interactions between the endocannabinoid system and the main neurotransmitter systems of the central nervous system in the context of drug addiction. With this aim, we have systematically reviewed the main findings of most of the existing literature that explores cross-talk in the five brain areas that are most traditionally implicated in addiction: amygdala, prefrontal cortex, nucleus accumbens, hippocampus and ventral tegmental area (VTA). The neurotransmission systems influenced by the pharmacology of the endocannabinoid system in these brain areas, which are reviewed here, are gamma-aminobutyric acid (GABA), glutamate, the main biogenic amines (dopamine, noradrenaline and serotonin), acetylcholine and opioids. We show that all of these neurotransmitter systems can be modulated differentially in each brain area by the activation or deactivation of cannabinoid CB1 brain receptors. Specifically, most of the studies relate to the hippocampus and nucleus accumbens. Moreover, the neurotransmitter with the fewest number of related studies is acetylcholine (excepting in the hippocampus), whereas there is a large number that evaluates GABA, glutamate and dopamine. Finally, we propose a possible interpretation of the role of the endocannabinoid system in the phenomenon of addiction.

Cannabis and the developing brain: insights from behavior

The isolation and identification, in 1964, of delta-9-tetrahydrocannabinol (THC), the primary psychoactive compound in cannabis, opened the door to a whole new field of medical research. The exploration of the therapeutic potential of THC and other natural and synthetic cannabinoid compounds was paralleled by the discovery of the endocannabinoid system, comprising cannabinoid receptors and their endogenous ligands, which offered exciting new insights into brain function. Besides its well-known involvement in specific brain functions, such as control of movement, memory and emotions, the endocannabinoid system plays an important role in fundamental developmental processes such as cell proliferation, migration and differentiation. For this reason, changes in its activity during stages of high neuronal plasticity, such as the perinatal and the adolescent period, can have long-lasting neurobehavioral consequences. Here, we summarize human and animal studies examining the behavioral and neurobiological effects of in utero and adolescent exposure to cannabis. Since cannabis preparations are widely used and abused by young people, including pregnant women, understanding how cannabinoid compounds affect the developing brain, leading to neurobehavioral alterations or neuropsychiatric disorders later in life, is a serious health issue. In addition, since the endocannabinoid system is emerging as a novel therapeutic target for the treatment of several neuropsychiatric diseases, a detailed investigation of possible adverse effects of cannabinoid compounds on the central nervous system (CNS) of immature individuals is warranted.

Dysregulation of the endogenous cannabinoid system in adult rats prenatally treated with the cannabinoid agonist WIN 55,212-2

Cannabis is widely abused by women at reproductive age and during pregnancy. Animal studies showed a particular vulnerability of the developing brain to prenatal chronic cannabinoid administration. We determined whether prenatal exposure to WIN 55,212-2, a potent cannabinoid receptor agonist, affected (1) density, affinity and/or function of cannabinoid CB(1) receptors, (2) endogenous levels of the endocannabinoid anandamide, (3) activities of the major anandamide synthesising and hydrolysing enzymes, N-acyl-phosphatidylethanolamine-specific phospholipase D (NAPE-PLD) and fatty acid amide hydrolase (FAAH), respectively, in brain areas of adult male offspring rats. Furthermore, the effect of prenatal WIN 55,212-2 on spontaneous motility was analyzed. Pregnant rats were treated daily with WIN 55,212-2 (0.5 mg/kg, gestation day 5-20) or vehicle. [(3)H]CP 55,940 and WIN 55,212-2-stimulated [(35)S] GTPgammaS binding were carried out in cerebellum, cerebral cortex, hippocampus, striatum and limbic areas of male adult offspring. Levels of anandamide, FAAH and NAPE-PLD activity were also determined. EC(50) values for WIN 55,212-2-stimulated [(35)S]GTPgammaS binding were significantly different in hippocampus (-26%) and striatum (+27%) in WIN 55,212-2-treated rats. Cannabinoid CB(1) receptor density and affinity were not affected in any analyzed region. In the striatum, increased anandamide levels were associated with reduced FAAH and enhanced NAPE-PLD activities. Opposite changes in anandamide levels and enzymatic activities were detected in limbic areas of WIN 55,212-2-treated rats. Ambulatory activity between WIN 55,212-2- and vehicle-treated adult offspring did not vary. Our results show that prenatal exposure to cannabinoid agonist induces a long-term alteration of endocannabinoid system in brain areas involved in learning-memory, motor activity and emotional behavior.

