[Show abstract][Hide abstract] ABSTRACT: Rationale Acute administration of high doses of morphine reduced 50-kHz ultrasonic vocalizations (USVs). Although morphine meets the classical criteria for inducing 50-kHz USVs (it causes place preference and induces dopamine re-lease in nucleus accumbens), it also inhibits appetitive vocalizations. Objective The aims of this study were to (i) study the phar-macological impact of κ-opioid (KOR) and μ-opioid receptor (MOR) ligands on the emission of 50-kHz USVs triggered by social interaction after long-term isolation and (ii) analyze the concentrations of the main neurotransmitters in reward-related structures (ventral tegmental area (VTA), nucleus accumbens (NAcc), and medial prefrontal cortex (mPFC)). Methods In an attempt to define the effects of opioid-receptor activation on the reward system, we used a social interaction test (after 21 days isolation). HPLC analysis was used to determine the monoamine and amino acid concentrations in reward-related structures. Results U-50488 (10.0 mg/kg), morphine (5.0 and 1.0 mg/kg), and naltrexone (5.0 mg/kg) decreased, and nor-BNI (10.0 mg/kg) increased 50-kHz USVs. Acute pretreatment with nor-BNI or naltrexone reduced the 50-kHz suppression induced via morphine. The biochemical data showed several variations between groups regarding dopamine concentra-tions, serotonin, and their metabolites; these data may suggest that the levels of emitted ultrasound in the 50-kHz band are inversely proportional to the 5-hydroxyindoleacetic acid (5-HIAA)/3-methoxytyramine (3-MT) ratio in the VTA. Conclusions These results indicate an important role for KOR in the regulation of 50-kHz USV emissions and suggest that KOR activation may be a key mediator in the regulation of reward responses. Changes in the balance between serotonin and dopamine concentrations in the VTA may be a key predictor for 50-kHz USV emission.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to examine the effects of benzodiazepine (midazolam) administration on rat conditioned fear responses and on local brain activity (c-Fos and CRF expressions) of low- (LR) and high- (HR)anxiety rats after the first and second contextual fear test sessions. The animals were divided into LR and HR groups based on the duration of their conditioned freezing response in the first contextual fear test. The fear-re-conditioned LR and HR animals (28 days later) had increased freezing durations compared with those durations during the first conditioned fear test. These behavioral effects were accompanied by increased c-Fos expression in the medial amygdala (MeA), the basolateral amygdala (BLA), and the paraventricular hypothalamic nuclei and elevated CRF expression in the MeA. All these behavioral and immunochemical effects of fear re-conditioning were stronger in the LR group compared with the effects in the HR group. Moreover, in the LR rats, the re-conditioning led to decreased CRF expression in the primary motor cortex (M1) and to increased CRF expression in the BLA. The pretreatment of rats with midazolam before the second exposure to the aversive context significantly attenuated the conditioned fear response, lowered the serum corticosterone concentration, decreased c-Fos and CRF expressions in the MeA and in the BLA, and increased CRF complex density in M1 area only in the LR group. These studies have demonstrated that LR rats are more sensitive to re-exposure to fear stimuli and that midazolam pretreatment was associated with modified brain activity in the amygdala and in the prefrontal cortex in this group of animals. The current data may facilitate a better understanding of the neurobiological mechanisms responsible for individual differences in the psychopathological processes accompanying some anxiety disorders characterized by stronger reactivity to re-exposure to stressful challenges, e.g., posttraumatic stress disorder.
[Show abstract][Hide abstract] ABSTRACT: This study assessed behaviour, as measured by 50kHz calls related to positive affect, in rats with different fear conditioned response strengths: low-anxiety rats (LR) and high-anxiety rats (HR), after amphetamine injection in a two-injection protocol (TIPS). The results showed that the first dose of amphetamine evoked similar behavioural effects in frequency-modulated (FM) 50kHz calls in the LR and HR groups. The second injection of amphetamine resulted in stronger FM 50kHz calls in LR compared with HR rats. The biochemical data ('ex vivo' analysis) showed that the LR rats had increased basal levels of dopamine in the amygdala, and increased homovanilic acid (HVA), dopamine's main metabolite, in the amygdala and prefrontal cortex compared with HR rats. The 'in vivo' analysis (microdialysis study) showed that the LR rats had increased HVA concentrations in the basolateral amygdala in response to an aversively conditioned context. Research has suggested that differences in dopaminergic system activity in the amygdala and prefrontal cortex may be one of the biological factors that underlie individual differences in response to fear stimuli, which may also affect the rewarding effects of amphetamine.
