Ethanol consumption and serotonin-1A (5-HT1A) receptor function in heterozygous BDNF (+/-) mice

Heterozygous brain-derived neurotrophic factor (BDNF) (+/-) mice display abnormalities in central serotonergic neurotransmission, develop decrements in serotonergic innervation of the forebrain, and exhibit enhanced intermale aggressiveness. As disturbances of serotonin neurotransmission are implicated in alcohol abuse and aggression, we have examined in BDNF (+/-) mice alcohol drinking behavior, as well as central 5-hydroxytryptamine (5-HT)1A receptor function at the level of 5-HT1A receptor-G protein interaction. BDNF (+/-) mice displayed increased ethanol intake in a two-bottle choice procedure. There was no difference in the preference ratio for non-alcoholic tastants (i.e. quinine or saccharin) between genotypes. In the brains of alcohol-naive mice, we measured [35S]GTP gamma S binding stimulated by the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-dipropyl-aminotetralin hydrobromide (8-OH-DPAT; 1 microM). In BDNF (+/-) versus wild-type (WT) mice, 5-HT1A receptor-stimulated [35S]GTP gamma S binding was significantly attenuated in the median raphe nucleus. There was a decrease in (+/-)8-OH-DPAT-stimulated [35S]GTP gamma S binding in the dorsal raphe, which did not reach statistical significance. In the hippocampus, 5-HT1A receptor-stimulated [35S]GTP gamma S binding was significantly attenuated in BDNF (+/-) mice. 5-HT1A receptor-stimulated [35S]GTP gamma S binding was attenuated in the anterior cingulate cortex and lateral septum, although these reductions did not reach statistical significance. 5-HT1A receptor number was not different between genotypes in any area of brain examined, suggesting that 5-HT1A receptor function, specifically the capacity of the 5-HT1A receptor to activate G proteins, is attenuated in BDNF (+/-) mice.     

Aberrant striatal dopamine transmitter dynamics in brain-derived neurotrophic factor-deficient mice

Brain-derived neurotrophic factor (BDNF) modulates the synaptic transmission of several monoaminergic neuronal systems, including forebrain dopamine-containing neurons. Recent evidence shows a strong correlation between neuropsychiatric disorders and BDNF hypofunction. The aim of the present study was to characterize the effect of low endogenous levels of BDNF on dopamine system function in the caudate-putamen using heterozygous BDNF (BDNF(+/-) ) mice. Apparent extracellular dopamine levels in the caudate-putamen, determined by quantitative microdialysis, were significantly elevated in BDNF(+/-) mice compared with wildtype controls (12 vs. 5 nM, respectively). BDNF(+/-) mice also had a potentiated increase in dopamine levels following potassium (120 mM)-stimulation (10-fold) relative to wildtype controls (6-fold). Slice fast-scan cyclic voltammetry revealed that BDNF(+/-) mice had reductions in both electrically evoked dopamine release and dopamine uptake rates in the caudate-putamen. Superfusion of BDNF led to partial recovery of the electrically stimulated dopamine release response in BDNF(+/-) mice. Conversely, tissue accumulation of L-3,4-dihydroxyphenylalanine, extracellular levels of dopamine metabolites, and spontaneous locomotor activity were unaltered. Together, this study indicates that endogenous BDNF influences dopamine system homeostasis by regulating the release and uptake dynamics of pre-synaptic dopamine transmission.     

Reduction of BDNF expression in Fmr1 knockout mice worsens cognitive deficits but improves hyperactivity and sensorimotor deficits

