Prefrontal cortex astroglia modulate anhedonia-like behavior

Reductions of astroglia expressing glial fibrillary acidic protein (GFAP) are consistently found in the prefrontal cortex (PFC) of patients with depression and in rodent chronic stress models. Here, we examine the consequences of PFC GFAP+ cell depletion and cell activity enhancement on depressive-like behaviors in rodents. Using viral expression of diphtheria toxin receptor in PFC GFAP+ cells, which allows experimental depletion of these cells following diphtheria toxin administration, we demonstrated that PFC GFAP+ cell depletion induced anhedonia-like behavior within 2 days and lasting up to 8 days, but no anxiety-like deficits. Conversely, activating PFC GFAP+ cell activity for 3 weeks using designer receptor exclusively activated by designer drugs (DREADDs) reversed chronic restraint stress-induced anhedonia-like deficits, but not anxiety-like deficits. Our results highlight a critical role of cortical astroglia in the development of anhedonia and further support the idea of targeting astroglia for the treatment of depression.

Do SGLT2 inhibitors prevent preclinical diabetic retinopathy? A Prospective Pilot Optical Coherence Tomography Angiography Study

PURPOSE

To evaluate the effects of metformin alone and combined treatment with metformin and an SGLT2 inhibitor on retinal microvascular morphology using optical coherence tomography angiography (OCTA) in isolated type 2 diabetes mellitus (DM) patients with HbA1c above the expected target (>7%).

METHODS

Fifty patients with isolated DM, 7%<HbA1c<8%, without diabetic retinopathy (DR) using 500mg metformin ×2 for glycemic control were included in the study. OCTA and BMI measurements were obtained at the first evaluation. Treatment was changed to metformin 1000mg ×2. Patients who did not develop side effects due to the metformin were defined as the metformin-tolerant group (group-1). Patients who developed side effects were defined as the metformin-intolerant group (group-2), and their treatment was changed to metformin 500mg ×2 and empagliflozin 10mg. The second evaluation was performed three months after the last treatment change.

RESULTS

HbA1c was lower on the second evaluation in both groups (P<0.001, in both). On the second evaluation in group-1, a decrease was found in superficial perifoveal and deep parafoveal macular vascular plexus densities (P: 0.040 and P: 0.020, respectively). No statistically significant difference was observed in group-2.

CONCLUSION

SGLT2 inhibitors may contribute to preventing the development of preclinical DR. In patients with metformin intolerance, adding SGLT2 inhibitors may be a reasonable choice to protect the retina.

Evaluation of thiol-disulfide homeostasis in pseudoexfoliation glaucoma and primary open-angle glaucoma

Aims

This study aimed to compare the serum thiol-disulfide homeostasis, total antioxidant status (TAS), and total oxidant status (TOS) in patients with pseudoexfoliation glaucoma (PEG) patients, primary open-angle glaucoma (POAG) patients, and healthy individuals (control).

Methods

Ninety subjects were included in this study. Three groups were separated as PEG, POAG, and control. All groups were chosen to be similar in terms of age and gender. Blood samples were obtained following an overnight fasting state and were collected on the ice at 4°C. The serum samples were separated from the cells by centrifugation at 3000 rpm for 15 min and were stored at -80°C. Serum samples analyzed for TAS and TOS, native thiol, total thiol, disulfide, and native thiol/disulfide ratio.

Results

TAS and TOS levels of PEG patients were 1.2892 ± 0.0905 mmol/L; 5.0191 ± 2.7722 μmol/L, respectively. TAS and TOS levels of POAG patients were 1.2741 ± 0.1252 mmol/L; 4.1674 ± 1.7723 μmol/L, respectively. TAS and TOS levels of the control group were 2.3414 ± 0.1409 mmol/L; 4.0931 ± 0.1107 μmol/L, respectively. The TAS level was significantly lower in PEG and POAG groups compared to control. TOS level showed no significant differ ¬ ence between PEG, POAG, and control groups (P > 0.05). The mean serum total thiol and native thiol levels were significantly lower in patients with PEG compared to POAG and control group; there was no significant difference between the POAG and control group (P > 0.05). The mean serum disulfide level was significantly lower in patients with PEG compared to POAG (P = 0.018).

Conclusion

Low levels of TAS were observed in patients with glaucoma, which was likely a response to the increased oxidative stress observed in these patients. While total thiol and native thiol levels were higher in the PEG group, the disulfide level was higher in the POAG group. TAS and TOS levels showed no significant difference between POAG and PEG groups.

Structural changes of macula and optic disk of the fellow eye in patients with nonarteritic anterior ischemic optic neuropathy

PURPOSE

The aim was to assess the ganglion cell complex (GCC) thickness, retinal nerve fiber layer (RNFL) thickness and optic disk features in the affected eyes (AE) and unaffected fellow eyes (FE) of subjects with unilateral nonarteritic anterior ischemic optic neuropathy (NAION) and to compare with healthy control eyes (CE) using spectral domain-optical coherence tomography (SD-OCT).

METHODS

This study included 28 patients and age, sex and refraction-matched 28 control subjects. Mean GCC thickness and peripapillary RNFL thickness in four quadrants measured by cirrus SD-OCT were evaluated in both AE and FE of patients and CE. In addition, optic disk measurements obtained with OCT were evaluated.

RESULTS

Mean GCC thickness was significantly lower in AE compared with both FE and CE (P < 0.001), and mean GCC thickness in FE was significantly lower than CE (P = 0.022). In addition, mean RNFL thickness in superior and nasal quadrants significantly decreased in FE compared with CE (P = 0.020 and 0.010, respectively). Furthermore, AE had significantly greater optic disk cupping compared with both FE and CE (P < 0.001).

CONCLUSIONS

GCC and RNFL thickness decreased significantly at late stages of NAION, in both AE and FE compared with CE, suggesting that some subclinical structural changes may occur in FE despite lack of obvious visual symptoms. In addition, there was no significant difference in optic disk features between the CE and FE. And significantly greater optic disk cupping in the AE compared with both FE and CE supports the acquired enlargement of cupping after the onset of NAION.

