Differential effects of voluntary ethanol consumption on dopamine output in the nucleus accumbens shell of Roman high- and low-Avoidance rats: A behavioral and brain microdialysis study

The Roman high- (RHA) and low-Avoidance (RLA) rats were selectively bred for rapid vs poor acquisition of two-way active avoidance behavior. These lines differ in numerous behavioral traits, with RLA rats being more fearful/anxious than RHA rats, and the latter being novelty-seekers and showing larger intake of, and preference for, addictive substances including ethanol (ETH). Moreover, several differences in central dopaminergic, serotonergic, and GABAergic functions have been reported in these two lines. Since those neural systems are involved in the regulation of ETH consumption, it was considered of interest to investigate: 1) the differences in ETH intake and preference between RHA and RLA rats, 2) the effects of ETH on DA release in the shell of the nucleus accumbens (AcbSh) using brain microdialysis. ETH solutions of increasing concentrations (2%- 10%) were presented on alternate days in a free choice with water. To examine ETH intake and preference stability, animals were subsequently switched to daily presentations of 10% ETH for 10 consecutive days. RHA rats consumed significantly larger amounts of ETH and displayed higher ETH preference than did RLA rats throughout the acquisition and maintenance phases. Following chronic exposure to ETH the animals were habituated to a restricted access to ETH schedule (2% ETH, 2 h per day × 4 days) before surgical implantation of a dialysis probe in the AcbSh. Under these experimental conditions, voluntary ETH intake (2%, 1 h, p.o.) produced a significant increase in accumbal DA output in RHA rats but not in their RLA counterparts. Finally, the i.p. administration of ETH (0.25 g/kg) to naïve Roman rats produced a significant increment in accumbal DA output only in RHA rats. These results indicate that the mesolimbic dopaminergic system of RHA rats is more responsive to the effects of ETH than that of RLA rats

differential effects of voluntary ethanol consumption on dopamine output in the nucleus accumbens shell of roman high and low avoidance rats a behavioral and brain microdialysis study

The Roman high(RHA) and low-Avoidance (RLA) rats were selectively bred for rapid vs poor acquisition of two-way active avoidance behavior. These lines differ in numerous behavioral traits, with RLA rats being more fearful/anxious than RHA rats, and the latter being novelty-seekers and showing larger intake of, and preference for, addictive substances including ethanol (ETH). Moreover, several differences in central dopaminergic, serotonergic, and GABAergic functions have been reported in these two lines. Since those neural systems are involved in the regulation of ETH consumption, it was considered of interest to investigate: 1) the differences in ETH intake and preference between RHA and RLA rats, 2) the effects of ETH on DA release in the shell of the nucleus accumbens (AcbSh) using brain microdialysis. ETH solutions of increasing concentrations (2% - 10%) were presented on alternate days in a free choice with water. To examine ETH intake and preference stability, animals were subsequently switched to daily presentations of 10% ETH for 10 consecutive days. RHA rats consumed significantly larger amounts of ETH and displayed higher ETH preference than did RLA rats throughout the acquisition and maintenance phases. Following chronic exposure to ETH the animals were habituated to a restricted access to ETH schedule (2% ETH, 2 h per day × 4 days) before surgical implantation of a dialysis probe in the AcbSh. Under these experimental conditions, voluntary ETH intake (2%, 1 h, p.o.) produced a significant increase in accumbal DA output in RHA rats but not in their RLA counterparts. Finally, the i.p. administration of ETH (0.25 g/kg) to na?ve Roman rats produced a significant increment in accumbal DA output only in RHA rats. These results indicate that the mesolimbic dopaminergic system of RHA rats is more responsive to the effects of ETH than that of RLA rats

Effects of Tail Pinch on BDNF and trkB Expression in the Hippocampus of Roman Low- (RLA) and High-Avoidance (RHA) Rats

In this article, we describe the effects of tail pinch (TP), a mild acute stressor, on the levels of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor B (trkB) proteins in the hippocampus (HC) of the outbred Roman High- (RHA) and Low-Avoidance (RLA) rats, one of the most validated genetic models for the study of fear/anxiety- and stress-related behaviors. Using Western blot (WB) and immunohistochemistry assays, we show for the first time that TP induces distinct changes in the levels of BDNF and trkB proteins in the dorsal (dHC) and ventral (vHC) HC of RHA and RLA rats. The WB assays showed that TP increases BDNF and trkB levels in the dHC of both lines but induces opposite changes in the vHC, decreasing BDNF levels in RHA rats and trkB levels in RLA rats. These results suggest that TP may enhance plastic events in the dHC and hinder them in the vHC. Immunohistochemical assays, carried out in parallel to assess the location of changes revealed by the WB, showed that, in the dHC, TP increases BDNF-like immunoreactivity (LI) in the CA2 sector of the Ammon's horn of both Roman lines and in the CA3 sector of the Ammon's horn of RLA rats while, in the dentate gyrus (DG), TP increases trkB-LI in RHA rats. In contrast, in the vHC, TP elicits only a few changes, represented by decreases of BDNF- and trkB-LI in the CA1 sector of the Ammon's horn of RHA rats. These results support the view that the genotypic/phenotypic features of the experimental subjects influence the effects of an acute stressor, even as mild as TP, on the basal BDNF/trkB signaling, leading to different changes in the dorsal and ventral subdivisions of the HC