Prenatal exposure to the cannabinoid receptor agonist WIN 55,212-2 increases glutamate uptake through overexpression of GLT1 and EAAC1 glutamate transporter subtypes in rat frontal cerebral cortex

Prenatal exposure to the CB1 receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)-pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone) mesylate (WIN) at a daily dose of 0.5 mg/kg, and Delta9-tetrahydrocannabinol (Delta9-THC) at a daily dose of 5 mg/kg, reduced dialysate glutamate levels in frontal cerebral cortex of adolescent offspring (40-day-old) with respect to those born from vehicle-treated mothers. WIN treatment induced a statistically significant enhancement of Vmaxl-[3H]glutamate uptake, whereas it did not modify glutamate Km, in frontal cerebral cortex synaptosomes of adolescent rats. Western blotting analysis, performed either in membrane proteins derived from homogenates and in proteins extracted from synaptosomes of frontal cerebral cortex, revealed that prenatal WIN exposure enhanced the expression of glutamate transporter 1 (GLT1) and excitatory amino acid carrier 1 (EAAC1). Moreover, immunocytochemical analyses of frontal cortex area revealed a more intense GLT1 and EAAC1 immunoreactivity (ir) distribution in the WIN-treated group. Collectively these results show that prenatal exposure to the cannabinoid CB1 receptor agonist WIN increases expression and functional activity of GLT1 and EAAC1 glutamate transporters (GluTs) associated to a decrease of cortical glutamate outflow, in adolescent rats. These findings may contribute to explain the mechanism underlying the cognitive impairment observed in the offspring of mothers who used marijuana during pregnancy.

The emerging functions of endocannabinoid signaling during CNS development

In the postnatal brain, endocannabinoids acting as retrograde messengers regulate the function of many synapses. By contrast, the understanding of endocannabinoid functions that regulate fundamental developmental processes such as cell proliferation, migration, differentiation and survival during patterning of the CNS is just beginning to unfold. Increasing the knowledge of basic developmental and signaling principles that are controlled by endocannabinoids will provide important insights into the molecular mechanisms that establish functional neuronal circuits in the brain. Moreover, determining the molecular basis of permanent modifications to cellular structure and intercellular communication imposed by cannabis smoking during pregnancy will provide novel therapeutic targets for alleviating pathogenic changes in affected offspring. Here, we summarize recent findings regarding the ontogeny of the endocannabinoid system in neurons that sculpt the temporal and spatial diversity of cellular functions during CNS development.

Effects on development

This chapter will review the effects produced on neural development by maternal consumption of cannabinoids during gestation and lactation, with emphasis in the maturation of several neurotransmitter systems (dopamine, serotonin, opioids, cannabinoids, etc.) and possible modifications in their functional expression at the behavioral or neuroendocrine levels. In addition, we have analyzed the possible existence of a sexual dimorphism in these ontogenic effects of cannabinoids, as well as the possible molecular mechanism underlying such effects. In general, the results discussed support the view that exposure to cannabinoids during critical periods of development produces marked modifications in the functional expression of diverse neuronal systems in adulthood. Furthermore, the functions of endocannabinoids in the brain are large not only in adulthood, but also in the period of prenatal and postnatal development. Thus, endocannabinoids have been reported to be present in early ages and to play a role in the process of brain development: neural proliferation and migration, axonal elongation, synaptogenesis and/or myelogenesis.

Long-term behavioural and neuroendocrine effects of perinatal activation or blockade of CB1 cannabinoid receptors

The present work studied the long-term effects of chronic perinatal manipulation of cannabinoid CB1 receptors in male and female rats. Perinatal activation of cannabinoid CB1 receptors by chronic administration of delta9-tetrahydrocannabinol at different doses (0.1, 0.5, 2 mg/kg, p.o.) induced sexually dimorphic behavioural changes in adulthood, altering habituation of locomotion, immobility and exploratory activity. These behavioural effects were also accompanied by alterations in corticosterone levels in the adult period. Prenatal blockade of CB1 receptors by chronic administration of 3 mg/kg (s.c.) of SR141716A decreased immobility behaviour in male and female animals, without any significant changes in corticosterone plasma levels. Cannabinoid CB1 receptors appear to play an important role in the ontogeny of psychomotor behaviours, and activation or blockade of these receptors during stages of plasticity, such as the prenatal or perinatal periods, can induce long-term effects, as shown by sexually dimorphic changes in behavioural patterns in adulthood.