Analysis of corneal astigmatism with NIDEK axial length scan in caucasian cataract surgery candidates

Aims and Objectives

The aim of the study was to analyze and quantify the pattern of corneal astigmatism in Caucasian cataract surgery patients using a new optical biometer (axial length [AL] Scan, NIDEK Co., Gamagori, Japan).

Patients and Methods

The datasets of cataract surgery patients acquired between March 1, 2014, and April 15, 2016, were collected and analyzed. The corneal power (flat keratometry, steep keratometry, and mean keratometry), negative cylinder power, and axis of astigmatism were recorded. Keratometry values were optically measured by optical low coherence interferometry (AL-Scan, NIDEK Co., Ltd.,) before cataract extraction.

Results

The study comprised 1233 eyes of 838 consecutive cataract candidates with a mean age of 66.8 ± 10.7 years (range 40-97 years). The mean keratometry value and corneal astigmatism were 43.69 ± 1.61 D and 0.84 ± 0.70 D, respectively. Corneal astigmatism of 1.00 D or greater was found in 344 eyes (27.9%), and 548 eyes (44.4%) had against-the-rule astigmatism. A trend toward decreasing J0 and J45 with age was found by linear regression models. The per-year increase in age was associated with a J0 and J45 decrease of 0.002 D and 0.001D, respectively.

Conclusion

This study provides the distribution of astigmatism axis and power for cataract patients in age subsets from Turkey.

Long-wavelength macromolecular crystallography - First successful native SAD experiment close to the sulfur edge

Phasing of novel macromolecular crystal structures has been challenging since the start of structural biology. Making use of anomalous diffraction of natively present elements, such as sulfur and phosphorus, for phasing has been possible for some systems, but hindered by the necessity to access longer X-ray wavelengths in order to make most use of the anomalous scattering contributions of these elements. Presented here are the results from a first successful experimental phasing study of a macromolecular crystal structure at a wavelength close to the sulfur K edge. This has been made possible by the in-vacuum setup and the long-wavelength optimised experimental setup at the I23 beamline at Diamond Light Source. In these early commissioning experiments only standard data collection and processing procedures have been applied, in particular no dedicated absorption correction has been used. Nevertheless the success of the experiment demonstrates that the capability to extract phase information can be even further improved once data collection protocols and data processing have been optimised.

Remodeling of axo-spinous synapses in the pathophysiology and treatment of depression

Dendritic spines provide a compartment for assembly and functional organization of synaptic machinery that plays a fundamental role in neuronal communication and neuroplasticity. Studies in humans as well as in animal models have demonstrated abnormal spine architecture in several psychiatric disorders, including depression and other stress-related illnesses. The negative impact of stress on the density and organization of spines is thought to contribute to the behavioral deficits caused by stress exposure. Moreover, there is now evidence that medication-induced recovery involves changes in synaptic plasticity and dendrite morphology, including increased expression of pre- and postsynaptic plasticity-related proteins, as well as the density and function of axo-spinous synapses. Here we review the evidence from brain imaging and postmortem studies demonstrating that depression is accompanied by structural and functional alterations of cortical and limbic brain regions, including the prefrontal cortex, hippocampus and amygdala. In addition, we present more direct evidence from basic research studies that exposure to stress alters spine morphology, function and plasticity and that antidepressants, particularly new rapid acting agents, reverse these effects. Elucidation of the signaling pathways and molecular mechanisms that control spine synapse assembly and plasticity will contribute to a better understanding of the pathophysiology of depression and development of novel, more effective therapeutic agents.

Ezrin and osteonectin, two proteins associated with cell shape and growth, are enriched in the locus coeruleus

In an attempt to characterize proteins which are enriched or specifically expressed in the locus coeruleus (LC), a region of the brain which plays a critical role in opiate dependence and withdrawal, we have screened a bovine LC cDNA library with an LC minus cerebellum subtracted cDNA probe and isolated several (38) positively hybridizing clones. DNA sequence analysis revealed that two of the clones encoded ezrin and osteonectin, proteins normally associated with cell growth and morphology in peripheral tissues. Regional northern blots from bovine brain and in situ hybridization studies in rat show that ezrin is expressed at high levels in the LC with only low levels detectable in other brain regions. Osteonectin is also abundant in the LC, but in contrast to ezrin, is expressed at high levels in the dorsal raphe and substantia nigra. The results indicate that two proteins, ezrin and osteonectin, are highly enriched in the LC. This raises the possibility that these polypeptides, which play a role in the morphological response of some non-neuronal cell types to growth factors and to other intracellular signals, may also regulate these properties in noradrenergic and other selected neurons in the brain.

The roles of neurotrophic factor and Wnt signaling in depression

Depression is a debilitating disease with a lifetime prevalence of ~16% in the American population. In addition to the monoamine hypothesis, altered expressions of neurotrophic factors, growth factors, and Wnt signaling are implicated in the pathophysiology and treatment of depression. This review focuses on intracellular signaling cascades that underlie depression and treatment response.

Glial pathology in an animal model of depression: reversal of stress-induced cellular, metabolic and behavioral deficits by the glutamate-modulating drug riluzole

Growing evidence indicates that glia pathology and amino-acid neurotransmitter system abnormalities contribute to the pathophysiology and possibly the pathogenesis of major depressive disorder. This study investigates changes in glial function occurring in the rat prefrontal cortex (PFC) after chronic unpredictable stress (CUS), a rodent model of depression. Furthermore, we analyzed the effects of riluzole, a Food and Drug Administration-approved drug for the treatment of amyotrophic laterosclerosis, known to modulate glutamate release and facilate glutamate uptake, on CUS-induced glial dysfunction and depressive-like behaviors. We provide the first experimental evidence that chronic stress impairs cortical glial function. Animals exposed to CUS and showing behavioral deficits in sucrose preference and active avoidance exhibited significant decreases in 13C-acetate metabolism reflecting glial cell metabolism, and glial fibrillary associated protein (GFAP) mRNA expression in the PFC. The cellular, metabolic and behavioral alterations induced by CUS were reversed and/or blocked by chronic treatment with the glutamate-modulating drug riluzole. The beneficial effects of riluzole on CUS-induced anhedonia and helplessness demonstrate the antidepressant action of riluzole in rodents. Riluzole treatment also reversed CUS-induced reductions in glial metabolism and GFAP mRNA expression. Our results are consistent with recent open-label clinical trials showing the drug's effect in mood and anxiety disorders. This study provides further validation of hypothesis that glial dysfunction and disrupted amino-acid neurotransmission contribute to the pathophysiology of depression and that modulation of glutamate metabolism, uptake and/or release represent viable targets for antidepressant drug development.

