Glucagon-like peptide 1 receptor activation regulates cocaine actions and dopamine homeostasis in the lateral septum by decreasing arachidonic acid levels.

Agonism of the glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) has been effective at treating aspects of addictive behavior for a number of abused substances, including cocaine. However, the molecular mechanisms and brain circuits underlying the therapeutic effects of GLP-1R signaling on cocaine actions remain elusive. Recent evidence has revealed that endogenous signaling at the GLP-1R within the forebrain lateral septum (LS) acts to reduce cocaine-induced locomotion and cocaine conditioned place preference, both considered dopamine (DA)-associated behaviors. DA terminals project from the ventral tegmental area to the LS and express the DA transporter (DAT). Cocaine acts by altering DA bioavailability by targeting the DAT. Therefore, GLP-1R signaling might exert effects on DAT to account for its regulation of cocaine-induced behaviors. We show that the GLP-1R is highly expressed within the LS. GLP-1, in LS slices, significantly enhances DAT surface expression and DAT function. Exenatide (Ex-4), a long-lasting synthetic analog of GLP-1 abolished cocaine-induced elevation of DA. Interestingly, acute administration of Ex-4 reduces septal expression of the retrograde messenger 2-arachidonylglycerol (2-AG), as well as a product of its presynaptic degradation, arachidonic acid (AA). Notably, AA reduces septal DAT function pointing to AA as a novel regulator of central DA homeostasis. We further show that AA oxidation product γ-ketoaldehyde (γ-KA) forms adducts with the DAT and reduces DAT plasma membrane expression and function. These results support a mechanism in which postsynaptic septal GLP-1R activation regulates 2-AG levels to alter presynaptic DA homeostasis and cocaine actions through AA.

Progressive neurodegenerative and behavioural changes induced by AAV-mediated overexpression of α-synuclein in midbrain dopamine neurons.

Parkinson's disease (PD) is characterised by the progressive loss of nigral dopamine neurons and the presence of synucleinopathy. Overexpression of α-synuclein in vivo using viral vectors has opened interesting possibilities to model PD-like pathology in rodents. However, the attempts made so far have failed to show a consistent behavioural phenotype and pronounced dopamine neurodegeneration. Using a more efficient adeno-associated viral (AAV) vector construct, which includes a WPRE enhancer element and uses the neuron-specific synapsin-1 promoter to drive the expression of human wild-type α-synuclein, we have now been able to achieve increased levels of α-synuclein in the transduced midbrain dopamine neurons sufficient to induce profound deficits in motor function, accompanied by reduced expression of proteins involved in dopamine neurotransmission and a time-dependent loss of nigral dopamine neurons, that develop progressively over 2-4 months after vector injection. As in human PD, nigral cell loss was preceded by degenerative changes in striatal axons and terminals, and the appearance of α-synuclein positive inclusions in dystrophic axons and dendrites, supporting the idea that α-synuclein-induced pathology hits the axons and terminals first and later progresses to involve also the cell bodies. The time-course of changes seen in the AAV-α-synuclein treated animals defines distinct stages of disease progression that matches the pre-symptomatic, early symptomatic, and advanced stages seen in PD patients. This model provides new interesting possibilities for studies of stage-specific pathologic mechanisms and identification of targets for disease-modifying therapeutic interventions linked to early or late stages of the disease.

SK3 K+ channel-deficient mice have enhanced dopamine and serotonin release and altered emotional behaviors.

SK3 K(+) channels influence neuronal excitability and are present in 5-hydroxytryptamine (5-HT) and dopamine (DA) nuclei in the brain stem. We therefore hypothesized that SK3 channels affect 5-HT and DA neurotransmission and associated behaviors. To explore this, we used doxycycline-induced conditional SK3-deficient (T/T) mice. In microdialysis, T/T mice had elevated baseline levels of striatal extracellular DA and the metabolites dihydroxyphenylacetic acid and homovanillic acid. While baseline hippocampal extracellular 5-HT was unchanged in T/T mice, the 5-HT response to the 5-HT transporter inhibitor citalopram was enhanced. Furthermore, baseline levels of the 5-HT metabolite 5-hydroxyindoleacetic acid were elevated in T/T mice. T/T mice performed equally to wild type (WT) in most sensory and motor tests, indicating that SK3 deficiency does not lead to gross impairments. In the forced swim and tail suspension tests, the T/T mice displayed reduced immobility compared with WT, indicative of an antidepressant-like phenotype. Female T/T mice were more anxious in the zero maze. In contrast, anxiety-like behaviors in the open-field and four-plate tests were unchanged in T/T mice of both sexes. Home cage diurnal activity was also unchanged in T/T mice. However, SK3 deficiency had a complex effect on activity responses to novelty: T/T mice showed decreased, increased or unchanged activity responses to novelty, depending on sex and context. In summary, we report that SK3 deficiency leads to enhanced DA and 5-HT neurotransmission accompanied by distinct alterations in emotional behaviors.

