Emotional memory impairments in a genetic rat model of depression: involvement of 5-HT/MEK/Arc signaling in restoration.

Cognitive dysfunctions are common in major depressive disorder, but have been difficult to recapitulate in animal models. This study shows that Flinders sensitive line (FSL) rats, a genetic rat model of depression, display a pronounced impairment of emotional memory function in the passive avoidance (PA) task, accompanied by reduced transcription of Arc in prefrontal cortex and hippocampus. At the cellular level, FSL rats have selective reductions in levels of NMDA receptor subunits, serotonin 5-HT(1A) receptors and MEK activity. Treatment with chronic escitalopram, but not with an antidepressant regimen of nortriptyline, restored memory performance and increased Arc transcription in FSL rats. Multiple pharmacological manipulations demonstrated that procognitive effects could also be achieved by either disinhibition of 5-HT(1A)R/MEK/Arc or stimulation of 5-HT4R/MEK/Arc signaling cascades. Taken together, studies of FSL rats in the PA task revealed reversible deficits in emotional memory processing, providing a potential model with predictive and construct validity for assessments of procognitive actions of antidepressant drug therapies.

Defective group-II metaboropic glutamate receptors in the hippocampus of spontaneously depressed rats.

Spontaneously depressed flinders sensitive line (FSL) rats showed a reduced expression of mGlu2/3 metabotropic glutamate receptors in the hippocampus, as compared to "non-depressed" flinders resistant line (FRL) rats. No changes in mGlu2/3 receptor protein levels were found in other brain regions, including the amygdala, hypothalamus, and cerebral cortex. Biochemical analysis of receptor signalling supported the reduction of mGlu2/3 receptors in the hippocampus of FSL rats. Accordingly, the selective mGlu2/3 receptor agonist, LY379268 (1microM) reduced forskolin-stimulated cAMP formation by 56% and 32% in hippocampal slices from FRL and FSL rats, respectively. In addition, LY379268 enhanced 3,5-dihydroxyphenylglycine-stimulated inositol phospholipid hydrolysis from 65% to 215% in hippocampal slices from FRL rats, whereas it was inactive in slices from FRL rats. We also examined the behavioural response of FSL rats to systemic injection of LY379268 (0.5mg/kg, i.p., once a day for 1-21 days) by measuring the immobility time in the forced swim test, which is known to be increased in these rats. LY379268 was administered alone or combined with the classical antidepressant, chlorimipramine (10mg/kg, i.p.). LY379268 alone had no effect at any of the selected time-points, whereas chlorimipramine alone reduced the immobility time only after 21 days of treatment. In contrast, when combined with LY379268, chlorimipramine reduced the immobility time during the first 14 days of treatment. These data support the view that mGlu2/3 receptors might be involved in the pathophysiology of depressive disorders, and that pharmacological activation of these receptors may shorten the latency of antidepressant medication.

Impact of an intense stress on ethanol consumption in female rats characterized by their pre-stress preference: modulation by prenatal stress.

We examined the influence of prenatal stress on alcohol preference in adult female rats exposed to an intense stress. To take into account interindividual variability, the study was conducted in animals categorized as low or high alcohol preferring. After footshock, control high-preferring rats strongly reduced their alcohol consumption; in contrast, alcohol consumption was not changed in high-preferring rats that were prenatally stressed.

The wake-promoting drug modafinil stimulates specific hypothalamic circuits to promote adaptive stress responses in an animal model of PTSD.

Pharmacotherapeutic intervention during traumatic memory consolidation has been suggested to alleviate or even prevent the development of posttraumatic stress disorder (PTSD). We recently reported that, in a controlled, prospective animal model, depriving rats of sleep following stress exposure prevents the development of a PTSD-like phenotype. Here, we report that administering the wake-promoting drug modafinil to rats in the aftermath of a stressogenic experience has a similar prophylactic effect, as it significantly reduces the prevalence of PTSD-like phenotype. Moreover, we show that the therapeutic value of modafinil appears to stem from its ability to stimulate a specific circuit within the hypothalamus, which ties together the neuropeptide Y, the orexin system and the HPA axis, to promote adaptive stress responses. The study not only confirms the value of sleep prevention and identifies the mechanism of action of a potential prophylactic treatment after traumatic exposure, but also contributes to understanding mechanisms underlying the shift towards adaptive behavioral response.