Neurobiology and treatment of anxiety: signal transduction and neural plasticity

The stress-dependence and chronic nature of anxiety disorders along with the anxiolytic effectiveness of antidepressant drugs suggests that neuronal plasticity may play a role in the pathophysiology of anxiety. Intracellular signaling pathways are known in many systems to be critical links in the cascades from surface signals to the molecular alterations that result in functional plasticity. Chronic antidepressant treatments can regulate intracellular signaling pathways and can induce molecular, cellular, and structural changes over time. These changes may be important to the anxiolytic effectiveness of these drugs. In addition, the signaling proteins implicated in the actions of chronic antidepressant action, such as cAMP response element binding protein (CREB), have also been implicated in conditioned fear and in anxiety. The cellular mechanisms underlying conditioned fear indicate roles for additional signaling pathways; however, less is known about such mechanisms in anxiety. The challenge to identify intracellular signaling pathways and related molecular and structural changes that are critical to the etiology and treatment of anxiety will further establish the importance of mechanisms of neuronal plasticity in functional outcome and improve treatment strategies.

Pathophysiology of depression: the concept of synaptic plasticity

Neuronal plasticity or remodeling is most often discussed with regard to cellular and behavioral models of learning and memory. However, neuronal plasticity is a fundamental process by which the brain acquires information and makes the appropriate adaptive responses in future-related settings. Dysfunction of these fundamental processes could thereby contribute to the pathophysiology of mood disorders, and recovery could occur by induction of the appropriate plasticity or remodeling. These possibilities are supported by preclinical and clinical studies demonstrating that there are structural alterations that occur in response to stress and in patients with mood disorders. Moreover, antidepressant treatment may oppose these effects by regulation of signal transduction and gene expression pathways linked to neuronal plasticity. These findings comprise a novel conceptual framework for future studies of the etiology of mood disorders and for the development of novel therapeutic interventions.

Inducible, brain region-specific expression of a dominant negative mutant of c-Jun in transgenic mice decreases sensitivity to cocaine

Administration of cocaine induces the Fos family of transcription factors in the striatum, including the nucleus accumbens (NAc), a brain region important for the rewarding effects of addictive drugs. Several Fos proteins are induced acutely by cocaine, with stable isoforms of DeltaFosB predominating after chronic drug administration. However, it has been difficult to study the functional consequences of these Fos responses in vivo. Fos proteins heterodimerize with members of the Jun family to form active AP-1 transcription factor complexes. In the present study, we took advantage of this property and generated transgenic mice, using the tetracycline gene regulation system, that support the inducible, brain region-specific expression of a dominant negative mutant form of c-Jun (Deltac-Jun), which can antagonize the actions of Fos proteins. Expression of Deltac-Jun in the striatum and certain other brain regions of adult mice decreases their development of cocaine-induced conditioned place preference, suggesting reduced sensitivity to the rewarding effects of cocaine. In contrast, Deltac-Jun expression had no effect on cocaine-induced locomotor activity or sensitization. However, expression of Deltac-Jun in adult mice blocked the ability of chronic cocaine administration to induce three known targets for AP-1 in the NAc: the AMPA glutamate receptor subunit GluR2, the cyclin-dependent protein kinase Cdk5, and the transcription factor nuclear factor-kappaB (NFkappaB), without affecting several other proteins examined for comparison. Taken together, these results provide further support for an important role of AP-1-mediated transcription in some of the behavioral and molecular mechanisms underlying cocaine addiction.

Impairments of neuroplasticity and cellular resilience in severe mood disorders: implications for the development of novel therapeutics

Mood disorders have traditionally been conceptualized as neurochemical disorders, but there is now evidence from a variety of sources demonstrating regional reductions in central nervous system (CNS) volume, as well as reductions in the numbers and/or sizes of glia and neurons in discrete brain areas. Although the precise cellular mechanisms underlying these morphometric changes remain to be fully elucidated, the data suggests that mood disorders are associated with impairments of structural plasticity and cellular resilience. Recent preclinical and clinical studies have shown that signaling pathways involved in regulating cell survival and cell death are long-term targets for the actions of antidepressants and mood stabilizers. Antidepressants, lithium, and valproate indirectly regulate a number of factors involved in cell survival pathways, including CREB, BDNF, Bcl-2, and MAP kinases, and may thus bring about some of their delayed long term beneficial effects via underappreciated neurotrophic effects. The future development of treatments that more directly target molecules involved in critical CNS cell survival and cell death pathways thus hold promise as novel, improved long-term treatments for mood disorders.

Localization of phosphorylated cAMP response element-binding protein in immature neurons of adult hippocampus

Neurogenesis continues to occur in the adult hippocampus, although many of the newborn cells degenerate 1-2 weeks after birth. The number and survival of newborn cells are regulated by a variety of environmental stimuli, but very little is known about the intracellular signal transduction pathways that control adult neurogenesis. In the present study, we examine the expression of the phosphorylated cAMP response element-binding protein (pCREB) in immature neurons in adult hippocampus and the role of the cAMP cascade in the survival of new neurons. The results demonstrate that virtually all immature neurons, identified by triple immunohistochemistry for bromodeoxyuridine (BrdU) and polysialic acid-neural cell adhesion molecule (PSA-NCAM), are also positive for pCREB. In addition, upregulation of cAMP (via pharmacological inhibition of cAMP breakdown or by antidepressant treatment) increases the survival of BrdU-positive cells. A possible role for pCREB in the regulation of PSA-NCAM, a marker of immature neurons involved in neuronal remodeling and neurite outgrowth, is supported by cell culture studies demonstrating that the cAMP-CREB pathway regulates the expression of a rate-limiting enzyme responsible for the synthesis of PSA-NCAM. These findings indicate that the cAMP-CREB pathway regulates the survival, and possibly the differentiation and function, of newborn neurons.