Behavioural Brain Research 09/2014; 275. DOI:10.1016/j.bbr.2014.09.011 · 3.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the effect of valproate (ip, 500 mg/kg), which is regarded as a potent plasma protein tryptophan (TRP) displacer, on the central nervous system (hippocampal) and peripheral (plasma) levels of the aromatic amino acids (AAAs; e.g. TRP, tyrosine and phenylalanine) and branched-chain amino acids (BCAAs; e.g. valine, isoleucine and leucine) as well as the other amino acids (glutamate, GABA, alanine, glutamine, glycine, aspartate and taurine) involved in the regulation of neurotransmission. Furthermore, we investigated whether the changes in the BCAA/AAA ratio affected the hippocampal concentration of monoamines [serotonin (5-HT), dopamine (DA) and noradrenaline (NA)]. Valproic acid (VPA) administration potently modified the balance between the BCAA and AAA. In the brain, the significantly increased AAA and decreased BCAA concentrations were followed by a decrease in the BCAA/AAA ratio. In the plasma, VPA significantly decreased the BCAA and AAA levels. The changes in the BCAA and AAA levels were accompanied by an increase in the NA, DA and 5-HT levels as well as hippocampal 5-HT metabolism. This novel finding indicates that VPA, through the displacement of TRP from its protein-binding sites, could disturb the BCAA/AAA ratio, with central nervous system consequences, including the possible contribution to VPAs effects in affective disorders.
Neurotoxicity Research 11/2013; DOI:10.1007/s12640-013-9441-0 · 3.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The present study was designed to determine the role of the kynurenine pathway (KP) in the mechanism of action of valproate (VPA). Therefore, we investigated changes in the concentrations of tryptophan, kynurenic acid, and kynurenine in the brain and plasma following VPA administration (50, 250 and 500 mg/kg i.p.). The most important findings of our study were that VPA administration produced a progressive and strong increase in the central concentrations of kynurenic acid, kynurenine and tryptophan. Simultaneously, the TRP level in plasma declined, while the peripheral increase of kynurenic acid in plasma was weaker and occurred earlier than in the hippocampus. Bearing in mind that the observed effect may be a result of a strong VPA-induced displacement of tryptophan from its binding sites to plasma albumin, we checked the effect of ibuprofen administration (a prototypic drug used to study drug binding to serum albumin) on the KP. We found that ibuprofen evoked a similar pattern of changes in the KP activity as VPA. These new findings indicate the existence of a mechanism that could stimulate the production of kynurenic acid in the brain after VPA administration, and may partially contribute to the mechanisms of VPA action. The results of our experiment indicate that an increase in the brain's KYNA level may be achieved by TRP displacement from its binding site on the plasma albumin with the administration of different drugs, including VPA, ibuprofen, or short-chain fatty acids, with important clinical consequences.
[Show abstract][Hide abstract] ABSTRACT: The aim of our experiments was to assess the effect of acutely administered corticosterone on the expression of glucocorticoid receptors (GRs) in the brain of rats with high (HR) and low (LR) levels of anxiety. The rats were divided into groups according to their conditioned fear-induced freezing responses and then were subjected to a second conditioned fear session one week after the initial fear conditioning. Immunocytochemical analysis revealed that the second exposure to contextual aversive stimuli resulted in higher levels of GRs expression in cingulate cortex area 1 (Cg1), the secondary motor cortex (M2) of the prefrontal cortex and the dentate gyrus of the hippocampus (DG) in LR rats compared with HR rats. The pretreatment of HR rats with corticosterone (20mg/kg, sc) increased the expression levels of GRs in Cg1, the M2 area and the DG to the levels observed in the LR vehicle group. The increase in the GRs levels was accompanied by a significant decrease in the conditioned fear response in the HR group. The control animals that were not exposed to aversive stimuli had similar levels of receptor-related immunoreactivity in all brain regions, and corticosterone did not change these expression levels. Our results suggest that HR animals may have deficits in the expression of stress-induced GRs in the prefrontal cortex and the DG. In addition, pretreatment with corticosterone increases the expression of GRs and normalizes the fear response in HR rats.
