Agnieszka Zelek-Molik

Acute and repeated treatment with the 5-HT7 receptor antagonist SB 269970 induces functional desensitization of 5-HT7 receptors in rat hippocampus

BACKGROUND SB 269970, a 5-HT(7) receptor antagonist may produce a faster antidepressant-like effect in animal models, than do antidepressant drugs, e.g., imipramine. The present work was aimed at examining the effect of single and repeated (14 days) administration of SB 269970 on the 5-HT(7) receptor in the hippocampus. METHODS The reactivity of 5-HT(7) receptors was determined using 5-carboxamidotryptamine (5-CT), which increased the bursting frequency of spontaneous epileptiform activity in hippocampal slices. Additionally, the effects of SB 269970 administration on the affinity and density of 5-HT(7) receptors were investigated using [(3)H]-SB 269970 and the influence of SB 269970 and imipramine on mRNA expression levels of Gα(s) and Gα(12) mRNA were studied using RT-qPCR. RESULTS Acute and repeated treatment with SB 269970 led to attenuation of the excitatory effects of activation of 5-HT(7) receptors. Neither single nor repeated administration of SB 269970 changed the mean affinity of 5-HT(7) receptors for [(3)H]-SB 269970. Repeated, but not single, administration of SB 269970 decreased the maximum density of [(3)H]-SB 269970 binding sites. While administration of imipramine did not change the expression of mRNAs for Gα(s) and Gα(12) proteins after both single and repeated administration of SB 269970, a reduction in Gα(s) and Gα(12) mRNA expression levels was evident. CONCLUSIONS These findings indicate that even single administration of SB269970 induces functional desensitization of the 5-HT(7) receptor system, which precedes changes in the receptor density. This mechanism may be responsible for the rapid antidepressant-like effect of the 5-HT(7) antagonist in animal models.

Effects of the noradrenergic neurotoxin DSP-4 on the expression of α1-adrenoceptor subtypes after antidepressant treatment

We have previously reported that chronic imipramine and electroconvulsive treatments increase the α(1A)-adrenoceptor (but not the α(1B) subtype) mRNA level and the receptor density in the rat cerebral cortex. Furthermore, we have also shown that chronic treatment with citalopram does not affect the expression of either the α(1A)- or the α(1B)-adrenoceptor, indicating that the previously observed up-regulation of α(1A)-adrenoceptor may depend on the noradrenergic component of the pharmacological mechanism of action of these antidepressants. Here, we report that previous noradrenergic depletion with DSP-4 (50 mg/kg) (a neurotoxin selective for the noradrenergic nerve terminals) significantly attenuated the increase of α(1A)-adrenoceptor mRNA induced by a 14-day treatment with imipramine (IMI, 20 mg/kg, ip) and abolished the effect of electroconvulsive shock (ECS, 150 mA, 0.5 s) in the prefrontal cortex of the rat brain. The changes in the receptor protein expression (as reflected by its density) that were induced by IMI and ECS treatments were differently modulated by DSP-4 lesioning, and only the ECS-induced increase in α(1A)-adrenoceptor level was abolished. This study provides further evidence corroborating our initial hypothesis that the noradrenergic component of the action of antidepressant agents plays an essential role in the modulation of α(1A)-adrenoceptor in the rat cerebral cortex.

Disruption of glucocorticoid receptors in the noradrenergic system leads to BDNF up-regulation and altered serotonergic transmission associated with a depressive-like phenotype in female GRDBHCre mice

Recently, we have demonstrated that conditional inactivation of glucocorticoid receptors (GRs) in the noradrenergic system, may evoke depressive-like behavior in female but not male mutant mice (GR(DBHCre) mice). The aim of the current study was to dissect how selective ablation of glucocorticoid signaling in the noradrenergic system influences the previously reported depressive-like phenotype and whether it might be linked to neurotrophic alterations or secondary changes in the serotonergic system. We demonstrated that selective depletion of GRs enhances brain derived neurotrophic factor (BDNF) expression in female but not male GR(DBHCre) mice on both the mRNA and protein levels. The possible impact of the mutation on brain noradrenergic and serotonergic systems was addressed by investigating the tissue neurotransmitter levels under basal conditions and after acute restraint stress. The findings indicated a stress-provoked differential response in tissue noradrenaline content in the GR(DBHCre) female but not male mutant mice. An analogous gender-specific effect was identified in the diminished content of 5-hydroxyindoleacetic acid, the main metabolite of serotonin, in the prefrontal cortex, which suggests down-regulation of this monoamine system in female GR(DBHCre) mice. The lack of GR also resulted in an up-regulation of alpha2-adrenergic receptor (α2-AR) density in the female but not male mutants in the locus coeruleus. We have also confirmed the utility of the investigated model in pharmacological studies, which demonstrates that the depressive-like phenotype of GR(DBHCre) female mice can be reversed by antidepressant treatment with desipramine or fluoxetine, with the latter drug evoking more pronounced effects. Overall, our study validates the use of female GR(DBHCre) mice as an interesting and novel genetic tool for the investigation of the cross-connected mechanisms of depression that is not only based on behavioral phenotypes.

