Noradrenergic Neurotoxin DSP-4 Research Articles

Genetic loss of norepinephrine does not alter adult hippocampal neurogenesis in dopamine beta-hydroxylase deficient mice.

Norepinephrine (NE), and specific adrenoceptors, have been reported to influence distinct aspects of adult hippocampal neurogenesis, including latent stem cell activation, progenitor proliferation, and differentiation. These findings are predominantly based on the use of pharmacological approaches in both in vitro and in vivo systems. Here, we sought to assess the consequences of genetic ablation of NE on adult hippocampal neurogenesis, by examining dopamine β hydroxylase knockout (Dbh -/-) mice, which lack NE from birth. We find that Dbh -/- mice exhibit no difference in adult hippocampal progenitor proliferation and survival. Further, the number of immature newborn neurons, labeled using stage-specific developmental markers within the hippocampal neurogenic niche, was also unaltered in Dbh -/- mice. In contrast, the noradrenergic neurotoxin DSP-4, which had previously been shown to reduce adult hippocampal neurogenesis in rats, also resulted in a decline in hippocampal progenitor proliferation in C57/Bl6N mice. These findings indicate that pharmacological lesioning of noradrenergic afferents in adulthood, but not the complete genetic loss of NE from birth, impairs adult hippocampal neurogenesis in mice.

Vagus nerve stimulation improves locomotion and neuronal populations in a model of Parkinson's disease

BackgroundParkinson's disease (PD) is a progressive, neurodegenerative disorder with no disease-modifying therapies, and symptomatic treatments are often limited by debilitating side effects. In PD, locus coeruleus noradrenergic (LC-NE) neurons degenerate prior to substantia nigra dopaminergic (SN-DA) neurons. Vagus nerve stimulation (VNS) activates LC neurons, and decreases pro-inflammatory markers, allowing improvement of LC targets, making it a potential PD therapeutic. ObjectiveTo assess therapeutic potential of VNS in a PD model. MethodsTo mimic the progression of PD degeneration, rats received a systemic injection of noradrenergic neurotoxin DSP-4, followed one week later by bilateral intrastriatal injection of dopaminergic neurotoxin 6-hydroxydopamine. At this time, a subset of rats also had vagus cuffs implanted. After eleven days, rats received a precise VNS regimen twice a day for ten days, and locomotion was measured during each afternoon session. Immediately following final stimulation, rats were euthanized, and left dorsal striatum, bilateral SN and LC were sectioned for immunohistochemical detection of monoaminergic neurons (tyrosine hydroxylase, TH), α-synuclein, astrocytes (GFAP) and microglia (Iba-1). ResultsVNS significantly increased locomotion of lesioned rats. VNS also resulted in increased expression of TH in striatum, SN, and LC; decreased SN α-synuclein expression; and decreased expression of glial markers in the SN and LC of lesioned rats. Additionally, saline-treated rats after VNS, had higher LC TH and lower SN Iba-1. ConclusionsOur findings of increased locomotion, beneficial effects on LC-NE and SN-DA neurons, decreased α-synuclein density in SN TH-positive neurons, and neuroinflammation suggest VNS has potential as a novel PD therapeutic.

Effect of Noradrenergic Neurotoxin DSP-4 and Maprotiline on Heart Rate Spectral Components in Stressed and Resting Rats.

The effects of intraperitoneal DSP-4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, a noradrenergic neurotoxin) and maprotiline (an inhibitor of norepinephrine reuptake in synapses) on spectral components of heart rhythm variability were examined in outbred male and female rats treated with these agents in daily doses of 10 mg/kg for 3 days. At rest, DSP-4 elevated LF and VLF spectral components in male and female rats. Maprotiline elevated LF and VLF components in males at rest, increased HR and reduced all spectral components in resting females. Stress against the background of DSP-4 treatment sharply increased heart rate and reduced the powers of all spectral components (especially LF and VLF components). In maprotiline-treated rats, stress increased the powers of LF and VLF components. Thus, the central noradrenergic system participates in the formation of LF and VLF spectral components of heart rate variability at rest and especially during stressful stimulation, which can determine the phasic character of changes in the heart rate variability observed in stressed organism.