[Show abstract][Hide abstract] ABSTRACT: The aim of the experiment was to assess the effects of an acutely administered corticosterone on the expression of GABA-A receptor alpha-2 subunits in the brain structures of high (HR) and low (LR) anxiety rats (divided according to their conditioned fear-induced freezing response) subjected to a second conditioned fear session (1 week after fear conditioning). We found that corticosterone (20 mg/kg, sc) given to rats prior to the second conditioned fear session significantly enhanced a decrease in fear expression in the HR group. The behavioural effect of fear was accompanied by the increased expression of alpha-2 subunits in the basolateral amygdala (BLA) and the dentate gyrus of the hippocampus (DG) of the HR group. Corticosterone potentiated the effect of fear on alpha-2 subunit expression in the BLA, DG, the cingulate cortex area 1 and the secondary motor cortex (areas Cg1 and M2). The current study provides insight into the mechanisms that may be responsible for the beneficial effects of glucocorticoids in the therapy of some anxiety disorders.
Behavioural brain research 07/2012; 235(1):30-5. DOI:10.1016/j.bbr.2012.07.018 · 3.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We investigated the changes in hippocampal kynurenic acid (KYNA) concentrations and the amino acids involved in neuronal activity regulation following valproate (VPA) administration (400 mg/kg ip) in pentylenetetrazole-kindled rats (in vivo). We found a remarkably long-lasting increase in KYNA levels following VPA administration, and this effect correlated with a rise in GABA levels. No changes in the concentration of other analyzed amino acids were present. It is likely that the antiepileptic and neuroprotective properties of VPA may also be a consequence of an increase in the hippocampal KYNA concentration.
[Show abstract][Hide abstract] ABSTRACT: The role of the GABA-A alpha-2 receptor subunit in the basolateral amygdala (BLA), dentate gyrus of the hippocampus (DG) and prefrontal cortex (M2 area) during a fear session (performed one week after the conditioned fear test), was studied. We employed a model of high (HR) and low anxiety (LR) rats divided according to their conditioned freezing response. Pretreatment of rats with d-cycloserine immediately before the fear session attenuated fear response in HR and LR rats and increased the density of alpha-2 subunits in the BLA, M2 area and DG of HR animals. The less potent behavioural influence of midazolam (in HR group only) was linked to the increased expression of alpha-2 subunit in M2 area and DG. These results support a role of the GABA-A receptor alpha-2 subunit in processing of emotional cortico-hippocampal input to the BLA.
Behavioural brain research 08/2011; 225(2):655-9. DOI:10.1016/j.bbr.2011.08.029 · 3.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Our study demonstrated that the development of seizures during the electrically induced kindling of seizures is associated with significant changes in the concentration of kynurenic acid (KYNA) and its precursor, tryptophan (TRP). The primary finding of our study was an increase in KYNA levels and the KYNA/TRP ratio (a theoretical index of activity of the kynurenine pathway) in the amygdala and hippocampus of kindled animals. We also found decreases in the concentration of tryptophan in the hippocampus and prefrontal cortex. Changes in the concentration of KYNA and TRP in the amygdala were accompanied by a significant decrease in γ-Aminobutryic Acid (GABA) levels and an increase in the glutamate/GABA ratio. Moreover, we found a significant negative correlation between the local concentrations of KYNA and glutamate in the amygdala of kindled rats. However, there were no changes in the local concentrations of the following amino acids: glutamate, aspartate, glutamine, glycine, taurine and alanine. In conclusion, these new results suggest a modulatory influence of KYNA on the process of epileptogenesis, characterized by a negative relationship between the KYNA and glutamate systems in the amygdala.