Synaptic plasticity and mood disorders

Recent studies demonstrate that the molecular elements known to regulate neuronal plasticity in models of learning and memory are also involved in the actions of drugs used for the treatment of depression and bipolar disorder. This includes up-regulation of transcription factors, such as the cAMP response element binding protein and neurotrophic factors, such as brain derived neurotrophic factor. These findings raise the possibility that regulation of neural plasticity in specific neuronal circuits is integrally involved in the therapeutic intervention of mood disorders. Atypical antipsychotic drugs, including clozapine and olanzapine, are also effective for the treatment of bipolar disorder, and are used as add-on medication for unipolar depression. The possibility that these atypical antipsychotic drugs also influence the molecular determinants of synaptic plasticity that are involved in the response to drugs used for the treatment of mood disorders, is discussed.

[Molecular aspects of antidepressive therapy. Transsynaptic effects on signal transduction, gene expression and neuronal plasticity]

Simple neurotransmitter theories cannot sufficiently explain the mode of action of antidepressant drugs. Molecular pharmacological studies demonstrate that antidepressive treatment initially modulates the neurotransmitter-receptor interaction, subsequently influences signal transduction cascades beyond the synapse and gene transcription mechanisms, and ultimately triggers the expression of specific target genes. Such genes often code for molecules which play an important role in the maintenance of neural and synaptic plasticity. Chronic (but not acute) treatment with antidepressants modulates, for example, the cAMP-second-messenger system and increases the expression of neurotrophic factors. Furthermore, antidepressants promote hippocampal neurogenesis. Stress, an important risk factor for psychiatric disorders, often induces opposite effects. A better understanding of the molecular and cellular effects of stress and therapy with psychotropic drugs will stimulate the development of innovative treatment strategies for which an optimised antidepressant efficacy with a simultaneously improved tolerance is expected.

Regulation of adult neurogenesis by antidepressant treatment

Demonstration of neurogenesis in adult brain represents a major advance in our understanding of the cellular mechanisms underlying neuronal remodeling and complex behavior. Recent studies from our laboratory and others demonstrate that chronic administration of an antidepressant, including either a 5-HT or norepinephrine selective reuptake inhibitor, up-regulates neurogenesis in adult rodent hippocampus. Up-regulation of neurogenesis could block or reverse the effects of stress on hippocampal neurons, which include down-regulation of neurogenesis, as well as atrophy. The possibility that the cAMP signal transduction cascade contributes to the regulation of neurogenesis by antidepressants is supported by previous studies and by recent work. Although additional studies must be conducted to determine the significance of adult neurogenesis in humans, these findings will stimulate new avenues of research to identify the cellular and molecular basis of stress-related mood disorders as well as the development of novel therapeutic strategies.

Stress differentially regulates synaptophysin and synaptotagmin expression in hippocampus

BACKGROUND

In view of the effects of stress on synaptic plasticity, the regulation of synaptophysin and synaptotagmin expression by immobilization was analyzed by in situ hybridization.

METHODS

Rats were exposed to immobilization stress, which induced typical behavioral alterations, such as reduced locomotor activity after stress exposure. Determination of mRNA levels of the integral synaptic vesicle proteins was performed immediately after acute or chronic immobilization.

RESULTS

The results demonstrate that stress exposure leads to reduced expression of synaptophysin but increased expression of synaptotagmin in the hippocampus.

CONCLUSIONS

This rapid and differential regulation of synaptic vesicle proteins could be responsible for some of the morphological, biochemical, and behavioral changes observed after stress exposure. These changes may be relevant to such clinical disorders as psychoses, depression, and posttraumatic stress disorder that are sensitive to stress and involve changes in neural and synaptic plasticity.

Regulation of adult neurogenesis by psychotropic drugs and stress

Proliferation and maturation of neurons has been demonstrated to occur at a significant rate in discrete regions of adult brain, including the hippocampus and subventricular zone. Moreover, adult neurogenesis is an extremely dynamic process that is regulated in both a positive and negative manner by neuronal activity and environmental factors. It has been suggested to play a role in several important neuronal functions, including learning, memory, and response to novelty. In addition, exposure to psychotropic drugs or stress regulates the rate of neurogenesis in adult brain, suggesting a possible role for neurogenesis in the pathophysiology and treatment of neurobiological illnesses such as depression, post-traumatic stress disorder, and drug abuse. As the mechanisms that control adult neurogenesis continue to be identified, the exciting prospect of developing pharmacological agents that specifically regulate the proliferation and maturation of neurons in the adult brain could be fulfilled.

Expression of the cAMP response element binding protein (CREB) in hippocampus produces an antidepressant effect

BACKGROUND

Recent studies have demonstrated that chronic antidepressant treatment increases the expression of the cyclic amp (cAMP) response element binding protein (CREB) in rat hippocampus. The study presented here was conducted to determine if CREB is a relevant target that produces an antidepressant-like effect.

METHODS

We employed the herpes simplex virus (HSV)-mediated gene transfer technique to overexpress CREB and determined its effect on the learned helplessness and forced swim tests, two established models used for pharmacological screening of antidepressant drugs.

RESULTS

In the learned helplessness model, rats that received bilateral microinjection of HSV-CREB into the dentate gyrus showed significantly fewer escape failures in the subsequent conditioned avoidance test than those injected with control vector (HSV-LacZ). In contrast, microinjection of HSV-CREB in either the CA1 pyramidal cell layer of hippocampus or the prefrontal cortex did not produce an antidepressant response. In the forced swim test, CREB expression in the dentate gyrus resulted in a significantly shorter immobility time than those injected with HSV-LacZ.

CONCLUSIONS

These results demonstrate that over-expression of CREB in hippocampus results in an antidepressant effect and suggest that CREB may serve as a potential molecular target for novel therapeutic agents.

