Prenatal ethanol exposure impairs sensory processing and habituation to visual stimuli, effects normalized by enrichment of postnatal environmental.

BACKGROUND: Individuals with fetal alcohol spectrum disorders (FASD) often show processing deficits in all sensory modalities. Using an operant light reinforcement model, we tested whether prenatal ethanol exposure (PE) alters operant responding to elicit a contingent sensory stimulus-light onset (turning on the light) and habituation to this behavior in rats. We also explored whether postnatal environmental enrichment could ameliorate PE-induced deficits. METHODS: Pregnant Sprague Dawley rats were gavaged twice/day with 0 or 3 g/kg/treatment ethanol (15% w/v) during gestational days 8-20, mimicking second-trimester heavy PE in humans. The offspring were reared in a standard housing condition or an enriched condition. Adult male and female offspring underwent an operant light reinforcement experiment with either a short-access or a long-access procedure. A dishabituation test was also conducted to characterize the habituation process. RESULTS: In the short-access procedure, PE led to increased operant responding to the contingent light onset in both sexes reared in the standard housing condition. Such an effect was not observed in rats reared in enriched conditions due to an overall decrease in responding. Moreover, rats reared in enriched conditions showed greater short-term habituation. In the long access procedure, PE rats showed increased responding and impaired long-term habituation. The long-access procedure facilitated both short-term and long-term habituation in control and PE rats. CONCLUSION: Prenatal ethanol exposure increases responding to contingent light onset and impairs the long-term habituation process. The PE-induced deficits were ameliorated by rearing in the enriched environment and increasing the duration and frequency of exposure to light onset. The PE-induced effects are like increased sensation-seeking, a subtype of sensory-processing deficit that is often observed in individuals with FASD. Our findings could inform a suitable animal model for investigating the underlying mechanisms and possible intervention strategies for sensory deficits in FASD.

Moderate prenatal ethanol exposure leads to attention deficits in both male and female rats.

BACKGROUND: Attention deficits caused by prenatal ethanol (EtOH) exposure (PE) are a prevalent condition in fetal alcohol spectrum disorders (FASDs). Importantly, the deficits are observed in individuals with FASD who have normal IQs and show no dysmorphic facial features caused by heavy PE. These observations suggest that even moderate PE could lead to attention deficits. This possibility was investigated in the present study using a rat model. METHODS: Pregnant Sprague Dawley rats were administered EtOH (3 g/kg/day) or vehicle via intragastric gavage on gestational days 8 to 20. The blood EtOH concentration (BEC) in EtOH-treated rats was 87.7 ± 1.2 mg/dl (1 h after the gavage), similar to the BECs reported in other moderate PE studies in rodents. Moderate PE did not produce teratogenic effects on birthweight or litter size. The adult offspring underwent a 2-choice reaction time task. RESULTS: Moderate PE led to augmented action impulsivity in both sexes, indicated by more rapid response initiation and more premature responses. Deficits were more marked in males than in females. No greater lapses of attention, assessed by incorrect or relatively slow responses, were observed in rats of either sex with moderate PE. In addition, no deficits in learning or motor function were detected after moderate PE. Interestingly, rats with moderate PE completed more trials than controls. CONCLUSIONS: Our results confirm that moderate PE leads to attention deficits in both sexes, which is demonstrated by greater action impulsivity, but not more lapses of attention. This effect differs from that of heavy PE, as shown in our previous study, which is manifested as impaired action impulsivity and lapses of attention in both sexes.

Fatty-acid-binding protein 5 controls retrograde endocannabinoid signaling at central glutamate synapses.

Endocannabinoids (eCBs) are lipid-signaling molecules involved in the regulation of numerous behaviors and physiological functions. Released by postsynaptic neurons, eCBs mediate retrograde modulation of synaptic transmission and plasticity by activating presynaptic cannabinoid receptors. While the cellular mechanisms by which eCBs control synaptic function have been well characterized, the mechanisms controlling their retrograde synaptic transport remain unknown. Here, we demonstrate that fatty-acid-binding protein 5 (FABP5), a canonical intracellular carrier of eCBs, is indispensable for retrograde eCB transport in the dorsal raphe nucleus (DRn). Thus, pharmacological inhibition or genetic deletion of FABP5 abolishes both phasic and tonic eCB-mediated control of excitatory synaptic transmission in the DRn. The blockade of retrograde eCB signaling induced by FABP5 inhibition is not mediated by impaired cannabinoid receptor function or reduced eCB synthesis. These findings indicate that FABP5 is essential for retrograde eCB signaling and may serve as a synaptic carrier of eCBs at central synapses.

