Hippocampal GABAergic dysfunction in a rat chronic mild stress model of depression.

In major depression, one line of research indicates that a dysfunctional GABAergic inhibitory system is linked to the appearance of depressive symptoms. However, as the mechanistic details of such GABAergic deficit are largely unknown, we undertook a functional investigation of the GABAergic system in the rat chronic mild stress model of depression. Adult rats were exposed to an eight-week long stress protocol leading to anhedonic-like behavior. In hippocampal brain slices, phasic, and tonic GABA(A) receptor-mediated currents in dentate gyrus granule cells were examined using patch-clamp recordings. In granule cells, the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) was reduced to 41% in anhedonic-like rats, which was associated with a reduced probability of evoked GABA release. Using immunohistochemical analysis, there was no change in the number of parvalbumin-positive interneurons in the dentate gyrus. Notably, we observed a 60% increase in THIP-activated tonic GABA(A) mediated current in anhedonic-like rats, suggesting an upregulation of extrasynaptic GABA(A) receptors. Finally, five weeks treatment with the antidepressant escitalopram partially reversed the sIPSCs frequency. In summary, we have revealed a hippocampal dysfunction in the GABAergic system in the chronic mild stress model of depression in rats, caused by a reduction in action potential-dependent GABA release. Since the function of the GABAergic system was improved by antidepressant treatment, in parallel with behavioral read outs, it suggests a role of the GABAergic system in the pathophysiology of depression.

Drug-induced mild therapeutic hypothermia obtained by administration of a transient receptor potential vanilloid type 1 agonist.

BACKGROUND: The use of mechanical/physical devices for applying mild therapeutic hypothermia is the only proven neuroprotective treatment for survivors of out of hospital cardiac arrest. However, this type of therapy is cumbersome and associated with several side-effects. We investigated the feasibility of using a transient receptor potential vanilloid type 1 (TRPV1) agonist for obtaining drug-induced sustainable mild hypothermia. METHODS: First, we screened a heterogeneous group of TRPV1 agonists and secondly we tested the hypothermic properties of a selected candidate by dose-response studies. Finally we tested the hypothermic properties in a large animal. The screening was in conscious rats, the dose-response experiments in conscious rats and in cynomologus monkeys, and the finally we tested the hypothermic properties in conscious young cattle (calves with a body weight as an adult human). The investigated TRPV1 agonists were administered by continuous intravenous infusion. RESULTS: Screening: Dihydrocapsaicin (DHC), a component of chili pepper, displayed a desirable hypothermic profile with regards to the duration, depth and control in conscious rats. Dose-response experiments: In both rats and cynomologus monkeys DHC caused a dose-dependent and immediate decrease in body temperature. Thus in rats, infusion of DHC at doses of 0.125, 0.25, 0.50, and 0.75 mg/kg/h caused a maximal ΔT (°C) as compared to vehicle control of -0.9, -1.5, -2.0, and -4.2 within approximately 1 hour until the 6 hour infusion was stopped. Finally, in calves the intravenous infusion of DHC was able to maintain mild hypothermia with ΔT > -3°C for more than 12 hours. CONCLUSIONS: Our data support the hypothesis that infusion of dihydrocapsaicin is a candidate for testing as a primary or adjunct method of inducing and maintaining therapeutic hypothermia.

Increased susceptibility to cardiovascular effects of dihydrocapcaicin in resuscitated rats. Cardiovascular effects of dihydrocapsaicin.

BACKGROUND: Survivors of a cardiac arrest often have persistent cardiovascular derangements following cardiopulmonary resuscitation including decreased cardiac output, arrhythmias and morphological myocardial damage. These cardiovascular derangements may lead to an increased susceptibility towards the external and internal environment of the cardiovascular system as compared to the healthy situation. METHODS: Here we tested the hypothesis that the cardiovascular system in healthy rats and rats resuscitated from a cardiac arrest may be differentially affected by a transient receptor potential vanilloid type 1 agonist, by continuous intravenous infusion of dihydrocapsaicin (DHC). RESULTS: Compared to baseline, infusion of DHC caused an initial increase in mean arterial blood pressure in both healthy and resuscitated rats of 25% and 10%, respectively. Also, we observed an initial response of tachycardia in both healthy and resuscitated rats of 30% and 20%, respectively. Then, at high levels of DHC infusion (> 2.0 mg/kg/hr) we observed two single episodes of transient bradycardia and hypotension in 33% of the healthy rats, which was consistent with a TRPV1 agonist induced Bezold-Jarisch reflex. In contrast, in resuscitated rats we observed multiple episodes of bradycardia/hypotension in 100% of the rats and at a dose of DHC of 0.65 mg/kg/hr. Notably, this DHC effect could be completely blocked in the resuscitated rats by pre-treatment with atropine, a muscarinic acetylcholine antagonist. CONCLUSIONS: Our results indicate that the susceptibility of the rats towards TRPV1 agonist induced Bezold-Jarisch reflex is increased in those resuscitated from cardiac arrest compared to the healthy situation.

A reduced number of hippocampal granule cells does not associate with an anhedonia-like phenotype in a rat chronic mild stress model of depression.

