Effects of Hypoxia on the Activity of the Dopaminergic Neuron System in the Rat Striatum as Studied by In Vivo Brain Microdialysis

The purpose of the present study is to clarify the effects of hypoxia on the activity of the dopaminergic neurons in the brain and its mechanism of action. For this purpose, the effects of hypoxia on the extracellular levels of 3,4-dihy-droxyphenylethylamine (dopamine) were examined in the rat Striatum using in vivo brain microdialysis in the presence or absence of pretreatment with either tetrodotoxin (a blocker of voltage-dependent sodium channels) or nomifensine (a blocker of dopamine reuptake). Exposure to various degrees of hypoxia (15, 10, and 8% O₂ in N₂) increased dopamine levels in striatal dialysates to 200, 400, and 1,100%, respectively, of the control value. On reoxygenation, dopamine levels in the dialysates rapidly returned to the control level. Reexposure to hypoxia increased the dopamine levels to the same extent as during the first exposure. After addition of tetrodotoxin (40 mUM) to the perfusion fluid or pretreatment with nomifensine (100 mg/kg, i.p.), exposure to hypoxia no longer increased the dopamine levels. These results suggest that although hypoxia induces an increase in the extracellular dopamine levels (hence, an apparent increase in the activity of the dopaminergic neurons), this increase is not the result of an increase in dopamine release itself, but rather the result of inhibition of the dopamine reuptake mechanism.     

Synthesis and biological evaluation of novel 3,4-diaryl lactam derivatives as triple reuptake inhibitors

A series of 3,4-diarylpyrrolidin-2-one was designed, prepared and evaluated as triple reuptake inhibitors for antidepressant. Most compounds exhibited comparable in vitro efficacy as norepinephrine and dopamine transporter reuptake inhibitors. Especially, 2i showed better potency than GBR-12909 (IC₅₀ = 14 nM) which was used as reference compound for dopamine transporter. In addition, 2a and 2b showed inhibition (5.17 μM–85.6 nM) for three transporters.     

Comparison of the effects of serotonin selective,norepinephrine selective,and dual serotonin and norepinephrine reuptake inhibitors on lower urinary tract function in cats

Previous studies showed that the dual serotonin (5-hydroxytryptamine, 5-HT) and norepinephrine (NE) reuptake inhibitor, duloxetine, increases bladder capacity and urethral sphincter electromyographic (EMG) activity in a cat model of acetic acid-induced bladder irritation. The present study aimed to determine the relative importance of 5-HT versus NE reuptake inhibition for mediating these effects by examining drugs that are selective for either the 5-HT or NE system or both. Similar to duloxetine, venlafaxine (0.1 to 10 mg/kg), also a dual serotonin and norepinephrine reuptake inhibitor, produced marked increases in bladder capacity and EMG activity that were reversed by methiothepin (0.3 mg/kg). S-norfluoxetine (0.01 to 10 mg/kg), a serotonin selective reuptake inhibitor, produced small but significant increases in bladder capacity and EMG activity at doses of 3 and 10 mg/kg. Thionisoxetine (0.01 to 3.0 mg/kg), a NE selective reuptake inhibitor, produced no effects on bladder capacity or sphincter EMG activity. Surprisingly, co-administration of thionisoxetine and s-norfluoxetine up to doses of 1 mg/kg of each compound produced no effect on lower urinary tract function. These doses were the maximum that could be administered in combination due to drug-induced emergence of skeletal muscle activity in chloralose-anesthetized animals. These results indicate that there are unexplained pharmacological differences between the effects of single compounds that exhibit dual NE and 5-HT reuptake inhibition and a combination of compounds that exhibit selective NE and 5-HT reuptake inhibition on lower urinary tract function.     