Cocaine self-administration abolishes endocannabinoid-mediated long-term depression of glutamatergic synapses in the ventral tegmental area.

Drugs of abuse, including cocaine, alter the mechanisms underpinning synaptic plasticity, including long-term potentiation of glutamatergic synapses in the mesolimbic system. These effects are thought to underlie addictive behaviors. In the ventral tegmental area (VTA), glutamatergic synapses also exhibit long-term depression (LTD), a type of plasticity that weakens synaptic strength. This form of synaptic plasticity is induced by low-frequency stimulation and mediated by endocannabinoid (eCB) signaling, which also modulates addictive behaviors. However, it remains unknown whether eCB-LTD in the VTA could be altered by cocaine use. Therefore, the goal of the present study was to examine the impact of cocaine self-administration on eCB-LTD of glutamatergic synapses onto VTA dopaminergic (DA) neurons. To that end, male rats underwent cocaine (0.75 mg/kg/infusion) or saline self-administration under the fixed ratio 1 schedule for 6-9 days. One day after the last self-administration session, the magnitude of eCB-LTD was examined using ex vivo whole-cell recordings of putative VTA DA neurons from naïve rats and rats with saline or cocaine self-administration. The results revealed that cocaine self-administration abolished eCB-LTD. The cocaine-induced blockade of eCB-LTD in the VTA was mediated by an impaired function of presynaptic CB1 receptors. Collectively, these findings indicate that cocaine exposure blunts eCB-mediated synaptic plasticity in midbrain DA neurons. This effect could be one of the cellular mechanisms that mediate, at least in part, addictive behaviors.

Prenatal Ethanol Exposure and Postnatal Environmental Intervention Alter Dopaminergic Neuron and Microglia Morphology in the Ventral Tegmental Area During Adulthood.

BACKGROUND: Prenatal ethanol exposure (PE) impairs midbrain dopaminergic (DA) neuron function, which might contribute to various cognitive and behavioral deficits, including attention deficits and increased addiction risk, often observed in individuals with fetal alcohol spectrum disorders. Currently, the underlying mechanisms for PE-induced deficits are unclear. PE could lead to neuroinflammation by activating microglia, which play an important role in synaptic function. In the present study, we investigated PE effects on microglial activation and DA neuron density and morphology in the ventral tegmental area (VTA). Since postnatal environmental enrichment can reduce neuroinflammation and ameliorate several PE-induced behavioral deficits, we examined if a postnatal environmental intervention strategy using neonatal handling and postweaning complex housing could reverse PE effects on VTA DA neurons and microglia. METHODS: Pregnant rats received 0 or 6 g/kg/d ethanol by 2 intragastric intubations on gestation days 8 to 20. After birth, rats were reared in the standard laboratory or enriched condition. Male adult rats (8 to 12 weeks old) were used for immunocytochemistry. RESULTS: The results showed that PE decreased VTA DA neuron body size in standardly housed rats. Moreover, there was a significant decrease in numbers of VTA microglial branches and junctions in PE rats, suggesting morphological activation of microglia and possible neuroinflammation. The PE effects on microglia were normalized by postnatal environmental intervention, which also decreased the numbers of microglial branches and junctions in control animals, possibly via reduced stress. CONCLUSIONS: Our findings show an association between PE-induced morphological activation of microglia and impaired DA neuron morphology in the VTA. Importantly, postnatal environmental intervention rescues possible PE-induced microglial activation. These data support that environmental intervention can be effective in ameliorating cognitive and behavioral deficits associated with VTA DA neuron dysfunctions, such as attention deficits and increased addiction risk.

Target-specific modulation of the descending prefrontal cortex inputs to the dorsal raphe nucleus by cannabinoids.

