Transiently increased glutamate cycling in rat PFC is associated with rapid onset of antidepressant-like effects.

Several drugs have recently been reported to induce rapid antidepressant effects in clinical trials and rodent models. Although the cellular mechanisms involved remain unclear, reports suggest that increased glutamate transmission contributes to these effects. Here, we demonstrate that the antidepressant-like efficacy of three unique drugs, with reported rapid onset antidepressant properties, is coupled with a rapid transient rise in glutamate cycling in the medial prefronal cortex (mPFC) of awake rats as measured by ex vivo 1H-[13C]-nuclear magnetic resonance spectroscopy. Rats were acutely pretreated by intraperitoneal injection with a single dose of ketamine (1, 3, 10, 30 and 80 mg kg-1), Ro 25-6981 (1, 3 and 10 mg kg-1), scopolamine (5, 25 and 100 µg kg-1) or vehicle (controls). At fixed times after drug injection, animals received an intravenous infusion of [1,6-13C2]glucose for 8 min to enrich the amino-acid pools of the brain with 13C, followed by rapid euthanasia. The mPFC was dissected, extracted with ethanol and metabolite 13C enrichments were measured. We found a clear dose-dependent effect of ketamine and Ro 25-6981 on behavior and the percentage of 13C enrichment of glutamate, glutamine and GABA (γ-aminobutyric acid). Further, we also found an effect of scopolamine on both cycling and behavior. These studies demonstrate that three pharmacologically distinct classes of drugs, clinically related through their reported rapid antidepressant actions, share the common ability to rapidly stimulate glutamate cycling at doses pertinent for their antidepressant-like efficacy. We conclude that increased cycling precedes the antidepressant action at behaviorally effective doses and suggest that the rapid change in cycling could be used to predict efficacy of novel agents or identify doses with antidepressant activity.

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.

Altered cerebral glucose and acetate metabolism in succinic semialdehyde dehydrogenase-deficient mice: evidence for glial dysfunction and reduced glutamate/glutamine cycling.

Succinic semialdehyde dehydrogenase (SSADH) catalyzes the NADP-dependent oxidation of succinic semialdehyde to succinate, the final step of the GABA shunt pathway. SSADH deficiency in humans is associated with excessive elevation of GABA and gamma-hydroxybutyrate (GHB). Recent studies of SSADH-null mice show that elevated GABA and GHB are accompanied by reduced glutamine, a known precursor of the neurotransmitters glutamate and GABA. In this study, cerebral metabolism was investigated in urethane-anesthetized SSADH-null and wild-type 17-day-old mice by intraperitoneal infusion of [1,6-(13)C(2)]glucose or [2-(13)C]acetate for different periods. Cortical extracts were prepared and measured using high-resolution (1)H-[(13)C] NMR spectroscopy. Compared with wild-type, levels of GABA, GHB, aspartate, and alanine were significantly higher in SSADH-null cortex, whereas glutamate, glutamine, and taurine were lower. (13)C Labeling from [1,6-(13)C(2)]glucose, which is metabolized in neurons and glia, was significantly lower (expressed as mumol of (13)C incorporated per gram of brain tissue) for glutamate-(C4,C3), glutamine-C4, succinate-(C3/2), and aspartate-C3 in SSADH-null cortex, whereas Ala-C3 was higher and GABA-C2 unchanged. (13)C Labeling from [2-(13)C]acetate, a glial substrate, was lower mainly in glutamine-C4 and glutamate-(C4,C3). GHB was labeled by both substrates in SSADH-null mice consistent with GABA as precursor. Our findings indicate that SSADH deficiency is associated with major alterations in glutamate and glutamine metabolism in glia and neurons with surprisingly lesser effects on GABA synthesis.

Mild prenatal stress enhances learning performance in the non-adopted rat offspring.

The present study was designed to investigate whether mild stress during pregnancy affects offspring behaviors, including learning performance. Prenatal stress was induced by short-lasting, mild restraint stress, which had previously been shown to facilitate the morphological development of fetal brain neurons. Adult offspring whose dams had been restrained in a small cage for 30min daily from gestation day 15 to 17 showed enhanced active avoidance and radial maze learning performance. In addition, the prenatally stressed rats showed weaker emotional responses than unstressed control, as indicated by decreases both in ambulation upon initial exposure to an open field and in Fos expression in the amygdala induced by physical stress. The observed effects of prenatal stress on learning performance and emotional behavior were attenuated by foster rearing by unstressed dams. Fos expression in the hypothalamic paraventricular nucleus following physical stress and corticosterone secretion during physical and psychological stress did not differ between the prenatally stressed and unstressed control rats. From these results we suggest that mild prenatal stress facilitates learning performance in the adult offspring. The enhancement of learning performance appears to be accompanied by reduced emotionality, but not by any apparent alterations in hypothalamic-pituitary-adrenal responses. In addition, the observation of differential behaviors in the adopted and non-adopted animals supports the notion that the postnatal environment modifies the behavioral effects of prenatal stress.