Effects of morphine and methadone treatment on mRNA expression of Gα(i) subunits in rat brains.

Methadone is clinically effective as substitution therapy in patients with opioid dependence. The diversity of methadone and morphine in their intracellular activity is postulated. We compared the effects of repeated daily treatment of Sprague-Dawley rats with morphine (10 mg/kg) and methadone (1 mg/kg) on the expression of the Gα(i1-i3) mRNAs in several rat brain areas using RT-qPCR. We found that both opioid receptor agonists decreased Gα(i3) mRNA in only the nucleus accumbens. Although there was no difference in the influence of morphine and methadone on Gα(i), our results indicate that among Gα(i) subunits, the Gα(i3) is specifically involved in the mechanism of action of both drugs.

Cryptic peptide derived from the rat neuropeptide FF precursor affects G-proteins linked to opioid receptors in the rat brain.

Recently, we reported the discovery of a novel amino acid sequence derived from the NPFF precursor NAWGPWSKEQLSPQA, which blocked the expression of conditioned place preference induced by morphine and reversed the antinociceptive activity of morphine (5mg/kg, s.c.) in the tail-immersion test in rats. Here, we name it as NPNA (Neuropeptide NA from its flanking amino acid residues). The synthetic peptide influenced the expression of mRNA coding for Galpha(i1), (i2), and (i3) subunits. The results provide further evidence that yet another bioactive sequence might be present within the NPFF precursor.

Suppression of pro-inflammatory cytokine expression and lack of anti-depressant-like effect of fluoxetine in lipopolysaccharide-treated old female mice

Abstract Some antidepressants show a significantly lower efficacy in elderly patients, particularly in women. Previous studies have shown that antidepressants administered to young animals reduced depression‐like symptoms induced by lipopolysaccharide (LPS). The aim of this study was to find out whether the antidepressant and anti‐inflammatory properties of fluoxetine (FLU) can be observed also in old female C57BL/6J mice. A depression‐like state was evoked by the administration of LPS (100 &mgr;g/kg for 4 consecutive days) which was followed by reduction of sucrose preference (anhedonia) and enhancement of immobility‐time in the forced swim test (FST). Animals, which received FLU (10 mg/kg, 11 days) exhibited a decreased LPS‐induced expression of some inflammatory cytokines in the hippocampus and spleen but this effect was not accompanied by beneficial changes in animals’ behavior. Despite the lack of antidepressant‐properties of FLU in this model, our studies have proven significant profound anti‐inflammatory properties of chronic FLU treatment which may suggest its suitability for fending off inflammatory processes in the elderly. HighlightsFluoxetine did not reduce depressive behavior induced in senescent females by LPS injection.Fluoxetine attenuated LPS‐induced expression of pro‐inflammatory cytokines in the periphery and in the brain.Fluoxetine inhibited of proliferative activity of Con A‐stimulated splenocytes.

Multiple Administration of Endogenous Amines TIQ and 1MeTIQ Protects Against a 6-OHDA-Induced Essential Fall of Dopamine Release in the Rat Striatum: In Vivo Microdialysis Study

Parkinson’s disease (PD) represents one of the neurodegenerative disorders which are caused by degeneration of dopaminergic neurons in the nigrostriatal pathway. Different toxins, e.g., 6-hydroxydopamine (6-OHDA), are used to model PD in animals. 6-OHDA is a neurotoxin which damages catecholaminergic neurons via production of oxygen radicals. Tetrahydroisoquinolines (TIQs) are endogenous amines which are present in the mammalian brain. Some of them, like TIQ and 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), demonstrate neuroprotective properties. These compounds act as reversible MAO inhibitors and this way block free radical formation. To continue our previous experiments, we evaluated the effect of acute and chronic treatment with TIQ and 1MeTIQ on locomotor/exploratory activity and the release of dopamine as well as its metabolite 3-methoxytyramine (3-MT) in the striatum of unilaterally 6-OHDA-lesioned and sham-operated rats using in vivo microdialysis methodology. Additionally, the changes in the concentration of tyrosine hydroxylase in the substantia nigra were measured. A unilateral 6-OHDA lesion in the substantia nigra produces a strong reduction in the release of dopamine (approx. 70%) and 3-MT (approx. 50%) in the rat striatum. This effect was completely inhibited by multiple administration of TIQ and 1MeTIQ. The results obtained from the in vivo microdialysis study suggest that multiple treatment with both endogenous amines, TIQ and 1MeTIQ, protects dopaminergic neurons against a 6-OHDA-induced deficit of dopamine release. Furthermore, these amines were able to maintain physiological functions of striatal dopamine neurons damaged by a unilateral 6-OHDA lesion.

