Slices Of Striatum Research Articles

Glycine elicits release of acetylcholine from the nucleus tractus solitarii in rat

Previous studies have suggested that cardiovascular responses elicited by injection of glycine into the nucleus tractus solitarii (NTS) depend upon interactions between glycinergic and cholinergic neuronal elements in NTS. Release of acetylcholine in response to glycine is one such interaction that has been shown in slices of hippocampus and striatum. In this study we sought to test the hypothesis that glycine causes release of acetylcholine from neurotransmitter stores in NTS. We compared release from NTS with that from adjacent hypoglossal nucleus and from caudate nucleus. Release of radiolabeled acetylcholine was determined in vitro after incubating NTS with [ 3H]choline. Exposure of NTS and caudate nucleus, but not hypoglossal nucleus, to glycine caused release of acetylcholine in a calcium-dependent manner that varied with concentration of glycine in the incubation medium. The maximally effective concentration (1 mM) of glycine elicited 136% increases over basal levels. Glycine did not elicit release of [ 3H]acetylcholine from tissue when calcium ion had been removed from the bath. Acetylcholine also was not released if tissue was incubated with either strychnine (10 μM) or hemicholinium-3 (1 mM) prior to exposure to glycine (1 mM). Thus, glycine, acting at strychnine-sensitive receptors in NTS, elicits release of acetylcholine from a portion of locally synthetized neurotransmitter stores.

Differential effects of dopamine agonists on evoked dopamine release from slices of striatum and nucleus accumbens in rats

The effects of dopamine receptor agonists on electrically evoked dopamine release from slices of nucleus accumbens were compared with the effects on release from striatal slices in rats. Apomorphine, which has equal potency at the dopamine D 2 and D 3 receptors, reduced the evoked dopamine release from both regions to the same extent (ED 50, 0.42 μM for nucleus accumbens; ED 50, 0.46 μM for striatum). Quinpirole of 7-[ 3H]hydroxy- N,N-di- n-propyl-2-aminotetralin (7-OHDPAT), which are much more potent at the D 3 receptor than at the D 2 receptor, reduced the evoked dopamine release from the nucleus accumbens (ED 50, 0.12 μM for quinpirole; 0.02 μM for 7-OHDPAT) much more than the release from the striatum (ED 50, 1.6 μM for quinpirole; 0.55 μM for 7-OHDPAT). These results suggest that the contribution of D 3 receptors in nucleus accumbens to regulate dopamine release from dopamine nerve terminals is much greater than that in striatum.

Neurotrophin-4 selectively promotes survival of striatal neurons in organotypic slice culture

The neurotrophins (NGF, BDNF, NT-3, and NT-4) provide trophic support to subpopulations of neurons in the central and peripheral nervous systems. We examined organotypic slices of neonatal mouse striatum maintained in medium supplemented with neurotrophins or with CNTF to determine which of these factors influence the survivability of striatal neurons. Neuron counts at the end of the culture period revealed that NT-4 was the only factor that had a significant effect on neuronal survival, suggesting that NT-4 is a trophic factor for striatal neurons in organotypic slices.

1-methyl-4-phenylpyridinium has greater neurotoxic effect after selenium deficiency than after vitamin E deficiency in rat striatum

The present study was designed to assess the extent of the protective effect of antioxidative capacity of dopaminergic neurons against the possible oxidative stress produced by 1-methyl-4-phenylpyridinium. We have studied the direct effect of 1-methyl-4-phenylpyridinium on striatum slices from rats fed with selenium-deficient or vitamin E-deficient diets for 30 days. Glutathione peroxidase activity decreased significantly after selenium dietary restriction. Our results showed that the effect of 1-methyl-4-phenylpyridinium on dopamine and its metabolites 3,4-dihydroxyphenylacetic acid, homovanillic acid and 3-methoxytyramine in animals with both restriction diets was higher than in controls. However, this effect was significantly greater in animals with low selenium diets than with vitamin E-deficient diets in terms of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid, which were all significantly more depleted by 1-methyl-4-phenylpyridinium in selenium-deficient rats than in vitamin E-deficient rats. Therefore, considering changes in the levels of dopamine and its metabolites as an index of 1-methyl-4-phenylpyridinium toxicity, our results seem to indicate that the glutathione-glutathione peroxidase system has a greater protector effect than vitamin E.