[Show abstract][Hide abstract] ABSTRACT: In this paper, we studied differences in the density of N-methyl-D-aspartate (NMDA) receptor GluN2B subunits in the brains of low (LR) and high (HR) anxiety rats subjected to extinction trials and re-learning of a conditioned fear response, modeling a natural course of anxiety disorders. Classifications of animals as LR or HR was determined by fear-induced freezing responses in the contextual fear test. Increased basal concentrations of GluN2B subunits were observed in the amygdala of HR rats as compared to the unconditioned control group by Western blot analysis. Re-exposure of HR animals to the fear-conditioned context resulted in elevated concentrations of GluN2B subunits in the amygdala, hippocampus and the prefrontal cortex compared to LR rats as well as in the hippocampus and prefrontal cortex vs. the control group. In addition, it was shown that re-test of a conditioned fear increased the number of cells expressing GluN2B subunits in the basolateral amygdala, dentate gyrus of the hippocampus and secondary motor cortex (M2) in the HR group relative to the LR group. Together, these data suggest that animals that are more anxious have altered patterns of GluN2B subunit expression in the frontal cortex and limbic structures, which control emotional behaviour.
Journal of physiology and pharmacology: an official journal of the Polish Physiological Society 08/2011; 62(4):473-82. · 2.72 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Predisposition to addictions is presumably related to a dysfunction of the brain reward system, which can be 'compensated' by the intake of different psychoactive drugs. Hence, animals showing propensity for developing dependence to a specific drug class may also be useful for modeling other addictions. We compared the effects of repeated (14 daily doses) morphine (10 mg/kg) or methadone (2 mg/kg) treatment followed by a 2-week withdrawal and a morphine challenge (5 mg/kg) on locomotor activity, brain Fos expression and selected brain regional levels of dopamine, serotonin and their metabolites in the 38th generations of selectively bred Warsaw low-alcohol-preferring (WLP) and Warsaw high-alcohol-preferring (WHP) rat lines. The rats were given the opioids during the active (i.e. dark) phase of their daily cycle. Drug-naïve WHP rats compared to their WLP counterparts showed higher locomotor activity in an open field test and higher propensity for lasting behavioral sensitization to morphine. Morphine did not significantly enhance, but suppressed Fos expression in certain brain regions of drug-naïve WLP and WHP rats. Fos expression revealed considerable differences in the responses of WLP and WHP rats to morphine challenge, particularly after methadone pretreatment. These differences were associated with differences in monoamine metabolite levels that were suggestive of elevated basal ganglia and lowered frontal cortical dopamine function, and of lowered somatosensory cortex serotonin function, in the morphine-challenged WHP rats (irrespective of the pretreatment type). Hence, the WLP/WHP line pair may be useful for the search of factors that underlie the propensity for developing opiate dependence.
Progress in Neuro-Psychopharmacology and Biological Psychiatry 03/2011; 35(2):588-97. DOI:10.1016/j.pnpbp.2010.12.028 · 4.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The influence of intracerebroventricular-administered selective corticotropin-releasing factor receptor 2 (CRF(2)) antagonists (antisauvagine-30, astressin-2B), on rat anxiety-like behavior, expression levels of c-Fos and CRF, and plasma corticosterone levels were examined in the present study. In fear-conditioned animals, both CRF receptor antagonists enhanced a conditioned freezing fear response and increased the conditioned fear-elevated concentration of serum corticosterone. Exogenously administered antisauvagine-30 increased the aversive context-induced expression of c-Fos in the 1 and 2 areas of the cingulate cortex (Cg1, Cg2), the central amygdala (CeA) and parvocellular neurons of the paraventricular hypothalamic nucleus (pPVN), and it enhanced the effect of conditioned fear in the secondary motor cortex (M2) and medial amygdala (MeA). Immunocytochemistry demonstrated an increase in CRF expression in the Cg1, M2 areas of the cortex, and pPVN, and it revealed the effect of conditioned fear in the CeA 35 min after antisauvagine-30 administration and 10 min after the conditioned fear test. Furthermore, astressin-2B, another CRF(2) receptor antagonist, enhanced expression of c-Fos and CRF in the CeA and pPVN, and revealed the effect of conditioned fear in the Cg1. These data support a model in which an excess in CRF(1) receptor activation, combined with reduced CRF(2) receptor signaling, may contribute to stronger expression of anxiety-like responses.