Fragile X syndrome (FXS) is a common cause of inherited intellectual disability and a well-characterized form of autism spectrum disorder. As brain-derived neurotrophic factor (BDNF) is implicated in the pathophysiology of FXS we examined the effects of reduced BDNF expression on the behavioral phenotype of an animal model of FXS, Fmr1 knockout (KO) mice, crossed with mice carrying a deletion of one copy of the Bdnf gene (Bdnf(+/-)). Fmr1 KO mice showed age-dependent alterations in hippocampal BDNF expression that declined after the age of 4 months compared to wild-type controls. Mild deficits in water maze learning in Bdnf(+/-) and Fmr1 KO mice were exaggerated and contextual fear learning significantly impaired in double transgenics. Reduced BDNF expression did not alter basal nociceptive responses or central hypersensitivity in Fmr1 KO mice. Paradoxically, the locomotor hyperactivity and deficits in sensorimotor learning and startle responses characteristic of Fmr1 KO mice were ameliorated by reducing BNDF, suggesting changes in simultaneously and in parallel working hippocampus-dependent and striatum-dependent systems. Furthermore, the obesity normally seen in Bdnf(+/-) mice was eliminated by the absence of fragile X mental retardation protein 1 (FMRP). Reduced BDNF decreased the survival of newborn cells in the ventral part of the hippocampus both in the presence and absence of FMRP. Since a short neurite phenotype characteristic of newborn cells lacking FMRP was not found in cells derived from double mutant mice, changes in neuronal maturation likely contributed to the behavioral phenotype. Our results show that the absence of FMRP modifies the diverse effects of BDNF on the FXS phenotype.     

Effects of brain-derived neurotrophic factor (BDNF) on glial cells and serotonergic neurones during development

Serotonergic neurones are among the first to develop in the central nervous system. Their survival and maturation is promoted by a variety of factors, including serotonin itself, brain-derived neurotrophic factor (BDNF) and S100beta, an astrocyte-specific Ca(2+) binding protein. Here, we used BDNF-deficient mice and cell cultures of embryonic raphe neurones to determine whether or not BDNF effects on developing serotonergic raphe neurones are influenced by its action on glial cells. In BDNF-/- mice, the number of serotonin-immunoreactive neuronal somata, the amount of the serotonin transporter, the serotonin content in the striatum and the hippocampus, and the content of 5-hydroxyindoleacetic acid in all brain regions analysed were increased. By contrast, reduced immunoreactivity was found for myelin basic protein (MBP) in all brain areas including the raphe and its target region, the hippocampus. Exogenously applied BDNF increased the number of MBP-immunopositive cells in the respective culture systems. The raphe area displayed selectively reduced immunoreactivity for S100beta. Accordingly, S100beta was increased in primary cultures of pure astrocytes by exogenous BDNF. In glia-free neuronal cultures prepared from the embryonic mouse raphe, addition of BDNF supported the survival of serotonergic neurones and increased the number of axon collaterals and primary dendrites. The latter effect was inhibited by the simultaneous addition of S100beta. These results suggest that the presence of BDNF is not a requirement for the survival and maturation of serotonergic neurones in vivo. BDNF is, however, required for the local expression of S100beta and production of MBP. Therefore BDNF might indirectly influence the development of the serotonergic system by stimulating the expression of S100beta in astrocytes and the production MBP in oligodendrocytes.     

Involvement of p38alpha in kainate-induced seizure and neuronal cell damage

We investigated how p38alpha mitogen-activated protein kinase (p38) is related to kainate-induced epilepsy and neuronal damages, by using the mice with a single copy disruption of the p38 alpha gene (p38alpha(+/-)). Mortality rate and seizure score of p38alpha(+/-) mice administered with kainate were significantly reduced compared with the case of wild-type (WT) mice. This was clearly supported by the electroencephalography data in which kainate-induced seizure duration and frequency in the brain of p38alpha(+/-) mice were significantly suppressed compared to those of WT mice. As a consequence of seizure, kainate induced delayed neuronal damages in parallel with astrocytic growth in the hippocampus and ectopic innervation of the mossy fibers into the stratum oriens in the CA3 region of hippocampus in WT mice, whose changes were moderate in p38alpha(+/-) mice. Likewise, kainate-induced phosphorylation of calcium/calmodulin-dependent kinase II in the hippocampus of p38alpha (+/-) mice was significantly decreased compared to that of WT mice. These results suggest that p38alpha signaling pathway plays an important role in epileptic seizure and excitotoxicity.     