Several clinical and preclinical studies have indicated that hippocampal shrinkage and decreased neurogenesis are implicated in the pathology of depression. Recent animal studies have shown, however, that the development of depression-related symptoms may take place through neurogenesis-independent pathways. To evaluate whether the stress-induced morphological changes in the hippocampal formation are causally related to the development of anhedonia-like symptoms, we combined the chronic mild stress (CMS) rat model of depression with stereological estimations of the number of proliferating progenitors, the total number of granule cells, and the volume of the ventral hippocampal formation (VHF). First, we found that stress-susceptible and stress-resilient animals, as categorized according to the behavioral read-out, both have a decrease in hippocampal cell proliferation. Our results also indicated that the anhedonia-like state in CMS rats develops prior to maximal suppression of cell proliferation, but correlates with a reduction in the total number of granule cells in the VHF. Furthermore, recovery from depression-related symptoms correlated with re-establishment of proliferation rates, but not with the total number of granule cells. Notably, decreases in the number of granule cells occurred independently of the induction of an anhedonia-like phenotype. There were no stress-induced changes in the volume of the VHF. We conclude that cell proliferation and a reduction in the total number of granule cells in the VHF are triggered by chronic stress, but do not associate with development of an anhedonia-like state in rats.

Cognitive deficits in the rat chronic mild stress model for depression: relation to anhedonic-like responses.

The chronic mild stress (CMS) protocol is widely used to evoke depressive-like behaviours in laboratory rats. The aim of the present study was to examine the effects of chronic stress on cognitive performance. About 70% of rats exposed to 7 weeks of chronic mild stress showed a gradual reduction in consumption of a sucrose solution, indicating an anhedonic-like state. The remaining rats did not reduce their sucrose intake, but appeared resilient to the stress-induced effects on sucrose intake. Cognitive profiling of the CMS rats revealed that chronic stress had a negative effect on performance in the spontaneous alternation test, possibly reflecting a deficit in working memory. This effect was independent of whether the stressed rats were anhedonic-like or stress-resilient as measured by their sucrose intake. CMS did not influence performance in passive avoidance and auditory cued fear conditioning, however, in rats displaying an anhedonic-like profile, CMS increased freezing behaviour in contextual fear conditioning.

The number of granule cells in rat hippocampus is reduced after chronic mild stress and re-established after chronic escitalopram treatment.

Stress and depression cause structural changes in the hippocampal formation. Some of these can be reversed by chronic antidepressant treatment. In the present study, we examined the changes in the total number of granule cells and the volume of the granule cell layer after exposing rats to chronic mild stress and chronic escitalopram treatment. Furthermore, we investigated which classes of immature granule cells are affected by stress and targeted by escitalopram. Rats were initially exposed to 2 weeks of CMS and 4 weeks of escitalopram treatment with concurrent exposure to stress. The behavioral changes, indicating a decrease in sensitivity to a reward, were assessed in terms of sucrose consumption. We found a significant 22.4% decrease in the total number of granule cells in the stressed rats. This decrease was reversed in the stressed escitalopram treated rats that responded to the treatment, but not in the rats that did not respond to escitalopram treatment. These changes were not followed by alterations in the volume of the granule cell layer. We also showed a differential regulation of dentate neurons, in different stages of development, by chronic stress and chronic escitalopram treatment. Our study shows that the anhedonia-like state in the CMS rats is associated with a reduced number of granule cells. We conclude that escitalopram acts on specific cellular targets during neuronal differentiation and that recovery from anhedonia-like behavior in rats may be the consequence of an escitalopram mediated increase in specific subtypes of immature dentate neurons.

Proteomic investigation of the ventral rat hippocampus links DRP-2 to escitalopram treatment resistance and SNAP to stress resilience in the chronic mild stress model of depression.

The development of depression as well as recovery from depression is most likely accompanied by a change in protein expression profiles. The purpose of the present study was to quantitatively investigate global protein expression differences independent of any hypothesis describing depression etiology and recovery. Thus two-dimensional differential in-gel electrophoresis was employed to compare the ventral hippocampal proteomes between different treatment groups in the chronic mild stress (CMS) model of depression. The CMS paradigm induces anhedonic behaviour, which is a major symptom of depression, by exposing rats to a series of mild stressors for 7 weeks, with antidepressant treatment during the last 4 weeks. In the CMS model, animals were split into six different groups at the end of treatment; unchallenged control escitalopram (n = 12), unchallenged control vehicle (n = 12), CMS vehicle (n = 12), CMS escitalopram responders (n = 11), CMS escitalopram non-responders (n = 13) and CMS resilient (stress resistant) (n = 12). Protein levels in the ventral rat hippocampus were compared between the groups to provide putative markers of anhedonia, escitalopram resistance, and stress resilience. Twenty-eight candidate protein spots were selected, of which 13 were successfully identified using tandem mass spectrometry. DRP-2 (dihydropyrimidinase-related protein-2) was a potential marker for escitalopram resistance, whereas alpha-SNAP and beta-SNAP were associated with stress resilience. Furthermore, several molecular chaperones and cytoskeleton organisers were identified as being differentially expressed. Our data indicate that neuronal adaptation is an essential element of depression etiology and recovery, suggesting the involvement of cellular plasticity in the underlying molecular mechanism.

