Thomas Roskoden

Anxiety-related behavior and densities of glutamate, GABAA, acetylcholine and serotonin receptors in the amygdala of seven inbred mouse strains

The amygdala is a brain region involved in the regulation of anxiety-related behavior. The purpose of this study was to correlate anxiety-related behavior of inbred mouse strains (BA//c, BALB/cJ, C3H/HeJ, C57BL/6J, CPB-K, DBA/2J, NMRI) to receptor binding in the amygdala. Binding site densities of receptors (NMDA, AMPA, kainate, GABA(A), serotonin, muscarinergic M(1)-M(2)) were measured with quantitative receptor autoradiography using tritiated ligands. Measurements of fear-sensitized acoustic startle response (ASR; induced by footshocks), elevated plus maze (EPM) behavior and receptor binding studies showed differences between the strains except for AMPA and muscarinergic M(2) receptors. Factor analysis revealed a Startle Factor with positive loadings of the density of serotonin and kainate receptors, and the amplitudes of the baseline and fear-sensitized ASRs. A second Anxiety-related Factor only correlated with the fear-sensitized ASR and anxiety parameters on the EPM but not receptor densities. There were also two General Activity Factors defined by (negative) correlations with entries to closed arms of the EPM. Because the density of NMDA and muscarinergic M(1) receptors also correlated negatively with the two factors, these receptors had a positive effect on general activity. In contrast, correlations of GABA(A), serotonin, and kainate receptors had the opposite sign as compared to closed arm entries. It is concluded that hereditary variations in the amygdala, particularly in kainate and serotonin receptors, play a role for the baseline and fear-sensitized ASR, whereas the general activity is influenced by many neurotransmitter receptor systems.

Risperidone and haloperidol promote survival of stem cells in the rat hippocampus

Altered neuroplasticity contributes to the pathophysiology of schizophrenia. However, the idea that antipsychotics may act, at least in part, by normalizing neurogenesis has not been consistently supported. Our study seeks to determine whether hippocampal cell proliferation is altered in adult rats pretreated with ketamine, a validated model of schizophrenia, and whether chronic administration with neuroleptic drugs (haloperidol and risperidone) affect changes of cell genesis/survival. Ketamine per se has no effect on cell proliferation. Its withdrawal, however, significantly induced cell proliferation/survival in the hippocampus. Risperidone and haloperidol supported cell genesis/survival as well. During ketamine withdrawal, however, their application did not affect cell proliferation/survival additionally. TUNEL staining indicated a cell-protective potency of both neuroleptics with respect to a ketamine-induced cell death. As RT-PCR and Western blot revealed that the treatment effects of risperidone and haloperidol seemed to be mediated through activation of VEGF and MMP2. The mRNA expression of NGF, BDNF, and NT3 was unaffected. From the respective receptors, only TrkA was enhanced when ketamine withdrawal was combined with risperidone or haloperidol. Risperidone also induced BCL-2. Ketamine withdrawal has no effect on the expression of VEGF, MMP2, or BCL-2. It activated the expression of BDNF. This effect was normalized by risperidone or haloperidol. The findings indicate a promoting effect of risperidone and haloperidol on survival of young neurons in the hippocampus by enhancing the expression of the anti-apoptotic protein BCL-2 and by activation of VEGF/MMP2, whereby an interference with ketamine and thus a priority role of the NMDA system was not evident.

Modulation of mRNA expression of the neurotrophins of the nerve growth factor family and their receptors in the septum and hippocampus of rats after transient postnatal thyroxine treatment I. Expression of nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, and neurotrophin 4 mRNA

Abstract Early postnatal application of thyroid hormones to rats results in morphological changes of the septo-hippocampal cholinergic and the hippocampal mossy fiber systems. Modulation in the expression of either neurotrophins and/or their receptors is postulated to be involved in these effects. In a recent study, we showed that, after thyroxine application, the mRNA expression of neurotrophins of the nerve-growth-factor (NGF) family is significantly upregulated both in septum and hippocampus. To test whether the neurotrophin receptors (the low-affinity neurotrophin receptor p75 and the specific high-affinity receptors trkA, trkB, and trkC) were also affected by hormone administration, newborn rats were treated daily with subcutaneous injections of thyroxine until postnatal day 12 (P12) at latest. Control animals received corresponding injections of saline. The pups were sacrificed at defined intervals from P9 to P14. The septal areas and the hippocampi were analyzed using the reverse-transcription polymerase chain reaction (RT-PCR) method for quantification of p75, trkA, trkB, and trkC mRNA levels. Analysis of variance over the total investigation period revealed no significant general increases of the gene expressions of either neurotrophin receptor, neither in the septum nor in the hippocampus, although previous results have shown marked changes in neurotrophin levels. On particular postnatal days, significant upregulation could be observed in hippocampus for trkB and trkC. From these and recent data, we conclude that modulation of neurotrophin expression rather than neurotrophin-receptor expression contributes to the morphological modifications within the hippocampal mossy fiber system and the septo-hippocampal cholinergic system.

