Ethanol Blocks Long-Term Potentiation of GABAergic Synapses in the Ventral Tegmental Area Involving ��-Opioid Receptors

It is well documented that ethanol exposure alters GABA (γ-aminobutyric acid)-releasing synapses, and ethanol addiction is associated with endogenous opioid system. Emerging evidence indicates that opioids block long-term potentiation in the fast inhibitory GABA_A receptor synapses (LTP_GABA) onto dopamine-containing neurons in the ventral tegmental area (VTA), a brain region essential for reward-seeking behavior. However, how ethanol affects LTP_GABA is not known. We report here that in acute midbrain slices from rats, clinically relevant concentrations of ethanol applied both in vitro and in vivo prevents LTP_GABA, which is reversed, respectively, by in vitro and in vivo administration of naloxone, a μ-opioid receptor (MOR) antagonist. Furthermore, the blockade of LTP_GABA induced by a brief in vitro ethanol treatment is mimicked by DAMGO ([-Ala², N-MePhe⁴, Gly-ol]-enkephalin), a MOR agonist. Paired-pulse ratios are similar in slices, 24 h after in vivo injection with either saline or ethanol. Sp-cAMPS, a stable cAMP analog, and pCPT-cGMP, a cGMP analog, potentiates GABA_A-mediated inhibitory postsynaptic currents in slices from ethanol-treated rats, indicating that a single in vivo ethanol exposure does not maximally increase GABA release, instead, ethanol produces a long-lasting inability to generate LTP_GABA. These neuroadaptations to ethanol might contribute to early stage of addiction.     

Lipopolysaccharide-Induced Depressive-Like Behavior is Associated with α1-Adrenoceptor Dependent Downregulation of the Membrane GluR1 Subunit in the Mouse Medial Prefrontal Cortex and Ventral Tegmental Area

Background:

Chronic stress-induced depressive-like behavior is relevant to inflammatory immune activation. However, the neurobiological alterations in the brain following the central inflammatory immune activation remain elusive.

Methods:

Therefore, we investigated the neurobiological alterations during depressive-like behavior induced in mice by systemic administration of lipopolysaccharide (LPS; 1.2mg/kg administered twice at a 30-min interval via intraperitoneal injection).

Results:

At 24h after the second administration of LPS, an increased immobility time in the tail suspension test and the forced swimming test were observed, as well as reduced sucrose preference. Protein levels of the AMPA receptor GluR1 were significantly decreased at the plasma membrane in the medial prefrontal cortex (mPFC) and ventral tegmental area (VTA), while levels of the GluR2 were increased at the plasma membrane in the nucleus accumbens (NAc) at 24h after LPS. However, total GluR1 and GluR2 protein levels in the mPFC, VTA, and NAc were not affected by LPS. Moreover, LPS facilitated release of noradrenaline in the mPFC and VTA, but not in the NAc. Consistently, systemic administration of prazosin, an α₁-adrenoceptor antagonist, blocked the LPS-induced downregulation of the membrane GluR1 subunit in both the mPFC and VTA and also blocked the upregulation of the membrane GluR2 subunit in the NAc. Intracerebroventricular administration of prazosin 30min before LPS injection abrogated the LPS-induced depressive-like behaviors. In opposition, administration of propranolol, a β-adrenoceptor antagonist, did not affect the LPS-induced downregulation of GluR1, the upregulation of GluR2, or the depressive-like behavior.

Conclusions:

These results suggest that LPS-activated α₁-adrenoceptor-induced downregulation of membrane GluR1 in the mPFC and VTA is associated with inflammation-induced depressive-like behavior.     

