Effects of HIV gp120 on Neuroinflammation in Immunodeficient vs. Immunocompetent States.

HIV affects 37 million people worldwide, 25-69% of which develop HIV-associated neurocognitive disorders (HAND) regardless of antiviral treatment. HIV infection of the brain decreases cognitive function, disrupts/impairs learning and memory, and reduces quality of life for those affected. HIV-induced neuroinflammation has been associated with viral proteins such as gp120 and Tat, which remain elevated in the CNS even in patients with low peripheral viremia counts. In this study, we examined the effects of gp120 on neuroinflammation in immunodeficient vs. immunocompetent states by examining neuroinflammatory markers in gp120tg mice with or without systemic immunodeficiency caused by murine retroviral administration (LP-BM5 murine AIDS). Changes in inflammatory cytokine/chemokine mRNA expression was complex and dependent upon expression of gp120 protein, immunodeficiency status, brain region (hippocampus, frontal lobe, or striatum), and age. Gp120 expression reduced hippocampal synaptophysin expression but did not affect animals' learning/memory on the spontaneous T-maze test in our experimental conditions. Our results emphasize the critical role of the neuroinflammatory micro-environment and the peripheral immune system context in which gp120 acts. Multiple factors, particularly system-level differences in the immune response of different brain regions, need to be considered when developing treatment for HAND. Graphical Abstract.

Contribution of CD137L to Sensory Hypersensitivity in a Murine Model of Neuropathic Pain.

CD137L (4-1BBL) is a costimulatory molecule whose signaling can promote monocyte/macrophage functions; however, CD137L-mediated microglial response and its role in neuropathic pain remain unknown. We investigated CD137L following peripheral nerve injury-induced neuropathic pain using a spinal nerve L5 transection (L5Tx) murine model in both sexes. First, C57BL/6_CD137L knock-out (KO) mice displayed decreased mechanical and diminished heat hypersensitivity compared to wild-type (WT) controls, beginning on day 3 to up to day 35 post-L5Tx. Purified anti-mouse CD137L neutralizing monoclonal antibody (0.1 or 0.5 µg) was also used to identify CD137L's window of action in BALB/c mice. Anti-CD137L antibody was intrathecally administered either from day 0 (before surgery) to day 7 (early treatment), or from day 6 to 13 post-L5Tx (late treatment), and nociceptive thresholds were assessed before surgery to up to day 35 post-surgery. Early treatment with anti-CD137L reduced L5Tx-induced mechanical but not heat hypersensitivity, while later treatment did not alter either sensitivity. Pro- versus anti-inflammatory responses within the lumbar spinal cord following L5Tx were further evaluated via quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC) in time-course studies. Following L5Tx, female CD137L KO mice did not show increased iNOS mRNA and had reduced numbers of IL-1ß+ cells compared to WT. At 21 d post-surgery, CD137L KO mice had higher total numbers of arginase (Arg)-1+ cells and Arg-1+ microglia. Altogether, results indicate that spinal cord CD137L contributes to the development of peripheral nerve injury-induced neuropathic pain, which may be in part mediated through CD137L's modulation of the pro- and anti-inflammatory balance within the spinal cord.

Antinociceptive effects of JWH015 in female and male rats.

Despite greater chronic pain prevalence in females compared with males, and the analgesic potential of cannabinoid receptor type 2 (CB2) agonists, CB2 agonists have rarely been tested in females. The aim of the present study was to compare the antinociceptive effects of a CB2-preferring agonist, (2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone (JWH015), in female and male rats against acute pain and persistent inflammatory pain. JWH015 (5-20 mg/kg, intraperitoneally) produced dose-dependent and time-dependent increases in latency to respond on the tail withdrawal and paw pressure tests that did not differ statistically between the sexes. JWH015 dose-dependently decreased locomotor activity in both sexes, but was more potent in females than males. JWH015 produced little catalepsy in either sex. In females, the antinociceptive effects of JWH015 against acute pain were blocked by rimonabant and SR144528, whereas locomotor suppression was antagonized by rimonabant. When administered 3 days after intraplantar injection of complete Freund's adjuvant, JWH015 produced a significantly greater antiallodynic effect in females at the highest dose tested (10 mg/kg, intraperitoneally). Antiallodynic effects of JWH015 were antagonized by rimonabant and SR144528 in both sexes. These studies indicate that systemically administered JWH015 produced antinociception that was both CB1 and CB2 receptor-mediated in both sexes. Unlike [INCREMENT]-9-tetrahydrocannabinol and other nonselective cannabinoid agonists, the CB2-preferring agonist JWH015 may produce more equivalent antinociception in females and males.

Gonadal hormones do not alter the development of antinociceptive tolerance to delta-9-tetrahydrocannabinol in adult rats.