Serotonin (5-HT) neurons located in the raphe nuclei modulate a wide range of behaviors by means of an expansive innervation pattern. In turn, the raphe receives a vast array of synaptic inputs, and a remaining challenge lies in understanding how these individual inputs are organized, processed, and modulated in this nucleus to contribute ultimately to the core coding features of 5-HT neurons. The details of the long-range, top-down control exerted by the medial prefrontal cortex (mPFC) in the dorsal raphe nucleus (DRN) are of particular interest, in part, because of its purported role in stress processing and mood regulation. Here, we found that the mPFC provides a direct monosynaptic, glutamatergic drive to both DRN 5-HT and GABA neurons and that this architecture was conducive to a robust feed-forward inhibition. Remarkably, activation of cannabinoid (CB) receptors differentially modulated the mPFC inputs onto these cell types in the DRN, in effect regulating the synaptic excitatory/inhibitory balance governing the excitability of 5-HT neurons. Thus, the CB system dynamically reconfigures the processing features of the DRN, a mood-related circuit believed to provide a concerted and distributed regulation of the excitability of large ensembles of brain networks.

Prenatal Ethanol Exposure Persistently Alters Endocannabinoid Signaling and Endocannabinoid-Mediated Excitatory Synaptic Plasticity in Ventral Tegmental Area Dopamine Neurons.

Prenatal ethanol exposure (PE) leads to increased addiction risk which could be mediated by enhanced excitatory synaptic strength in ventral tegmental area (VTA) dopamine (DA) neurons. Previous studies have shown that PE enhances excitatory synaptic strength by facilitating an anti-Hebbian form of long-term potentiation (LTP). In this study, we investigated the effect of PE on endocannabinoid-mediated long-term depression (eCB-LTD) in VTA DA neurons. Rats were exposed to moderate (3 g/kg/d) or high (6 g/kg/d) levels of ethanol during gestation. Whole-cell recordings were conducted in male offspring between 4 and 10 weeks old.We found that PE led to increased amphetamine self-administration. Both moderate and high levels of PE persistently reduced low-frequency stimulation-induced eCB-LTD. Furthermore, action potential-independent glutamate release was regulated by tonic eCB signaling in PE animals. Mechanistic studies for impaired eCB-LTD revealed that PE downregulated CB1 receptor function. Interestingly, eCB-LTD in PE animals was rescued by metabotropic glutamate receptor I activation, suggesting that PE did not impair the synthesis/release of eCBs. In contrast, eCB-LTD in PE animals was not rescued by increasing presynaptic activity, which actually led to LTP in PE animals, whereas LTD was still observed in controls. This result shows that the regulation of excitatory synaptic plasticity is fundamentally altered in PE animals. Together, PE leads to impaired eCB-LTD at the excitatory synapses of VTA DA neurons primarily due to CB1 receptor downregulation. This effect could contribute to enhanced LTP and the maintenance of augmented excitatory synaptic strength in VTA DA neurons and increased addiction risk after PE.SIGNIFICANCE STATEMENT Prenatal ethanol exposure (PE) is among many adverse developmental factors known to increase drug addiction risk. Increased excitatory synaptic strength in VTA DA neurons is a critical cellular mechanism for addiction risk. Our results show that PE persistently alters eCB signaling and impairs eCB-LTD at the excitatory synapses, an important synaptic plasticity that weakens synaptic strength. These effects combined with PE-induced anti-Hebbian long-term potentiation reported in a previous study could result in the maintenance of enhanced excitatory synaptic strength in VTA DA neurons, which in turn contributes to PE-induced increase in addiction risk. Our findings also suggest that restoring normal eCB signaling in VTA DA neurons could be a useful strategy for treating behavioral symptoms caused by PE.

Fatty acid binding protein deletion prevents stress-induced preference for cocaine and dampens stress-induced corticosterone levels.

Genetic and pharmacological manipulation of endocannabinoid (eCB) signaling has previously been shown to have an important role on the rewarding properties of drugs of abuse, including cocaine. Recently, fatty acid binding proteins (FABPs) have been proposed as intracellular transporters of the endocannabinoid anandamide (AEA) as well as other bioactive lipids to their catabolic enzyme, fatty acid amide hydrolase (FAAH). The role of these transporters in modulating the brains reward system has yet to be investigated. This study examined the effects of genetic deletion of FABP 5/7 on cocaine preference, as assessed by the Conditioned Place Preference (CPP) paradigm. Male and female wild type (WT) and FABP 5/7 KO mice showed similar acquisition of cocaine CPP, with no differences found in overall locomotor activity. In addition, while male and female WT mice showed stress-induced CPP for cocaine, male and female FABP 5/7 KO mice failed to show a stress-induced preference for the cocaine-paired chamber. Additionally, serum corticosterone levels were analyzed to explore any potential differences in stress response that may be responsible for the lack of stress-induced preference for cocaine. Serum samples were obtained in animals under basal conditions as well as following a 30-min tube restraint stress. Male and female FABP 5/7 KO mice showed reduced corticosterone levels under stress compared to their WT counterparts. The reduction in corticosterone response under stress may mediate that lack of a stress-induced preference for cocaine in the FABP 5/7 KO mice. Thus, the role of FABPs may play an important role in drug-seeking behavior under stressful conditions.