Clinical Vagus Nerve Stimulation Paradigms Induce Pronounced Brain and Body Hypothermia in Rats

Vagus nerve stimulation (VNS) is a widely used neuromodulation technique that is currently used or being investigated as therapy for a wide array of human diseases such as epilepsy, depression, Alzheimer's disease, tinnitus, inflammatory diseases, pain, heart failure and many others. Here, we report a pronounced decrease in brain and core temperature during VNS in freely moving rats. Two hours of rapid cycle VNS (7s on/18s off) decreased brain temperature by around [Formula: see text]C, while standard cycle VNS (30[Formula: see text]s on/300[Formula: see text]s off) was associated with a decrease of around [Formula: see text]C. Rectal temperature similarly decreased by more than [Formula: see text]C during rapid cycle VNS. The hypothermic effect triggered by VNS was further associated with a vasodilation response in the tail, which reflects an active heat release mechanism. Despite previous evidence indicating an important role of the locus coeruleus-noradrenergic system in therapeutic effects of VNS, lesioning this system with the noradrenergic neurotoxin DSP-4 did not attenuate the hypothermic effect. Since body and brain temperature affect most physiological processes, this finding is of substantial importance for interpretation of several previously published VNS studies and for the future direction of research in the field.

Noradrenergic regulation of plasticity marker expression in the adult rodent piriform cortex

The adult rodent piriform cortex has been reported to harbor immature neurons that express markers associated with neurodevelopment and plasticity, namely polysialylated neural cell adhesion molecule (PSA-NCAM) and doublecortin (DCX). We characterized the expression of PSA-NCAM and DCX across the rostrocaudal axis of the rat piriform cortex and observed higher numbers of PSA-NCAM and DCX positive cells in the posterior subdivision. As observed in the rat piriform cortex, Nestin-GFP reporter mice also revealed a similar gradient of GFP-positive cells with an increasing rostro-caudal gradient of expression. Given the extensive noradrenergic innervation of the piriform cortex and its role in regulating piriform cortex function and synaptic plasticity, we addressed the influence of norepinephrine (NE) on piriform cortex plasticity marker expression. Depletion of NE by treatment with the noradrenergic neurotoxin DSP-4 significantly increased the number of DCX and PSA-NCAM immunopositive cells in the piriform cortex of adult rats. Similarly, DSP-4 treated Nestin-GFP reporter mice revealed a robust induction of GFP-positive cells within the piriform cortex following NE depletion. Genetic loss of NE in dopamine β-hydroxylase knockout (Dbh −/−) mice phenocopied the effects of DSP-4, with an increase noted in PSA-NCAM and DCX positive cells in the piriform cortex. Further, chronic α2-adrenergic receptor stimulation with the agonist guanabenz increased PSA-NCAM and DCX positive cells in the piriform cortex of adult rats and GFP-positive cells in the piriform cortex of Nestin-GFP mice. By contrast, chronic α2-adrenergic receptor blockade with the antagonist yohimbine reduced PSA-NCAM and DCX positive cells in the piriform cortex of adult rats. Our results provide novel evidence for a role of NE in regulating the expression of plasticity markers, including PSA-NCAM, DCX, and nestin, within the adult mouse and rat piriform cortex.

P.1.e.008 - The effect of serotonergic receptor activation in the paraventricular nuclei of the hypothalamus on the expression of liver cytochrome P450

The aim of the present study was to examine the effect of the brain noradrenergic system on the expression of cytochrome P450 in the liver. The experiment was carried out on male Wistar rats. Intracerebroventricular injection of the noradrenergic neurotoxin DSP-4 diminished noradrenaline level in the brain. Simultaneously, significant decreases in the serum concentration of the growth hormone, testosterone and the thyroid hormone thyroxine, as well as an increase in corticosterone level were observed. The concentrations of triiodothyronine and the cytokines interleukine 2 (IL-2) and 6 (IL-6) were not changed by DSP-4. The neurotoxin produced complex changes in the functioning of cytochrome P450. Significant decreases in the activity of liver CYP2C11 (measured as a rate of the 2α- and 16α-hydroxylation of testosterone) and CYP3A (measured as a rate of the 2β- and 6β-hydroxylation of testosterone) were found. In contrast, the activity of CYP1A (measured as a rate of caffeine metabolism) rose, while that of CYP2A (measured as a rate of the 7α-hydroxylation of testosterone), CYP2C6 (measured as a rate of the 7-hydroxylation of warfarin) and CYP2D (the 1′-hydroxylation of bufuralol) remained unchanged. The changes in the activity of CYP1A, CYP2C11 and CYP3A correlated positively with those in CYP protein levels and with the CYP mRNA levels of CYP1A1, CYP2C11 and CYP3A1/2 genes, respectively. The obtained results indicate an important role of the brain noradrenergic system in the neuroendocrine regulation of liver cytochrome P450 expression, which may be of significance in pathological states involving this system, or during pharmacotherapy with drugs affecting noradrenergic transmission.

