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.

Neurobehavioral Profiles of Six Genetically-based Rat Models of Schizophrenia- related Symptoms.

Schizophrenia is a chronic and severe mental disorder with high heterogeneity in its symptoms clusters. The effectiveness of drug treatments for the disorder is far from satisfactory. It is widely accepted that research with valid animal models is essential if we aim at understanding its genetic/ neurobiological mechanisms and finding more effective treatments. The present article presents an overview of six genetically-based (selectively-bred) rat models/strains, which exhibit neurobehavioral schizophrenia-relevant features, i.e., the Apomorphine-susceptible (APO-SUS) rats, the Low-prepulse inhibition rats, the Brattleboro (BRAT) rats, the Spontaneously Hypertensive rats (SHR), the Wisket rats and the Roman High-Avoidance (RHA) rats. Strikingly, all the strains display impairments in prepulse inhibition of the startle response (PPI), which remarkably, in most cases are associated with novelty-induced hyperlocomotion, deficits of social behavior, impairment of latent inhibition and cognitive flexibility, or signs of impaired prefrontal cortex (PFC) function. However, only three of the strains share PPI deficits and dopaminergic (DAergic) psychostimulant-induced hyperlocomotion (together with prefrontal cortex dysfunction in two models, the APO-SUS and RHA), which points out that alterations of the mesolimbic DAergic circuit are a schizophrenia-linked trait that not all models reproduce, but it characterizes some strains that can be valid models of schizophrenia-relevant features and drug-addiction vulnerability (and thus, dual diagnosis). We conclude by putting the research based on these genetically-selected rat models in the context of the Research Domain Criteria (RDoC) framework, suggesting that RDoC-oriented research programs using selectively-bred strains might help to accelerate progress in the various aspects of the schizophrenia-related research agenda.

Acute Stress Induces Different Changes on the Expression of BDNF and trkB in the Mesocorticolimbic System of Two Lines of Rats Differing in Their Response to Stressors.

The present work was undertaken to investigate the effects of acute forced swimming (FS) on the levels of brain-derived neurotrophic factor (BDNF) and tyrosine kinase receptor B (trkB) proteins in: the ventral tegmental area (VTA); the nucleus accumbens (Acb) shell and core compartments; and the anterior cingulate (ACg), prelimbic (PL) and infralimbic (IL) territories of the prefrontal cortex of genetic models of vulnerability (RLA, Roman low-avoidance rats) and resistance (RHA, Roman high-avoidance rats) to stress-induced depression. We report for the first time that FS induced very rapid and distinct changes in the levels of BDNF and trkB proteins in different areas of the mesocorticolimbic system of RHA and RLA rats. Thus, (1) in the VTA and Acb core, FS elicited a significant increase of both BDNF- and trkB-LI in RHA but not RLA rats, whereas in the Acb shell no significant changes in BDNF- and trkB-LI across the line and treatment were observed; (2) in RLA rats, the basal levels of BDNF-LI in the IL/PL cortex and of trkB-LI in the ACg cortex were markedly lower than those of RHA rats; moreover, BDNF- and trkB-LI in the IL/PL and ACg cortex were increased by FS in RLA rats but decreased in their RHA counterparts. These results provide compelling evidence that the genetic background influences the effects of stress on BDNF/trkB signaling and support the view that the same stressor may impact differently on the expression of BDNF in discrete brain areas.

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 ΔFosB) and neural plasticity (Arc and BDNF/trkB), as determined either by Western Blot (BDNF, trkB, Arc, and ΔFosB) or immunohistochemistry (BDNF, trkB, Arc, and c-Fos), in the hippocampus 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 naïve 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 ΔFosB 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.

c-Fos, ΔFosB, BDNF, trkB and Arc Expression in the Limbic System of Male Roman High- and Low-Avoidance Rats that Show Differences in Sexual Behavior: Effect of Sexual Activity.