The purpose of this study was to determine whether sex differences in the development of antinociceptive tolerance to delta-9-tetrahydrocannabinol (THC) are due to activational effects of gonadal hormones. Rats were sham-gonadectomized (sham-GDX) or gonadectomized (GDX). GDX females received no hormone replacement (GDX+0), estradiol (GDX+E2), progesterone (GDX+P4), or both (GDX+E2/P4). GDX male rats received no hormone (GDX+0) or testosterone (GDX+T). Two weeks later, antinociceptive potency of THC was determined (pre-chronic test) on the warm water tail withdrawal and paw pressure assays. Vehicle or a sex-specific THC dose (females, 5.7mg/kg, males, 9.9mg/kg) was administered twice-daily for 9days, then the THC dose-effect curves were re-determined (post-chronic test). On the pre-chronic test (both assays), THC was more potent in sham-GDX females than males, and gonadectomy did not alter this sex difference. In GDX females, P4 significantly decreased THC's antinociceptive potency, whereas E2 had no effect. In GDX males, T did not alter THC's antinociceptive potency. After chronic THC treatment, THC's antinociceptive potency was decreased more in sham-GDX females than males, on the tail withdrawal test; this sex difference in tolerance was not altered in GDX or hormone-treated groups. These results suggest that greater antinociceptive tolerance in females, which occurred despite females receiving 40% less THC than males, is not due to activational effects of gonadal hormones.

Sex differences in antinociceptive tolerance to delta-9-tetrahydrocannabinol in the rat.

BACKGROUND: Sex differences in cannabinoid effects have been reported in rodents, with adult females typically being more sensitive than adult males. The present study compared the development of antinociceptive tolerance to delta-9-tetrahydrocannabinol (THC) in adult, gonadally intact female vs. male rats. METHODS: Cumulative dose-effect curves were obtained for THC (1.0-18 mg/kg i.p.) on warm water tail withdrawal and paw pressure tests. Vehicle or the sex-specific ED80 dose for THC was administered twice daily for 9 days; THC dose-effect curves were then re-determined. RESULTS: On the pre-chronic test day, THC was significantly more potent in females than males in producing antinociception on the tail withdrawal and paw pressure tests. After 9 days of twice-daily THC treatment (5.4 mg/kg/injection in females and 7.6 mg/kg/injection in males), THC potency on both tests decreased more in females than males. On the tail withdrawal test, chronic THC produced 4.2- vs. 2.8-fold increases in ED50 values in females vs. males, respectively. On the paw pressure test, chronic THC produced 4.4- vs. 2.9-fold increases in ED50 values in females vs. males, respectively. Chronic THC treatment did not significantly disrupt estrous cycling in females. CONCLUSIONS: These results demonstrate that--even when sex differences in acute THC potency are controlled--females develop more antinociceptive tolerance to THC than males. Given the importance of drug tolerance in the development of drug dependence, these results suggest that females may be more vulnerable than males to developing dependence after chronic cannabinoid exposure.

Cyclic ovarian hormone modulation of supraspinal Δ9-tetrahydrocannabinol-induced antinociception and cannabinoid receptor binding in the female rat.

Estrous cycle-related fluctuations in delta-9-tetrahydrocannabinol (THC)-induced antinociception have been observed in the rat. The aim of this study was to determine which major ovarian hormone modulates the antinociceptive effects of i.c.v. THC, and whether hormone modulation of THC's behavioral effects could be due to changes in brain cannabinoid receptors (CBr). Vehicle (oil) or hormones (estradiol or progesterone, or both) were administered to female rats on days 3 and 7 post-ovariectomy. On the morning or afternoon of day 8 or day 9, vehicle or THC (100 µg) was administered i.c.v. Paw pressure, tail withdrawal, locomotor activity and catalepsy tests were conducted over a 3-h period. Estradiol (with and without progesterone) enhanced THC-induced paw pressure antinociception only. Ovarian hormones time-dependently modulated CBr in brain structures that mediate antinociception and locomotor activity, but the changes observed in CBr did not parallel changes in behavior. However, the time course of CBr changes must be further elucidated to determine the functional relationship between receptor changes and antinociceptive sensitivity to THC.

Sex differences in cannabinoid 1 vs. cannabinoid 2 receptor-selective antagonism of antinociception produced by delta9-tetrahydrocannabinol and CP55,940 in the rat.

The purpose of this study was to determine whether sex differences in cannabinoid (CB)-induced antinociception and motoric effects can be attributed to differential activation of CB(1) or CB(2) receptors. Rats were injected intraperitoneally with vehicle, rimonabant [5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (SR141716A), a putative CB(1) receptor-selective antagonist; 0.1-10 mg/kg] or 5-(4-chloro-3-methylphenyl)-1-[(4-methylphenyl)methyl]-N-[(1S,2S,4R)-1,3,3-trimethylbicyclo[2.2.1]hept-2-yl]-1H-pyrazole-3-carboxamide (SR144528) (a putative CB(2) receptor-selective antagonist; 1.0-10 mg/kg). Thirty minutes later, Δ(9)-tetrahydrocannabinol (THC; 1.25-40 mg/kg) or 5-(1,1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]phenol (CP55,940) (0.05-1.6 mg/kg) was injected. Paw pressure and tail withdrawal antinociception, locomotor activity, and catalepsy were measured. Rimonabant dose-dependently antagonized THC and CP55,940 in each test, but was up to 10 times more potent in female than male rats on the nociceptive tests; estimates of rimonabant affinity (apparent pK(B)) for the CB(1) receptor were approximately 0.5 to 1 mol/kg higher in female than male rats. SR144528 partially antagonized THC-induced tail withdrawal antinociception and locomotor activity in females, but this antagonism was not dose-dependent or consistent; no SR144528 antagonism was observed in either sex tested with CP55,940. Neither the time course of rimonabant antagonism nor the plasma levels of rimonabant differed between the sexes. Rimonabant and SR144528 did not antagonize morphine-induced antinociception, and naloxone did not antagonize THC-induced antinociception in either sex. These results suggest that THC produces acute antinociceptive and motoric effects via activation of CB(1), and perhaps under some conditions, CB(2) receptors, in female rats, whereas THC acts primarily at CB(1) receptors in male rats. Higher apparent pK(B) for rimonabant in female rats suggests that cannabinoid drugs bind with greater affinity to CB(1) receptors in female than male rats, probably contributing to greater antinociceptive effects observed in female compared with male rats.