Early postnatal corticosterone administration regulates neurotrophins and their receptors in septum and hippocampus of the rat

The principal glucocorticoid in rats, corticosterone, interacts with neurons in the limbic system and leads to morphological and behavioral changes. Putative corticosterone-triggered mediators are neurotrophins. In the present study we investigated the effects of early postnatal corticosterone treatment in rats on neurotrophic factors of the nerve growth factor (NGF) family and their receptors. Newborn rats were treated with corticosterone-containing polymers until postnatal day 12. The mRNA and protein levels of the neurotrophins of the NGF family (NGF, BDNF, NT-3 and NT-4/5) and their receptors (trkA, trkB, trkC and p75) were quantified in septum and hippocampus using RT-PCR. In the septal region, we found an unchanged mRNA expression after corticosterone treatment, whereas in the hippocampus there was a general increase in mRNA. Particularly, the gene expression of NGF, NT-3, and the high affinity receptors trkA, trkB and trkC increased significantly. Quantification of the neurotrophin protein levels using an ELISA revealed significant treatment effects for NGF and NT-4/5 in the hippocampus. The present study of corticosterone treatment in young rats demonstrates interactions of steroid hormones with neurotrophic factors and their receptors in the septo-hippocampal system during the first two postnatal weeks.

Effect of early thyroxine treatment on brain-derived neurotrophic factor mRNA expression and protein amount in the rat medial septum/diagonal band of Broca

There is evidence that morphological alterations concerning deficiency or abundance of thyroid hormones (TH) may be mediated by brain-derived neurotrophic factor (BDNF). It has been demonstrated that the mRNA-expression of BDNF is increased after TH-treatment during the first postnatal weeks. After transient treatment of newborn rats with thyroxine mRNA expression, protein concentration and number and size of BDNF-immunopositive neurons were quantified in the medial septum/vertical diagonal Band of Broca (MS/vDB). The number and size of BDNF-immunopositive neurons were estimated in young (P10) and adult (4 months). The amount of mRNA and protein are significantly increased in TH-treated rats at P10 compared to control animals. TH-treated animals showed a significant decrease of BDNF-immunopositive cell numbers in the adulthood. The results demonstrate a correlated increase of BDNF mRNA and protein in the septum at P10 which is an important stage of differentiation processes in the septohippocampal system. These results provide further evidence that BDNF is a possible candidate for the mediation the TH effects in the MS/vDB.

Transient early postnatal corticosterone treatment of rats leads to accelerated aquisition of a spatial radial maze task and morphological changes in the septohippocampal region

In the present study new-born rats were treated with corticosterone (CORT) between postnatal days 1 and 12. At the age of 16-20 weeks, these animals were tested for spatial learning capacity using an eight-arm radial maze. After behavioral testing, density of cholinergic fibers and sizes of the mossy fiber terminal fields in the hippocampus and number of cholinergic and GABAergic neurons in the septal area were quantified. In the radial arm maze CORT-treated animals initially showed better working memory performance than controls. However, control animals showed a significant improvement of spatial working memory in the last trials and reached similar working memory scores as compared to treated animals. At neither day of training differences in reference memory errors were found between groups. In the diagonal band of Broca, both numbers of cholinergic and GABAergic neurons were increased after corticosterone treatment. The fiber systems in hippocampus showed no significant differences between groups. In conclusion, early postnatal stress induced by CORT administration in neonatal rats results in mild, yet significant morphological and behavioral changes in later life.

Expression of mRNA of Neurotrophic Factors and their Receptors are Significantly Altered After Subchronic Ketamine Treatment

The neurotrophic factors play an important role in the maintenance of neurone viability and neuronal communication which are considered to be altered in schizophrenia. Subchronic application of ketamine (Ket) was found to be a useful model in schizophrenia research. To further validate this model the mRNA levels of neurotrophic factors NGF, NT-3, and BDNF and their receptors TrkA, TrkB, and TrkC, respectively, were measured in different brain areas in Ket-pretreated rats subchronically dosed with the atypical antipsychotic drug risperidone (Ris). With the exception of NGF in the frontal cortex, Ket pretreatment did change NGF, NT-3, and BDNF mRNA levels in the frontal cortex, the hippocampus, the striatum, the thalamus/hypothalamus region, and in the cerebellum. These changes correspond with changes at their tyrosine kinase receptors. Ris treatment normalised altered NT-3 levels in the hippocampus and balanced BDNF levels in the same structure. It was concluded that the Ket model might reflect distinct alterations in neurotrophic factor activity as found in schizophrenic patients and, moreover, that Ris treatment rebalances disturbed neurotrophic factor activity.