Serotonin transporter function, but not expression, is dependent on brain-derived neurotrophic factor (BDNF): in vivo studies in BDNF-deficient mice

In the present study, we used high-speed chronoamperometry to examine serotonin (5-HT) transporter (5-HTT) function in vivo in 2-, 5-, and 10-month-old brain-derived neurotrophic factor (BDNF)+/- mice. The rate of clearance of exogenously applied 5-HT was measured in CA3 region of hippocampus. In 2-month-old mice, the rate of 5-HT clearance did not differ between BDNF+/+ and BDNF+/- mice. In BDNF+/+ mice, 5-HT clearance rate (Tc) increased markedly with age. In contrast, Tc remained relatively static in BDNF+/- mice across 2-, 5-, and 10-month age groups. At 5 months of age, female BDNF+/+ mice had a lower maximal velocity (Vmax) for 5-HT clearance than male BDNF+/+ mice. There was a similar trend in 5-month-old BDNF+/- mice, but this did not reach statistical significance. There was an age-dependent increase in KT value for 5-HT clearance (i.e., decreased in vivo affinity of 5-HTT), but no significant effect of genotype or gender. 5-HTT density, as measured by [3H]cyanoimipramine binding, was not different between BDNF+/+ and BDNF+/- mice, although there was a significant increase in 5-HTT binding with age. The selective 5-HT reuptake inhibitor fluvoxamine (50 and 100 pmol) significantly decreased 5-HT clearance in BDNF+/+ mice, but not in BDNF+/- mice. Our data suggest that the profoundly reduced ability of 5- and 10-month-old BDNF+/- mice to clear 5-HT is not because of a decrease in the total number of 5-HTTs, but may be due to functional deficits in the 5-HTT, e.g., in the machinery/signaling required for insertion of 5-HTTs into the plasma membrane and/or activation of the 5-HTT once it is positioned to take up 5-HT from extracellular fluid.     

Serotonin (5-HT) transporter (SERT) function after graded destruction of serotonergic neurons

The degree of occupancy of the serotonin transporter (SERT) by selective serotonin reuptake inhibitors (SSRIs) appears to be critical in determining therapeutic response. To gain insight into the extent of occupancy required to alter serotonergic neurotransmission we used high-speed chronoamperometry to determine the extent of serotonergic destruction required to reduce the clearance of exogenously administered serotonin from extracellular fluid in the CA3 region of the hippocampus. Rats were pretreated with various doses of 5,7-dihydroxytryptamine to produce either a low, intermediate or high loss of SERTs. Clearance of 5-HT was reduced only in rats with > 90% loss of SERT. In these rats, there was also a trend for peak signal amplitudes to be greater. There was no significant difference in these parameters between the sham group and those with low or intermediate loss of SERTs. The SSRI, fluvoxamine, prolonged clearance of 5-HT in sham, low and intermediate groups, whereas there was no effect of fluvoxamine in those rats with > 90% loss of SERT. Functional loss of SERT activity occurs when destruction of serotonergic innervation is greater than 90% but serotonin clearance and efficacy of fluvoxamine is maintained with as few as one fifth of a full complement of SERTs.     

Studies on the up regulation of alpha-adrenoceptors on rat hippocampal perikarya by chemical lesion of the median raphe nucleus

Neurotoxin-induced lesion of the serotonergic raphe-hippocampal pathway produced about a 50% increase in the density of a nM affinity alpha-adrenergic binding site for (3H)WB-4101 in rat hippocampus 18 days postlesion without altering the specific binding of (3H)5-HT to serotonergic receptors. The chronic i.c.v. infusion of serotonin by minipump started at the appropriate time averted or reverted the effect. The dynamics of noradrenergic neurotransmission in the hippocampus was not impaired by lesion of the median raphe nucleus as determined by the uptake and turnover of noradrenaline as well as its release - as reflected by the normetanephrine concentration. In addition, neurotoxin-induced lesion of the dorsal noradrenergic bundle failed to alter either the Bmax or the Kd of (3H)WB-4101 binding to the nM site. Kainic acid-induced destruction of perikarya depressed the nM (3H)WB-4101 binding sites by 60% and completely prevented the up regulation caused by lesion of the median raphe nucleus. Thus, the supersensitivity-like response of the adrenoceptors to the lack of serotonin appears to be localized on kainate-sensitive cells within the hippocampus.     