ECS-Induced mossy fiber sprouting and BDNF expression are attenuated by ketamine pretreatment

Recent evidence suggests hippocampal and possibly cortical atrophy is associated with major depression. Chronic electroconvulsive seizures (ECS) induce brain-derived neurotrophic factor (BDNF) expression and sprouting of the mossy fiber pathway in the hippocampus, effects that may be related to electroconvulsive therapy's (ECT) mechanism of action. The objective of this study was to investigate the role of NMDA (N-methyl-D-aspartate) receptor in mediating the ECS-induced mossy fiber sprouting and BDNF expression. Timm histochemistry and in situ hybridization methodologies were used to determine the effect of pretreatment with ketamine, an NMDA antagonist, on ECS-induced sprouting and BDNF expression. The results demonstrate the ability of ketamine pretreatment to attenuate ECS-induced sprouting in the dentate gyrus and BDNF expression in the medial prefrontal cortex and the dentate gyrus. In addition, we found a significant decrease in seizure duration with ketamine pretreatment. These data suggest that NMDA receptor activation contributes to both the regulation of neurotrophic factor expression and the morphological changes associated with seizure activity. However, other effects resulting from shortened seizure duration and seizure intensity cannot be excluded. These findings are of increasing interest, as they relate to the use of ECT in the treatment of depression, and the specific anesthetic agents that are used.

Depresssion--emerging insights from neurobiology

An emerging hypothesis suggests that the pathogenesis and treatment of depression is likely to involve a plasticity of neuronal pathways. The inability of neuronal systems to exhibit appropriate, adaptive plasticity could contribute to the pathogenesis of depression. Antidepressant treatments may exert their therapeutic effects by stimulating appropriate adaptive changes in neuronal systems. Recent studies have demonstrated that chronic antidepressant administration up-regulates the cAMP signal transduction cascade resulting in an increased expression and function of the transcription factor CREB. Enhanced CREB expression leads to an up-regulation of specific target genes, including the neurotrophin BDNF. Chronic antidepressant treatments enhance BDNF expression within hippocampal and cortical neurons and can prevent the stress-induced decrease in BDNF expression. Stress has been shown to: (i) induce neuronal atrophy/death; and (ii) decrease neurogenesis of hippocampal neurons. Clinical studies indicate significant hippocampal damage in cases of major, recurrent depression. It is possible that antidepressant treatments through enhanced expression of growth and survival promoting factors like BDNF may prevent or reverse the atrophy and damage of hippocampal neurons. Indeed, studies have indicated that chronic antidepressant treatments enhance hippocampal neurogenesis, promote neuronal sprouting and prevent atrophy. The molecular mechanisms underlying the effects of antidepressant treatments including adaptations in the cAMP transduction cascade, CREB and BDNF gene expression, and structural neuronal plasticity are discussed.

Regulation of GFRalpha-1 and GFRalpha-2 mRNAs in rat brain by electroconvulsive seizure

The influence of both acute and chronic electroconvulsive seizure (ECS) or antidepressant drug treatments on expression of mRNAs encoding glial cell line-derived neurotrophic factor (GDNF) and its receptors, GFRalpha-1, GFRalpha-2, and c-Ret proto-oncogene (RET) in the rat hippocampus was examined by in situ hybridization. Two hours after acute ECS, levels of GFRalpha-1 mRNA in the dentate gyrus were significantly increased. This increase peaked to nearly 3-fold at 6 h after acute ECS and returned to basal levels 24 h after treatment. Chronic (once daily for 10 days) ECS significantly increased the expression of GFRalpha-1 mRNA nearly 5-fold after the last treatment. Levels of GFRalpha-2 mRNA in the dentate gyrus were also significantly increased by acute and chronic ECS, although this effect was less than that observed for GFRalpha-1. Maximum induction of GFRalpha-2 was 30% and 70% compared to sham in response to acute or chronic ECS, respectively. Levels of GDNF and RET mRNAs were not significantly changed following either acute or chronic ECS treatment at the time points examined. Chronic (14 days) administration of different classes of antidepressant drugs, including tranylcypromine, desipramine, or fluoxetine, did not significantly affect the GDNF, GFRalpha-1, GFRalpha-2, or RET mRNA levels in CA1, CA3, and dentate gyrus areas of hippocampus. The results demonstrate that acute ECS increases the expression of GFRalpha-1 and GFRalpha-2 and that these effects are enhanced by chronic ECS. The results also imply that regulation of the binding components of GDNF receptor complex may mediate the adaptive responses of the GDNF system to acute and chronic stimulation.

Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus

Recent studies suggest that stress-induced atrophy and loss of hippocampal neurons may contribute to the pathophysiology of depression. The aim of this study was to investigate the effect of antidepressants on hippocampal neurogenesis in the adult rat, using the thymidine analog bromodeoxyuridine (BrdU) as a marker for dividing cells. Our studies demonstrate that chronic antidepressant treatment significantly increases the number of BrdU-labeled cells in the dentate gyrus and hilus of the hippocampus. Administration of several different classes of antidepressant, but not non-antidepressant, agents was found to increase BrdU-labeled cell number, indicating that this is a common and selective action of antidepressants. In addition, upregulation of the number of BrdU-labeled cells is observed after chronic, but not acute, treatment, consistent with the time course for the therapeutic action of antidepressants. Additional studies demonstrated that antidepressant treatment increases the proliferation of hippocampal cells and that these new cells mature and become neurons, as determined by triple labeling for BrdU and neuronal- or glial-specific markers. These findings raise the possibility that increased cell proliferation and increased neuronal number may be a mechanism by which antidepressant treatment overcomes the stress-induced atrophy and loss of hippocampal neurons and may contribute to the therapeutic actions of antidepressant treatment.

Neuronal plasticity and survival in mood disorders

Studies at the basic and clinical levels demonstrate that neuronal atrophy and cell death occur in response to stress and in the brains of depressed patients. Although the mechanisms have yet to be fully elucidated, progress has been made in characterizing the signal transduction cascades that control neuronal atrophy and programmed cell death and that may be involved in the action of antidepressant treatment. These pathways include the cyclic adenosine monophosphate and neurotrophic factor signal transduction cascades. It is notable that these same pathways have been demonstrated to play a pivotal role in cellular models of neural plasticity. This overlap of plasticity and cell survival pathways, together with studies demonstrating that neuronal activity enhances cell survival, suggests that neuronal atrophy and death could result from a disruption of the mechanisms underlying neural plasticity. The role of these pathways and failure of neuronal plasticity in stress-related mood disorders are discussed.

cAMP response element-mediated gene transcription is upregulated by chronic antidepressant treatment

Regulation of gene transcription via the cAMP-mediated second messenger pathway has been implicated in the actions of antidepressant drugs, but studies to date have not demonstrated such an effect in vivo. To directly study the regulation of cAMP response element (CRE)-mediated gene transcription by antidepressants, transgenic mice with a CRE-LacZ reporter gene construct were administered one of three different classes of antidepressants: a norepinephrine selective reuptake inhibitor (desipramine), a serotonin selective reuptake inhibitor (fluoxetine), or a monoamine oxidase inhibitor (tranylcypromine). Chronic, but not acute, administration of these antidepressants significantly increased CRE-mediated gene transcription, as well as the phosphorylation of CRE binding protein (CREB), in several limbic brain regions thought to mediate the action of antidepressants, including the cerebral cortex, hippocampus, amygdala, and hypothalamus. These results demonstrate that chronic antidepressant treatment induces CRE-mediated gene expression in a neuroanatomically differentiated pattern and further elucidate the molecular mechanisms underlying the actions of these widely used therapeutic agents.