BDNF levels are increased by aminoindan and rasagiline in a double lesion model of Parkinson׳s disease

The anti-Parkinsonian drug rasagiline is a selective, irreversible inhibitor of monoamine oxidase and is used in the treatment of Parkinson׳s disease (PD). Its postulated neuroprotective effects may be attributed to MAO inhibition, or to its propargylamine moiety. The major metabolite of rasagiline, aminoindan, has shown promising neuroprotective properties in vitro but there is a paucity of studies investigating in vivo effects of this compound. Therefore, we examined neuroprotective effects of rasagiline and its metabolite aminoindan in a double lesion model of PD. Male Fisher 344 rats received i.p. injections of the noradrenergic neurotoxin DSP-4 and intra-striatal stereotaxic microinjections of the dopamine neurotoxin 6-OHDA. Saline, rasagiline or aminoindan (3mg/kg/day s.c.) were delivered via Alzet minipumps for 4 weeks. Rats were then tested for spontaneous locomotion and a novel object recognition task. Following behavioral testing, brain tissue was processed for ELISA measurements of growth factors and immunohistochemistry. Double-lesioned rats treated with rasagiline or aminoindan had reduced behavioral deficits, both in motor and cognitive tasks compared to saline-treated double-lesioned rats. BDNF levels were significantly increased in the hippocampus and striatum of the rasagiline- and aminoindan-lesioned groups compared to the saline-treated lesioned group. Double-lesioned rats treated with rasagiline or aminoindan exhibited a sparing in the mitochondrial marker Hsp60, suggesting mitochondrial involvement in neuroprotection. Tyrosine hydroxylase (TH) immunohistochemistry revealed a sparing of TH-immunoreactive terminals in double-lesioned rats treated with rasagiline or aminoindan in the striatum, hippocampus, and substantia nigra.These data provide evidence of neuroprotection by aminoindan and rasagiline via their ability to enhance BDNF levels.

The role of brain noradrenergic system in the regulation of liver cytochrome P450 expression

The aim of the present study was to examine the effect of the brain noradrenergic system on the expression of cytochrome P450 in the liver. The experiment was carried out on male Wistar rats. Intracerebroventricular injection of the noradrenergic neurotoxin DSP-4 diminished noradrenaline level in the brain. Simultaneously, significant decreases in the serum concentration of the growth hormone, testosterone and the thyroid hormone thyroxine, as well as an increase in corticosterone level were observed. The concentrations of triiodothyronine and the cytokines interleukine 2 (IL-2) and 6 (IL-6) were not changed by DSP-4. The neurotoxin produced complex changes in the functioning of cytochrome P450. Significant decreases in the activity of liver CYP2C11 (measured as a rate of the 2α- and 16α-hydroxylation of testosterone) and CYP3A (measured as a rate of the 2β- and 6β-hydroxylation of testosterone) were found. In contrast, the activity of CYP1A (measured as a rate of caffeine metabolism) rose, while that of CYP2A (measured as a rate of the 7α-hydroxylation of testosterone), CYP2C6 (measured as a rate of the 7-hydroxylation of warfarin) and CYP2D (the 1′-hydroxylation of bufuralol) remained unchanged. The changes in the activity of CYP1A, CYP2C11 and CYP3A correlated positively with those in CYP protein levels and with the CYP mRNA levels of CYP1A1, CYP2C11 and CYP3A1/2 genes, respectively. The obtained results indicate an important role of the brain noradrenergic system in the neuroendocrine regulation of liver cytochrome P450 expression, which may be of significance in pathological states involving this system, or during pharmacotherapy with drugs affecting noradrenergic transmission.