5-HTT Deficiency Affects Neuroplasticity and Increases Stress Sensitivity Resulting in Altered Spatial Learning Performance in the Morris Water Maze but Not in the Barnes Maze

The purpose of this study was to evaluate whether spatial hippocampus-dependent learning is affected by the serotonergic system and stress. Therefore, 5-HTT knockout (-/-), heterozygous (+/-) and wildtype (+/+) mice were subjected to the Barnes maze (BM) and the Morris water maze (WM), the latter being discussed as more aversive. Additionally, immediate early gene (IEG) expression, hippocampal adult neurogenesis (aN), and blood plasma corticosterone were analyzed. While the performance of 5-HTT-/- mice in the BM was undistinguishable from both other genotypes, they performed worse in the WM. However, in the course of the repeated WM trials 5-HTT-/- mice advanced to wildtype level. The experience of a single trial of either the WM or the BM resulted in increased plasma corticosterone levels in all genotypes. After several trials 5-HTT-/- mice exhibited higher corticosterone concentrations compared with both other genotypes in both tests. Corticosterone levels were highest in 5-HTT-/- mice tested in the WM indicating greater aversiveness of the WM and a greater stress sensitivity of 5-HTT deficient mice. Quantitative immunohistochemistry in the hippocampus revealed increased cell counts positive for the IEG products cFos and Arc as well as for proliferation marker Ki67 and immature neuron marker NeuroD in 5-HTT-/- mice compared to 5-HTT+/+ mice, irrespective of the test. Most differences were found in the suprapyramidal blade of the dentate gyrus of the septal hippocampus. Ki67-immunohistochemistry revealed a genotype x environment interaction with 5-HTT genotype differences in naïve controls and WM experience exclusively yielding more Ki67-positive cells in 5-HTT+/+ mice. Moreover, in 5-HTT-/- mice we demonstrate that learning performance correlates with the extent of aN. Overall, higher baseline IEG expression and increased an in the hippocampus of 5-HTT-/- mice together with increased stress sensitivity may constitute the neurobiological correlate of raised alertness, possibly impeding optimal learning performance in the more stressful WM.     

5-HT(1A) receptor mutant mice exhibit enhanced tonic, stress-induced and fluoxetine-induced serotonergic neurotransmission

Mutant mice that lack serotonin(1A) receptors exhibit enhanced anxiety-related behaviors, a phenotype that is hypothesized to result from impaired autoinhibitory control of midbrain serotonergic neuronal firing. Here we examined the impact of serotonin(1A) receptor deletion on forebrain serotonin neurotransmission using in vivo microdialysis in the frontal cortex and ventral hippocampus of serotonin(1A) receptor mutant and wild-type mice. Baseline dialysate serotonin levels were significantly elevated in mutant animals as compared with wild-types both in frontal cortex (mutant = 0.44 +/- 0.05 n M; wild-type = 0.28 +/- 0.03 n M) and hippocampus (mutant = 0.46 +/- 0.07 n M; wild-type = 0.27 +/- 0.04 n M). A stressor known to elicit enhanced anxiety-like behaviors in serotonin(1A) receptor mutants increased dialysate 5-HT levels in the frontal cortex of mutant mice by 144% while producing no alteration in cortical 5-HT in wild-type mice. There was no phenotypic difference in the effect of this stressor on serotonin levels in the hippocampus. Fluoxetine produced significantly greater increases in dialysate 5-HT content in serotonin(1A) receptor mutants as compared with wild-types, with two- and three-fold greater responses being observed in the hippocampus and frontal cortex, respectively. This phenotypic effect was mimicked in wild-types by pretreatment with the serotonin(1A) antagonist 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide (p-MPPI). These results indicate that deletion of central serotonin(1A) receptors results in a tonic disinhibition of central serotonin neurotransmission, with a greater dysregulation of serotonin release in the frontal cortex than ventral hippocampus under conditions of stress or increased interstitial serotonin levels.     