Relationship between body temperature and brain monoamines during the development of tolerance to Δ9-tetrahydrocannabinol in the rat

The development of tolerance to ⁹-tetrahydrocannabinol (⁹-THC) was examined. Rats with permanently indwelling intravenous catheters were injected daily with ⁹-THC, 2 mg/kg, for up to 10 days and on each day subjective behaviour and body weight of each rat were noted. Tolerance appeared to develop to both the exciatory and depressant behavioural effects of ⁹-THC, whereas the rate of gain, in body weight of ⁹-THC treated rats, was retarded and tolerance to this phenomenon did not develop over the experimental period. On days 1, 2, 3, 5, 6 and 10 body temperature was recorded continuously for at least 2 h after ⁹-THC and in other groups of rats the brain levels of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured spectrophotofluorimetrically 1 h after ⁹-THC. Tolerance developed to the ⁹-THC-induced hypothermia by day 3, and on days 6 and 10 hyperthermia, was observed. ⁹-THC did not markedly affect the brain levels of NA or DA over the experimental period. The brain levels of 5-HT were unchanged, on days 1–5 but there was a decrease on days 6 and 10. On days 1, 2, and 3 brain levels of 5-HIAA were raised, whereas on day 6 there was a decrease. These results show that ⁹-THC induces tolerance to the hypothermia and elevation of brain 5-HIAA levels in a linear manner. An inverse relationship appears to exist between these two parameters.     

Pain-Related Depression of the Mesolimbic Dopamine System in Rats: Expression,Blockade by Analgesics,and Role of Endogenous κ-opioids

Pain is often associated with depression of behavior and mood, and relief of pain-related depression is a common goal of treatment. This study tested the hypothesis that pain-related behavioral depression is mediated by activation of endogenous κ-opioid systems and subsequent depression of mesolimbic dopamine release. Adult male Sprague–Dawley rats were implanted with electrodes targeting the medial forebrain bundle (for behavior studies of intracranial self-stimulation (ICSS)) or with cannulae for microdialysis measures of nucleus accumbens dopamine (NAc DA). Changes in ICSS and NAc DA were examined after treatment with a visceral noxious stimulus (intraperitoneal injection of dilute lactic acid) or an exogenous κ-agonist ({"type":"entrez-nucleotide","attrs":{"text":"U69593","term_id":"4205069","term_text":"U69593"}}U69593). Additional studies examined the sensitivity of acid and {"type":"entrez-nucleotide","attrs":{"text":"U69593","term_id":"4205069","term_text":"U69593"}}U69593 effects to blockade by two analgesics (the nonsteroidal antiinflammatory drug ketoprofen and the μ-opioid agonist morphine) or by the κ-antagonist norbinaltorphimine (norBNI). The effects of acid were also examined on mRNA expression for prodynorphin (PDYN) and κ-opioid receptors (KORs) in mesocorticolimbic brain regions. Both acid and {"type":"entrez-nucleotide","attrs":{"text":"U69593","term_id":"4205069","term_text":"U69593"}}U69593 depressed ICSS and extracellular levels of NAc DA. Pain-related acid effects were blocked by ketoprofen and morphine but not by norBNI. The {"type":"entrez-nucleotide","attrs":{"text":"U69593","term_id":"4205069","term_text":"U69593"}}U69593 effects were blocked by norBNI but not by ketoprofen, and were only attenuated by morphine. Acid did not significantly alter PDYN or KOR in NAc, but it produced a delayed increase in PDYN in prefrontal cortex. These results support a key role for the mesolimbic DA system, but a more nuanced role for endogenous κ-opioid systems, in mediating acute pain-related behavioral depression in rats.     

Transfer of the discriminative stimulus effects of Δ9-THC and nicotine from one operant response to another in rats

Objective  

Transfer of the discriminative stimulus effects of two drugs from one operant (original-response) to a topographically different response (transfer-response) that was spared drug discrimination training was investigated.     