Upper-airway inflammation in relation to dust spiked with aldehydes or glucan.

OBJECTIVES: Organic dust is associated with adverse effects on human airways. This study was done to investigate whether the addition of beta-(1,3)-D glucan or aldehydes to office dust causes enhanced inflammation in human airways. METHODS: Thirty-six volunteers were exposed randomly to clean air, office dust, dust spiked with glucan, and dust spiked with aldehydes. The three dust exposures contained between 332 and 379 microg dust/m(3). Spiking with 1 gram of dust was done with 10 milligrams of glucan or 0.1 microliters of aldehydes. Acoustic rhinometry, rhinostereometry, nasal lavage, and lung function tests were applied. RESULTS: After the exposures to dust spiked with the glucan and aldehydes, the nasal volume decreased (-1.33 and -1.39 cm(3) (mean), respectively) when compared with the -0.9 cm(3) after clean air or office dust (P=0.036 for a difference in decrease between exposures). After 2-3 hours the aldehyde-spiked dust caused a 0.6-mm swelling of the inferior turbinate, and glucan-spiked dust produced a 0.7-mm swelling (P=0.039 for a difference in the swelling between the four exposures). The preexposure nasal lavage cleaned off the mucosa, and lower cytokine concentrations were found after all of the exposures. For interleukin-8, this decrease in concentration was smaller after the dust exposures spiked with glucan and aldehydes (-2.9 and -25.8 pg/ml, respectively) than after office dust or clean air (-65.9 and -74.1 pg/ml, respectively) (P=0.042). The nasal eosinophil cell concentration increased after exposure to dust spiked with glucan (P=0.045). CONCLUSIONS: beta-(1,3)-D glucan and aldehydes in office dust enhance the inflammatory effects of dust on the upper airways.

Hippocampal cytogenesis correlates to escitalopram-mediated recovery in a chronic mild stress rat model of depression.

From clinical studies it is known that recurrent depressive episodes associate with a reduced hippocampal volume. Conversely, preclinical studies have shown that chronic antidepressant treatment increases hippocampal neurogenesis. Consequently, it has been suggested that a deficit in hippocampal neurogenesis is implicated in the pathophysiology of depression. To study a potential correlation between recovery and hippocampal cytogenesis, we established the chronic mild stress (CMS) rat model of depression. When rats are subjected to CMS, several depressive symptoms develop, including the major symptom anhedonia. Rats were exposed to stress for 2 weeks and subsequently to stress in combination with antidepressant treatment for 4 consecutive weeks. The behavioral deficit measured in anhedonic animals is a reduced intake of a sucrose solution. Prior to perfusion animals were injected with bromodeoxyuridine (BrdU), a marker of proliferating cells. Brains were sectioned horizontally and newborn cells positive for BrdU were counted in the dentate gyrus and tracked in a dorsoventral direction.CMS significantly decreased sucrose consumption and cytogenesis in the ventral part of the hippocampal formation. During exposure to the antidepressant escitalopram, given as intraperitoneally dosages of either 5 or 10 mg/kg/day, animals distributed in a bimodal fashion into a group, which recovered (increase in sucrose consumption), and a subgroup, which refracted treatment (no increase in sucrose consumption). Chronic treatment with escitalopram reversed the CMS-induced decrease in cytogenesis in the dentate gyrus of the ventral hippocampal formation, but in recovered animals only. Our data show a correlation between recovery from anhedonia, as measured by cessation of behavioral deficits in the CMS model, and an increase in cytogenesis in the dentate gyrus of the ventral hippocampal formation.

Estrogenic effects in vitro and in vivo of the fungicide fenarimol.

The fungicide fenarimol has the potential to induce endocrine disrupting effects via several mechanisms since it possesses both estrogenic and antiandrogenic activity and inhibits aromatase activity in cell culture studies. Hence, the integrated response of fenarimol in vivo is not easy to predict. In this study, we demonstrate that fenarimol is also estrogenic in vivo, causing significantly increased uterine weight in ovariectomized female rats. In addition, mRNA levels of the estrogen responsive gene lactoferrin (LF) were decreased in uteri, serum FSH levels were increased, and T3 levels decreased in fenarimol-treated animals. To our knowledge, only two other pesticides (o,p-DDT and methoxychlor) have previously been reported to induce an estrogenic response in the rodent uterotrophic bioassay. A pronounced xenoestrogenicity in serum samples from rats treated with fenarimol and estradiol benzoate (E2B) separately or in combination was observed, demonstrating the usefulness of this approach for estimating the integrated internal exposure to xenoestrogens. The MCF-7 cell proliferation assay was used to investigate further the dose-response curves for the estrogenic, antiestrogenic, and aromatase inhibiting properties of fenarimol in vitro. The results indicates that fenarimol exhibits a dual effect being aromatase inhibitor at low concentrations and estrogenic at higher concentrations.