Effects of brain‐derived neurotrophic factor on dopaminergic function and motor behavior during aging

Brain‐derived neurotrophic factor (BDNF) is critical in synaptic plasticity and in the survival and function of midbrain dopamine neurons. In this study, we assessed the effects of a partial genetic deletion of BDNF on motor function and dopamine (DA) neurotransmitter measures by comparing Bdnf^+/? with wildtype mice (WT) at different ages. Bdnf^+/? and WT mice had similar body weights until 12 months of age; however, at 21 months, Bdnf^+/? mice were significantly heavier than WT mice. Horizontal and vertical motor activity was reduced for Bdnf^+/? compared to WT mice, but was not influenced by age. Performance on an accelerating rotarod declined with age for both genotypes and was exacerbated for Bdnf^+/? mice. Body weight did not correlate with any of the three behavioral measures studied. Dopamine neurotransmitter markers indicated no genotypic difference in striatal tyrosine hydroxylase, DA transporter (DAT) or vesicular monoamine transporter 2 (VMAT2) immunoreactivity at any age. However, DA transport via DAT (starting at 12 months) and VMAT2 (starting at 3 months) as well as KCl‐stimulated DA release were reduced in Bdnf^+/? mice and declined with age suggesting an increasingly important role for BDNF in the release and uptake of DA with the aging process. These findings suggest that a BDNF expression deficit becomes more critical to dopaminergic dynamics and related behavioral activities with increasing age.     

Impairment of adolescent hippocampal plasticity in a mouse model for Alzheimer's disease precedes disease phenotype

The amyloid precursor protein (APP) was assumed to be an important neuron-morphoregulatory protein and plays a central role in Alzheimer's disease (AD) pathology. In the study presented here, we analyzed the APP-transgenic mouse model APP23 using 2-dimensional gel electrophoresis technology in combination with DIGE and mass spectrometry. We investigated cortex and hippocampus of transgenic and wildtype mice at 1, 2, 7 and 15 months of age. Furthermore, cortices of 16 days old embryos were analyzed. When comparing the protein patterns of APP23 with wildtype mice, we detected a relatively large number of altered protein spots at all age stages and brain regions examined which largely preceded the occurrence of amyloid plaques. Interestingly, in hippocampus of adolescent, two-month old mice, a considerable peak in the number of protein changes was observed. Moreover, when protein patterns were compared longitudinally between age stages, we found that a large number of proteins were altered in wildtype mice. Those alterations were largely absent in hippocampus of APP23 mice at two months of age although not in other stages compared. Apparently, the large difference in the hippocampal protein patterns between two-month old APP23 and wildtype mice was caused by the absence of distinct developmental changes in the hippocampal proteome of APP23 mice. In summary, the absence of developmental proteome alterations as well as a down-regulation of proteins related to plasticity suggest the disturption of a normally occurring peak of hippocampal plasticity during adolescence in APP23 mice. Our findings are in line with the observation that AD is preceded by a clinically silent period of several years to decades. We also demonstrate that it is of utmost importance to analyze different brain regions and different age stages to obtain information about disease-causing mechanisms.     