Male Roman High- (RHA) and Low-Avoidance (RLA) rats display significant differences in sexual behavior (RHA rats exhibit higher sexual motivation and better copulatory performance than RLA rats). These differences are very evident in sexually naïve rats (which copulate with a receptive female rat for the first time), and are still present, although reduced, after five copulatory tests, when sexual experience has been acquired. Since sexual activity is a natural reward that induces neural activation and synaptic plastic changes in limbic brain areas, we studied whether the differences in sexual activity between these rat lines are accompanied by changes in the expression of markers of neural activation and plasticity, i.e., c-Fos, ΔFosB (a truncated form of FosB), Brain-Derived Neurotrophic Factor (BDNF) and its tyrosine kinase receptor B (trkB) and Activity regulated cytoskeleton-associated (Arc) protein in the ventral tegmental area (VTA), nucleus accumbens (Acb) (core and shell) and medial prefrontal cortex (mPFC) of sexually naïve and experienced RHA and RLA rats by Western Blot and/or immunohistochemistry. This study shows that these markers changed differentially in the VTA, Acb and mPFC of RHA and RLA rats, after sexual activity. In both rat lines, the changes were very evident in naïve rats, tended to disappear in experienced rats and were higher in RHA than RLA rats. These findings confirm that sexual activity induces neural activation in limbic brain areas involved in motivation and reward, leading to changes in synaptic plasticity with sexual experience acquisition, and show that these depend on the animals' genotypic/phenotypic characteristics.

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.

Involvement of dopamine in the differences in sexual behaviour between Roman high and low avoidance rats: an intracerebral microdialysis study.

Outbred Roman high- (RHA) and low-avoidance (RLA) rats are selected for respectively rapid vs. poor acquisition of the active avoidance response and display different copulatory patterns when exposed to a sexually receptive female, with RHA rats showing more robust sexual motivation and better performance than RLA rats also after repeated sexual activity. Here we show that the distinct patterns of sexual behaviour of the Roman lines are correlated with differences in the activity of the dopaminergic mesolimbic system, which plays a key role in sexual motivation and copulatory performance. Thus, differential increases in the concentrations of dopamine and its main metabolite 3,4-dihydroxyphenylacetic acid, occurred in dialysates obtained from the nucleus accumbens shell of naïve and sexually experienced Roman rats during the anticipatory and consummatory phases of sexual activity. These differences were particularly evident between sexually naïve RHA and RLA rats and tended to diminish but still persisted between sexually experienced rats, as did the differences in sexual behaviour. Analysis of the biochemical and behavioural findings showed that, while in RHA rats sexual experience caused a shift in the changes in both the dopaminergic activity and copulation towards the first period of the sexual test, in RLA rats sexual experience increased dopaminergic activity and copulation throughout the entire test. Therefore, this study adds experimental support to the view that the different sexual patterns of the Roman lines are due, at least in part, to a more robust functional tone of the mesolimbic dopaminergic system of RHA rats.

Dopamine is involved in the different patterns of copulatory behaviour of Roman high and low avoidance rats: studies with apomorphine and haloperidol.

Outbred Roman high- (RHA) and low-avoidance (RLA) rats, originally selected for rapid vs. poor acquisition of active avoidance in a shuttle box, show differential copulatory patterns when exposed to a receptive female. Indeed, in the first copulation test male RHA rats show more mounts, intromissions and ejaculations than RLA rats. Such differences do not disappear in subsequent copulation tests, with sexually experienced RHA rats always showing higher levels of sexual motivation and performance than their RLA counterparts. This study shows that the different copulatory patterns of sexually experienced RHA and RLA rats are differentially facilitated by apomorphine, a mixed D1/D2-like dopamine receptor agonist, and impaired by haloperidol, a D2-like dopamine receptor antagonist, given at doses which facilitate and impair, respectively, copulatory behaviour in Sprague Dawley rats used as an external reference strain. Accordingly, apomorphine-induced facilitation and haloperidol-induced impairment of copulatory behaviour were more robust in RLA than RHA rats, as indicated by their effects on several copulatory parameters including mount, intromission and ejaculation latencies, mount, intromission and ejaculation frequencies, post ejaculatory interval, inter-intromission interval and copulatory efficacy. Pretreatment with haloperidol also reduced the facilitatory effect of apomorphine more effectively in RLA than RHA rats. These results suggest that the different copulatory patterns of RHA and RLA rats are mainly due to a lower dopaminergic tone at level of the mesolimbic and incerto-hypothalamic dopaminergic systems of RLA vs. RHA rats, which play a key role in sexual behaviour.