Fatty acid-binding proteins 5 and 7 gene deletion increases sucrose consumption and diminishes forced swim immobility time.

Inhibition and genetic deletion of fatty acid-binding proteins (FABPs) 5 and 7 have been shown to increase the levels of the endocannabinoid anandamide as well as the related N-acylethanolamine's palmitoylethanolamide and oleoylethanolamide. This study examined the role of these FABPs on forced-swim (FS) behavior and on sucrose consumption in two experiments: (experiment 1) using wild-type (WT) mice treated with the FABP inhibitor SBFI26 or vehicle and (experiment 2) using WT and FABP5/7 deficient mice. Results from experiment 1 showed that acute treatment with SBFI26 did not have any effect on sucrose intake or FS behavior in mice. In experiment 2, male and female FABP5/7 deficient mice showed significant increases in sucrose consumption (25 and 21%, respectively) compared with their WT counterparts. In addition, immobility time during the FS was decreased by 27% in both male and female FABP5/7 knockout mice compared with their WT counterparts. The fact that such differences were seen between the acute pharmacological approach and the genetic approach (gene deletion) of FABP needs to be further investigated. The function of FABPs and their specific effects on endocannabinoid anandamide, oleoylethanolamide, and palmitoylethanolamide may play an important role in the development of reward and mood behaviors and could provide opportunities for potential therapeutic targets.

Slack KNa Channels Influence Dorsal Horn Synapses and Nociceptive Behavior.

Abstract: The sodium-activated potassium channel Slack (Kcnt1, Slo2.2) is highly expressed in dorsal root ganglion neurons where it regulates neuronal firing. Several studies have implicated the Slack channel in pain processing, but the precise mechanism or the levels within the sensory pathway where channels are involved remain unclear. Here, we furthered the behavioral characterization of Slack channel knockout mice and for the first time examined the role of Slack channels in the superficial, pain-processing lamina of the dorsal horn. We performed whole-cell recordings from spinal cord slices to examine the intrinsic and synaptic properties of putative inhibitory and excitatory lamina II interneurons. Slack channel deletion altered intrinsic properties and synaptic drive to favor an overall enhanced excitatory tone. We measured the amplitudes and paired pulse ratio of paired excitatory post-synaptic currents at primary afferent synapses evoked by electrical stimulation of the dorsal root entry zone. We found a substantial decrease in the paired pulse ratio at synapses in Slack deleted neurons compared to wildtype, indicating increased presynaptic release from primary afferents. Corroborating these data, plantar test showed Slack knockout mice have an enhanced nociceptive responsiveness to localized thermal stimuli compared to wildtype mice. Our findings suggest that Slack channels regulate synaptic transmission within the spinal cord dorsal horn and by doing so establishes the threshold for thermal nociception.

Melatonin receptor activation increases glutamatergic synaptic transmission in the rat medial lateral habenula.

Melatonin (MLT) is secreted from the pineal gland and mediates its physiological effects through activation of two G protein-coupled receptors, MT1 and MT2 . These receptors are expressed in several brain areas, including the habenular complex, a pair of nuclei that relay information from forebrain to midbrain and modulate a plethora of behaviors, including sleep, mood, and pain. However, so far, the precise mechanisms by which MLT control the function of habenula neurons remain unknown. Using whole cell recordings from male rat brain slices, we examined the effects of MLT on the excitability of medial lateral habenula (MLHb) neurons. We found that MLT had no significant effects on the intrinsic excitability of MLHb neurons, but profoundly increased the amplitude of glutamate-mediated evoked excitatory post-synaptic currents (EPSC). The increase in strength of glutamate synapses onto MLHb neurons was mediated by an increase in glutamate release. The MLT-induced increase in glutamatergic synaptic transmission was blocked by the competitive MT1 /MT2 receptor antagonist luzindole (LUZ). These results unravel a potential cellular mechanism by which MLT receptor activation enhances the excitability of MLHb neurons. The MLT-mediated control of glutamatergic inputs to the MLHb may play a key role in the modulation of various behaviors controlled by the habenular complex.