Alterations in heavy and light neurofilament proteins in hippocampus following chronic ECS administration

Chronic administration of electroconvulsive seizures (ECS), one of the most effective treatments for depression, induces sprouting of the mossy fibers in the hippocampus. This sprouting requires chronic ECS administration and appears to occur in the absence of hilar neuronal loss. Dynamic regulation of cytoarchitecture plays a vital role in such profound alterations of neuronal morphology. In particular, alterations in the neurofilament protein subunits have been implicated in neurite sprouting, neuronal regeneration, and growth. The present study was carried out to determine the influence of chronic ECS administration on the neurofilament subunits and other molecular markers of neuronal plasticity. Chronic ECS administration decreases the level of phosphorylated heavy neurofilament subunit (NF-H). In addition, the total level of the light neurofilament subunit (NF-L) but not the medium neurofilament subunit (NF-M) is decreased following chronic ECS treatment. Other cytoskeletal proteins, including actin, microtubule-associated protein (MAP-2), and tau, are not influenced by chronic ECS administration. Expression of the growth-associated protein (F1/GAP-43) also remains unchanged following chronic ECS treatment. The changes observed in neurofilaments may be part of the cytoskeletal remodeling that contributes to the mossy fiber sprouting induced by chronic ECS treatment.

Role of corticotropin-releasing factor receptor-1 in opiate withdrawal

Previous studies indicate that corticotropin-releasing factor (CRF) contributes to the anxiety-like and aversive states associated with drug-induced withdrawal. The present study extends this work by analyzing the CRF receptor subtype involved in withdrawal responses. First, the influence of a selective CRF receptor-1 (CRF-R1) antagonist, CP-154,526, on opiate withdrawal behavior was examined. Pretreatment with the CRF-R1 antagonist significantly attenuated several behavioral signs of naltrexone-induced morphine withdrawal, including writhing, chewing, weight loss, lacrimation, salivation, and irritability, measured during the first hour of withdrawal. Next the expression of CRF-R1 was determined as a second measure of the involvement of this receptor in opiate withdrawal. Naltrexone-induced morphine withdrawal resulted in down-regulation of CRF-R1 mRNA in several brain regions, including the frontal cortex, parietal cortex, striatum, nucleus accumbens, and amygdala, but not in the hypothalamus or periaqueductal gray. Expression of CRF-R2, the other major CRF receptor subtype, was not down-regulated significantly by withdrawal in any of the regions examined, although morphine alone significantly increased levels of this receptor subtype. Taken together, the behavioral and receptor regulation findings indicate that CRF-R1 is the primary mediator of the actions of the CRF system on opiate withdrawal, although it is possible that CRF-R2 contributes to the response.

Administration of a cAMP phosphodiesterase 4 inhibitor enhances antidepressant-induction of BDNF mRNA in rat hippocampus

The influence of two selective phosphodiesterase 4 (PDE4) inhibitors, rolipram and Ro 20-1724, on the induction of BDNF mRNA by antidepressant treatment was examined. Coadministration of rolipram or Ro 20-1724 with an antidepressant (either desipramine or Org 4428) for 21 d resulted in a significant induction of BDNF mRNA in hippocampus relative to administration of vehicle. Coadministration of a PDE4 inhibitor with an antidepressant for 7 or 14 d also increased levels of BDNF mRNA. In contrast, acute coadministration did not influence levels of BDNF mRNA. In situ hybridization analysis demonstrated that the induction of BDNF mRNA in response to the repeated coadministration paradigm occurs in the dentate gyrus granule and CA1 and CA3 pyramidal cell layers of hippocampus. These findings demonstrate that coadministration shortens the time required for the upregulation of BDNF mRNA, supporting the possibility that this treatment may provide an effective therapy for major depression.

Identification and functional analysis of novel cAMP response element binding protein splice variants lacking the basic/leucine zipper domain

Two novel cAMP response element binding protein (CREB) splice variants were found by reverse transcription-polymerase chain reaction cloning by using mouse brain RNA as a template. One splice variant, named Delta-14, lacks 14 nucleotides at the beginning of exon 9 of the CREBDelta isoform. The other, named Delta-35, lacks 35 nucleotides at the beginning of exon 8 of CREBDelta. These nucleotide deletions cause frame shifts for codon usage, producing proteins which conserve the major phosphorylation site (Ser(133)) but lack the basic/leucine zipper domain, which is essential for binding to DNA and to other transcription factors. Both variants are widely expressed in peripheral tissues, but are enriched in brain, thymus, and testis. CREBDelta-14 and Delta-35 variant proteins were expressed by using an in vitro translation system and by transfecting into human embryonic kidney 293 cells. Both variants were detected by a CREB antibody that recognizes the CREBDelta amino terminus, but not by an antibody which recognizes the CREBDelta carboxy terminus, as would be predicted based on the frame shift. Activation of the cAMP pathway increased phospho-CREB immunoreactivity, indicating that these variants are substrates of cAMP-dependent protein kinase. In addition, immunocytochemical analysis demonstrated that CREBDelta-14 and Delta-35 are primarily cytosolic, whereas CREBalpha is predominantly in the nucleus. Finally, expression of CREBDelta-14 or Delta-35 decreased cAMP responsive element-chloramphenicol acetyltransferase reporter activity, demonstrating that both can function as repressors of endogenous CREB.