The influence of orally administered docosahexaenoic acid on cognitive ability in aged mice

The purpose of this study was to investigate whether or not the role of docosahexaenoic acid (DHA) supplementation on cognitive capability was related with brain-derived neurotrophic factor (BDNF), nitric oxide (NO) and dopamine (DA) in aged mice. Kunming-line mice were treated with 50 and 100 mg/kg/day of DHA via oral gavage for seven successive weeks. The cognitive ability of mice was assessed by step-through and passageway water maze tests. The levels of NO in hippocampus and striatum tissues were assessed by spectrophotometric method. The levels of DA in hippocampus and striatum tissues were assessed by high-performance liquid chromatography with electrochemical detection. The protein levels of BDNF in hippocampus tissue were assessed by Western blotting. The results showed that the cognitive capability of mice was significantly different between the DHA-treated groups and the control group; the protein level of BDNF was significantly increased in the hippocampus; the levels of NO and DA were significantly increased in hippocampus and striatum tissues. In conclusion, during aging, DHA supplementation can improve the cognitive function in mice and can increase the protein level of BDNF in hippocampus tissue and the levels of NO and DA in hippocampus and striatum tissues. Taken together, our results suggest that DHA supplementation could improve the cognitive dysfunction due to aging, to some extent, and it may have a relationship with increasing the protein level of BDNF and the level of NO and DA.     

Modulation of the hippocampal alpha-adrenoceptor population by lesion of the serotonergic raphe-hippocampal pathway in rats

Electrolytic lesion of the ascending serotonergic fibers in the median raphe nucleus or in both the median raphe nucleus and dorsal raphe nucleus caused after 18 days more than 80% depletion of serotonin in the hippocampus and frontal cortex, respectively, without affecting norepinephrine and acetylcholine contents. alpha 1-Adrenoceptor binding of (3H) WB-4104 was increased in the hippocampus but not in the frontal cortex. Scatchard analysis revealed that the increase in (3H) WB-4101 binding in the lesioned hippocampus was the result of an elevated density of alpha 1-adrenergic receptors of about 65%. This phenomenon began 8 days postlesion and persisted for at least 90 days postlesion. Similar qualitative and quantitative results were obtained following chemical lesion of the serotonergic cells of origin in the median raphe nucleus with 5,7-dihydroxytryptamine. Selectivity of the phenomenon was further demonstrated as or beta-adrenoceptor binding with (3H) dihydroalprenolol and cholinergic muscarinic receptor binding with (3H) dexetimide were not significantly affected in the hippocampus. By comparison, when norepinephrine in the hippocampus was depleted by more than 90% by bilateral lesion of the ascending noradrenergic fibers with 6-hydroxydopamine (18 days), the alpha 1-adrenoceptor number was significantly increased by only about 20% while the beta-adrenoceptor number was enhance by 40%. The area-selective increase in alpha 1-adrenoceptor number in the hippocampus in the presence of unchanged norepinephrine content and in the absence of serotonin probably signifies that serotonin actively participates in the modulation of the noradrenergic receptor population.     

Gender-Dependent Modulation of Brain Monoamines and Anxiety-like Behaviors in Mice with Genetic Serotonin Transporter and BDNF Deficiencies

1. Brain-derived neurotrophic factor (BDNF) supports serotonergic neuronal development and our recent study found that heterozygous mice lacking one BDNF gene allele interbred with male serotonin transporter (SERT) knockout mice had greater reductions in brain tissue serotonin concentrations, greater increases in anxiety-like behaviors and greater ACTH responses to stress than found in the SERT knockout mice alone.2. We investigated here whether there might be gender differences in these consequences of combined SERT and BDNF deficiencies by extending the original studies to female mice, and also to an examination of the effects of ovariectomy and tamoxifen in these female mice, and of 21-day 17-β estradiol implantation to male mice.3. We found that unlike the male SERT×BDNF-deficient mice, female SERT×BDNF mice appeared protected by their gender in having significantly lesser reductions in serotonin concentrations in hypothalamus and other brain regions than males, relative to controls. Likewise, in the elevated plus maze, female SERT×BDNF-deficient mice demonstrated no increases in the anxiety-like behaviors previously found in males.4. Furthermore, female SERT×BDNF mice did not manifest the ∼40% reduction in the expression of TrkB receptors or the ∼30% reductions in dopamine and its metabolites that male SERT×BDNF did. After estradiol implantation in male SERT×BDNF mice, hypothalamic serotonin was significantly increased compared to vehicle-implanted mice. These findings support the hypothesis that estrogen may enhance BDNF function via its TrkB receptor, leading to alterations in the serotonin circuits, which modulate anxiety-like behaviors.5. This double-mutant mouse model contributes to the knowledge base that will help in understanding gene×gene×gender interactions in studies of SERT and BDNF gene polymorphisms in human genetic diseases such as anxiety disorders and depression.     