Chronic stress impairs α1-adrenoceptor-induced endocannabinoid-dependent synaptic plasticity in the dorsal raphe nucleus.

Alpha 1-adrenergic receptors (α1-ARs) control the activity of dorsal raphe nucleus (DRn) serotonin (5-HT) neurons and play crucial role in the regulation of arousal and stress homoeostasis. However, the precise role of these receptors in regulating glutamate synapses of rat DRn 5-HT neurons and whether chronic stress exposure alters such regulation remain unknown. In the present study, we examined the impact of chronic restraint stress on α1-AR-mediated regulation of glutamate synapses onto DRn 5-HT neurons. We found that, in the control condition, activation of α1-ARs induced an inward current and long-term depression (LTD) of glutamate synapses of DRn 5-HT neurons. The α1-AR LTD was initiated by postsynaptic α1-ARs but mediated by a decrease in glutamate release. The presynaptic expression of the α1-AR LTD was signaled by retrograde endocannabinoids (eCBs). Importantly, we found that chronic exposure to restraint stress profoundly reduced the magnitude of α1-AR LTD but had no effect on the amplitude of α1-AR-induced inward current. Chronic restraint stress also reduced the CB1 receptor-mediated inhibition of EPSC and the eCB-mediated depolarization-induced suppression of excitation. Collectively, these results indicate that chronic restraint stress impairs the α1-AR LTD by reducing the function of presynaptic CB1 receptors and reveal a novel mechanism by which noradrenaline controls synaptic strength and plasticity in the DRn. They also provide evidence that chronic stress impairs eCB signaling in the DRn, which may contribute, at least in part, to the dysregulation of the stress homeostasis.

Oxytocin excites dorsal raphe serotonin neurons and bidirectionally gates their glutamate synapses.

Oxytocin (OXT) modulates wide spectrum of social and emotional behaviors via modulation of numerous neurotransmitter systems, including serotonin (5-HT). However, how OXT controls the function of dorsal raphe nucleus (DRN) 5-HT neurons remains unknown. Here, we reveal that OXT excites and alters the firing pattern of 5-HT neurons via activation of postsynaptic OXT receptors (OXTRs). In addition, OXT induces cell-type-specific depression and potentiation of DRN glutamate synapses by two retrograde lipid messengers, 2-arachidonoylglycerol (2-AG) and arachidonic acid (AA), respectively. Neuronal mapping demonstrates that OXT preferentially potentiates glutamate synapses of 5-HT neurons projecting to medial prefrontal cortex (mPFC) and depresses glutamatergic inputs to 5-HT neurons projecting to lateral habenula (LHb) and central amygdala (CeA). Thus, by engaging distinct retrograde lipid messengers, OXT exerts a target-specific gating of glutamate synapses on the DRN. As such, our data uncovers the neuronal mechanisms by which OXT modulates the function of DRN 5-HT neurons.

Prenatal ethanol exposure leads to persistent anxiety-like behavior during adulthood indicated by reduced horizontal and vertical exploratory behaviors.

Background: Fetal alcohol spectrum disorders (FASD) caused by prenatal ethanol exposure (PE) consist of many cognitive/behavioral deficits. Studies have reported that PE leads to impairments of learning and memory, attention, executive function, and anxiety. Open field (OF) is a common behavioral model which offers comprehensive ethological information. Here, we analyzed multiple parameters of OF to examine anxiety behavior and habituation after PE. Material and Methods: Pregnant Sprague Dawley rats were gavaged twice/day with 0 or 3 g/kg/treatment ethanol (15% w/v) during gestational day (GD) 8-20, mimicking second-trimester heavy PE in humans. The control and PE adult offspring were subjected to OF task in different ambient light levels with or without acute stress. Results: Prenatal ethanol exposure did not influence the overall locomotor activities or habituation in the OF. In lower ambient light, no PE effects could be detected. In higher ambient light, female PE rats showed less activities in the center zone, indicative of increased anxiety. Males show lower activities in the center zone only after acute stress. Rats spent <2% of the time in the center zone compared to >75% of the time in the corner zone where they engaged in frequent rearing activities (vertical exploration; exploratory rearing). Prenatal ethanol exposure led to lower rearing activities in the corner in both males and females. Acute stress masks the PE effects in males but not in females. Discussion: The results support that heavy PE leads to persistent anxiety-like behavior during adulthood in both sexes. This conclusion is supported by using multiple parameters of exploratory behavior in the OF, including the rearing activities in the corner to reach reliable quantification of anxiety-like behavior.