Morphine-induced place preference affects mRNA expression of G protein α subunits in rat brain

BACKGROUND The conditioned place preference (CPP) test is an animal model serving to assess addictive potential of drugs in which environmental cues become associated with the subjective effects of drugs of abuse. Morphine, a known addictive drug, is an agonist of opioid receptors that couple to the G(i/o) family of guanine nucleotide-binding proteins (GP). We have recently found that chronic treatment with morphine affects mRNA levels of GPs that are not coupled to opioid receptors (OR). Therefore, in this study, we investigated the influence of morphine-induced CPP on mRNA expression of the Gα subunits, G(i/o), G(s), G(q/11), and G(12), in the rat prefrontal cortex (PFC) and nucleus accumbens (NAc) using standard PCR techniques. METHODS CPP and NO-CPP experiments were conducted; Wistar rats were either subjected to the standard CPP procedure or were injected with morphine (or saline) in their home cage. All rats were decapitated 24 h after the last injection. RESULTS We found that mRNA levels of Gα(q), Gα(11) and Gα(12) were increased after morphine in non-conditioned treatment in the PFC but remained unchanged in the NAc. In rats showing conditioned place preference to morphine, levels of Gα(i2) in the PFC and levels of Gα(oA) in the NAc were diminished by ≈58% and ≈30%, respectively (p < 0.05 vs. saline), but levels of Gα(s-l) in NAc were increased (≈60%, p = 0.05). CONCLUSION Our data indicate that only G(i/o) and G(s) were specifically changed in animals after morphine-induced CPP, thus suggesting that the effect was related to learning environmental cues associated with morphine.

The Protective Effect of Repeated 1MeTIQ Administration on the Lactacystin-Induced Impairment of Dopamine Release and Decline in TH Level in the Rat Brain

Parkinson’s disease (PD) is a neurodegenerative disorder of the central nervous system (CNS) caused by a progressive loss of nigrostriatal dopaminergic neurons. Dysfunction of the ubiquitin-proteasome system (UPS) plays an important role in the pathogenesis of PD. Intranigral administration of the UPS inhibitor lactacystin is used to obtain a valuable animal model for investigating putative neuroprotective treatments for PD. 1-Methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) is an endogenous amine that displays neuroprotective properties. This compound acts as a reversible monoamine oxidase (MAO) inhibitor and a natural free radical scavenger. In the present experiment, we investigated the effect of acute and chronic treatment with 1MeTIQ on locomotor activity and the release of dopamine as well as its metabolites in the striatum of unilaterally lactacystin-lesioned and sham-operated rats using in vivo microdialysis. Additionally, changes in the level of tyrosine hydroxylase (TH) in the substantia nigra were measured. Unilateral lactacystin injection into the substantia nigra caused significant impairment of dopamine release (approx. 45%) and a marked decline in the TH level. These effects were completely antagonized by multiple treatments with 1MeTIQ. The results obtained from the in vivo microdialysis study as well as from the ex vivo experiments suggest that multiple administration of 1MeTIQ protects dopaminergic neurons against the lactacystin-induced decline in TH concentration in the substantia nigra and prevents disturbances of dopamine release in the striatum. We have demonstrated that 1MeTIQ is capable of maintaining the physiological functions of the striatal dopamine neurons damaged by unilateral lactacystin lesion.

Erratum to: Neuroprotective Effect of the Endogenous Amine 1MeTIQ in an Animal Model of Parkinson’s Disease

In the original publication, the acknowledgment section was published incorrectly. The correct acknowledgment is given below: Acknowledgments The authors would like to thank Maria Kafel and Krzysztof Michalski for technical assistance. This study was financially supported through a grant from the National Science Centre, Grant No. DEC-2012/ 07/B/NZ7/01149, and statutory funds from the Institute of Pharmacology, Polish Academy of Sciences, Krakow, Poland.