Long-term effects on cortical glutamate release induced by prenatal exposure to the cannabinoid receptor agonist (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinyl-methyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone: an in vivo microdialysis study in the awake rat

The aim of the present in vivo microdialysis study was to investigate whether prenatal exposure to the CB(1) receptor agonist WIN55,212-2 mesylate (WIN; (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinyl-methyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone), at a dose of 0.5 mg/kg (s.c. from the fifth to the 20th day of gestation), that causes neither malformations nor overt signs of toxicity, influences cortical glutamate extracellular levels in adult (90-day old) rats. Dam weight gain, pregnancy length and litter size at birth were not significantly affected by prenatal treatment with WIN. Basal and K(+)-evoked dialysate glutamate levels were lower in the cerebral cortex of adult rats exposed to WIN during gestation than in those born from vehicle-treated mothers. In both group of animals WIN (0.1 mg/kg, i.p.) increased dialysate glutamate levels. However, while the blockade of the CB1 receptors with the selective receptor antagonist SR141716A completely counteracted the WIN-induced increase in those rats exposed to vehicle during gestation, it failed to antagonise the increase in those born from WIN-treated dams. These findings suggest that prenatal exposure to the CB1 receptor agonist WIN, at a concentration which is not associated with gross malformations and/or overt signs of toxicity, induces permanent alterations in cortical glutamatergic function. The possibility that these effects might underlie, at least in part, some of the cognitive deficits affecting the offspring of marijuana users is discussed.

Cannabinoids and gene expression during brain development

Cannabis is the most commonly used illicit drug in western societies, in particular among young people. It is consumed even by women during pregnancy and lactation, which result in a variety of disturbances in the development of their offspring, because, like other habit-forming drugs, cannabinoids, the psychoactive ingredients of marijuana, can cross the placental barrier and be secreted in the maternal milk. Through this way, cannabinoids affect the ontogeny of various neurotransmitter systems leading to changes in different behavioral patterns. Dopamine and endogenous opioids are among the neurotransmitters that result more affected by perinatal cannabinoid exposure, which, when animals mature, produce changes in motor activity, drug-seeking behavior, nociception and other processes. These disturbances are likely originated by the capability of cannabinoids to influence the expression of key genes for both neurotransmitters, in particular, the enzyme tyrosine hydroxylase and the opioid precursor proenkephalin. In addition, cannabinoids seem to be also able to influence the expression of genes encoding for neuron-glia cell adhesion molecules, which supports a potential influence of cannabinoids on the processes of cell proliferation, neuronal migration or axonal elongation in which these proteins are involved. In support of this possibility, CB1 receptors, which represent the major targets for the action of cannabinoids, are abundantly expressed in certain brain regions, such as the subventricular areas, which have been involved in these processes during brain development. Finally, cannabinoids might also be involved in the apoptotic death that occurs during brain development, possibly by influencing the expression of Bcl-2/Bax system. Also in support of this option, CB1 receptors are transiently expressed during brain development in different group of neurons which do not contain these receptors in the adult brain. This paper will review all evidence relating cannabinoids to the expression of key genes for neural development, trying to establish the future research addressed to elucidate the mechanisms involved in the epigenetic action of cannabinoids during brain development.

Effects of perinatal exposure to delta 9-tetrahydrocannabinol on operant morphine-reinforced behavior