Fatty acid binding proteins are novel modulators of synaptic epoxyeicosatrienoic acid signaling in the brain.

Fatty acid binding proteins (FABPs) govern intracellular lipid transport to cytosolic organelles and nuclear receptors. More recently, FABP5 has emerged as a key regulator of synaptic endocannabinoid signaling, suggesting that FABPs may broadly regulate the signaling of neuroactive lipids in the brain. Herein, we demonstrate that brain-expressed FABPs (FABP3, FABP5, and FABP7) interact with epoxyeicosatrienoic acids (EETs) and the peroxisome proliferator-activated receptor gamma agonist 15-deoxy-Δ12,14-Prostaglandin J2 (15d-PGJ2). Among these lipids, EETs displayed highest affinities for FABP3 and FABP5, and 11,12-EET was identified as the preferred FABP ligand. Similarly, 15d-PGJ2 interacted with FABP3 and FABP5 while binding to FABP7 was markedly lower. Molecular modeling revealed unique binding interactions of the ligands within the FABP binding pockets and highlighted major contributions of van der Waals clashes and acyl chain solvent exposure in dictating FABP affinity and specificity. Functional studies demonstrated that endogenous EETs gate the strength of CA1 hippocampal glutamate synapses and that this function was impaired following FABP inhibition. As such, the present study reveals that FABPs control EET-mediated synaptic gating, thereby expanding the functional roles of this protein family in regulating neuronal lipid signaling.

Endocannabinoids mediate the glucocorticoid-induced inhibition of excitatory synaptic transmission to dorsal raphe serotonin neurons.

Glucocorticoids play a critical role in the modulation of stress responses by controlling the function of the serotonin (5-HT) system. However, the precise effects of glucocorticoids on the excitability of dorsal raphe (DR) 5-HT neurons remain unknown. In this study, we investigated the effects of glucocorticoids on excitatory synaptic transmission to putative DR 5-HT neurons. We found that corticosterone or the synthetic glucocorticoid agonist dexamethasone rapidly suppressed glutamatergic synaptic transmission to DR 5-HT neurons by inhibiting glutamate release in the DR. This inhibitory effect was mimicked by membrane-impermeable glucocorticoids, indicating the involvement of membrane-located corticosteroid receptors. The glucocorticoid-induced inhibition of glutamatergic transmission was mediated by the activation of postsynaptic G-protein-coupled receptors and signalled by retrograde endocannabinoid (eCB) messengers. Examination of the downstream mechanisms revealed that glucocorticoids enhance eCB signalling via an inhibition of cyclooxygenase-2. Together, these findings unravel a novel mechanism by which glucocorticoids control the excitability of DR 5-HT neurons and provide new insight into the rapid effects of stress hormones on the function of the 5-HT system.

Mechanisms of endocannabinoid transport in the brain.

The endocannabinoids 2-arachidonoylglycerol (2-AG) and anandamide are among the best studied lipid messengers in the brain. By activating cannabinoid receptors in the CNS, endocannabinoids tune synaptic function, thereby influencing a variety of physiological and behavioural processes. Extensive research conducted over the last few decades has considerably enhanced our understanding of the molecular mechanisms and physiological functions of the endocannabinoid system. It is now well-established that endocannabinoids are synthesized by postsynaptic neurons and serve as retrograde messengers that suppress neurotransmitter release at central synapses. While the detailed mechanisms by which endocannabinoids gate synaptic function and behavioural processes are relatively well characterized, the mechanisms governing endocannabinoid transport at central synapses remain ill defined. Recently, several studies have begun to unravel the mechanisms governing intracellular and intercellular endocannabinoid transport. In this review, we will focus on new advances in the mechanisms of intracellular and synaptic endocannabinoid transport in the CNS. LINKED ARTICLES: This article is part of a themed issue on New discoveries and perspectives in mental and pain disorders. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.17/issuetoc.

Fatty Acid-Binding Protein 5 Modulates Brain Endocannabinoid Tone and Retrograde Signaling in the Striatum.