Dopamine, Noradrenaline and Differences in Sexual Behavior between Roman High and Low Avoidance Male Rats: A Microdialysis Study in the Medial Prefrontal Cortex

Roman High- (RHA) and Low-Avoidance (RLA) outbred rats, which differ for a respectively rapid vs. poor acquisition of the active avoidance response in the shuttle-box, display differences in sexual activity when put in the presence of a sexually receptive female rat. Indeed RHA rats show higher levels of sexual motivation and copulatory performance than RLA rats, which persist also after repeated sexual activity. These differences have been correlated to a higher tone of the mesolimbic dopaminergic system of RHA rats vs. RLA rats, revealed by the higher increase of dopamine found in the dialysate obtained from the nucleus accumbens of RHA than RLA rats during sexual activity. This work shows that extracellular dopamine and noradrenaline (NA) also, increase in the dialysate from the medial prefrontal cortex (mPFC) of male RHA and RLA rats put in the presence of an inaccessible female rat and more markedly during direct sexual interaction. Such increases in dopamine (and its main metabolite 3,4-dihydroxyphenylacetic acid, DOPAC) and NA were found in both sexually naïve and experienced animals, but they were higher: (i) in RHA than in RLA rats; and (ii) in sexually experienced RHA and RLA rats than in their naïve counterparts. Finally, the differences in dopamine and NA in the mPFC occurred concomitantly to those in sexual activity, as RHA rats displayed higher levels of sexual motivation and copulatory performance than RLA rats in both the sexually naïve and experienced conditions. These results suggest that a higher dopaminergic tone also occurs in the mPFC, together with an increased noradrenergic tone, which may be involved in the different copulatory patterns found in RHA and RLA rats, as suggested for the mesolimbic dopaminergic system

Prepulse inhibition predicts spatial working memory performance in the inbred Roman high- and low-avoidance rats and in genetically heterogeneous NIH-HS rats: relevance for studying pre-attentive and cognitive anomalies in schizophrenia

Animal models of schizophrenia-relevant symptoms are increasingly important for progress in our understanding of the neurobiological basis of the disorder and for discovering novel and more specific treatments. Prepulse inhibition (PPI) and working memory, which are impaired in schizophrenic patients, are among the symptoms/processes modeled in those animal analogues. We have evaluated whether a genetically-selected rat model, the Roman high-avoidance inbred strain (RHA-I), displays PPI deficits as compared with its Roman low-avoidance (RLA-I) counterpart and the genetically heterogeneous NIH-HS rat stock. We have investigated whether PPI deficits predict spatial working memory impairments (in the Morris water maze; MWM) in these three rat types (Experiment 1), as well as in a separate sample of NIH-HS rats stratified according to their extreme (High, Medium, Low) PPI scores (Experiment 2). The results from Exp. 1 show that RHA-I rats display PPI and spatial working memory deficits compared to both RLA-I and NIH-HS rats. Likewise, in Exp. 2, “Low-PPI” NIH-HS rats present significantly impaired working memory with respect to “Medium-PPI” and “High-PPI” NIH-HS subgroups. Further support to these results comes from correlational, factorial and multiple regression analyses, which reveal that PPI is positively associated with spatial working memory performance. Conversely, cued learning in the MWM was not associated with PPI.Thus, using genetically-selected and genetically heterogeneous rats, the present study shows, for the first time, that PPI is a positive predictor of performance in a spatial working memory task. These results may have translational value for schizophrenia symptom research in humans, as they suggest that either by psychogenetic selection or by focusing on extreme PPI scores from a genetically heterogeneous rat stock, it is possible to detect a useful (perhaps “at risk”) phenotype to study cognitive anomalies linked to schizophrenia

Effects of forced swimming stress on ERK and histone H3 phosphorylation in limbic areas of Roman high-and low-avoidance rats