Male Roman high and low avoidance rats show different patterns of copulatory behaviour: comparison with Sprague Dawley rats.

Roman high- (RHA) and low-avoidance (RLA) rats, selectively bred for, respectively, rapid vs. extremely poor acquisition of avoidant behaviour in the shuttle-box, display different coping strategies when exposed to aversive environmental conditions: RLA rats are reactive copers and show hyperemotional behaviour characterized by hypomotility and freezing, while RHA rats show a proactive coping behaviour aimed at gaining control over the stressor. RHA rats also display a robust sensation/novelty seeking profile, high baseline levels of impulsivity, and marked preference for, and intake of, natural and drug rewards. This study shows that the Roman lines also differ in sexual behaviour, a main source of natural reward. Thus, male RHA rats engaged in copulatory activity with a receptive female showing more mounts, intromissions and ejaculations in the first copulation test as compared with their RLA counterparts and Sprague Dawley rats used as an external reference strain. Such differences decreased only partially in subsequent copulation tests, with RHA rats always showing higher levels of sexual motivation and performance than RLA rats. Accordingly, analysis of copulatory parameters of five copulation tests performed at 3-day intervals confirmed that the Roman lines display different patterns of copulatory activity that persist after stabilization of copulatory behaviour by sexual experience. Finally, the weight of the testes, epididymides and seminal vesicles increased to a similar extent in both Roman lines after sexual activity. These results are discussed in terms of the relative contribution of differences in brain neurotransmission (mainly dopamine) and neuroendocrine function to the different patterns of copulatory behaviour of the Roman lines.

Dopamine agonist-induced penile erection and yawning: a comparative study in outbred Roman high- and low-avoidance rats.

The effects on penile erection and yawning of subcutaneous (SC) injections of the mixed dopamine D1/D2-like agonist apomorphine (0.02-0.2 mg/kg) were studied in outbred Roman high- (RHA) and low-avoidance (RLA) male rats, two lines selectively bred for their respectively rapid versus poor acquisition of the active avoidance response in the shuttle-box, and compared with the effects observed in male Sprague-Dawley (SD) rats. Apomorphine dose-response curves were bell-shaped in all rat lines/strains. Notably, more penile erections and yawns were recorded mainly in the ascending part of these curves (e.g., apomorphine 0.02-0.08 mg/kg) in both RLA and RHA rats compared to SD rats, with RLA rats showing the higher response (especially for yawning) with respect to RHA rats. Similar results were found with PD-168,077 (0.02-0.2 mg/kg SC), a D4 receptor agonist, which induced penile erection but not yawning. In all rat lines/strains, apomorphine responses were markedly reduced by the D2 antagonist L-741,626, but not by the D3 antagonist, SB277011A, whereas the D4 antagonists L-745,870 and FAUC213 elicited a partial, yet statistically significant, inhibitory effect. In contrast, the pro-erectile effect of PD-168,077 was completely abolished by L-745,870 and FAUC213, as expected. The present study confirms and extends previously reported differences in dopamine transmission between RLA and RHA rats and between the SD strain and the Roman lines. Moreover, it confirms previous studies supporting the view that dopamine receptors of the D2 subtype play a predominant role in the pro-yawning and pro-erectile effect of apomorphine, and that the selective stimulation of D4 receptors induces penile erection.