The endocannabinoid (eCB) anandamide (AEA) and 2-arachidonoylglycerol (2-AG) are endogenous lipid neurotransmitters that regulate an array of physiological functions, including pain, stress homeostasis, and reward. Fatty acid-binding protein 5 (FABP5) is a key modulator of intracellular eCB transport and inactivation. Recent evidence suggests that FABP5 controls synaptic 2-AG signaling at excitatory synapses in the dorsal raphe nucleus. However, it is currently not known whether this function extends to other brain areas. To address this, we first profiled eCB levels across several brain areas in FABP5 knockout mice and wild-type controls and report that FABP5 deletion elevates AEA levels in the striatum, prefrontal cortex, midbrain, and thalamus, as well as midbrain 2-AG levels. The expression of eCB biosynthetic and catabolic enzymes was largely unaltered in these regions, although minor sex and region-specific changes in the expression of 2-AG catabolic enzymes were observed in female FABP5 KO mice. Robust FABP5 expression was observed in the striatum, a region where both AEA and 2-AG control synaptic transmission. Deletion of FABP5 impaired tonic 2-AG and AEA signaling at striatal GABA synapses of medium spiny neurons, and blunted phasic 2-AG mediated short-term synaptic plasticity without altering CB1R expression or function. Collectively, these results support the role of FABP5 as a key regulator of eCB signaling at excitatory and inhibitory synapses in the brain.

Prenatal ethanol exposure causes anxiety-like phenotype and alters synaptic nitric oxide and endocannabinoid signaling in dorsal raphe nucleus of adult male rats.

Mood disorders, including anxiety and depression caused by prenatal ethanol exposure (PE) are prevalent conditions in fetal alcohol spectrum disorders (FASDs). Prenatal ethanol exposure is associated with persistent dysfunctions of several neurotransmitter systems, including the serotonin (5-HT) system, which plays a major role in mood regulation and stress homeostasis. While PE is known to disrupt the development of the 5-HT system, the cellular mechanisms by which it alters the function of dorsal raphe nucleus (DRn) 5-HT neurons and their synaptic inputs remain unknown. Here, we used a second-trimester binge-drinking pattern PE (two daily gavages of 15% w/v ethanol at 3 g/kg, 5-6 h apart) during gestational days 8 - 20 and measured anxiety-like behaviors of adult male rats using the elevated plus (EPM) and zero (ZM) mazes. We also employed ex-vivo electrophysiological and pharmacological approaches to unravel the mechanisms by which PE alters the excitability and synaptic transmission onto DRn 5-HT neurons. We found that PE enhanced anxiety-like behaviors in adult male rats and induced a persistent activation of DRn 5-HT neurons. The PE-induced activation of DRn 5-HT neurons was largely mediated by potentiation of DRn glutamate synapses, which was caused by activation of the nitrergic system and impaired endocannabinoid signaling. As such, the present study reveals "push-pull" effects of PE on nitrergic and eCB signaling, respectively, which mediate the enhanced activity of DRn 5-HT neurons and could contribute to anxiety-like behaviors observed in animal model of FASD.

Adolescent chronic unpredictable stress leads to increased anxiety and attention deficit/hyperactivity-like symptoms in adulthood.

BACKGROUND: Early-life adversities during development (e.g., child abuse and neglect) are linked to multiple behavioral and cognitive dysfunctions, such as attention deficit/hyperactivity disorder (ADHD) and anxiety disorders, which have high comorbidity. However, the impact of adversities during adolescence, a crucial period in early life for these disorders, is understudied. Using a chronic unpredictable stress (CUS) model in rats, we investigated whether adversities in adolescence could lead to increased anxiety and ADHD-like symptoms in adulthood. METHODS: Mid- to late-adolescent (5-7-week-old) male and female Sprague-Dawley rats underwent a mild CUS procedure for 2 weeks. Various stressors were applied in an unpredictable way. Rats of both sexes were then trained with a 2-choice reaction time (2-CRT) task during adulthood, which are designed to detect ADHD-like symptoms, including increased impulsivity and lapse of attention. In addition, an open field test was conducted to examine if CUS resulted in a persistent increase in anxiety-like behavior during adulthood. RESULTS: Both male and female rats with CUS exposure travelled shorter distances in the open field and spent less time in the center zone, indicating increased anxiety. In the 2-CRT task, rats of both sexes with CUS exposure showed increased impulsivity. Augmented lapses of attention were observed in female but not male rats. CONCLUSION: Chronic unpredictable stress during adolescence increases anxiety and leads to ADHD-like symptoms in both male and female rats in adulthood. The deficits are more severe in females than in males. These observations support that adversities during adolescence persistently increase anxiety, which is comorbid with attention deficits.