Moderate caloric restriction initiated in rodents during adulthood sustains function of the female reproductive axis into advanced chronological age

Age-related ovarian failure in women heralds the transition into postmenopausal life, which is characterized by a loss of fertility and increased risk for cardiovascular disease, osteoporosis and cognitive dysfunction. Unfortunately, there are no options available for delaying loss of ovarian function with age in humans. Rodent studies have shown that caloric restriction (CR) can extend female fertile lifespan; however, much of this work initiated CR at weaning, which causes stunted adolescent growth and a delayed onset of sexual maturation. Herein we tested in mice if CR initiated in adulthood could delay reproductive aging. After 4 months of CR, the ovarian follicle reserve was doubled compared to ad libitum (AL)-fed age-matched controls, which in mating trials exhibited a loss of fertility by 15.5 months of age. In CR females returned to AL feeding at 15.5 months of age, approximately one-half remained fertile for 6 additional months and one-third continued to deliver offspring through 23 months of age. Notably, fecundity of CR-then-AL-fed females and postnatal offspring survival rates were dramatically improved compared with aging AL-fed controls. For example, between 10 and 23 months of age, only 22% of the 54 offspring delivered by AL-fed females survived. In contrast, over 73% of the 94 pups delivered by 15.5- to 23-month-old CR-then-AL-fed mice survived without any overt complications. These data indicate that in mice adult-onset CR maintains function of the female reproductive axis into advanced age and dramatically improves postnatal survival of offspring delivered by aged females.     

Apparent diffusion coefficient in the aging mouse brain: a magnetic resonance imaging study

Novel magnetic resonance imaging sequences have and still continue to play an increasing role in neuroimaging and neuroscience. Among these techniques, diffusion-weighted imaging (DWI) has revolutionized the diagnosis and management of diseases such as stroke, neoplastic disease and inflammation. However, the effects of aging on diffusion are yet to be determined. To establish reference values for future experimental mouse studies we tested the hypothesis that absolute apparent diffusion coefficients (ADC) of the normal brain change with age. A total of 41 healthy mice were examined by T2-weighted imaging and DWI. For each animal ADC frequency histograms (i) of the whole brain were calculated on a voxel-by-voxel basis and region-of-interest (ROI) measurements (ii) performed and related to the animals' age. The mean entire brain ADC of mice <3 months was 0.715(+/-0.016) x 10(-3) mm2/s, no significant difference to mice aged 4 to 5 months (0.736(+/-0.040) x 10(-3) mm2/s) or animals older than 9 months 0.736(+/-0.020) x 10(-3) mm2/s. Mean whole brain ADCs showed a trend towards lower values with aging but both methods (i + ii) did not reveal a significant correlation with age. ROI measurements in predefined areas: 0.723(+/-0.057) x 10(-3) mm2/s in the parietal lobe, 0.659(+/-0.037) x 10(-3) mm2/s in the striatum and 0.679(+/-0.056) x 10(-3) mm2/s in the temporal lobe. With advancing age, we observed minimal diffusion changes in the whole mouse brain as well as in three ROIs by determination of ADCs. According to our data ADCs remain nearly constant during the aging process of the brain with a small but statistically non-significant trend towards a decreased diffusion in older animals.     