A Jacob/Nsmf Gene Knockout Results in Hippocampal Dysplasia and Impaired BDNF Signaling in Dendritogenesis.

Jacob, the protein encoded by the Nsmf gene, is involved in synapto-nuclear signaling and docks an N-Methyl-D-Aspartate receptor (NMDAR)-derived signalosome to nuclear target sites like the transcription factor cAMP-response-element-binding protein (CREB). Several reports indicate that mutations in NSMF are related to Kallmann syndrome (KS), a neurodevelopmental disorder characterized by idiopathic hypogonadotropic hypogonadism (IHH) associated with anosmia or hyposmia. It has also been reported that a protein knockdown results in migration deficits of Gonadotropin-releasing hormone (GnRH) positive neurons from the olfactory bulb to the hypothalamus during early neuronal development. Here we show that mice that are constitutively deficient for the Nsmf gene do not present phenotypic characteristics related to KS. Instead, these mice exhibit hippocampal dysplasia with a reduced number of synapses and simplification of dendrites, reduced hippocampal long-term potentiation (LTP) at CA1 synapses and deficits in hippocampus-dependent learning. Brain-derived neurotrophic factor (BDNF) activation of CREB-activated gene expression plays a documented role in hippocampal CA1 synapse and dendrite formation. We found that BDNF induces the nuclear translocation of Jacob in an NMDAR-dependent manner in early development, which results in increased phosphorylation of CREB and enhanced CREB-dependent Bdnf gene transcription. Nsmf knockout (ko) mice show reduced hippocampal Bdnf mRNA and protein levels as well as reduced pCREB levels during dendritogenesis. Moreover, BDNF application can rescue the morphological deficits in hippocampal pyramidal neurons devoid of Jacob. Taken together, the data suggest that the absence of Jacob in early development interrupts a positive feedback loop between BDNF signaling, subsequent nuclear import of Jacob, activation of CREB and enhanced Bdnf gene transcription, ultimately leading to hippocampal dysplasia.

Species-relevant inescapable stress differently influences memory consolidation and retrieval of mice in a spatial radial arm maze

Stress affects learning and there are both facilitating and impairing actions of stressors on memory processes. Here we investigated the influence of acute exposure to 2,5-dihydro-2,4,5-trimethylthiazoline (TMT), an ethological relevant stressor for rodents, on spatial memory formation and performance in a radial arm maze (RAM) task and studied TMT effects on corticosterone levels in GAD67-GFP knock-in mice and their wildtype littermates. Our results suggest that predator odor-exposure differently affects consolidation and retrieval of memory in a hippocampus-dependent spatial learning task in adult male mice, independently from their genotypes. Acute TMT-stress before retrieval facilitates performance, whereas repeated TMT-stress during consolidation exerts no influence. Additionally, we found genotype specific effects of TMT on corticosterone release. While TMT-stress tend to result in increased corticosterone release in wildtypes there was a significant decrease in transgenic mice. Taken together, these findings indicate that biologically significant predator odor-induced stress can have different actions on the strength of spatial memory formation depending on the timing with regard to memory phases. Furthermore, we suppose an impact of GABAergic mechanisms on HPA-stress axis activation to TMT resulting in absent peripheral corticosterone release of GAD67-GFP mice.

Reduced number of CRF-containing neurons in the central amygdala correlated with enhanced locomotor activity following early postnatal corticosterone treatment in the Wistar rat

In the present study, newborn rats were implanted with corticosterone (CORT) containing polymers at postnatal day 0 (releasing rate 320-80 microg CORT/kg body weight and day). Controls received a CORT-free implant. All implants were removed at postnatal day 12. At the age of 16-20 weeks, these animals were tested for emotional behavior using an elevated plus-maze and fear-sensitized acoustic startle response. On the elevated plus-maze significant differences were found between hormone treated and control animals. The CORT-group demonstrated higher numbers of entries into closed arms and all arms, and the time spent in the center of the maze was significantly enhanced. Hormone-treated and control rats showed a significant fear sensitization of the acoustic startle response. However, no significant differences were observed between the two groups. The number of CRF-immunopositive neurons in the central nucleus of the amygdala was decreased after CORT treatment, whereas the number of NPY-immunopositive neurons and total number of neurons in the amygdala did not differ significantly between both groups. In conclusion, early postnatal stress induced by CORT administration in neonatal rats led to a higher locomotor activity correlated with changes in the number of CRF containing neurons in the central nucleus of the amygdala.