Elevated cortical extracellular fluid glutamate in transgenic mice expressing human mutant (G93A) Cu/Zn superoxide dismutase

Transgenic mice expressing a mutated (G93A) human Cu/Zn superoxide dismutase (SOD1) develop motor neuron pathology and clinical symptoms similar to those seen in patients with amyotrophic lateral sclerosis. Loss of motor neurons is most prominent in lumbar, followed by cervical cord and then brainstem. No significant cell death has been reported in motor cortex. The integrity of the cortical glutamate reuptake systems was evaluated using intracerebral microdialysis and western immunoblot assays for the glutamate transporters GLT-1, GLAST, and EAAC1. The basal extracellular fluid levels of aspartate, glutamate, glutamine, 3,4-dihydroxyphenylacetic acid, and 5-hydroxyindole-3-acetic acid were evaluated by HPLC. The extraction fraction of L-3H]glutamate, corrected with [14C]mannitol, was also evaluated. GLT-1, EAAC1, and GLAST protein levels were determined by semiquantitative chemiluminescence immunoblot of proteins from membrane-enriched fractions. The relative optical density of film was translated into relative protein level by comparison with a standard control mouse. The SOD1 mutant mice demonstrated a significant (p < 0.05) increase in basal levels of extracellular aspartate and glutamate. In addition, when the glutamate extraction fraction was challenged with exogenous unlabeled glutamate (500 microM) by reversed microdialysis, the glutamate extraction fraction in the mutant SOD1 mice was decreased significantly from control levels. The SOD1 mutant mice demonstrated no difference in the cortical protein levels of the glutamate transporter subtypes. This study demonstrates that in areas of no visible pathology and no loss of glutamate transporter proteins, SOD1 mutant mice have elevated extracellular fluid aspartate and glutamate levels and a decreased capacity to clear glutamate from the extracellular space.     

5-Hydroxytryptamine (5-HT) Cellular Sequestration during Chronic Exposure Delays 5-HT3 Receptor Resensitization due to Its Subsequent Release

The serotonergic synapse is dynamically regulated by serotonin (5-hydroxytryptamine (5-HT)) with elevated levels leading to the down-regulation of the serotonin transporter and a variety of 5-HT receptors, including the 5-HT type-3 (5-HT₃) receptors. We report that recombinantly expressed 5-HT₃ receptor binding sites are reduced by chronic exposure to 5-HT (IC₅₀ of 154.0 ± 45.7 μm, t_½ = 28.6 min). This is confirmed for 5-HT₃ receptor-induced contractions in the guinea pig ileum, which are down-regulated after chronic, but not acute, exposure to 5-HT. The loss of receptor function does not involve endocytosis, and surface receptor levels are unaltered. The rate and extent of down-regulation is potentiated by serotonin transporter function (IC₅₀ of 2.3 ± 1.0 μm, t_½ = 3.4 min). Interestingly, the level of 5-HT uptake correlates with the extent of down-regulation. Using TX-114 extraction, we find that accumulated 5-HT remains soluble and not membrane-bound. This cytoplasmically sequestered 5-HT is readily releasable from both COS-7 cells and the guinea pig ileum. Moreover, the 5-HT level released is sufficient to prevent recovery from receptor desensitization in the guinea pig ileum. Together, these findings suggest the existence of a novel mechanism of down-regulation where the chronic release of sequestered 5-HT prolongs receptor desensitization.     

Diurnal Variation in the Function of Serotonin Terminals in the Rat Hypothalamus

The high-affinity binding of [3H]imipramine is associated with the serotonin (5-hydroxytryptamine; 5-HT) transporter in the brain and in platelets. In the rat hypothalamus it has been reported that the density of these sites is increased in the dark period of the day, and this could result in an alteration in the release of 5-HT. The electrically evoked release of [3H]5-HT was thus studied in preloaded hypothalamic slices prepared from rats kept under 12:12 h light/dark or dark/light schedules. The fractional release of [3H]5-HT evoked by electrical stimulation, but not by the 5-HT releasing agent fenfluramine, was significantly decreased during the dark period when compared with the light period. The effects of the 5-HT reuptake blocker citalopram, of the two 5-HT autoreceptor agonists 5-methoxytryptamine and RU 24969, and of the 5-HT autoreceptor antagonist methiothepin on the release of [3H]5-HT were the same in both groups of rats. In conclusion, the release of [3H]5-HT from prelabelled rat hypothalamic slices is decreased during the dark period of the day. This modification is not reflected by changes in the effects of citalopram, an inhibitor of 5-HT reuptake, to modify the overflow of [3H]5-HT. The sensitivity and efficacy of agonists of the 5-HT autoreceptor are the same during the light and dark periods of the day.     