Alterations in the Levels of Monoamines in Discrete Brain Regions of Clomipramine-Induced Animal Model of Endogenous Depression

It has been hypothesized that the dysfunction of the serotonergic and catecholaminergic neurotransmission is involved in the pathogenesis of depression. These hypotheses are being tested in a novel rat model of depression developed by the treatment of antidepressant-clomipramine neonataly from postnatal day 8 to 21. After the attainment of adulthood, these rats mimicked the features of the human endogenous depression showing significant decrease in the aggressive behavior and food intake. Biogenic amine estimations in these rats revealed that the levels of serotonin and noradrenaline were decreased significantly (P < 0.001) in frontal cortex, hippocampus, brain stem, septum and hypothalamus, while the levels of dopamine were decreased significantly (P < 0.001) only in the hippocampus compared to normal control and vehicle treated groups of rats. Our results demonstrate the dysfunction of serotonergic and noradrenergic neurotransmission, with lesser involvement of dopaminergic neurotransmission in the clomipramine induced experimental model of depression.     

Induction of brain-derived neurotrophic factor by convulsant drugs in the rat brain: involvement of region-specific voltage-dependent calcium channels

A high level of hippocampal brain-derived neurotrophic factor (BDNF) in normally aged as compared with young rats suggests that it is important to maintain a considerable level of hippocampal BDNF during aging in order to keep normal hippocampal functions. To elucidate possible mechanisms of endogenous BDNF increase, changes in levels of BDNF were studied in the rat brain following systemic administration of various convulsant agents; excitotoxic glutamate agonists, NMDA, kainic acid and (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA); GABA receptor antagonists, picrotoxin, pentylenetetrazole (PTZ) and lindane (gamma-hexachlorocyclohexane); and L-type voltage-dependent calcium channel agonist, BAY-K 8644. Kainic acid and AMPA, but not NMDA, caused remarkable increases in BDNF protein in the rat hippocampus and entorhinal cortex. Picrotoxin, PTZ and lindane stimulated BDNF production in the entorhinal cortex and also in the hippocampus of rats showing very severe convulsions. On the other hand, BAY-K 8644 treatment increased BDNF levels in the neocortex and entorhinal cortex. Maximal levels of BDNF protein were observed at 12--24 h, 8--16 h and 6 h following administration of kainic acid, PTZ and BAY-K 8644, respectively. Kainic acid stimulated BDNF synthesis in presynaptic hippocampal granule neurons, but not in postsynaptic neurons with its receptors, while PTZ and BAY-K 8644 produced the same effects in postsynaptic neurons in the entorhinal cortex (in granule neurons in the hippocampus) and in the whole cortex, respectively. Nifedipine inhibited almost completely BAY-K 8644, but not PTZ, effects. omega-Conotoxin GVIA and DCG-IV partially blocked kainic acid-induced enhancement of BDNF, indicating involvement of L-type and N-type voltage-dependent calcium channels, respectively. In addition, BDNF levels in the hippocampus of mice deficient in D-myo-inositol-1,4,5-triphosphate receptor gene were scarcely different from those in the same region of controls, suggesting little involvement of intracellular calcium increase through this receptor. BAY-K 8644, but not kainic acid or PTZ, stimulated the phosphorylation of cyclic AMP responsive element binding protein. Our results indicate convulsant-dependent stimulation of BDNF production and involvement of region-specific voltage-dependent calcium channels.     

Specifics of monoaminergic regulation of the central nervous system of hibernating animals (Citellus undulatus)

Seasonal features of open-field behavior of Yakut ground squirrels (Citellus undulatus) and changes in the brain MAO A activity were studied. It was found that all parameters of exploratory activity in the open field and holeboard test reached the values characteristic of summer animals very rapidly, within a few days or (in some cases) even within the first 24 hours after the arousal from hibernation in the middle of April. In autumn these parameters decreased to their minimum values 1.5-2 months prior to hibernation. Biochemical analysis showed that in April the activity of MAO A measured with serotonin as a substrate in the hippocampus was 1.8 times (p < 0.05) higher than the activity of MAO A with respect to noradrenaline. In contrast, in autumn the MAO A activity determined with noradrenaline as a substrate was 2.5 (p < 0.05) times higher than the activity a MAO A with respect to serotonin. Taken together, these data indicate that the seasonal features of the higher nervous activity of hibernating animals depend on the balance between serotonergic and noradrenergic systems in different periods of the annual cycle.