Effects of the noradrenergic neurotoxin DSP-4 on the expression of α1-adrenoceptor subtypes after antidepressant treatment

AbstractWe have previously reported that chronic imipramine and electroconvulsive treatments increase the α1A-adrenoceptor (but not the α1B subtype) mRNA level and the receptor density in the rat cerebral cortex. Furthermore, we have also shown that chronic treatment with citalopram does not affect the expression of either the α1A- or the α1B-adrenoceptor, indicating that the previously observed up-regulation of α1A-adrenoceptor may depend on the noradrenergic component of the pharmacological mechanism of action of these antidepressants. Here, we report that previous noradrenergic depletion with DSP-4 (50mg/kg) (a neurotoxin selective for the noradrenergic nerve terminals) significantly attenuated the increase of α1A-adrenoceptor mRNA induced by a 14-day treatment with imipramine (IMI, 20mg/kg, ip) and abolished the effect of electroconvulsive shock (ECS, 150mA, 0.5s) in the prefrontal cortex of the rat brain. The changes in the receptor protein expression (as reflected by its density) that were induced by IMI and ECS treatments were differently modulated by DSP-4 lesioning, and only the ECS-induced increase in α1A-adrenoceptor level was abolished. This study provides further evidence corroborating our initial hypothesis that the noradrenergic component of the action of antidepressant agents plays an essential role in the modulation of α1A-adrenoceptor in the rat cerebral cortex.

Interference of the noradrenergic neurotoxin DSP4 with neuronal and nonneuronal monoamine transporters

The haloalkylamine DSP4 (N[-2-chloroethyl]-N-ethyl-2-bromobenzylamine) is a noradrenergic neurotoxin, which is used for the chemical denervation of noradrenergic neurons, and it has been proposed to be a selective substrate for the neuronal, Na(+)- and Cl(-)-dependent noradrenaline transporter (NAT). In the present study, we investigated whether DSP4 not only interacts with the human NAT (hNAT) but also with other neuronal monoamine transporters such as the transporters for dopamine (hDAT) and serotonin (hSERT) or with nonneuronal (Na(+)-independent) monoamine transporters also known as organic cation transporters (OCTs), such as hOCT(1), hOCT(2), and hOCT(3). Using human embryonic kidney HEK293 cells heterologously expressing the corresponding transporter, we show that DSP4 irreversibly inhibits the hNAT, hDAT, hSERT, and hOCT(3). However, this inhibition includes a reversible component at the hDAT, hSERT, and hOCT(3) but not at the hNAT. The inhibitory potency of DSP4 at the neuronal transporters was highest at the hNAT (IC(50) about 5 microM), and it was about five and 40 times lower at the hSERT and hDAT, respectively. DSP4 inhibited all three hOCTs with high potency (IC(50) about 1 microM) but in a completely reversible manner at hOCT(1) and hOCT(2). Cytotoxicity by 24-h exposure of hNAT- or hOCT-expressing cells to low DSP4 concentrations (<10 microM) could be observed only in hNAT-expressing cells. Thus, DSP4's high-affinity uptake through the NAT together with its completely irreversible mode of interaction with the NAT may contribute to its selectivity as noradrenergic neurotoxin.

Monoaminergic regulation of Sonic hedgehog signaling cascade expression in the adult rat hippocampus

Monoamines are implicated in the modulation of adult hippocampal neurogenesis in depression models and following chronic antidepressant treatment. Given the key role of Sonic hedgehog (Shh) in adult neurogenesis, we examined whether monoaminergic perturbations regulate the expression of Shh or its co-receptors Smoothened (Smo) and Patched (Ptc). Combined depletion of both serotonin and norepinephrine with para-chlorophenylalanine (PCPA) resulted in a significant decrease in Smo and Ptc mRNA within the dentate gyrus subfield of the hippocampus. However, selective depletion of serotonin, using the serotonergic neurotoxin 5,7-dihyrdroxytryptamine (5,7-DHT), or norepinephrine, using the noradrenergic neurotoxin DSP-4, did not alter expression of Shh and its co-receptors, Smo and Ptc. Acute treatment with the monoamine releasing agent, para-chloroamphetamine (PCA) significantly upregulated Smo mRNA within the dentate gyrus. However, acute or chronic treatment with pharmacological antidepressants that modulate monoaminergic neurotransmission did not regulate Shh cascade expression. These results indicate that robust changes in monoamine levels can regulate the expression of the Shh signaling cascade in the adult rodent brain.