Behavioural brain research 03/2011; 221(1):155-65. DOI:10.1016/j.bbr.2011.02.036 · 3.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The influence of intracerebroventricullary-administered urocortin-2, a selective corticotropin-releasing factor receptor 2 (CRF(2)) agonist, on rat anxiety-like behaviour, the expression of c-Fos and CRF, and plasma corticosterone levels was examined in the present study. When applied to animals exposed to the conditioned fear-induced context, urocortin-2 enhanced a conditioned freezing fear response. Urocortin-2 also significantly decreased rat exploratory activity in the open field test. Exogenous urocortin-2 increased the conditioned fear-induced expression of c-Fos in the central amygdala (CeA), and parvocellular neurons of the paraventricular hypothalamic nucleus (pPVN), and revealed the effect of conditioned fear in the medial amygdala (MeA). In the fear-conditioned animals, immunocytochemistry showed an increase in the density of CRF-related immunoreactive complexes in the lateral septum (LS), 35min after urocortin-2 administration and 10min after the conditioned fear test, compared with saline-pretreated fear-conditioned animals. These data suggest a role of urocortin-2 in the behavioural and immunocytochemical responses to stress, in which it strengthens the measures of anxiety-like responses.
[Show abstract][Hide abstract] ABSTRACT: Apart from its role as an inhibitory neurotransmitter, γ-aminobutyric acid is also thought to regulate various stages of cell proliferation and differentiation in the brain and periphery. The present study aimed to assess the levels of γ-aminobutyric acid and its biochemical precursor glutamic acid (glutamate) in benign parotid tumours and in unstimulated parotid saliva.
Unstimulated parotid saliva was collected bilaterally, using the swab method, in 20 patients with unilateral pleomorphic adenoma or Warthin's tumour. Samples of tumour and adjacent salivary tissue were collected during tumour resection.
Concentrations of γ-aminobutyric acid and glutamate, but not aspartate, were significantly higher in the tumour tissue than in the non-tumour tissue. There was no significant difference in salivary concentrations of γ-aminobutyric acid, glutamate or aspartate, comparing the involved and non-involved side.
The present results provide preliminary evidence that γ-aminobutyric acid may be involved in the growth of benign parotid tumours.
The Journal of Laryngology & Otology 12/2010; 125(5):492-6. DOI:10.1017/S0022215110002574 · 0.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, we investigated how midazolam and d-cycloserine regulate the tonic activity and/or phasic reactivity of brain neurotransmitter systems to fear-evoking stimuli in rats with varying intensities of a fear response. We used a new animal model composed of high (HR) and low (LR) anxiety rats, selected according to their behaviour in the contextual fear test (i.e., the duration of a freezing response was used as a discriminating variable). In these rats, we examined the effects of both drugs on the release of glutamate and GABA in the basolateral amygdala (BLA) during the first extinction trial of a conditioned fear test. The results showed that administration of d-cycloserine (15 mg/kg, i.p.) significantly enhanced the inhibition of an aversive context-induced freezing response observed during the extinction session in HR and LR rats. In contrast, midazolam (0.75 mg/kg, i.p.) accelerated the attenuation of fear responses only in HR rats. The less anxious behaviour of LR animals given saline was accompanied by elevated basal levels of glutamate in the BLA, in comparison with HR rats, and a stronger elevation of GABA in response to contextual fear. In HR animals, the pretreatment of rats with d-cycloserine and midazolam significantly increased the local concentration of GABA and inhibited the expression of contextual fear. These findings suggest that animals more vulnerable to stress have innate deficits in brain systems that control the activity of the BLA mediating the central effect of stress. These results contribute to our understanding of observed individual differences in the effects of anxiolytic drugs among patients with anxiety disorders.
Neurobiology of Learning and Memory 11/2010; 94(4):468-80. DOI:10.1016/j.nlm.2010.08.014 · 4.04 Impact Factor