Knockdown of brain-derived neurotrophic factor in specific brain sites precipitates behaviors associated with depression and reduces neurogenesis.

Depression has been associated with reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus. In addition, animal studies suggest an association between reduced hippocampal neurogenesis and depressive-like behavior. These associations were predominantly established based on responses to antidepressant drugs and alterations in BDNF levels and neurogenesis in depressive patients or animal models for depressive behavior. Nevertheless, there is no direct evidence that the actual reduction of the BDNF protein in specific brain sites can induce depressive-like behaviors or affect neurogenesis in vivo. Using BDNF knockdown by RNA interference and lentiviral vectors injected into specific subregions of the hippocampus we show that a reduction in BDNF expression in the dentate gyrus, but not the CA3, reduces neurogenesis and affects behaviors associated with depression. Moreover, we show that BDNF has a critical function in neuronal differentiation, but not proliferation in vivo. Finally, we found that a specific BDNF knockdown in the ventral subiculum induces anhedonic-like behavior. These findings provide substantial support for the neurotrophic hypothesis of depression and specify anatomical and neurochemical targets for potential antidepressant interventions. Moreover, the specific effect of BDNF reduction on neuronal differentiation has broader implications for the study of neurodevelopment and neurodegenerative diseases.

Structure-activity relationship of trihexyphenidyl analogs with respect to the dopamine transporter in the on going search for a cocaine inhibitor.

A series of trihexyphenidyl (THP) analogs were used to search for a derivative that could serve as a cocaine inhibitor. A compound that blocks binding of the cocaine analog carboxyfluorotropane (CFT), allows dopamine uptake and exhibits low side effects could serve as a good candidate for that purpose. All analogs were tested for the extent to which they inhibit CFT binding, dopamine uptake and n-methyl scopolamine (NMS) binding. Several structure-function relationships emerged. Methylation/halogenation of THP's benzene ring enhanced the compound's ability to block CFT binding in comparison to its ability to block dopamine uptake (5a-e). Replacement of the cyclohexyl ring with a benzene ring tended to create compounds that had lower affinities to the dopamine transporter (7b compared to THP, 7d compared to 5h, 7c compared to 8c) and modification of THP's piperidine ring tended to enhance affinity to the dopamine transporter (5f-h, 8a, 8c). One analog (5f) that showed little muscarinic activity indicating that it would probably have few side effects was investigated for its effects as an in vivo cocaine inhibitor. However, it showed few antagonistic effects in vivo. Nevertheless, this work greatly elucidates the structure-function relationships required for potential cocaine inhibitors and so lays out promising directions for future research.

Neuroactive steroids: their mechanism of action and their function in the stress response.

Steroids are usually identified as genomic regulators, yet recently a body of evidence has accumulated demonstrating specific plasma membrane effects, as well as coordinative effects, of some steroids on both membrane and intracellular receptors. The resulting rapid (<1 min) modulation of cellular activity has strongly suggested a non-genomic, and possibly modulatory, role for certain steroid compounds, and dramatic effects on membranes of excitable as well as other tissues have been demonstrated. Steroid synthesis and metabolism have been shown to exist in the CNS, and the effects have been seen in both the central and peripheral nervous systems. The major groups of neuroactive steroids, and their metabolites, have been progesterone, deoxycorticosterone, and some androgens, notably dihydroxyepiandrosterone (DHEA). These compounds show increased concentrations both in blood and in the brain following stress and they have also been associated with anxiolytic effects and antiepileptic activity. In the periphery, some of these compounds show remarkable inhibitory effects on the secretion of catecholamines and other neurotransmitters. The mechanism for the majority of the effects of these steroids is via their effect on receptor-mediated binding to ligand-gated ion channels. Activation of the GABAA receptor complex, resulting in the opening of its central chloride channel, is the major target of the neuroactive steroids, resulting in re-polarization of the plasma membrane and inhibition of further neuronal firing. The anxiolytic, anti-convulsant and sedative-hypnotic actions of these neuroactive steroids have resulted in their being used as therapeutic agents for the treatment of anxiety, epilepsy, insomnia, and possibly for the alteration of pain thresholds.

Catecholamine secretion from bovine adrenal chromaffin cells induced by the dextrorotatory isomer of anatoxin-a.

1. The nicotinic agonist (+)anatoxin-a was studied in acute preparations of adrenal chromaffin cells and was compared with other known stimulants in this system. 2. (+)Anatoxin-a was found to be a potent stimulant of catecholamine secretion with EC50=545.7 nM, which was 5.8 times as strong as nicotine (EC50=3,165 nM). (+)Anatoxin-a action was time dependent and saturable. 3. The pharmacological characteristics of (+)anatoxin-a were tested by using nicotinic and muscarinic antagonists (mecamylamine and atropine, respectively). Mecamylamine (1 microM) and atropine (100 microM) inhibited the secretion induced by (+)anatoxin-a (1 microM), as well as that induced by nicotine (10 microM), acetylcholine (10 microM and 100 microM) and oxotremorine-M (100 microM). 4. The calcium requirement for (+)anatoxin-a action was tested in comparison with the aforementioned stimulants. Addition of the calcium antagonist verapamil (10 microM) or the calcium chelator EGTA (3 mM) reduced all stimulants' action. 5. These results show that the (+)enantiomer of anatoxin-a is both dose and time dependent. Its action is mediated through the classical operation of the nicotinic acetylcholine receptor, by using calcium influx.

