Monoamine control of the pacemaker kernel and cycle frequency in the lobster pyloric network.
(9/446)The monoamines dopamine (DA), serotonin (5HT), and octopamine (Oct) can each sculpt a unique motor pattern from the pyloric network in the stomatogastric ganglion (STG) of the spiny lobster Panulirus interruptus. In this paper we investigate the contribution of individual network components in determining the specific amine-induced cycle frequency. We used photoinactivation of identified neurons and pharmacological blockade of synapses to isolate the anterior burster (AB) and pyloric dilator (PD) neurons. Bath application of DA, 5HT, or Oct enhanced cycle frequency in an isolated AB neuron, with DA generating the most rapid oscillations and Oct the slowest. When an AB-PD or AB-2xPD subnetworks were tested, DA often reduced the ongoing cycle frequency, whereas 5HT and Oct both evoked similar accelerations in cycle frequency. However, in the intact pyloric network, both DA and Oct either reduced or did not alter the cycle frequency, whereas 5HT continued to enhance the cycle frequency as before. Our results show that the major target of 5HT in altering the pyloric cycle frequency is the AB neuron, whereas DA's effects on the AB-2xPD subnetwork are critical in understanding its modulation of the cycle frequency. Octopamine's effects on cycle frequency require an understanding of its modulation of the feedback inhibition to the AB-PD group from the lateral pyloric neuron, which constrains the pacemaker group to oscillate more slowly than it would alone. We have thus demonstrated that the relative importance of the different network components in determining the final cycle frequency is not fixed but can vary under different modulatory conditions. (+info)
Phosphorylation and sequestration of serotonin transporters differentially modulated by psychostimulants.
(10/446)Many psychotropic drugs interfere with the reuptake of dopamine, norepinephrine, and serotonin. Transport capacity is regulated by kinase-linked pathways, particularly those involving protein kinase C (PKC), resulting in transporter phosphorylation and sequestration. Phosphorylation and sequestration of the serotonin transporter (SERT) were substantially impacted by ligand occupancy. Ligands that can permeate the transporter, such as serotonin or the amphetamines, prevented PKC-dependent SERT phosphorylation. Nontransported SERT antagonists such as cocaine and antidepressants were permissive for SERT phosphorylation but blocked serotonin effects. PKC-dependent SERT sequestration was also blocked by serotonin. These findings reveal activity-dependent modulation of neurotransmitter reuptake and identify previously unknown consequences of amphetamine, cocaine, and antidepressant action. (+info)
Studies on the acute and chronic effects of reboxetine on extracellular noradrenaline and other monoamines in the rat brain.
(11/446)1 The effect of reboxetine, a novel antidepressant drug that potently and selectively inhibits neuronal noradrenaline (NA) uptake, on brain extracellular monoamines was studied by microdialysis. 2 Fifteen mg kg-1 i.p. reboxetine raised extracellular NA in the frontal cortex (by 242%) and dorsal hippocampus (by 240%). 3 Idazoxan (1 mg kg-1 s.c.), given 60 min after 15 mg kg-1 reboxetine, markedly potentiated the effect on extracellular NA in the frontal cortex (by 1580%) and dorsal hippocampus (by 1360%), but had no effect by itself. 4 Twenty-four hours after the last injection of a chronic schedule (15 mg kg-1 i.p. once daily for 14 days) reboxetine had no effect on basal extracellular concentrations of NA in the dorsal hippocampus and a challenge dose of reboxetine (15 mg kg-1) raised extracellular NA similarly in rats treated chronically with reboxetine (by 353%) and saline (by 425%). 5 Ten and 20 microg kg-1 i.p. clonidine dose-dependently reduced hippocampal extracellular NA similarly in rats given chronic reboxetine (by 32% and 57%) and saline (by 42% and 56%). 6 Extracellular concentrations of dopamine and 5-HT in the striatum were similar in rats treated chronically with reboxetine and saline. A challenge dose of reboxetine (15 mg kg-1) had no effect on striatal extracellular dopamine and slightly increased striatal extracellular 5-HT to a similar extent in rats treated chronically with reboxetine (by 137%) and saline (by 142%). 7 The results suggest that combining reboxetine with an alpha2-adrenoceptor antagonist may facilitate its antidepressant activity. Repeated treatment confirmed that reboxetine is fairly selective for the noradrenergic system but provided no evidence of adaptive changes in that system that could facilitate its effect on extracellular NA. (+info)
The adrenergic receptor agonist, clonidine, potentiates the anti-parkinsonian action of the selective kappa-opioid receptor agonist, enadoline, in the monoamine-depleted rat.