Elevation of Il6 is associated with disturbed let-7 biogenesis in a genetic model of depression.

Elevation of the proinflammatory cytokine IL-6 has been implicated in depression; however, the mechanisms remain elusive. MicroRNAs (miRNAs) are small non-coding RNAs that inhibit gene expression post-transcriptionally. The lethal-7 (let-7) miRNA family was suggested to be involved in the inflammation process and IL-6 was shown to be one of its targets. In the present study, we report elevation of Il6 in the prefrontal cortex (PFC) of a genetic rat model of depression, the Flinders Sensitive Line (FSL) compared to the control Flinders Resistant Line. This elevation was associated with an overexpression of LIN28B and downregulation of let-7 miRNAs, the former an RNA-binding protein that selectively represses let-7 synthesis. Also DROSHA, a key enzyme in miRNA biogenesis was downregulated in FSL. Running was previously shown to have an antidepressant-like effect in the FSL rat. We found that running reduced Il6 levels and selectively increased let-7i and miR-98 expression in the PFC of FSL, although there were no differences in LIN28B and DROSHA expression. Pri-let-7i was upregulated in the running FSL group, which associated with increased histone H4 acetylation. In conclusion, the disturbance of let-7 family biogenesis may underlie increased proinflammatory markers in the depressed FSL rats while physical activity could reduce their expression, possibly through regulating primary miRNA expression via epigenetic mechanisms.

A pilot Swedish twin study of affective illness, including hospital- and population-ascertained subsamples.

OBJECTIVE: We sought to compare the probandwise concordance rate (PRC) for affective illness (AI) in monozygotic (MZ) and dizygotic (DZ) twins in samples ascertained through psychiatric hospitalization vs samples from the general population. METHODS: Twins were ascertained through psychiatric hospitalization for AI from the Swedish Psychiatric Twin Registry or as a matched sample from the population-based Swedish Twin Registry. Lifetime diagnoses were based on a mailed questionnaire containing, in self-report format, DSM-III-R criteria for mania and major depression. Returned questionnaires were obtained from 1484 individuals and both members of 486 pairs, of whom 154 were classified as MZ, 326 as DZ, and six of unknown zygosity. RESULTS: No evidence was found for violations of the equal environment assumption. Using either a narrow or broad diagnostic approach, the risk for AI in cotwins of proband twins was independent of the gender, polarity (ie, unipolar vs bipolar) and mode of ascertainment of the affected proband (ie, via hospitalization vs from the general population). Combining both subsamples, PRC for total AI using narrow diagnostic criteria was 48.2% in MZ and 23.4% in DZ twins. Using broad diagnostic criteria, the parallel figures were 69.7% and 34.9%. The risk for bipolar illness was substantially increased in the cotwins of probands with bipolar AI. CONCLUSIONS: Genetic factors play a major role in the etiology of AI in Sweden, as assessed by self-report questionnaire. Heritable factors appear to be equally important in AI as ascertained in clinical and epidemiological samples.

Evaluating prolactin response to dopamine agonists in schizophrenia. Methodological problems.

Serum prolactin (PRL) level was assessed after challenges with apomorphine hydrochloride, saline, dopamine hydrochloride, or levodopa-carbidopa (Sinemet) in 19 control and 38 chronic schizophrenic subjects. Baseline PRL level varied inversely with age. High correlations existed between baseline PRL level and any subsequent absolute measure of PRL after administration of a dopamine agonist or placebo. Percent decrease was not a function of baseline concentrations and was therefore the only independent measure of drug response. Baseline PRL level was generally lower during exacerbation than remission in patients studied during two states of illness. Percent PRL level decrease after apomorphine administration was significantly greater in normal subjects than in schizophrenics. Correction of apomorphine responses for corresponding placebo (saline) values abolished differences between groups. Prolactin responses after dopamine or levodopa-carbidopa did not differ; however, placebo correction was not possible.

Apomorphine and schizophrenia. Treatment, CSF, and neuroendocrine responses.

Previous studies have variably reported the efficacy of apomorphine in treatment of schizophrenia and tardive dyskinesia. Stimulation of dopamine neuron autoreceptors is the presumed mode of action. Low-dose apomorphine (0.75 mg subcutaneously) and placebo were administered to 25 male schizophrenics to evaluate the drug's effect on psychotic and tardive dyskinetic symptoms. No significant improvement or deterioration was seen. Concomitant measurements of plasma prolactin and growth hormone levels and CSF homovanillic acid level indicated that the dose used was centrally active. These results indicate that an active though nonsedating dose of apomorphine does not ameliorate symptoms of schizophrenia or tardive dyskinesia.

