Aspects of Prostaglandin Glycerol Ester Biology.

The Cyclooxygenase enzymes (COX-1 and COX-2) incorporate 2 molecules of O2 into arachidonic acid (AA), resulting in an array of bioactive prostaglandins. However, much work has been done showing that COX-2 will perform this reaction on several different AA-containing molecules, most importantly, the endocannabinoid 2-arachidonoylglycerol (2-AG). The products of 2-AG oxygenation, prostaglandin glycerol esters (PG-Gs), are analogous to canonical prostaglandins. This chapter reviews the literature detailing the production, metabolism, and bioactivity of these compounds, as well as their detection in intact animals.

Intravenous Prenatal Nicotine Exposure Alters METH-Induced Hyperactivity, Conditioned Hyperactivity, and BDNF in Adult Rat Offspring.

In the USA, approximately 15% of women smoke tobacco cigarettes during pregnancy. In utero tobacco smoke exposure produces somatic growth deficits like intrauterine growth restriction and low birth weight in offspring, but it can also negatively influence neurodevelopmental outcomes in later stages of life, such as an increased incidence of obesity and drug abuse. Animal models demonstrate that prenatal nicotine (PN) alters the development of the mesocorticolimbic system, which is important for organizing goal-directed behavior. In the present study, we determined whether intravenous (IV) PN altered the initiation and/or expression of methamphetamine (METH)-induced locomotor sensitization as a measure of mesocorticolimbic function in adult rat offspring. We also determined whether PN and/or METH exposure altered protein levels of BDNF (brain-derived neurotrophic factor) in the nucleus accumbens, the dorsal striatum, and the prefrontal cortex of adult offspring. BDNF was of interest because of its role in the development and maintenance of the mesocorticolimbic pathway and its ability to modulate neural processes that contribute to drug abuse, such as sensitization of the dopamine system. Dams were injected with IV nicotine (0.05 mg/kg/injection) or saline, 3×/day on gestational days 8-21. Testing was conducted when offspring reached adulthood (around postnatal day 90). Following 3 once daily habituation sessions the animals received a saline injection and baseline locomotor activity was measured. PN and prenatal saline (PS)-exposed offspring then received 10 once daily injections of METH (0.3 mg/kg) to induce locomotor sensitization. The animals received a METH injection (0.3 mg/kg) to assess the expression of sensitization following a 14-day period of no injections. A day later, all animals were injected with saline and conditioned hyperactivity was assessed. Brain tissue was harvested 24 h later. PN animals habituated more slowly to the activity chambers compared to PS controls. PN rats treated with METH showed significant enhancement of locomotor behavior compared to PS rats following acute and repeated injections; however, PN did not produce differential initiation or expression of behavioral sensitization. METH produced conditioned hyperactivity, and PN rats exhibited a greater conditioned response of hyperactivity relative to controls. PN and METH exposure produced changes in BDNF protein levels in all three regions, and complex interactions were observed between these two factors. Logistic regression revealed that BDNF protein levels, throughout the mesocorticolimbic system, significantly predicted the difference in the conditioned hyperactive response of the animals: both correlations were significant, but the predicted relationship between BDNF and context-elicited activity was stronger in the PN (r = 0.67) compared to the PS rats (r = 0.42). These findings indicate that low-dose PN exposure produces long-term changes in activity and enhanced sensitivity to the locomotor effects of METH. The enhanced METH-induced contextual conditioning shown by the PN animals suggests that offspring of in utero tobacco smoke exposure have greater susceptibility to learn about drug-related conditional stimuli, such as the context. The PN-induced alterations in mesocorticolimbic BDNF protein lend further support for the hypothesis that maternal smoking during pregnancy produces alterations in neuronal plasticity that contribute to drug abuse vulnerability. The current findings demonstrate that these changes are persistent into adulthood.

Targeting diacylglycerol lipase reduces alcohol consumption in preclinical models.