(12/446)1. The treatment of Parkinson's disease relies predominantly upon dopamine replacement therapy, usually with l-dihydroxyphenylalanine (L-DOPA). However, side-effects of long-term treatment, such as L-DOPA-induced dyskinesias can be more debilitating than the disease itself. Non-dopaminergic treatment strategies might therefore be advantageous. 2. The aim of this study was to investigate the potential anti-parkinsonian efficacy of the kappa-opioid receptor agonist, enadoline, and the alpha-adrenoreceptor agonist, clonidine, both alone or in combination, in the reserpine-treated rat model of Parkinson's disease. 3. Rats were treated with reserpine (3 mg kg-1), and experiments carried out 18 h later, at which time they exhibited profound akinesia (normal animals 1251+/-228 mobile counts h-1, reserpine-treated animals 9+/-2 mobile counts h-1). Both enadoline and clonidine increased locomotion in reserpine-treated rats in a dose-dependent manner. The maximum locomotor-stimulating effect of enadoline alone was seen at a dose of 0.2 mg kg-1 (208+/-63 mobile counts h-1). The maximum effect of clonidine was seen at a dose of 2 mg kg-1 (536+/-184 mobile counts h-1). 4. Co-administration of enadoline (0.1 mg kg-1) and clonidine (0.01 - 0.1 mg kg-1) at sub-threshold doses, synergistically increased locomotion. 5. The synergistic stimulation of locomotion in the reserpine-treated rat involved activation of kappa-opioid receptors and a combination of both alpha1 and alpha2-adrenoreceptors. 6. The results presented suggest a need for further studies on the potential of stimulating kappa-opioid and/or alpha-adrenoreceptors as a therapy for Parkinson's disease. Furthermore, the studies may offer potential mechanistic explanations of the ability of alpha2-adrenergic receptor antagonist to reduce L-DOPA-induced dyskinesia in Parkinson's disease. (+info)
Rats selectively bred for responsiveness to 5-hydroxytryptamine(1A) receptor stimulation: differences in differential reinforcement of low rate 72-second performance and response to serotonergic drugs.
(13/446)High (+/-)-8-hydroxy-dipropylaminotetralin HBr (8-OH-DPAT)-sensitive (HDS) rats and low 8-OH-DPAT-sensitive (LDS) rats were selectively bred for differences in sensitivity to the hypothermic effect of the 5-hydroxytryptamine(1A) (5-HT(1A)) receptor agonist 8-OH-DPAT in 30 to 35-day-old rat pups. These rats were trained on the differential reinforcement of low rate 72-s operant schedule. On this schedule, LDS rats had a higher response rate and a lower reinforcement rate than HDS rats. Drugs with primary action on the 5-HT system, 8-OH-DPAT, ketanserin, and fluoxetine, decreased response rate of HDS and LDS rats but increased the reinforcement rate of only the LDS rats. However, a drug with primary action on the norepinephrine system, desipramine, decreased response rate and increased reinforcement rate of HDS and LDS rats, suggesting that norepinephrine function was similar in the two lines of rats. The finding with desipramine indicates that increases in reinforcers on the differential reinforcement of low rate 72-s task are not simply dependent on baseline response or reinforcement rate. We also observed that 8-OH-DPAT engenders a greater hypothermic response in adult (90-day-old) HDS rats than in adult LDS rats. The 5-HT(1A) receptor antagonist WAY-100635 antagonized the hypothermic response. Tissue levels of 8-OH-DPAT from several brain regions in LDS and HDS rats did not differ from each other at either 15- or 30-min postinjection. Because the LDS and HDS rats have different responses to 5-HT-acting drugs, these rats may be useful for studying the role of the serotonergic system in depression. (+info)
Nerve growth factor (NGF) augments cortical and hippocampal cholinergic functioning after p75NGF receptor-mediated deafferentation but impairs inhibitory avoidance and induces fear-related behaviors.