Stressful events evoke molecular adaptations of neural circuits through chromatin remodeling and regulation of gene expression. However, the identity of the molecular pathways activated by stress in experimental models of depression is not fully understood. We investigated the effect of acute forced swimming (FS) on the phosphorylation of the extracellular signal-regulated kinase (ERK)1/2 (pERK) and histone H3 (pH3) in limbic brain areas of genetic models of vulnerability (RLA, Roman low-avoidance rats) and resistance (RHA, Roman high-avoidance rats) to stress-induced depression-like behavior. We demonstrate that FS markedly increased the density of pERK-positive neurons in the infralimbic (ILCx) and the prelimbic area (PrLCx) of the prefrontal cortex (PFCx), the nucleus accumbens, and the dorsal blade of the hippocampal dentate gyrus to the same extent in RLA and RHA rats. In addition, FS induced a significant increase in the intensity of pERK immunoreactivity (IR) in neurons of the PFCx in both rat lines. However, RHA rats showed stronger pERK-IR than RLA rats in the ILCx both under basal and stressed conditions. Moreover, the density of pH3-positive neurons was equally increased by FS in the PFCx of both rat lines. Interestingly, pH3-IR was higher in RHA than RLA rats in PrLCx and ILCx, either under basal conditions or upon FS. Finally, colocalization analysis showed that in the PFCx of both rat lines, almost all pERK-positive cells express pH3, whereas only 50% of the pH3-positive neurons is also pERK-positive. Moreover, FS increased the percentage of neurons that express exclusively pH3, but reduced the percentage of cells expressing exclusively pERK. These results suggest that (i) the distinctive patterns of FS-induced ERK and H3 phosphorylation in the PFCx of RHA and RLA rats may represent molecular signatures of the behavioural traits that distinguish the two lines and (ii) FS-induced H3 phosphorylation is, at least in part, ERK-independent

Neuroplastic changes in c-Fos, ΔFosB, BDNF, trkB, and Arc expression in the hippocampus of male Roman rats: differential effects of sexual activity

Sexual activity causes differential changes in the expression of markers of neural activation (c-Fos and Delta FosB) and neural plasticity (Arc and BDNF/trkB), as determined either by Western Blot (BDNF, trkB, Arc, and Delta FosB) or immunohistochemistry (BDNF, trkB, Arc, and c-Fos), in the hippocam pus of male Roman high (RHA) and low avoidance (RLA) rats, two psychogenetically selected rat lines that display marked differences in sexual behavior (RHA rats exhibit higher sexual motivation and better copulatory performance than RLA rats). Both methods showed (with some differences) that sexual activity modifies the expression levels of these markers in the hippocampus of Roman rats depending on: (i) the level of sexual experience, that is, changes were usually more evident in sexually naive than in experienced rats; (ii) the hippocampal partition, that is, BDNF and Arc increased in the dorsal but tended to decrease in the ventral hippocampus; (iii) the marker considered, that is, in sexually experienced animals BDNF, c-Fos, and Arc levels were similar to those of controls, while Delta FosB levels increased; and (iv) the rat line, that is, changes were usually larger in RHA than RLA rats. These findings resemble those of early studies in RHA and RLA rats showing that sexual activity influences the expression of these markers in the nucleus accumbens, medial prefrontal cortex, and ventral tegmental area, and show for the first time that also in the hippocampus sexual activity induces neural activation and plasticity, events that occur mainly during the first phase of the acquisition of sexual experience and depend on the genotypic/phenotypic characteristics of the animals

I ratti delle linee Roman (High e Low Avoidance) presentano differenze nel comportamento sessuale: ruolo del sistema dopaminergico mesolimbico

I RATTI DELLE LINEE ROMAN (HIGH E LOW AVOIDANCE) PRESENTANO DIFFERENZE NEL COMPORTAMENTO SESSUALE: RUOLO DEL SISTEMA DOPAMINERGICO MESOLIMBICO. Introduzione. I ratti delle linee Roman (RHA, High avoidance e RLA, Low avoidance) mostrano tratti comportamentali divergenti: i primi sono impulsivi e proni all’abuso di sostanze mentre i secondi sono iper-emotivi e proni a sviluppare sintomi depressivi. I ratti Roman differiscono anche nel comportamento sessuale: gli RHA, infatti, mostrano una maggiore motivazione e migliori prestazioni rispetto agli RLA. L’obiettivo di questo studio era indagare se queste differenze sono relate ad alterazioni nella funzione del sistema dopaminergico mesolimbico, che gioca un ruolo chiave nel comportamento motivato. Metodi. Sono stati misurati con la metodica della microdialisi intracerebrale i livelli di dopamina liberata nel nucleo accumbens di ratti RHA e RLA mai esposti prima a stimoli sessuali (naïve) oppure esperienti, quando esposti ad una femmina recettiva inaccessibile e durante la copula. Contemporaneamente, sono stati misurati diversi indici comportamentali motivazionali e di performance sessuale. L’analisi statistica è stata eseguita con ANOVA per disegni misti, seguita da test post hoc (P < 0.05). Risultati. Nei ratti RHA si riscontra una maggiore liberazione di dopamina nel nucleo accumbens rispetto ai ratti RLA sia in presenza di una femmina recettiva inaccessibile che durante l’interazione sessuale. Similmente a quanto osservato con i parametri comportamentali, le differenze sono maggiori tra i gruppi naïve, tendono a diminuire tra i gruppi esperienti, ma persistono anche dopo stabilizzazione del comportamento dovuta all’esperienza. Conclusioni. Le differenze di comportamento sessuale delle linee Roman possono essere dovute al differente tono funzionale del sistema dopaminergico mesolimbico, che nei ratti RLA appare più debole rispetto ai ratti RHA. Questa differente funzione del sistema dopaminergico mesolimbico può essere implicata anche nelle alterazioni presenti in altri aspetti del comportamento motivato di questi animali (ad es., assunzione di sostanze d’abuso, vulnerabilità alla depressione)