Ontogenetic noradrenergic lesion alters histaminergic activity in adult rats

To determine whether noradrenergic nerves might have a modulatory role on the sensitivity or reactivity of histaminergic receptor systems in brain, behavioral effects of the respective histamine H1, H2 and H3 antagonists S(+)chlorpheniramine, cimetidine and thioperimide in control adult rats were compared to the effects in adult rats that had been lesioned as neonates with the noradrenergic neurotoxin DSP-4. On the 1st and 3rd days after birth rat pups were treated with either saline or DSP-4 (50 mg/kg sc), then returned to their home cages with the dam. At 8 weeks when rats were tested, S(+)chlorpheniramine (10 mg/kg ip) was found to increase locomotor activity in intact and DSP-4 lesioned rats, while cimetidine (5 mg/kg, ip) and thioperimide (5 mg/kg, ip) increased activity several-fold solely in the DSP-4 group. Exploratory activity, nociceptive activity, and irritability were little altered by the histamine antagonists, although oral activity was increased by thioperimide in intact and lesioned rats, and by cimetidine or S(+)chlorpheniramine in DSP-4 rats. High performance liquid chromatography with electrochemical detection was used to determine that DSP-4 produced a 90% reduction in frontal cortex, hippocampus and hypothalamus, with a 90% elevation of NE in cerebellum--reflecting reactive sprouting of noradrenergic fibers consequent to lesion of noradrenergic tracts projecting to proximal brain regions. These findings indicate that perinatal noradrenergic fiber lesioning in rat brain is associated with an altered behavioral spectrum by histamine H1, H2 and H3 receptor antagonists, thereby implicating histaminergic systems as modulators of noradrenergic systems in brain.

Noradrenergic control of odor recognition in a nonassociative olfactory learning task in the mouse

The present study examined the influence of pharmacological modulations of the locus coeruleus noradrenergic system on odor recognition in the mouse. Mice exposed to a nonrewarded olfactory stimulation (training) were able to memorize this odor and to discriminate it from a new odor in a recall test performed 15 min later. At longer delays (30 or 60 min), the familiar odor was no longer retained, and both stimuli were perceived as new ones. Following a post-training injection of the alpha(2)-adrenoceptor antagonist dexefaroxan, the familiar odor was still remembered 30 min after training. In contrast, both the alpha(2)-adrenoceptor agonist UK 14304 and the noradrenergic neurotoxin DSP-4 prevented the recognition of the familiar odor 15 min after the first exposure. Noradrenaline release in the olfactory bulb, assessed by measurement of the extracellular noradrenaline metabolite normetanephrine, was increased by 62% following dexefaroxan injection, and was decreased by 38%-44% after treatment with UK 14304 and DSP-4. Performance of mice in the recall test was reduced by a post-training injection of the beta-adrenoceptor antagonist propranolol or the alpha(1)-antagonist prazosin, thus implicating a role for beta- and alpha(1)-adrenoceptors in the facilitating effects of noradrenaline on short-term olfactory recognition in this model.

Effects of the noradrenergic neurotoxin DSP4 on spatial memory in the rat

Patients with attention-deficit/hyperactivity disorder (ADHD) show various cognitive impairments such as deficits in attention or working memory. Most symptoms of ADHD are thought to be associated with a dysbalance between the neurotransmitters noradrenaline and dopamine in the brain. In order to investigate the role of noradrenaline in this context we have produced a central depletion of noradrenaline in rats by administering different doses (10, 20 or 50 mg/kg body weight) of the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) and assessing the behavioral consequences with a modified hole board task. The administration of DSP4 affected the working memory error, while reference memory and motor functions were not affected. The use of different doses of DSP4 to influence prefrontal functions and to understand the dysbalance of dopamine and noradrenaline in ADHD appears to be a promising approach.