Neural plasticity to stress and antidepressant treatment

Adaptations at the cellular and molecular levels in response to stress and antidepressant treatment could represent a form of neural plasticity that contributes to the pathophysiology and treatment of depression. At the cellular level, atrophy and death of stress-vulnerable neurons in the hippocampus, as well as decreased neurogenesis of hippocampal neurons, has been reported in preclinical studies. Clinical studies also provide evidence for atrophy and cell death in the hippocampus, as well as the prefrontal cortex. It is possible that antidepressant treatment could oppose these adverse cellular effects, which may be regarded as a loss of neural plasticity, by blocking or reversing the atrophy of hippocampal neurons and by increasing cell survival and function. The molecular mechanisms underlying these effects are discussed, including the role of the cAMP signal transduction cascade and neurotrophic factors.

Polymorphisms of the human apolipoprotein E promoter and bleomycin hydrolase gene: risk factors for Alzheimer's dementia?

In addition to the apolipoprotein E (ApoE) tri-allele polymorphism, genetic variants of the apolipoprotein E promoter (-491A/T) and the bleomycin hydrolase (BH-PEN) gene have also been proposed as genetic risk factors for Alzheimer's dementia (AD). Since reports about the relevance of these polymorphisms for the pathogenesis of AD have been contradictory, we performed an association study with some modifications. First, the control group in this study was made up of non-demented psychiatric inpatients, rather than healthy subjects. This procedure allows the specificity of the relationship between a given genotype and AD (as opposed to other psychiatric disorders) to be determined. Second, as an alternative to preexisting relatively time consuming techniques, BH-PEN polymorphism was determined using a simplified method based on PCR genotyping. We found a significant linkage disequilibrium between the -491A/T and ApoE polymorphisms. However, no direct association was observed between the -491A/T or BH-PEN polymorphism and AD.

Expression of the transcription factor deltaFosB in the brain controls sensitivity to cocaine

Acute exposure to cocaine transiently induces several Fos family transcription factors in the nucleus accumbens, a region of the brain that is important for addiction. In contrast, chronic exposure to cocaine does not induce these proteins, but instead causes the persistent expression of highly stable isoforms of deltaFosB. deltaFosB is also induced in the nucleus accumbens by repeated exposure to other drugs of abuse, including amphetamine, morphine, nicotine and phencyclidine. The sustained accumulation of deltaFosB in the nucleus accumbens indicates that this transcription factor may mediate some of the persistent neural and behavioural plasticity that accompanies chronic drug exposure. Using transgenic mice in which deltaFosB can be induced in adults in the subset of nucleus accumbens neurons in which cocaine induces the protein, we show that deltaFosB expression increases the responsiveness of an animal to the rewarding and locomotor-activating effects of cocaine. These effects of deltaFosB appear to be mediated partly by induction of the AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole) glutamate receptor subunit GluR2 in the nucleus accumbens. These results support a model in which deltaFosB, by altering gene expression, enhances sensitivity to cocaine and may thereby contribute to cocaine addiction.

Repeated stress increases catalytic TrkB mRNA in rat hippocampus

Northern blot analysis was utilized to distinguish between catalytic and truncated TrkB mRNA on the basis of transcript size. Repeated (10 days), but not acute, immobilization stress significantly increased levels of catalytic TrkB mRNA, but did not influence expression of truncated TrkB transcripts in rat hippocampus. Exposure to another paradigm, a combination of different, unpredictable stressors, also increased levels of catalytic, but not truncated, TrkB mRNA. In situ hybridization analysis demonstrated that chronic stress up-regulated TrkB mRNA in CA1 and CA3 pyramidal and dentate gyrus granule cells layers of hippocampus. As previously reported, both acute and chronic immobilization stress decreased expression of BDNF mRNA, suggesting that up-regulation of catalytic TrkB mRNA may be a compensatory adaptation to repeated stress.

Region-specific regulation of RGS4 (Regulator of G-protein-signaling protein type 4) in brain by stress and glucocorticoids: in vivo and in vitro studies

The present study demonstrates that the regulator of G-protein-signaling protein type 4 (RGS4) is differentially regulated in the locus coeruleus (LC) and the paraventricular nucleus (PVN) of the hypothalamus by chronic stress and glucocorticoid treatments. Acute or chronic administration of corticosterone to adult rats decreased RGS4 mRNA levels in the PVN but increased these levels in the LC. Similarly, chronic unpredictable stress decreased RGS4 mRNA levels in the PVN but had a strong trend to increase these levels in the LC. Chronic stress also decreased RGS4 mRNA levels in the pituitary. The molecular mechanisms of RGS4 mRNA regulation were further investigated in vitro in the LC-like CATH.a cell line and the neuroendocrine AtT20 cell line using the synthetic corticosterone analog dexamethasone. Consistent with the findings in vivo, dexamethasone treatment caused a dose- and time-dependent decrease in RGS4 mRNA levels in AtT20 cells but a dose- and time-dependent increase in CATH.a cells. RGS4 mRNA regulation seen in these two cell lines seems to be attributable, at least in part, to opposite changes in mRNA stability. The differential regulation of RGS4 expression in the LC and in key relays of the hypothalamic-pituitary-adrenal axis could contribute to the brain's region-specific and long-term adaptations to stress.

Stimulation of adenylyl cyclase and induction of brain-derived neurotrophic factor and TrkB mRNA by NKH477, a novel and potent forskolin derivative

The present study was undertaken to examine whether NKH477, a novel and potent water-soluble forskolin derivative, stimulates adenylyl cyclase and regulates brain-derived neurotrophic factor (BDNF) and TrkB expression in the rat brain. Administration of NKH477 at a dose of 1.0 mg/kg, but not 0.1 mg/kg, increased levels of cyclic AMP (cAMP) in a time-dependent manner in frontal cortex and hippocampus. Repeated administration of NKH477 (1.0 mg/kg) for 7 or 14 days also increased levels of cAMP in these two brain regions, indicating that the response does not desensitize with chronic treatment. In addition, administration of NKH477 at the 1 mg/kg dose increased the expression of BDNF and TrkB mRNA in frontal cortex and hippocampus. This effect was observed after single, as well as repeated (7 or 14 days), administration of NKH477. These results demonstrate that NKH477 administration rapidly increases cAMP levels in brain and provides evidence that stimulation of this second messenger system increases the expression of BDNF and TrkB mRNA.