(14/446)Nerve growth factor (NGF) enhances cholinergic functioning in animals with a compromised cholinergic basal forebrain (CBF). Immunotoxic lesions targeting low-affinity NGF receptor (p75NGF receptor)-bearing CBF neurons provide a selective model for testing the effects of NGF on residual cholinergic neurons. Rats received PBS or the immunotoxin 192IgG-saporin (192Sap) intracerebroventricularly at two doses (1 or 2.7 microg) known to produce different degrees of cholinergic deficit. Seven weeks after lesioning, half of each group received either NGF or cytochrome c intracerebroventricularly for 7 weeks. The two doses of 192Sap produced 50 and 80% depletions of choline acetyltransferase (ChAT) activity in the neocortex and hippocampus. NGF produced the greatest increase in ChAT activity in controls, intermediate in low-lesioned, and smallest in highly lesioned animals. NGF-treated animals showed reduced weight gain, hyper-responsiveness to acoustic stimuli, and decreased inhibitory avoidance. Although general motor behavior was affected by neither 192Sap nor NGF in an open field task, highly lesioned rats took longer to reach the platform during water maze testing. Impaired spatial orientation in finding a hidden platform at the previously acquired position was mitigated by NGF. Hypertrophic changes of residual CBF neurons, Schwann cell hyperplasia, and aberrant axonal sprouting around the medulla were observed in NGF-treated animals only, independent of the preexisting lesion. Our results indicate that NGF has a limited capacity to enhance functioning of residual CBF neurons. More importantly, NGF augmented fear-related behaviors and adverse neuroproliferative changes that may restrict its therapeutic use. (+info)
FA-70, a novel selective and irreversible monoamine oxidase-A inhibitor: effect on monoamine metabolism in mouse cerebral cortex.
(15/446)A series of indolealkylamine derivatives has been previously designed and evaluated with the aim of finding the most potent and selective novel monoamine oxidase (MAO) inhibitors to be used in the therapy of neurological and affective disorders. Among them, FA70, a 5-hydroxy-indolealkylamine derivative, has been characterized in vitro as a potent, irreversible, and mechanism-based inhibitor of the MAO-A isoform. The comparison with clorgyline, analyzed under the same experimental conditions, confirmed FA70 as the most potent MAO-A inhibitor. The ex vivo effect of FA70 on MAO activity in mouse cerebral cortex was similar to that observed in vitro, showing more efficacy than in peripheral tissues. The ex vivo effect of FA70 on amine metabolism also was evaluated after acute and chronic treatment, and the results showed that between both MAO isoforms, MAO-A is the only one responsible for monoamine metabolism in this region of the brain. The ex vivo effect of FA70 on dopamine content was correlated with the activation effect on tyrosine hydroxylase activity, the enzyme responsible for the regulation of the limiting step in catecholamine synthesis. (+info)
Effects of fenfluramine combined with electroacupuncture on monoamine release in periaqueductal gray of rat brain.
(16/446)AIM: To study the changes of monoamines in ventrolatoral periaqueductal gray of rat brain before and after electroacupuncture (EA) analgesia (EAA) was enhanced by fenfluramine (Fen), a 5-hydroxytryptamine (5-HT) releaser. METHODS: Monoamines were collected by in vivo microdialysis and measured by HPLC connected with electrochemical detector. RESULTS: The level of norepinephrine (Nor) after EA was decreased (P < 0.05 vs NS group). The contents of 5-HT, 5-hydroxyindol acetic acid (5-HIAA), dopamine (DA), and homovanillic acid (HVA) in periaqueductal gray dialysate were increased (P < 0.05 vs NS group). When Fen was combined with EA, the level of 5-HT and 5-HIAA were further increased (P < 0.05 vs NS + EA group). There was no obvious change of Nor, DA, and HVA. CONCLUSION: Fen potentiating EAA may be related to further activation of serotoninergic system. (+info)