THC-methadone and THC-naltrexone interactions on discrimination, antinociception, and locomotion in rats.

This study examined cannabinoid-opioid interactions within the same subjects on measures of discrimination, antinociception, horizontal locomotion, and catalepsy. Male Sprague-Dawley rats were trained to discriminate Δ(9)-tetrahydrocannabinol (THC, 3 mg/kg) from vehicle. THC alone (0.32-10 mg/kg) dose-dependently increased THC-appropriate lever responding and decreased response rate. THC alone also produced paw pressure antinociception and decreased locomotor activity, but did not produce catalepsy. Methadone (0.32-5.6 mg/kg) and naltrexone (0.32-3.2 mg/kg) alone produced low THC-appropriate lever responding up to doses that decreased response rate. When combined with THC, methadone (1.0 mg/kg) flattened the THC discrimination curve, but did not affect antinociceptive or motoric effects of THC. Naltrexone did not alter any effects of THC. In rats that were not trained to discriminate THC from vehicle, 1.0 mg/kg methadone did enhance THC antinociception. These results suggest that µ-opioid receptor agonists can disrupt the discriminative stimulus effects of cannabinoids while not significantly altering their antinociceptive or motoric effects, in chronically drug-exposed subjects. Further research is required to determine whether opioid enhancement of cannabinoid antinociception is limited to acute exposure, or simply requires higher doses in chronically drug-exposed subjects.

Antinociception and sedation following intracerebroventricular administration of Δ9-tetrahydrocannabinol in female vs. male rats.

Systemically administered cannabinoids produce greater antinociceptive and sedative effects in female compared to male rats. Sex differences in the brain endocannabinoid system have also been reported. The aim of this study was to determine whether sex differences in antinociceptive and motoric effects of a cannabinoid can be attributed to supraspinal mechanisms. Vehicle or Δ9-tetrahydrocannabinol (THC, 100 µg) was administered i.c.v., and behavioral effects were compared between gonadally intact male and female rats, and among females in different estrous stages (early proestrus, late proestrus, estrus and diestrus). Antinociception on the tail withdrawal and paw pressure tests after i.c.v. THC was slightly but not significantly greater in females (pooled across estrous stages) compared to males. THC suppressed locomotor activity similarly in all groups, with the exception that only males showed hyperlocomotion at 4 h post-injection. When females in the four estrous stages were compared, females in late proestrus showed significantly greater THC-induced antinociception than females in estrus (and males). These results suggest that supraspinal mechanisms may contribute to greater systemic THC effects in females compared to males, and to estrous stage-dependent differences in THC effects among females.

Effects of cannabinoid drugs on the reinforcing properties of food in gestationally undernourished rats.

Involvement of the endocannabinoids in hyperphagia has been demonstrated, however, behavioral characterization of its role in food reinforcement is limited. The present study investigated whether 2-arachidonoyl glycerol, an endocannabinoid ligand, and rimonabant, a CB1 antagonist, change the reinforcing properties of food in gestationally undernourished rats (a putative model of obesity) vs controls. Albino dams were food deprived by 0 to 45% of their free-feeding weights up to day 18 of their gestational period. Their offspring were allowed to free-feed until postnatal day 75. Then, behavior of the offspring was placed under progressive ratio schedules of sucrose reinforcement. After baseline data were established, intraperitoneal injections of 2-AG (0.03-3.75 mg/kg), and rimonabant (SR141716, 0.3-3.0 mg/kg) were administered and compared across group. Results show gestationally undernourished (GU) rats as adults weighed less than controls at the time of testing and female offspring allowed to free-feed for over 35 weeks exhibited lower body weights than controls. Under baseline, GU rats had lower breakpoints than controls. 2-AG and rimonabant significantly increased and decreased, respectively, breakpoint and responses made per session, suggesting involvement of the cannabinoid system in food reinforcement. When comparing peak doses of 2-AG on breakpoint, gestationally undernourished rats exhibited lower peak doses than controls. These data suggest that under the gestation deprivation method employed, GU rats were thinner and had lower food reinforcer efficacy than controls, and may have heightened sensitivity to 2-AG.