Short term effect of steroids on catecholamine secretion from bovine adrenal medulla chromaffin cells.

Bovine chromaffin cells were used to examine neuronal modulation, as their function is similar to sympathetic post-ganglionic neurons. The effect of steroids on evoked catecholamine secretion from primary culture of bovine adrenal medullary cells was investigated. A wide range of progestins, androgens and estrogens was found to have a significant effect on catecholamine secretion induced by the natural neurotransmitter acetylcholine (ACh). The androgens (especially androstandione and androsterone), as a class were the most effective in inhibition of stimulated secretion, while the estrogens had little, to no, effect. Among all steroids tested, progesterone had the most significant effect, other progestins were less potent. Progesterone inhibited catecholamine secretion evoked by ACh, nicotine and oxotremorine-M in a dose-dependent manner with similar IC50 values in the microM range. It also blocked the secretion evoked by high potassium concentration (59 nM) or veratradine (100 microM), but no effect was seen on the secretion evoked by the calcium ionophore A-23187 (10 microM). Progesterone inhibition of ACh or oxotremorine-M stimulation was immediate and sustained. These results suggest that progesterone and other steroids might have a membrane effect probably acting through blockade of calcium influx necessary for the secretory response.

Strychnine affects catecholamine secretion from bovine adrenal medulla chromaffin cells.

The effect of strychnine on evoked release of catecholamines from a primary culture of bovine adrenal medullary cells was investigated. Strychnine at > 1 microM inhibited catecholamine release stimulated by 10 microM acetylcholine, or 10 microM nicotine, but not by excess K+ (59 mM), the sodium ionophore veratridine (100 microM) or the calcium ionophore A-23187 (10 microM). The inhibitory response elicited by exposure of the cells to strychnine was rapid (< 3 min) and competitive with acetylcholine. High concentrations of acetylcholine (1 mM) completely overcame this inhibition. Strychnine might be acting on a regulatory site of the nicotinic-cholinergic receptor, which is genetically similar to the strychnine-binding 48 KD subunit of the glycine receptor.

Alteration of platelet benzodiazepine receptors by stress of war.

Mitochondrial benzodiazepine receptors play a major role in steroidogenesis. The authors determined plasma cortisol levels, platelet levels of mitochondrial benzodiazepine receptors, and anxiety and depression scores in 11 civilians exposed to the Persian Gulf war. The density of mitochondrial benzodiazepine receptors was 22% and 15% lower before and during the war, respectively, than 4 weeks after the end of the war. Relief of stress led to an increase in receptors, which correlated with the improvement in anxiety but not mood.

The platelet benzodiazepine receptor is unaltered in obsessive-compulsive disorder.

Mitochondrial benzodiazepine receptors (MBR) are sensitive to anxiety and stress. The aim of the present study was to investigate whether platelet MBR are altered in untreated obsessive-compulsive disorder (OCD) patients and whether chronic treatment with clomipramine (CMI) regulates these receptors. MBR were assessed in 13 drug-free OCD patients as compared with 15 healthy controls. Seven of the 13 patients were treated with CMI (200-300 mg/day). The density and affinity of the receptors to their ligand [3H]PK 11195 in OCD patients and controls were not affected by the CMI treatment despite the clinical improvement. It seems that, in contrast to generalized anxiety disorder, OCD is not associated with alterations in platelet benzodiazepine receptors.

"Peripheral" benzodiazepine receptor density is not altered by methylphenidate treatment in children with attention-deficit hyperactivity disorder.

ABSTRACT "Peripheral" benzodiazepine receptors (PBRs) are located in the central nervous system and the periphery, are involved in the release of dopamine, and are sensitive to agents active at the dopaminergic system. Because attention-deficit hyperactivity disorder (ADHD) is related to dysregulation of dopaminergic neurotransmission, and because benzodiazepines can potentially aggravate the symptoms of ADHD, we have assessed the possible involvement of PBRs in the pathophysiology and pharmacotherapy of ADHD. [(3)H]PK 11195 was used to label platelet PBRs. Platelet PBRs were measured in eight ADHD boys (aged 9-15 years) before and after 4 weeks of treatment with methylphenidate 10-20 mg/day. ADHD patients before treatment did not differ from age-matched healthy controls in [(3)H]PK 11195 binding values. Four weeks of methylphenidate treatment did not significantly affect platelet PBR density in children with ADHD, despite the beneficial clinical effects. These results do not support the involvement of the PBRs in the pathophysiology of ADHD or in the therapeutic effects of methylphenidate.

Platelet peripheral benzodiazepine receptors in repeated stress.

[3H]PK 11195 binding to platelet membranes and plasma stress hormones were studied in soldiers at the beginning of a parachute training course, following 6 days of preparatory exercises, and after the fourth actual parachute jump. A slight reduction (15%; NS) in the number of peripheral benzodiazepine receptors (PBR) was detected at the end of the exercise period, prior to the first jump. Reduced (26%; P less than 0.05) density of PBR was observed immediately after the repeated actual jumps. Equilibrium dissociation constants were not affected by the stressful situation. Plasma cortisol and prolactin levels remained unaltered during the entire study period.