The present study examined the effects of Delta(9)-tetrahydrocannabinol (Delta(9)-THC) when administered during the perinatal period on morphine self-administration in adulthood. To this end, pregnant Wistar rats were daily exposed to Delta(9)-THC from the fifth day of gestation up to pup weaning, when they were separated by gender and left to mature to be used for analyses of operant food- and morphine-reinforced behavior in a progressive ratio (PR) schedule. We also analyzed dopaminergic activity (DOPAC/DA) in reward-related structures during specific phases of the behavioral study. In both reinforcement paradigms, food and morphine, females always reached higher patterns of self-administration than males, but this occurred for the two treatment groups, Delta(9)-THC or vehicle. These higher patterns measured in females corresponded with a higher DOPAC/DA in the nucleus accumbens prior to the onset of morphine self-administration in comparison to males. Interestingly, DOPAC/DA was lower in Delta(9)-THC-exposed females compared to oil-exposed females and similar to oil- and Delta(9)-THC-exposed males. In addition, Delta(9)-THC-exposed females also exhibited a reduction in DOPAC/DA in the ventral tegmental area, which did not exist in males. All these changes, however, disappeared after 15 days of morphine self-administration and they did not reappear after 15 additional days of extinction of this response. Our data suggest that females are more vulnerable than males in a PR schedule for operant food and morphine self-administration; perinatal Delta(9)-THC exposure is not a factor influencing this vulnerability. The neurochemical analysis revealed that the activity of limbic dopaminergic neurons prior to morphine self-administration was higher in females than males, as well as that the perinatal Delta(9)-THC treatment reduced the activity of these neurons only in females, although this had no influence on morphine vulnerability in these animals.

Therapeutic potential of cannabinoids in CNS disease

The major psychoactive constituent of Cannabis sativa, delta(9)-tetrahydrocannabinol (delta(9)-THC), and endogenous cannabinoid ligands, such as anandamide, signal through G-protein-coupled cannabinoid receptors localised to regions of the brain associated with important neurological processes. Signalling is mostly inhibitory and suggests a role for cannabinoids as therapeutic agents in CNS disease where inhibition of neurotransmitter release would be beneficial. Anecdotal evidence suggests that patients with disorders such as multiple sclerosis smoke cannabis to relieve disease-related symptoms. Cannabinoids can alleviate tremor and spasticity in animal models of multiple sclerosis, and clinical trials of the use of these compounds for these symptoms are in progress. The cannabinoid nabilone is currently licensed for use as an antiemetic agent in chemotherapy-induced emesis. Evidence suggests that cannabinoids may prove useful in Parkinson's disease by inhibiting the excitotoxic neurotransmitter glutamate and counteracting oxidative damage to dopaminergic neurons. The inhibitory effect of cannabinoids on reactive oxygen species, glutamate and tumour necrosis factor suggests that they may be potent neuroprotective agents. Dexanabinol (HU-211), a synthetic cannabinoid, is currently being assessed in clinical trials for traumatic brain injury and stroke. Animal models of mechanical, thermal and noxious pain suggest that cannabinoids may be effective analgesics. Indeed, in clinical trials of postoperative and cancer pain and pain associated with spinal cord injury, cannabinoids have proven more effective than placebo but may be less effective than existing therapies. Dronabinol, a commercially available form of delta(9)-THC, has been used successfully for increasing appetite in patients with HIV wasting disease, and cannabinoid receptor antagonists may reduce obesity. Acute adverse effects following cannabis usage include sedation and anxiety. These effects are usually transient and may be less severe than those that occur with existing therapeutic agents. The use of nonpsychoactive cannabinoids such as cannabidiol and dexanabinol may allow the dissociation of unwanted psychoactive effects from potential therapeutic benefits. The existence of other cannabinoid receptors may provide novel therapeutic targets that are independent of CB(1) receptors (at which most currently available cannabinoids act) and the development of compounds that are not associated with CB(1) receptor-mediated adverse effects. Further understanding of the most appropriate route of delivery and the pharmacokinetics of agents that act via the endocannabinoid system may also reduce adverse effects and increase the efficacy of cannabinoid treatment. This review highlights recent advances in understanding of the endocannabinoid system and indicates CNS disorders that may benefit from the therapeutic effects of cannabinoid treatment. Where applicable, reference is made to ongoing clinical trials of cannabinoids to alleviate symptoms of these disorders.

The open field as a paradigm to measure the effects of drugs on anxiety-like behaviors: a review

The open field is a very popular animal model of anxiety-like behavior. An overview of the literature on the action elicited by effective or putative anxiolytics in animal subjected to this procedure indicates that classical treatments such as benzodiazepine receptor full agonists or 5-HT(1A) receptor full or partial agonists elicit an anxiolytic-like effect in this procedure in most cases (approximately 2/3). However, compounds (triazolobenzodiazepines such as adinazolam and alprazolam, selective serotonin reuptake inhibitors) that have a different spectrum of therapeutic efficacy in anxiety disorders such as panic attacks, generalized anxiety disorder or obsessive-compulsive disorder were poorly effective as anxiolytics in the open field test, suggesting that this paradigm may not model features of anxiety disorders. The procedure is also relevant for the study of compounds endowed with anxiogenic effects, as such effects were detected after treatments with benzodiazepine receptor inverse agonists or with corticotropin releasing factor (CRF) receptor agonists.

