Parkinson's disease (PD) is characterized by the progressive loss of nigrostriatal dopamine (DA) neurons leading to motor disturbances and cognitive impairment. Current pharmacotherapies relieve PD symptoms temporarily but fail to prevent or slow down the disease progression. In this study, we investigated the molecular mechanisms by which the non-selective cannabinoid receptor agonist WIN55,212-2 (WIN) protects mouse nigrostriatal neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity and neuroinflammation. Stereological analyses showed that chronic treatment with WIN (4 mg/kg, i.p.), initiated 24 hr after MPTP administration, protected against MPTP-induced loss of tyrosine hydroxylase positive (TH + ) neurons in the substantia nigra pars compacta (SNc) independently of CB 1 cannabinoid receptor activation. The neuroprotective effect of WIN was accompanied by increased DA and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the SNc and dorsal striatum of MPTP-treated mice. Three days post-MPTP, we found significant microglial activation and up-regulation of CB 2 cannabinoid receptors in the ventral midbrain. Treatment with WIN or the CB 2 receptor agonist JWH015 (4 mg/kg, i.p.) reduced MPTP-induced microglial activation, whereas genetic ablation of CB 2 receptors exacerbated MPTP systemic toxicity. Furthermore, chronic WIN reversed MPTPassociated motor deficits, as revealed by the analysis of forepaw step width and percentage of faults using the inverted grid test. In conclusion, our data indicate that agonism at CB 2 cannabinoid receptors protects against MPTP-induced nigrostriatal degeneration by inhibiting microglial activation/infiltration and suggest that CB 2 receptors represent a new therapeutic target to slow the degenerative process occurring in PD.

Mood disorders cause much suffering and are the single greatest cause of lost productivity worldwide. Although multiple medications, along with behavioral therapies, have proven effective for some individuals, millions of people lack an effective therapeutic option. A common serotonin (5-HT) transporter (5-HTT/SERT, SLC6A4) polymorphism is believed to confer lower 5-HTT expression in vivo and elevates risk for multiple mood disorders including anxiety, alcoholism, and major depression. Importantly, this variant is also associated with reduced responsiveness to selective 5-HT reuptake inhibitor antidepressants. We hypothesized that a reduced antidepressant response in individuals with a constitutive reduction in 5-HTT expression could arise because of the compensatory expression of other genes that inactivate 5-HT in the brain. A functionally upregulated alternate transporter for 5-HT may prevent extracellular 5-HT from rising to levels sufficiently high enough to trigger the adaptive neurochemical events necessary for therapeutic benefit. Here we demonstrate that expression of the organic cation transporter type 3 (OCT3, SLC22A3), which also transports 5-HT, is upregulated in the brains of mice with constitutively reduced 5-HTT expression. Moreover, the OCT blocker decynium-22 diminishes 5-HT clearance and exerts antidepressantlike effects in these mice but not in WT animals. OCT3 may be an important transporter mediating serotonergic signaling when 5-HTT expression or function is compromised.5HTTLPR ͉ antidepressant ͉ polymorphism ͉ hippocampus ͉ chronamperometry

F15599 is a novel agonist with high selectivity and efficacy at serotonin 5-HT(1A) receptors (5-HT(1A)Rs). In signal transduction, electrophysiological and neurochemical tests, F15599 preferentially activates post-synaptic 5-HT(1A)Rs in rat frontal cortex. Such a profile may translate to an improved profile of therapeutic activity for mood disorders. The in-vivo effects of F15599 were therefore compared with those of a related compound, F13714, in rat models of antidepressant activity and 5-HT(1A)R activation: forced swimming test (FST), conditioned stress-induced ultrasonic vocalization, 5-HT syndrome, plasma corticosterone and body temperature. Acute administration of F15599 or F13714 reduced immobility in the FST at low doses; these effects were long lasting and the effects of F15599 were maintained after repeated (5 d, p.o.) administration. Both compounds decreased ultrasonic vocalization duration at low doses. In contrast, higher doses of F15599 were required to induce lower lip retraction, elements of the 5-HT behavioural syndrome, hypothermia and to increase plasma corticosterone levels. Notably, there was a greater separation of ED50 between FST and other effects for F15599 than for F13714. Thus, the in-vivo potency of F15599 in models of antidepressant/anti-stress activity is similar to that of F13714, despite the fact that the latter has an in-vitro potency two orders of magnitude greater. In contrast F15599 has a lower propensity than F13714 to induce other serotonergic signs. The distinctive pharmacological profile of F15599 suggests that preferential targeting of post-synaptic 5-HT(1A)Rs constitutes a promising strategy for improved antidepressant therapy.

PK 26124, a proposed excitatory amino acid antagonist, was compared to mephenesin and phencyclidine (PCP). In pigeons, PK 26124 and mephenesin produced loss of righting that was to some extent associated with eye closure and muscle relaxation, whereas PCP produced catalepsy, i.e., loss of righting without eye closure and without muscle relaxation. PK 26124, but not mephenesin, produced PCP-like discriminative stimulus effects in some but not all pigeons. In rats, PK 26124 and mephenesin produced loss of righting but did not induce locomotion, sniffing, swaying and falling, unlike PCP. In rhesus monkeys, PK 26124 did not induce ketamine-like discriminative stimulus effects. While PK 26124 may share some biochemical properties with excitatory amino acid antagonists these do not lead to behavioral effects similar to PCP.

GHB is used therapeutically and recreationally, although the precise mechanism of action responsible for its different behavioral effects is not entirely clear. The purpose of this review is to summarize how behavioral procedures, especially drug discrimination procedures, have been used to study the mechanism of action of GHB. More specifically, we will review several different drug discrimination procedures and discuss how they have been used to qualitatively and quantitatively study different components of the complex mechanism of action of GHB. A growing number of studies have provided evidence that the behavioral effects of GHB are mediated predominantly by GABA B receptors. However, there is also evidence that the mechanisms mediating the effects of GHB and the prototypical GABA B receptor agonist baclofen are not identical, and that other mechanisms such as GHB receptors and subtypes of GABA A and GABA B receptors might contribute to the effects of GHB. These findings are consistent with the different behavioral profile, abuse liability, and therapeutic indications of GHB and baclofen. A better understanding of the similarities and differences between GHB and baclofen, as well as the pharmacological mechanisms of action underlying the recreational and therapeutic effects of GHB, could lead to more effective medications with fewer adverse effects.

No abstract

No abstract

No abstract