Immunochemical detection of BDNF in the brain of a rat model of depression

Several lines of evidence show a relationship between alterations in the mechanisms that control the expression of neurotrophic factors and mood disorders (1). In particular, support for the role of brain-derived neurotrophic factor (BDNF) in the pathogenesis of depression and related deficits in neuronal plasticity comes from evidence that a reduction of BDNF expression has been found in postmortem brains and serum of depressed subjects and that the BDNF gene is required for the response to antidepressant drugs. With the aim to contribute to the characterization of the molecular and neuronal systems involved in the pathogenesis of depression and in the mechanism of action of the antidepressant treatments, here we use the outbread Roman High- (RHA) and Roman Low-Avoidance (RLA) rat lines, psychogenetically selected for rapid versus poor acquisition of active avoidance, respectively, and bearing several behavioral characteristics closely resembling the cardinal symptoms of depression (2), to investigate on the immunochemical occurrence of BDNF in selected areas of the RHA and RLA rat brain by means of western blot (WB) and immunohistochemistry. WB analysis indicates that the relative levels of BDNF patently and markedly differed in the hippocampus, where they were significantly lower by 58% in RLA vs RHA rats (p = 0.0014). In the remaining examined areas, namely the prefrontal cortex, the caudate-putamen complex proper, the core and shell regions of the nucleus accumbens and the ventral tegmental area, the relative BDNF levels did not show statistically significant differences. In tissue sections, BDNF-like immunoreactive (LI) material labelled neuronal cell bodies, proximal processes and varicose nerve fibers, with an uneven distribution in telencephalic cerebral cortex, hippocampus, amygdala, nucleus accumbens, caudate-putamen complex proper, thalamus and ventral tegmentum of the midbrain. Densitometric analysis of immunostained brain sections were used to quantify differences among the two rat lines. The results obtained provide a morphological evidence for a differential expression of BDNF in specific areas of RLA vs RHA rat brains and may form the morphological basis to understand the regulation of the trophic machinery in depression

Immunochemical detection of trkB receptor in the brain of a rat model of depression

The outbread Roman High- (RHA) and Roman Low-Avoidance (RLA) rat lines were psychogenetically selected for rapid versus poor acquisition of active avoidance, respectively, and differ in many behavioural traits that closely resemble the cardinal symptoms of depression (1). Beyond the monoamine hypothesis of depression, compelling evidence suggests that mood disorders are characterized by reduced neuronal plasticity. Consistently, it has been shown that exposure to stress and antidepressant treatment modulate the expression of neurotrophic molecules and their relevant receptors, and that these changes show an anatomical specificity (2). With the aim to characterize the molecular and neuronal systems involved in the pathogenesis of depression and in the mechanism of action of the antidepressant treatments, here we investigate on the immunochemical occurrence of trkB, the high affinity tyrosinekinase receptor for brain-derived neurotrophic factor (BDNF), in selected areas of the RHA and RLA rat brain by means of western blot (WB) and immunohistochemistry. WB analysis indicates that the relative levels of trkB patently and markedly differed in the prefrontal cortex and the hippocampus, where they were lower in RLA vs RHA rats, and in the caudate-putamen complex proper where, by contrast, they were higher in RLA vs RHA rats. No statistically significant differences were seen in nucleus accumbens and ventral tegmental area. In tissue sections, trkB-like immunoreactive (LI) labelling was mainly localized to neuronal cell bodies and proximal processes, unevenly distributed in the telencephalic cerebral cortex, the hippocampus, and the ventral tegmentum of the midbrain. Densitometric analysis of immunostained brain sections revealed that differences among the two groups are consistent to a good extent with WB data. As a whole, the finding of a different expression of trkB receptor in the RLA vs RHA rat brains implies the occurrence of an altered neuronal responsiveness to BDNF in specific brain regions and may contribute to outline the molecular and morphological basis for the distinct vulnerability to depression in the two rat lines