Exposure to cannabinoids in the development of endogenous cannabinoid system

New data strengthen the idea of a prominent role for endocannabinoids in the modulation of a wide variety of neurobiological functions. Among these, two functions, control of movement and antinociception, have attracted the maximal interest because of the possibility that cannabinoids and related compounds might be used with a therapeutic purpose. However, the functions of endocannabinoids in the brain, and also in the periphery, are large and involve, not only the adulthood, but also the period of prenatal and postnatal development, when endocannabinoids have been reported to be significantly present and to play a role in processes of brain development as neuronal proliferation and migration, axonal elongation, synaptogenesis and/or myelinogenesis. The present review article will summarize the different studies carried out on this topic and will suggest future lines of research to clarify the role of endocannabinoids and their receptors in the development.

Neurodevelopmental liabilities of substance abuse

The perinate is particularly risk-prone to chemical species which have the potential of inducing neuronal apoptosis or necrosis and thereby adversely altering development of the brain, to produce life-long functional and behavioral deficits. This paper is an overview for many substances of abuse, but the purview is much more broadened by the realization that even elevated levels of estrogens and corticosteroids in the pregnant mother can act as neuroteratogens, by passing via the placenta and altering neural development or inducing apoptosis in the perinate. Finally, therapeutic risks of anesthetics are highlighted, as these too induce neuronal apoptosis in the neonate by either blocking N-methyl-D-aspartate receptors or by acting as gamma-aminobutyric acid agonists. By understanding the mechanisms involved it may ultimately be possible to interrupt the mechanistic scheme and thereby prevent neuroteratological processes.

Changes in prodynorphin and POMC gene expression in several brain regions of rat fetuses prenatally exposed to Delta(9)-tetrahydrocannabinol

Recently, we demonstrated that prenatal Delta(9)-tetrahydrocannabinol (Delta(9)-THC) exposure alters proenkephalin mRNA levels in several brain regions of rat fetuses. In the present study, we analyzed mRNA levels of the two other opioid peptide precursors, prodynorphin and pro-opiomelanocortin (POMC), in several brain nuclei of rat fetuses which were exposed daily to Delta(9)-THC from day 5 of gestation. Prenatal Delta(9)-THC exposure altered POMC and prodynorphin mRNA levels in most of the brain areas studied at different fetal ages, but the effects were sex-dependent. Thus, POMC mRNA levels increased in Delta(9)-THC-exposed females, but decreased in Delta(9)-THC-exposed males at GD21 in the arcuate nucleus, cerebral cortex and habenular nuclei. POMC mRNA levels also increased in the arcuate nucleus and cerebral cortex of Delta(9)-THC-exposed fetuses at GD18. Prodynorphin mRNA levels were not altered by the prenatal Delta(9)-THC exposure in the striatum, cerebral cortex, hippocampus and hypothalamic structures of fetuses at GD16 and GD18, but a sexually dimorphic response was observed at GD21. Thus, prodynorphin mRNA levels increased in the cerebral cortex, hippocampus and paraventricular hypothalamic nucleus of Delta(9)-THC-exposed females, whereas no changes were observed in Delta(9)-THC-exposed males. In summary, Delta(9)-THC exposure altered the prenatal development of POMC and prodynorphin mRNA levels in several brain structures. Changes in POMC were similar to those reported previously for proenkephalin, increases in females but decreases in males, whereas changes in prodynorphin were only observed in females.

The endogenous cannabinoid system and brain development

Cannabinoid receptors and their endogenous ligands constitute a novel modulatory system that is involved in specific brain functions, such as nociception, control of movement, memory and neuroendocrine regulation. Recently, it has also been suggested that this system is involved in brain development. Studies have used a variety of techniques to elucidate the effects of cannabinoids during development, as well as to characterize the presence of elements of the endogenous cannabinoid system (receptors and ligands) in the developing brain. Collectively, they suggest that endocannabinoids participate in brain development through the activation of second-messenger-coupled cannabinoid receptors.