Plasma prostaglandin E2 metabolite--measured as 11-deoxy-15-keto-13,14-dihydro-11 beta,16 xi-cyclo-PGE2--in twins with schizophrenic disorder.

Blood samples were obtained from 18 twin pairs, and the major prostaglandin E2 (PGE2) plasma metabolite 15-keto-13,14-dihydro-PGE2 was measured by RIA after its conversion to 11-deoxy-15-keto-13,14-dihydro-11 beta,16 xi-cyclo-PGE2. Significant positive correlations were found in all the twin pairs, in 11 pairs diagnosed as DSM-III schizophrenic disorder and schizoid/schizotypal personality disorder, and in the 5 nonschizophrenic pairs. These results indicate that synthesis of prostaglandins (PGs) is in part genetically determined. With regard to absolute PGE2 metabolite levels, the data did not support the hypothesis of increased PGE2 in schizophrenia. Thus, seven of eight schizophrenic probands had lower metabolite concentrations than their healthy twin siblings, and in one pair they were similar. Furthermore, schizophrenic probands and their healthy sibling controls, taken as a group, had lower PGE2 metabolite levels than the group comprised of affective disorder probands and their respective controls. These findings raise the possibility that a change in PGE2 may be associated with schizophrenic and also possibly with affective disorders.

Venlafaxine but not bupropion decreases cerebrospinal fluid 5-hydroxyindoleacetic acid in unipolar depression.

BACKGROUND: While the antidepressants venlafaxine and bupropion are known to have different neurochemical profiles in vitro, their effects on human cerebral metabolism in vivo have not been directly compared. METHODS: Cerebrospinal fluid (CSF) levels of 5-hydroxyindoleacetic acid (5-HIAA), serotonin, 3-methoxy-4-hydroxyphenylglycol (MHPG), homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) were examined in 14 never-hospitalized outpatients with unipolar depression and 10 age-similar healthy controls. Patients received a baseline lumbar puncture (LP), which was repeated after at least 6 weeks of randomized monotherapy with either venlafaxine or bupropion, while controls received only a baseline LP. RESULTS: Patients (n = 9) receiving venlafaxine showed a significant decrease (42%) in their CSF 5-HIAA concentrations after treatment, but no change in other CSF measures. In contrast, patients receiving bupropion (n = 8) showed no change in CSF measures compared to pretreatment values. CONCLUSIONS: While the mechanism for this differential effect of venlafaxine remains to be determined, the current study provides confirmation of the different aminergic effects of venlafaxine and bupropion.

Oral physostigmine treatment of patients with Alzheimer's disease.

Twelve patients with Alzheimer's disease received 0.0, 0.5, 1.0, 1.5, and 2.0 mg of oral physostigmine every 2 hours for 3-5 days; symptoms after each dose were assessed with the Alzheimer's Disease Assessment Scale. Placebo and the dose associated with the least severe symptoms were then readministered for 3-5 days each. Of the 10 patients who completed the study, three showed clinically significant improvement on the highest physostigmine dose in both phases, four more were marginally improved in both phases, and three had inconsistent responses to physostigmine. Cortisol measures obtained during a sleep study suggest that patients whose symptoms improved on physostigmine were those in whom oral physostigmine enhanced central cholinergic activity.

Correlates of lateral ventricular size in chronic schizophrenia, II: biological measures.

CSF homovanillic acid levels showed a significant negative correlation with ventricle-brain ratios (VBRs) in a group of drug-free chronic schizophrenic male veterans, while CSF 5-hydroxyindoleacetic acid levels showed a similar, nearly significant trend. The response of plasma human growth hormone to 0.75 mg of apomorphine also demonstrated a significant negative correlation with VBR in this group, but other measures of central neurotransmitter activity were unrelated to ventricular size.

Cortisol and Alzheimer's disease, I: Basal studies.