Altered regulation of glutamate release and decreased functional activity and expression of GLT1 and GLAST glutamate transporters in the hippocampus of adolescent rats perinatally exposed to Δ9-THC

The long-term effects of perinatal Δ⁹-tetrahydrocannabinol (Δ⁹-THC) exposure – from gestational day (GD) 15 to postnatal day (PND) 9 – on hippocampal glutamatergic neurotransmission were studied in slices from the 40-day-old offspring of Δ⁹-THC exposed (Δ⁹-THC-rats) and vehicle-exposed (control) dams. Basal and in K+-evoked endogenous hippocampal glutamate outflow were both significantly decreased in Δ⁹-THC-rats. The effect of short Δ⁹-THC exposure (0.1 μM) on K⁺-evoked glutamate release disclosed a loss of the stimulatory effect of Δ⁹-THC on hippocampal glutamate release in Δ⁹-THC-rats, but not in controls. In addition, l-[³H]-glutamate uptake was significantly lower in hippocampal slices from Δ⁹-THC-rats, where a significant decrease in glutamate transporter 1 (GLT1) and glutamate/aspartate transporter (GLAST) protein was also detected. Collectively, these data demonstrate that perinatal exposure to cannabinoids induces long-term impairment in hippocampal glutamatergic neurotransmission that persist into adolescence.     

A validated method for the simultaneous quantification of cannabidiol, Δ9-tetrahydrocannabinol,and their metabolites in human plasma and application to plasma samples from an oral cannabidiol open-label trial

Cannabidiol (CBD) and Δ⁹-tetrahydrocannabinol (THC) are the two best known and most extensively studied phytocannabinoids within Cannabis sativa. An increasing number of preclinical studies and clinical trials have been conducted with one or both compounds, often probing their therapeutic effects in conditions such as paediatric epilepsy, anxiety disorders or chronic pain. Accurate monitoring of THC and CBD and their metabolites is essential for tracking treatment adherence and pharmacokinetics. However, fully validated methods for the comprehensive analysis of major Phase I CBD metabolites are yet to be developed due to a historical lack of commercially available reference material. In the present study, we developed, optimised and validated a method for the simultaneous quantification of CBD, THC and their major Phase I metabolites 6-hydroxy-CBD (6-OH-CBD), 7-hydroxy-CBD (7-OH-CBD), 7-carboxy-CBD (7-COOH-CBD), 11-hydroxy-tetrahydrocannabinol (11-OH-THC) and 11-carboxy-tetrahydrocannabinol (11-COOH-THC) as per Food and Drug Administration (FDA) guidelines for bioanalytical method validation. The method is accurate, reproducible, sensitive and can be carried out in high-throughput 96-well formats, ideal for larger scale clinical trials. Deuterated internal standards for each analyte were crucial to account for variable matrix effects between plasma lots. The application of the method to plasma samples, taken from people who had been administered oral CBD as part of an open-label trial of CBD effects in anxiety disorders, demonstrated its immediate utility in ongoing and upcoming clinical trials. The method will prove useful for future studies involving CBD and/or THC and can likely accommodate the inclusion of additional metabolites as analytical reference materials become commercially available.     

Population Pharmacokinetic Modeling to Describe the Total Plasma and Free Brain Levels of Fluconazole in Healthy and <Emphasis Type="BoldItalic">Cryptococcus neoformans</Emphasis> Infected Rats: How Does the Infection Impact the Drug’s Levels on Biophase?

Purpose

The present work aimed to evaluate the influence of experimental meningitis caused by C. neoformans on total plasma and free brain concentrations of fluconazole (FLC) in Wistar rats.

Method

The infection was induced by the administration of 100 μL of inoculum (1.10⁵ CFU) through the tail vein. Free drug in the brain was assessed by microdialisys (μD). Blood and μD samples were collected at pre-determined time points up to 12 h after intravenous administration of FLC (20 mg/kg) to healthy and infected rats. The concentration-time profiles were analyzed by non-compartmental and population pharmacokinetics approaches.

Results

A two-compartmental popPK model was able to simultaneously describe plasma and free drug concentrations in the brain for both groups investigated. Analysis of plasma and μD samples showed a better FLC distribution on the brain of infected than healthy animals (1.04?±?0.31 vs 0.69?±?0.14, respectively). The probability of target attainment was calculated by Monte Carlo simulations based on the developed popPK model for 125 mg/kg dose for rats and 400–2000 mg for humans.

Conclusions

FLC showed a limited use in monotherapy to the treatment of criptoccocosis in rats and humans to value of MIC >8 μg/mL.