Norepinephrine regulates locomotor hyperactivity in the mouse mutant coloboma

An imbalance between dopaminergic and noradrenergic systems is implicated in hyperactivity disorders such as attention deficit hyperactivity disorder (ADHD) and Tourette syndrome. We have identified the mouse mutant coloboma as an animal model for examining the neurological basis of hyperactivity. Coloboma mice exhibit spontaneous locomotor hyperactivity that is a result of a reduction in SNAP-25, a presynaptic protein that regulates exocytotic release. These mice exhibit an imbalance in catecholamine regulation whereby brain dopamine (DA) utilization is reduced while norepinephrine (NE) concentrations are significantly increased. Further, calcium-dependent NE release was also increased in these hyperactive mice, despite the reduction in SNAP-25. To determine the role of NE in the expression of hyperactivity, brain NE concentrations were reduced using the specific noradrenergic neurotoxin DSP-4 [ N-(2-chloroethyl)- N-ethyl-2-bromobenzylamine hydrochloride]. DSP-4 treatment specifically decreased NE concentrations, but had no effect on brain DA or serotonin. Depletion of NE by DSP-4 through either systemic or central administration significantly reduced the locomotor activity in coloboma mice. These results suggest that NE regulation in the CNS plays an important role in the expression of hyperactivity in this mouse model, consistent with results of human studies and current models of ADHD.

The antidepressant activity of inositol in the forced swim test involves 5-HT 2 receptors

The effect of inositol as an antidepressant was previously demonstrated in both animal models of depression-like behavior and in clinical trials. Unlike most antidepressant drugs, inositol does not have a clear target in the synapse and was not demonstrated to alter monoamine levels in the brain. The present study attempted to draw a psychopharmacological profile of inositol's behavioral effects by exploring the interactions between the drug and specific receptor agonists and antagonists in the forced swim test. Rats received inositol treatment (or control) in combination with the serotonergic metabolism inhibitor PCPA or with the noradrenergic neurotoxin DSP-4. Results indicated that PCPA but not DSP-4 abolished the ability of inositol to cause a reduction in immobility time in the forced swim test. In mice, the specific 5-HT 2A/5-HT 2C antagonist ritanserin, but not the 5-HT 1A/5-HT 1B/β adrenergic antagonist pindolol, abolished inositol's effect in the forced swim test. The 5-HT 2A/5-HT 2C agonist DOI and the 5-HT 1A agonist 8-OH-DPAT did not have any significant effects on inositol's activity. The present data indicates that the antidepressant effect of inositol may involve 5-HT 2 receptors. It is thus possible that the effects of reuptake antidepressant drugs and the effects of inositol may have a common final pathway.

Thyroid function and clinical subtypes of major depression

The effect of inositol as an antidepressant was previously demonstrated in both animal models of depression-like behavior and in clinical trials. Unlike most antidepressant drugs, inositol does not have a clear target in the synapse and was not demonstrated to alter monoamine levels in the brain. The present study attempted to draw a psychopharmacological profile of inositol's behavioral effects by exploring the interactions between the drug and specific receptor agonists and antagonists in the forced swim test. Rats received inositol treatment (or control) in combination with the serotonergic metabolism inhibitor PCPA or with the noradrenergic neurotoxin DSP-4. Results indicated that PCPA but not DSP-4 abolished the ability of inositol to cause a reduction in immobility time in the forced swim test. In mice, the specific 5-HT2A/5-HT2C antagonist ritanserin, but not the 5-HT1A/5-HT1B/β adrenergic antagonist pindolol, abolished inositol's effect in the forced swim test. The 5-HT2A/5-HT2C agonist DOI and the 5-HT1A agonist 8-OH-DPAT did not have any significant effects on inositol's activity. The present data indicates that the antidepressant effect of inositol may involve 5-HT2 receptors. It is thus possible that the effects of reuptake antidepressant drugs and the effects of inositol may have a common final pathway.

Noradrenergic lesion antagonizes desipramine-induced adaptation of NMDA receptors

Repeated administration of the tricyclic antidepressant, desipramine, for 28 days to mice effected a decrease in the potency of glycine to displace [ 3H]5,7-dichlorokynurenic acid (5,7-DCKA) in mouse cortical homogenates. Pre-treatment with the noradrenergic neurotoxin DSP-4, while having no effect alone, attenuated the desipramine-induced effect. The present findings support a norepinephrine-dependent adaptation of the NMDA receptor complex in vivo following chronic desipramine treatment. The inter-relationship of norepinephrine and glutamate transmission may provide insight into the mechanism underlying the action of antidepressant drugs.