Alcohol use disorder (AUD) is associated with substantial morbidity, mortality, and societal cost, and pharmacological treatment options for AUD are limited. The endogenous cannabinoid (eCB) signaling system is critically involved in reward processing and alcohol intake is positively correlated with release of the eCB ligand 2-Arachidonoylglycerol (2-AG) within reward neurocircuitry. Here we show that genetic and pharmacological inhibition of diacylglycerol lipase (DAGL), the rate limiting enzyme in the synthesis of 2-AG, reduces alcohol consumption in a variety of preclinical models ranging from a voluntary free-access model to aversion resistant-drinking and dependence-like drinking induced via chronic intermittent ethanol vapor exposure in mice. DAGL inhibition during either chronic alcohol consumption or protracted withdrawal was devoid of anxiogenic and depressive-like behavioral effects. Lastly, DAGL inhibition also prevented ethanol-induced suppression of GABAergic transmission onto midbrain dopamine neurons, providing mechanistic insight into how DAGL inhibition could affect alcohol reward. These data suggest reducing 2-AG signaling via inhibition of DAGL could represent an effective approach to reduce alcohol consumption across the spectrum of AUD severity.

Detection of Cyclooxygenase-2-Derived Oxygenation Products of the Endogenous Cannabinoid 2-Arachidonoylglycerol in Mouse Brain.

Cyclooxygenase-2 (COX-2) catalyzes the formation of prostaglandins, which are involved in immune regulation, vascular function, and synaptic signaling. COX-2 also inactivates the endogenous cannabinoid (eCB) 2-arachidonoylglycerol (2-AG) via oxygenation of its arachidonic acid backbone to form a variety of prostaglandin glyceryl esters (PG-Gs). Although this oxygenation reaction is readily observed in vitro and in intact cells, detection of COX-2-derived 2-AG oxygenation products has not been previously reported in neuronal tissue. Here we show that 2-AG is metabolized in the brain of transgenic COX-2-overexpressing mice and mice treated with lipopolysaccharide to form multiple species of PG-Gs that are detectable only when monoacylglycerol lipase is concomitantly blocked. Formation of these PG-Gs is prevented by acute pharmacological inhibition of COX-2. These data provide evidence that neuronal COX-2 is capable of oxygenating 2-AG to form a variety PG-Gs in vivo and support further investigation of the physiological functions of PG-Gs.

IV prenatal nicotine exposure increases the reinforcing efficacy of methamphetamine in adult rat offspring.

BACKGROUND: Maternal smoking during pregnancy is correlated with increased substance use in offspring. Research using rodent models shows that gestational nicotine exposure produces enduring alterations in the neurodevelopment of motivational systems, and that rats prenatally treated with nicotine have altered motivation for drug reinforcement on fixed-ratio (FR) schedules of reinforcement. OBJECTIVE: The present study investigated methamphetamine (METH) self-administration in adult offspring prenatally exposed to intravenous (IV) nicotine or saline using a progressive-ratio (PR) schedule of reinforcement. METHODS: Pregnant rats were administered IV prenatal saline (PS) or nicotine (PN; 0.05mg/kg/infusion), 3×/day during gestational days 8-21. At postnatal day 70, offspring acquired a lever-press response for sucrose (26%, w/v; FR1-3). Rats were trained with METH (0.05mg/kg/infusion), and following stable FR responding, animals were tested using a progressive-ratio (PR) schedule for three different doses of METH (0.005, 0.025, and 0.05mg/kg/infusion). RESULTS: METH infusion, active lever presses, and the ratio breakpoint are reported. PN-exposed animals exhibited more METH-maintained responding than PS controls, according to a dose×prenatal treatment interaction (e.g., infusions). PN rats self-administered more METH infusions between the range of 0.025 and 0.05, but not for the 0.005mg/kg/infusion dose. CONCLUSIONS: IV PN-exposure produced enhanced motivation to self-administer METH. These findings indicate that pregnant women who smoke tobacco may impart neurobiological changes in offspring's motivational systems that render them increasingly vulnerable to drug abuse during adulthood.

Intravenous prenatal nicotine exposure increases orexin expression in the lateral hypothalamus and orexin innervation of the ventral tegmental area in adult male rats.