Hippocampal mossy fiber sprouting induced by chronic electroconvulsive seizures

Stress, which can precipitate and exacerbate depression, causes atrophy and in severe cases death of hippocampal neurons. Atrophy of the hippocampus has also been observed in patients suffering from recurrent major depression. The present study examines the influence of electroconvulsive seizures, one of the most effective treatments for depression, on the morphology and survival of hippocampal neurons. The results demonstrate that chronic administration of electroconvulsive seizures induces sprouting of the granule cell mossy fiber pathway in the hippocampus. This sprouting is dependent on repeated administration of electroconvulsive seizures, reaches a maximum 12 days after the last treatment and is long lasting (i.e. up to six months). Electroconvulsive seizure-induced sprouting occurs in the absence of neuronal loss, indicating that sprouting is not a compensatory response to cell death. This is different from the sprouting induced by kindling or excitotoxin treatment, which induce cell death along with recurrent seizures. Electroconvulsive seizure-induced sprouting is significantly diminished in brain-derived neurotrophic factor heterozygote knockout mice, indicating that this neurotrophic factor contributes to mossy fiber sprouting. However, infusion of brain-derived neurotrophic factor into the hippocampus does not induce sprouting of the mossy fiber pathway. The results demonstrate that chronic administration of electroconvulsive seizures induces mossy fiber sprouting and suggest that increased expression of brain-derived neurotrophic factor is necessary, but not sufficient for the induction of this sprouting. Although the functional consequences remain unclear, sprouting of the mossy fiber pathway would appear to oppose the actions of stress and could thereby contribute to the therapeutic actions of electroconvulsive seizure therapy.

Role of 5-HT2A receptors in the stress-induced down-regulation of brain-derived neurotrophic factor expression in rat hippocampus

Immobilization stress decreases the expression of BDNF mRNA in the rat hippocampus, and this effect could contribute to the atrophy of hippocampal neurons. This study examines the influence of selective 5-HT, as well as norepinephrine, receptor antagonists on the stress-induced down-regulation of BDNF mRNA. Pretreatment with a selective 5-HT2A receptor antagonist, MDL100,907, significantly blocked the influence of stress on expression of BDNF mRNA. In contrast, pretreatment with either a selective 5-HT2C or 5-HT1A receptor antagonist did not influence the stress-induced decrease in levels of BDNF mRNA. The stress-induced decrease was also not influenced by pretreatment with antagonists of beta(1/2)- or alpha1-adrenergic, or CRF-R1 receptors. The results demonstrate that 5-HT2A receptors mediate, at least in part, the stress-induced down-regulation of BDNF expression in the rat hippocampus.

Chronic antidepressant administration increases the expression of cAMP-specific phosphodiesterase 4A and 4B isoforms

The influence of chronic antidepressant administration on expression of the three major phosphodiesterase (PDE) 4 subtypes found in brain (PDE4A, PDE4B, and PDE4D) was examined. The treatments tested included representatives of four major classes of antidepressants: selective reuptake inhibitors of serotonin (sertraline and fluoxetine) or norepinephrine (desipramine), a monoamine oxidase inhibitor (tranylcypromine), and electroconvulsive seizure. Expression of PDE4A and PDE4B, but not PDE4D, mRNA and immunoreactivity were significantly increased in rat frontal cortex by chronic administration of each of the four classes of antidepressants. We also found that antidepressant administration significantly increased the expression of PDE4B mRNA in the nucleus accumbens, a brain region thought to mediate pleasure and reward that could also contribute to the anhedonia often observed in depressed patients. In contrast, expression of PDE4A and PDE4B were not influenced by short-term treatment (1 or 7 d) and were not influenced by chronic administration of nonantidepressant psychotropic drugs (cocaine or haloperidol), demonstrating the time dependence and pharmacological specificity of these effects. Upregulation of PDE4A and PDE4B may represent a compensatory response to antidepressant treatment and activation of the cAMP system. The possibility that targeted inhibition of these PDE4 subtypes may produce an antidepressant effect is discussed.

Regulation of cocaine reward by CREB

Cocaine regulates the transcription factor CREB (adenosine 3', 5'-monophosphate response element binding protein) in rat nucleus accumbens, a brain region that is important for addiction. Overexpression of CREB in this region decreases the rewarding effects of cocaine and makes low doses of the drug aversive. Conversely, overexpression of a dominant-negative mutant CREB increases the rewarding effects of cocaine. Altered transcription of dynorphin likely contributes to these effects: Its expression is increased by overexpression of CREB and decreased by overexpression of mutant CREB. Moreover, blockade of kappa opioid receptors (on which dynorphin acts) antagonizes the negative effect of CREB on cocaine reward. These results identify an intracellular cascade-culminating in gene expression-through which exposure to cocaine modifies subsequent responsiveness to the drug.

Essential role of the fosB gene in molecular, cellular, and behavioral actions of chronic electroconvulsive seizures

The role of Fos-like transcription factors in neuronal and behavioral plasticity has remained elusive. Here we demonstrate that a Fos family member protein plays physiological roles in the neuronal, electrophysiological, and behavioral plasticity associated with repeated seizures. Repeated electroconvulsive seizures (ECS) induced isoforms of DeltaFosB in frontal cortex, an effect that was associated with increased levels of the NMDA receptor 1 (NMDAR1) glutamate receptor subunit. Induction of DeltaFosB and the upregulation of NMDAR1 occurred within the same neurons in superficial layers of neocortex. Activator protein-1 (AP-1) complexes composed of DeltaFosB were bound to a consensus AP-1 site in the 5'-promoter region of the NMDAR1 gene. The upregulation of NMDAR1 was absent in mice with a targeted disruption of the fosB gene. In addition, repeated ECS treatment caused progressively shorter motor seizures (tolerance) in both rats and wild-type mice, as well as reduced NMDA-induced inward currents in pyramidal neurons from superficial layers of the neocortex of wild-type mice. These behavioral and electrophysiological effects were also significantly attenuated in fosB mutant mice. These findings identify fosB gene products as transcription factors critical for molecular, electrophysiological, and behavioral adaptations to motor seizures.