Depletion of brain norepinephrine: differential influence on anxiolyic treatment effects.

Previous studies have demonstrated that anxiolytic-like anticonflict effects can be produced by either (1) acute administration of traditional anti-anxiety compounds (benzodiazepines or barbiturates) or (2) chronic administration of tricyclic (TCA) or monoamine oxidase inhibitor (MAOI) anti-depressants. The present study determined the effects of noradrenergic neuronal depletion on these distinct anticonflict treatments. After 3 weeks of training in a repeated measures drink suppression conflict paradigm, water-restricted rats consumed 11-14 ml water/session (unpunished responding) and accepted 25-40 shocks/session (punished responding) during control (i.e., non-drug) 10-min test sessions. The noradrenergic neurotoxin DSP4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride; 65 mg/kg, IP] or its vehicle (saline; 1 ml/kg) was administered after 3 weeks of conflict testing. Conflict behavior was then evaluated for 8 weeks post-treatment. In separate groups of DSP4- and vehicle-pretreated subjects, the effects of acute administration (10-min pretreatment) of phenobarbital (5-40 mg/kg) or alprazolam (0.3-2.5 mg/kg) were determined. In a third experiment, the effects of chronic treatment with the TCA desipramine (DMI; 5 mg/kg, twice daily for 8 weeks) or the non-selective MAOI phenelzine (4.0 mg/kg, twice daily for 8 weeks) on conflict behavior were determined in additional groups of DSP4- or vehicle-pretreated subjects. DSP4 treatment produced a modest yet statistically significant decrease in punished responding (i.e., anxiogenic-like effect) relative to vehicle controls. DSP4 pretreatment did not alter the anticonflict effects of acute alprazolam or phenobarbital treatment. In contrast, DSP4 treatment completely abolished the anticonflict effects produced by chronic DMI or chronic phenelzine treatment. Thus, noradrenergic neuronal integrity appears to be required for the anxiolytic-like effects of chronic antidepressant treatment, but not for the anxiolytic-like effects of acute treatment with barbiturates and benzodiazepines.

The neuroprotective and neuronal rescue effects of (-)-deprenyl.

The pharmacological effects of (-)-deprenyl is multi-fold in its nature (dopamine sparing activity, neuroprotective and neuronal rescue effects), which cannot be explained solely by the irreversible MAO-B inhibitory action of the substance. Deprenyl slightly inhibits the re-uptake of noradrenaline and dopamine, but methylamphetamine, the metabolite of the inhibitor, by one order of magnitude is more potent in this respect, than the parent compound. Neither the metabolite nor (-)-deprenyl acts on the uptake of serotonin. The inhibitor has an intensive first pass metabolism after oral treatment. The in vivo pharmacokinetic studies with (-)-deprenyl, using the double labelled radioisotope technique (1.5 mg/kg; orally) in rats revealed that the molar concentration of methylamphetamine can reach the level suitable to induce a significant inhibition of amine uptake. Deprenyl, but especially methylamphetamine pre-treatment can prevent the noradrenaline release induced by the noradrenergic neurotoxin DSP-4. The uptake inhibitory effect of (-)-deprenyl and the metabolites is reversible. After repeated administration of (-)-deprenyl (1.5 mg/kg daily, for 8 days) sustained concentration of its metabolites was detected, compared to that of the acute studies. This can at least partly explain why (-)deprenyl should be administered daily to evoke therapeutic effects in Parkinson's disease. Administration of (-)-deprenyl in a low dose, following the toxic insult, can rescue the damaged neurones. The neuronal rescue effect of the drug was studied on M-1 human melanoma cells in tissue culture. The inhibitor reduced the apoptosis of serum-deprived M-1 cells, but the (+)-isomer failed to exert this effect. The (+/-)-desmethyl-deprenyl almost lacks the property to inhibit apoptosis. For neuroprotection and neuronal rescue an optimal dose of (-)-deprenyl should be administered, because to reach a well balanced concentration of the metabolites in tissues is critical.