In vivo electrical activity of brainstem neurons in fetal rats during asphyxia.

To see changes in the activity and the sensitivity to glutamate of fetal brain neurons during asphyxia, the electrical activity of brainstem neurons was recorded extracellularly in fetal rats which were still connected with the dams by the intact umbilical cord. In urethan-anesthetized pregnant rats, fetal asphyxia (2-10 min) was induced by occluding the umbilical cord with a surgical clip, while reperfusion of the umbilical blood flow was performed by local application of a relaxant of blood vessels to the occlusion site. The spontaneous discharge of fetal brainstem neurons was suppressed for a long period of time by umbilical cord occlusion. The suppression of the firing occurred 48-150 (78+/-7) s after the start of umbilical cord occlusion, and lasted even after fetal cortical PO(2) recovered to control level after reperfusion. The changes occurred with a marked reduction in spike amplitude. A similar suppression was observed for the spikes induced by iontophoretic application of glutamate, although fetal brainstem neurons were extremely sensitive to glutamate before asphyxia. The suppression of the spontaneous spikes became more notable and longer when asphyxia was repeated. These findings suggest that the long-lasting suppression of fetal neurons during asphyxia may contribute to a reduction of cellular energy requirements in the fetal brain, thereby playing a role in the resistance of fetal neurons to brain damage caused by asphyxia. Furthermore, the reduced sensitivity of fetal neurons to glutamate during asphyxia may also contribute to prevent brain damage due to excitotoxity of glutamate.

Induction and adaptation of Fos expression in the rat brain by two types of acute restraint stress.

The present study was designed to examine whether both induction and adaptation of brain Fos expression during acute stress depend on the intensity and duration of stressors. For this purpose, different durations of two types of acute stress, mild (restraint) and severe (immobilization) stress, were employed. Stress-induced Fos expression was analyzed quantitatively by immunohistochemistry. Adaptation of Fos expression to the acute stressors was not apparent in the hypothalamic paraventricular nucleus (PVN) or locus coeruleus (LC) but was observed in the amygdala, hippocampus, and cerebral cortex. A higher level of Fos expression was seen in the PVN, LC, and amygdala, following severe stress than was seen following mild stress. In the hippocampus, the dentate gyrus showed reduced Fos expression in response to stressors, although both mild and severe acute stress increased Fos expression in other regions of the hippocampus. The cingulate cortex showed increased Fos expression during mild stress, whereas long-duration severe stress reduced Fos expression. In the somatosensory cortex, both stressors increased Fos expression. These results indicate that the PVN and LC are relatively resistant to adaptation to acute stress compared to other brain regions. In addition, the PVN, LC, and amygdala may play important roles in the perception of the severity of stress.

The proliferation index of MIB-1 as a prognostic factor for patients with transitional cell carcinoma of the upper urinary tract.

BACKGROUND: Recently, several reports have shown that immunohistochemical analysis using MIB-1 antibody, which recognizes Ki-67 (a human nuclear antigen expressed of proliferating cells), is a useful method for determining the proliferative activity of various cancers. In this study, the authors evaluated the prognostic usefulness of the proliferation index using MIB-1 antibody in transitional cell carcinoma of the upper urinary tract. METHODS: Proliferation activity was investigated immunohistochemically using monoclonal antibody MIB-1 in formalin fixed, paraffin embedded tissues obtained from 67 specimens of renal pelvic and ureteral cancer. The MIB-1 proliferation index values were calculated from each sample as the percentage of positive nuclei expressed in tumor cells and the clinicopathologic correlation evaluated. RESULTS: The MIB-1 proliferation index values were correlated with prognostic parameters such as pathologic stage ( < or = pT1 vs. > or = pT2, P < 0.0005), histologic grade (G1 vs. G2, P < 0.01; G1 vs. G3, P < 0.0001; G2 vs. G3, P < 0.001), and prognosis (P < 0.0001). When patients were subgrouped using index values, patients with higher indices ( > or = 24%) had significantly poorer survival (P < 0.0001). This was especially observed in the G2 group, in which 9 of 10 patients in the higher indices subgroup had a high incidence of recurrence and died. In contrast, only 2 of 29 patients in the lower indices subgroup died. The higher indices subgroup had significantly worse cause specific survival (P < 0.0001). Furthermore, with regard to the muscle invasive tumors ( > or = pT2), the higher indices subgroup also had significantly worse cause specific survival (P < 0.0001). CONCLUSIONS: The results of the evaluation of prognostic parameters indicate that the MIB-1 proliferation index is a useful prognostic factor and may enhance the accuracy of conventional morphologic grading and pathologic staging systems.