Patients with Alzheimer's disease and nondemented elderly control subjects participated in studies of cortisol secretion during sleep and at 9:00 a.m. and were given dexamethasone suppression tests (DSTs) and lumbar punctures. Nocturnal and 9:00 a.m. cortisol concentrations were significantly higher in the demented patients. CSF MHPG negatively correlated with mean nocturnal cortisol. The most severely demented patients had the highest 9:00 a.m. and mean nocturnal cortisol concentrations. DST results did not distinguish samples with substantially different nocturnal cortisol concentrations. These results suggest that measurements of basal plasma cortisol concentrations and dexamethasone suppression provide different information but support the notion of somewhat higher than normal cortisol concentrations in Alzheimer's disease patients.

Cortisol and Alzheimer's disease, II: Dexamethasone suppression, dementia severity, and affective symptoms.

The course of Alzheimer's disease can be complicated by depressive illness, often presenting enigmatically. To determine whether the dexamethasone suppression test (DST) can help distinguish patients with coexisting dementia and depression from those with dementia alone, DSTs were conducted with 22 nondepressed Alzheimer's disease patients. Eleven patients were nonsuppressors. The nonsuppressors were older than the suppressors but did not differ in depression or dementia ratings. The 8:00 a.m. postdexamethasone cortisol level correlated with depressive symptoms. A relationship between severity of dementia and depressive symptoms was also demonstrated.

Age and the dexamethasone suppression test in depression.

The authors examined the effects of age on plasma cortisol concentrations of 81 depressed men after dexamethasone administration. Dexamethasone nonsuppression was significantly more frequent in patients older than age 55 than those younger. Similarly, older patients had significantly higher postdexamethasone cortisol concentrations than younger patients at all time points sampled. These differences could not be attributed to severity or to the prevalence of psychosis in older and younger depressed patients.

Neuroendocrine and neurochemical measurements in depression.

The authors performed dexamethasone suppression tests (DST), TRH infusions, 72-hour urine collections, and lumbar punctures on a group of male depressed patients. Approximately 60% of the patients were DST positive and 33% had a blunted TSH response. Two biologic variables, the 8 a.m. postdexamethasone cortisol and the postprobenecid CSF 5-hydroxyindoleacetic acid (5-HIAA), accounted for over half of the variance in the behavioral measure, the Hamilton score. Plasma cortisol elevation was associated with high 3-methoxy-4-hydroxyphenyl glycol (MHPG) excretion; TSH blunting was associated with low urinary MHPG excretion. Comprehensive biologic measures showed certain significant interrelationships and correlations with the severity of depression.

Basal and stimulated C-fos mRNA expression in the rat brain: effect of chronic dietary lithium.

The mechanisms underlying the therapeutic efficacy of lithium in affective disorders are poorly understood; however, previous studies have established an influence of lithium on receptor-coupled and postreceptor signal transduction mechanisms, including the transcription factor c-fos. We investigated the effect of chronic lithium on basal, stress-, muscarinic-, and haloperidol-induced c-fos mRNA expression in various rat brain regions. Chronic lithium produced significant reductions in basal c-fos expression in the frontal cortex and hippocampus, confirming our previous report. Stress-induced c-fos was significantly attenuated in the frontal cortex, hippocampus, and pituitary, was increased in the occipital cortex, and unchanged in the hypothalamus by chronic lithium. Pilocarpine-induced c-fos was significantly reduced in the frontal cortex and hippocampus by chronic lithium, but was enhanced in the occipital cortex and hypothalamus. Haloperidol-induced c-fos was augmented in the striatum and pituitary, but reduced in the frontal cortex by chronic lithium treatment. In regions in which haloperidol did not induce fos expression in control animals, fos levels after haloperidol were reduced after chronic lithium. One week after discontinuation of the lithium treatment, basal c-fos levels remained significantly lower in the frontal cortex and hippocampus, whereas the effects of stress, pilocarpine, or haloperidol on fos were normalized in most regions, except in the hippocampus, where the attenuated fos response to injection stress persisted. We suggest that repression of basal fos expression and inhibition and activation of inducible fos may be factors to be considered in the longer-term effects of lithium, leading to changes in expression of genes that regulate fos and are regulated by Fos, and ultimately to alterations in the functional activity of neural systems involved in the pathophysiology of affective disorder.

Changed concentrations of tachykinins and neuropeptide Y in brain of a rat model of depression: lithium treatment normalizes tachykinins.

