Brain monoamines and antidepressant-like responses in MRL/MpJ versus C57BL/6J mice
ABSTRACT The MRL/MpJ mouse demonstrates enhanced wound healing and tissue regeneration and increased neurotrophic mobilization to chronic antidepressant drug treatments. This study compared brain monoamine systems between MRL/MpJ and C57BL/6J mice as a potential basis for strain differences after chronic antidepressant treatment. MRL/MpJ mice had significantly higher tissue levels of serotonin and dopamine in multiple brain regions. Microdialysis studies demonstrated that baseline levels of extracellular serotonin did not differ between strains. However, acute administration of the selective serotonin reuptake inhibitor citalopram produced an increase in extracellular serotonin in the ventral hippocampus of MRL/MpJ mice that was twice as large as achieved in C57BL/6J mice. The greater effects in MRL/MpJ mice on 5-HT levels were not maintained after local perfusion of citalopram, suggesting that mechanisms outside of the hippocampus were responsible for the greater effect of citalopram after systemic injection. The density of serotonin and norepinephrine transporters in the hippocampus was significantly higher in MRL/MpJ mice. In addition, the expression of 5-HT(1A) mRNA was lower in the hippocampus, 5-HT(1B) mRNA was higher in the hippocampus and brain stem and SERT mRNA was higher in the brain stem of MRL/MpJ mice. The exaggerated neurotransmitter release in MRL/MpJ mice was accompanied by reduced baseline immobility in the tail suspension test and a greater reduction of immobility produced by citalopram or the tricyclic antidepressant desipramine. These data suggest that differences in the response to acute and chronic antidepressant treatments between the two strains could be attributed to differences in serotonin or catecholamine transmission.
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- "Using high pressure liquid chromatography (HPLC) analysis , we measured the levels of 5-HT and its metabolite 5- hydroxyindoleacetic acid (5-HIAA) to assess whether the changes in 5-HT 2A R-mediated responses were mediated by changes in cortical serotonin content. We found no differences between genotypes in 5-HT or 5-HIAA tissue content in the frontal cortex (Fig. 4A) and S1 cortex (Fig. 4B). "
ABSTRACT: Both the serotonin and glutamate systems have been implicated in the pathophysiology of schizophrenia, as well as in the mechanism of action of antipsychotic drugs. Psychedelic drugs act through the serotonin 2A receptor (5-HT2AR), and elicit a head-twitch response (HTR) in mice, which directly correlates to 5-HT2AR activation and is absent in 5-HT2AR knockout mice. The precise mechanism of this response remains unclear, but both an intrinsic cortico-cortical pathway and a thalamo-cortical pathway involving glutamate release have been proposed. Here, we used a genetic model of NMDAR hypofunction, a serine racemase knockout (SRKO) mouse, to explore the role of glutamatergic transmission in regulating the 5-HT2AR-mediated cellular and behavioral responses. SRKO mice treated with the 5-HT2AR agonist (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) showed a clearly diminished HTR and lower induction of c-fos mRNA. These altered functional responses in SRKO mice were not associated with changes in cortical or hippocampal 5-HT levels or in 5-HT2AR and metabotropic glutamate-2 receptor (mGluR2) mRNA and protein expression. Together, these findings suggest that D-serine-dependent NMDAR activity is involved in mediating the cellular and behavioral effects of 5-HT2AR activation.Behavioural brain research 11/2013; 259. DOI:10.1016/j.bbr.2013.11.022 · 3.39 Impact Factor
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ABSTRACT: Smoking is the largest preventable cause of death in the United States. Furthermore, a recent study found that <10% of quit attempts resulted in continuous abstinence for 1 year. With the introduction of pharmacotherapies like Chantix (varenicline), a selective α4β2 nicotinic partial agonist, successful quit attempts have significantly increased. Therefore, novel subtype-specific nicotinic drugs, such as sazetidine-A, present a rich area for investigation of therapeutic potential in smoking cessation. The present studies examine the anxiety-related behavioral and functional effects of the nicotinic partial agonists varenicline and sazetidine-A during withdrawal from chronic nicotine in mice. Our studies indicate that ventral hippocampal-specific infusions of sazetidine-A, but not varenicline, are efficacious in reducing nicotine withdrawal-related anxiety-like phenotypes in the novelty-induced hypophagia (NIH) paradigm. To further investigate functional differences between these partial agonists, we utilized voltage-sensitive dye imaging (VSDi) in ventral hippocampal slices to determine the effects of sazetidine-A and varenicline in animals chronically treated with saline, nicotine, or undergoing 24 h withdrawal. These studies demonstrate a functional dissociation of varenicline and sazetidine-A on hippocampal network activity, which is directly related to previous drug exposure. Furthermore, the effects of the nicotinic partial agonists in VSDi assays are significantly correlated with their behavioral effects in the NIH test. These findings highlight the importance of drug history in understanding the mechanisms through which nicotinic compounds may be aiding smoking cessation in individuals experiencing withdrawal-associated anxiety.Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 04/2013; 38(10). DOI:10.1038/npp.2013.105 · 7.83 Impact Factor
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ABSTRACT: Retrodialysis, as used in neuropharmacological research, is a technique for in vivo delivery of neuroactive agents with concurrent monitoring of their effects on cellular activity with a certain degree of spatial and temporal resolution. Typically, this is accomplished either by the use of a liquid-switch requiring multiple pumps, or by exchange of flow tubing requiring stopping and restarting dialysis. In the present study, we describe the use of a medium pressure injection valve for retrodialysis that overcomes these problems. The valve was configured with a loop to deliver 20μL of solution, and artificial CSF flow from the pump to the probe was established via this device. The application of this setup was evaluated in urethane anesthetized adult male C57BL/6J mice prepared with a CMA 11 probe implanted in the ventral hippocampus. By switching between the load and inject positions, the loop was filled with escitalopram solution (0.3μM) and delivered at a rate of 1μL/min at the probe for retrodialysis. Escitalopram (2mg/kg BW) was administered subcutaneously for microdialysis studies. During these treatments, dialysate fractions were collected for the determination of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA). Irrespective of route of escitalopram administration, the pattern of dialysate 5-HT, and 5-HIAA response was comparable to that reported by other investigators. Accordingly, the in-line valve assembly did not compromise retrodialysis or microdialysis sampling. The manipulations to carry out retrodialysis using the valve setup are easy and simple. An in-line injection valve is a promising adaptation for retrodialysis studies and can be incorporated as a standard part of in vivo dialysis instrumentation.Journal of pharmacological and toxicological methods 07/2013; DOI:10.1016/j.vascn.2013.06.002 · 2.15 Impact Factor