BACKGROUND: Approximately 18% of pregnant women continue to smoke tobacco cigarettes throughout pregnancy. Offspring exposed to tobacco smoke in utero exhibit a higher incidence of drug use in later stages of development relative to non-exposed children. Animal models indicate that prenatal nicotine (PN) exposure alone alters the development of the mesocorticolimbic dopamine (DA) system, which, in part, organizes motivated behavior and reward. The orexin/hypocretin neuropeptide system, which originates in the lateral hypothalamus (LH), projects to key areas of the mesocorticolimbic DA pathway. Previous research suggests that orexin exerts a major influence on motivation and reward. METHODS: The present experiments determined if intravenous (IV) PN exposure alters (1) the expression of orexin neurons and melanin-concentrating hormone (MCH; positive control) in the LH; and (2) orexin projections from the LH onto DA neurons in the ventral tegmental area (VTA). Dams were injected with IV nicotine (0.05 mg/kg/injection) or saline 3×/day during gestational days 8-21. Tissues from adult male offspring (∼130 days) were examined using immunohistochemistry. RESULTS: Relative to controls, offspring of IV PN exposure showed (1) increased numbers of orexin neurons in the LH, and no changes in the expression of MCH; and (2) increased orexin appositions on DA cells in the VTA. CONCLUSION: The findings indicate that the influence of PN exposure is enduring, and suggests that the PN-induced modification of orexin expression on mesolimbic circuitry may contribute to the reported changes in motivated behaviors related to food and drug reward observed in offspring prenatally exposed to nicotine.

Offspring of Prenatal IV Nicotine Exposure Exhibit Increased Sensitivity to the Reinforcing Effects of Methamphetamine.

Maternal smoking during pregnancy is associated with increased substance abuse in offspring. Preclinical research shows that in utero exposure to nicotine, the primary psychoactive compound in tobacco smoke, influences the neurodevelopment of reward systems and alters motivated behavior in offspring. The present study determined if prenatal nicotine (PN) exposure altered the sensitivity to the reinforcing and aversive effects of methamphetamine (METH) in offspring using a low dose, intravenous (IV) exposure method. Pregnant dams were administered nicotine (0.05 mg/kg/injection) or prenatal saline (PS) 3×/day on gestational days 8-21, and adult offspring were tested using METH self-administration (experiment 1) or METH-induced conditioned taste aversion (CTA; experiment 2) procedures. For METH self-administration, animals were trained to respond for IV METH (0.05 mg/kg/infusion; fixed-ratio 3) and they were tested on varying doses of the reinforcer (0.0005-1.0 mg/kg/infusion). For METH CTA, rats received three saccharin and METH pairings (0, 0.3, or 0.5 mg/kg, sc) followed by 14 daily extinction trials. Experiment 1: PN and PS animals exhibited inverted U-shaped dose-response curves; however, the PN animal's curve was shifted to the left, suggesting PN animals were more sensitive to the reinforcing effects of METH. Experiment 2: METH CTA was acquired in a dose-dependent manner and the factor of PN exposure was not related to the acquisition or extinction of METH-induced CTA. There were no sex differences in either experiment. These results indicate that IV PN-exposed adult offspring exhibited increased sensitivity to IV METH. This suggests that PN exposure, via maternal smoking, will alter the reinforcing effects of METH during later stages of development, and furthermore, will influence substance use vulnerability in adult human offspring.

Intravenous gestational nicotine exposure results in increased motivation for sucrose reward in adult rat offspring.

BACKGROUND: Prenatal tobacco smoke exposure is associated with alterations in motivated behavior in offspring, such as increased consumption of highly palatable foods and abused drugs. Animal models show that gestational nicotine (GN) exposure mediates changes in responding for sucrose and drug reward. METHODS: A novel, intermittent low-dose intravenous (IV) exposure model was used to administer nicotine (0.05 mg/kg/injection) or saline 3×/day to rats on gestational days 8-21. Two experiments investigated the effect of IV GN on (1) the habituation of spontaneous locomotor activity and on (2) sucrose reinforced responding in offspring. For the operant experiments, animals acquired fixed-ratio (FR-3) responding for sucrose, 26% (w/v), and were tested on varying concentrations (0, 3, 10, 30, and 56%; Latin-square) according to a FR-3, and then a progressive-ratio (PR) schedule. Male and female adult offspring were used. RESULTS: IV GN did not alter birth or growth weight, or the number of pups born. No between-group differences in habituation to spontaneous locomotor activity were observed. FR testing produced an inverted U-shaped response curve, and rats showed peak responding for 10% sucrose reinforcement. Neither gestation nor sex affected responding, suggesting equivalent sensitivity to varying sucrose concentrations. PR testing revealed that GN rats showed greater motivation for sucrose reinforcement relative to controls. CONCLUSIONS: A low-dose, IV GN exposure model resulted in increased motivation to respond for sucrose reinforcement in adult offspring. This suggests that using a low number of cigarettes throughout pregnancy will result in increased motivation for highly palatable foods in adult, and perhaps, adolescent offspring.