Lithium's therapeutic mechanism of action is unknown. In lithium-treated normal rats, increased striatal concentrations of neurokinin A (NKA)-like immunoreactivity (LI), substance P (SP-LI) and neuropeptide Y (NPY-LI) have been reported. To investigate whether these effects might be of therapeutic relevance, Flinders Sensitive Line rats (FSL), an animal model of depression, and control Flinders Resistant Line (FRL) rats were during a 6-week period fed chow to which either lithium or vehicle was admixed. Following sacrifice, the peptides were extracted from dissected brain regions and measured by radioimmunoassay. NKA-LI and SP-LI were markedly decreased in striatum and increased in frontal cortex in FSL compared to control FRL animals. Lithium treatment abolished these differences. Basal concentrations of NPY-LI were decreased in hippocampus of FSL rats, but unaffected by lithium. The present study suggests that changed tachykinins and NPY may underlie the characterized depressive-like phenotype of the FSL rats. It is hypothesized that altering tachykinin peptidergic neurotransmission in striatum and frontal cortex constitutes a mechanism of action of lithium and that such a mechanism might be of therapeutic relevance.

Early maternal deprivation alters hippocampal levels of neuropeptide Y and calcitonin-gene related peptide in adult rats.

Stressful events early in life are reported to be more prevalent among patients with an adult life psychiatric disorder. Early maternal deprivation is considered an animal model of early life stress. Maternally deprived adult rats display long-term alterations in the neuroendocrine system, brain and behavior that are in many ways analogous to depressive and schizophrenic symptomatology. Neuropeptide Y (NPY) and calcitonin-gene related peptide (CGRP) have been implicated in both disorders and also been suggested to play a role in the neuroadaptational response to stress. Consequently, male Wistar rat-pups were subjected to early maternal deprivation or control handling, on postnatal day (pnd) 9. On pnd 21, pups were weaned and split into two groups that were reared either on a saw-dust floor or on a grid-floor, considered to be a mild stressor. On pnd 67, all animals were subjected to the prepulse inhibition test. One week later, the animals were sacrificed, the brains removed and dissected on ice. Levels of NPY-like immunoreactivity (LI) and CGRP-LI were quantified by radioimmunoassay in brain regional extracts. Maternal deprivation led to a significant reduction in basal startle amplitude and disruption of prepulse inhibition. These findings were paralleled by significantly reduced levels of NPY and CGRP in the hippocampus and occipital cortex. It is hypothesised that these changes may be of relevance to aspects of schizophrenic and affective symptomatology. The present study further shows that brain NPY and, in particular, CGRP are sensitive to long-term mild stress and further implicate the involvement of these peptides in the neuroendocrine stress response.

Involvement of hippocampal neuropeptide Y in mediating the chronic actions of lithium, electroconvulsive stimulation and citalopram.

Neuropeptide Y (NPY) has been considered to be involved in the pathogenesis of affective disorders, and chronic treatment with lithium or electroconvulsive stimuli (ECS) has been shown to increase mRNA and peptide levels of NPY in rat brain tissue. Consequently, parameters reflective of NPYergic neurotransmission were studied in the hippocampus of rats following chronic treatment with lithium, ECS or the selective serotonin re-uptake inhibitor (SSRI), citalopram. Lithium (28 days, diet) and ECS (10 days, once daily) treatments caused a marked increase in levels of preproNPY mRNA in the CA1 area and dentate gyrus (DG). This increase was accompanied by an increase in extracellular levels of NPY in the dorsal hippocampus of freely moving rats as determined by microdialysis, suggesting that lithium and ECS treatments lead to an increased biosynthesis and release of NPY in this area. (125)I-peptide YY (PYY) binding was reduced by 40 and 60% respectively in the DG following the same treatments, showing that the increased release is accompanied by a down-regulation of corresponding binding sites. In contrast, citalopram (10 mg/kg i.p., twice daily for 28 days) caused a 100% increase in (125)I-PYY binding in CA, CA3 and DG while levels of preproNPY mRNA and extracellular NPY in the hippocampus were unaffected. The results indicate that various agents and stimuli exerting antidepressant effects in humans, such as chronic lithium, ECS and citalopram all increase NPYergic neurotransmission in the hippocampus by distinct modes of action. Moreover, NPY (6 microg) given intracerebroventricularly (i.c.v.) induced an antidepressant-like effect in the forced swim test. It is hypothesised that the increase in NPYergic neurotransmission may be associated with the mechanism of action of various antidepressant treatments in the alleviation of depression.