Local anaesthetics attenuates spinal nociception and HPA-axis activation during experimental laparotomy in pigs.

The effect of local anaesthetics on spinal nociception and activation of the hypothalamic-pituitary-adrenal axis (HPA-axis) was examined in a porcine model of abdominal surgery. A standardised laparotomy without visceral involvement was performed on 24 pigs. One group received a unilateral infiltration of mixed lidocaine and bupivacaine in skin, muscle and peritoneum of the surgical area prior to surgery (n=12), while local anaesthetics were replaced by isotonic saline in a second group (n=12). A sham group was subjected to anaesthesia (n=8), but did not undergo surgery. Two hours after surgery, half of the pigs from each group were perfused with formalin and the spinal cord was taken out for stereological quantification of the total number of Fos-like-immunoreactive (Fos-LI) neurones in the dorsal horn. Surgery with saline gave rise to a significant increase in the number of Fos-LI neurones ipsilaterally (107,001+/-16,548; p<0.001) as well as contralaterally (12,766+/-3,842; p<0.01) compared to the sham group. In animals undergoing surgery with LA, the number of Fos-LI neurones ipsilaterally was not significantly different from the sham group (p=0.78), and was reduced significantly both ipsilaterally (6960+/-1662; p<0.001) and contralaterally (3974+/-1131; p<0.05) compared to the saline group. In the other half of each group, blood samples, for determination of ACTH, cortisol, C-reactive protein and interleukin-6 concentrations, were drawn prior to and at predetermined time-points during and after surgery. Surgery with saline gave rise to dramatic increases in plasma ACTH and cortisol (p<0.01 and p<0.001, respectively) within 15 min of incision. In contrast, no changes from the initial concentrations of ACTH and cortisol were observed in pigs receiving local anaesthetics. No changes in plasma concentrations of C-reactive protein or interleukin-6 were observed in either of the groups. These results indicate that spinal nociception and HPA-axis activation caused by laparotomy in pigs can be attenuated by use of infiltration and incisional local anaesthetics prior to surgery. The present model provides a valuable tool in the evaluation of analgesic treatment during surgery, offering objective measures of both nociception and stress.

The role of alpha1- and alpha2-adrenoreceptors on venlafaxine-induced elevation of extracellular serotonin, noradrenaline and dopamine levels in the rat prefrontal cortex and hippocampus.

The role of adrenergic alpha1- and alpha2-adrenoreceptors in augmentation of venlafaxine-induced elevation of extracellular serotonin (5-HT),noradrenaline (NA) and dopamine (DA) levels in the rat prefrontal cortex (PFC) and hippocampus (HIPP) was studied by in vivo microdialysis in anaesthetized rats. The alpha1-adrenoreceptor antagonist prazosin given alone (0.3 mg/kg, s.c.) induced only a moderate reduction of hippocampal 5-HT and NA levels. The alpha2-adrenoreceptor antagonist idazoxan (1.5 mg/kg, s.c.) causes moderate increases in the levels of 5-HT and DA in the PFC. The mixed 5-HT and NA reuptake inhibitor venlafaxine (10 mg/kg, i.p.) increased the efflux of 5-HT, NA and DA almost equally, to approximately 200% of the control levels in the PFC. The levels of 5-HT increased to 310%, an effect approximately twice the effect on NA in the HIPP. Venlafaxine also produced a moderate increase in DA levels in the PFC but had no effect in the HIPP. Pre-treatment with prazosin caused a significant attenuation of the venlafaxine induced 5-HT effect in the PFC, and a moderate increase in DA levels in the HIPP. Prazosin had no significant effect on the venlafaxine-induced increase of the NA levels in PFC or HIPP. A combined treatment of venlafaxine with idazoxan increased the venlafaxine NA and DA effects in PFC by a factor of two and resulted in a very robust five-fold augmentation of NA and DA concentrations in the HIPP. In summary, idazoxan was found to produce a potent enhancement of the venlafaxine effect to increase extracellular NA and DA levels in the PFC and, in particular, in the HIPP. Idazoxan had no effect on venlafaxine-induced elevation of extracellular 5-HT levels in either PFC or HIPP and prazosin induced a decrease of 5-HT in the PFC. The present data suggest that blockade of alpha2-adrenoreceptors may play an important role in augmentation of the effects of mixed monoamine reuptake inhibitors.