Effect of Decreased Oxygen on In Vitro Release of Endogenous 3,4-Dihydroxyphenylethylamine from Mouse Striatum

The effects of hypoxia on release of endogenous 3,4-dihydroxyphenylethylamine (DA, dopamine) were investigated in mouse striatal slices. Following a 60-min preincubation, potassium increased DA release 12 times between zero and 1 min. By 10 min, uptake processes exceeded release and DA levels in the media decreased. Hypoxia (low oxygen) and anoxia (no oxygen) increased DA in the media by 120 and 205%, respectively, but did not alter dihydroxyphenylacetic acid concentrations. Under similar conditions, anoxia increased [3H]DA uptake eight-fold. For the uptake studies, the amount of DA added to the media was critical; in the presence of high concentrations of DA, anoxia reduced reuptake. Regardless of exogenous DA, hypoxia and anoxia increased extracellular DA, which may play a role in ischemic cell damage.     

In Vivo Dynamics of Norepinephrine Release-Reuptake in Multiple Terminal Field Regions of Rat Brain

Abstract: Electrical stimulation of the ascending dorsal tegmental bundle of the locus ceruleus was used to elicit controlled release of norepinephrine. Real-time in vivo monitoring in the brains of urethane-anesthetized rats was observed with high speed chronocoulometry at rapidly responding carbon fiber electrodes. Using modeling similar to that developed for dopamine release, the electrochemical signals were characterized as the balance between norepinephrine release per electrical stimulation pulse and apparent Michaelis-Menten reuptake parameters. Stimulation produced simultaneous overflow release at all terminal fields examined. The release and reuptake characteristics varied considerably in different regions. If the parameters are normalized to endogenous concentration in the terminal fields, release but not reuptake correlates with innervation density in several regions. Stimulated release results in norepinephrine overflow and transport in most brain regions with half-lives of 1–3 s and overflow distances of 25–50 µm at most. A surprising exception occurs in the upper layers of cortex (cingulate and sensory) where half-lives may be in the 10s of seconds and spatial reach may be up to 100 µm. The uptake in the outer cortical layers appears to be minimal and comparable with only nonspecific reuptake.     

The association between major depressive disorder,use of antidepressants and bone mineral density (BMD) in men

Objective:

Both depression and use of antidepressants have been negatively associated with bone mineral density (BMD) but mainly in studies among postmenopausal women. Therefore, the aim of this study was to investigate these relationships in men.

Methods:

Between 2006 and 2011, 928 men (aged 24-98 years) from the Geelong Osteoporosis Study completed a comprehensive questionnaire, clinical measurements and had BMD assessments at the forearm, spine, total hip and total body. Major depressive disorder (MDD) was identified using a structured clinical interview (SCID-I/NP). The cross-sectional associations between BMD and both MDD and antidepressant use were analyzed using multivariable linear regression.

Results:

Of the study population, 84 (9.1%) men had a single MDD episode, 50 (5.4%) had recurrent episodes and 65 (7.0%) were using antidepressants at the time of assessment. Following adjustments, recurrent MDD was associated with lower BMD at the forearm and total body (-6.5%, P=0.033 and -2.5%, P=0.033, respectively compared to men with no history of MDD), while single MDD episodes were associated with higher BMD at the total hip (+3.4%, P=0.030). Antidepressant use was associated with lower BMD only in lower-weight men (<75-110 kg depending on bone site).

Conclusions:

Both depression and use of antidepressants should be taken into account as possible risk factors for osteoporosis in men.