The effect of neuropeptides on the release of neurotransmitter amino acids from rat striatum

Neuropeptide Y (NPY), peptide YY (PYY), and galanin are found throughout the central nervous system with appreciable levels occurring in the striatum. In this study we have investigated the effects of these peptides on the potassium-stimulated release of endogenous neurotransmitter amino acids from slices of rat striatum. The release of glutamate was significantly reduced by nanomolar concentrations of each peptide, whilst the release of aspartate, γ-aminobutyric acid (GABA) and glycine was not affected. The reduction in release due to galanin (200 nM) was inhibited by glibenclamide (5 μM). These results support the view that NPY, PYY and galanin modulate neurotransmitter release possibly by a presynaptic action. The results with glibenclamide suggest that the action of galanin is mediated through and ATP-sensitive potassium channel.

No evidence for presynaptic opioid receptors on cholinergic, but presence of ?-receptors on dopaminergic neurons in the rabbit caudate nucleus: involvement of endogeneous opioids

The effects of various opioid receptor agonists and antagonists were studied in rabbit caudate nucleus slices preincubated with either [3H]dopamine or [3H]choline, superfused with medium (containing in most experiments the D2 receptor antagonist domperidone) and subjected to electrical field stimulation. The stimulation-evoked [3H]overflow from slices prelabeled with [3H]dopamine (evoked [3H]dopamine release) was significantly reduced by preferential kappa-opioid receptor agonists, like U-50,488 H, but not by mu- or delta-opioid receptor selective drugs. Opioid receptor antagonists shifted the concentration/response curve of U-50,488 H to the right (apparent pA2-value of the kappa-selective antagonist nor-binaltorphimine: 10.1) and enhanced the evoked dopamine release in the presence of a mixture of peptidase inhibitors. On the other hand, the [3H]overflow from rabbit caudate nucleus slices prelabeled with [3H]choline (evoked acetylcholine release) remained almost unaffected by any opioid receptor agonist, as long as the presynaptic D2 heteroreceptor was blocked with domperidone: in the absence of domperidone, U-50,488 H exhibited facilitatory effects. For comparison, the effects of the preferential delta-opioid receptor agonist DPDPE was also studied in slices of the rat striatum, where it clearly inhibited the evoked acetylcholine release. From our data we conclude that in the rabbit caudate nucleus the evoked dopamine release is inhibited by both exogenous and endogenous opioids via presynaptic kappa-opioid receptors, whereas the evoked release of acetylcholine is not, or only indirectly (via released dopamine) affected by opioids.

Early postnatal hypoxia induces long-term changes in the dopaminergic system in rats.

A rat model of a mild, chronic, early postnatal hypoxia, characterized by long-term consequences in the behavioural outcome, was used to study long-term consequences in the dopaminergic system. Exposure of newborn rats to an early postnatal hypoxia (hypobaric hypoxia, 11 kPa pO2 in the inspiratory air, 2nd-10th day of life, 10 hours daily) brings about the following lasting neurochemical changes: an increased stimulated dopamine release rate from striatum slices by about 30%, an increased low affinity, high capacity dopamine uptake into striatum synaptosomes by about 100%. The critical period to produce an increased release rate of dopamine was estimated as day 2-6 postnatally. There are no long-term changes in the concentration of dopamine and its metabolites and in the tyrosine hydroxylase activity in consequences of this early postnatal hypoxia. Treatment of newborn animals with L-DOPA (10-50 micrograms/g body weight) previous to hypoxia normalizes the DA release rate.

Protective effect of deprenyl against 1-methyl-4-phenylpyridinium neurotoxicity in rat striatum

Rats were treated with deprenyl for 3 weeks. Afterwards, slices of the corpus striatum were incubated with 1-methyl-4-phenylpyridinium ion (MPP +). Concentrations of dopamine and its metabolite concentrations were assayed. The effect of MPP + in animals treated with deprenyl was smaller than in controls, indicating that deprenyl protects against MPP +. We also measured superoxide dismutase (SOD) and catalase activities and carbonyl group content of the proteins. Both activities increased in deprenyl-treated rats, and the amount of carbonyl groups was unchanged. These results suggest that the protective effect of deprenyl is independent of the monoamine oxidase-B inhibitor and of the induction of SOD and catalase activities.

In vitro progesterone effects on 3H-dopamine release from rat corpus striatum slices obtained under different endocrine conditions

The release of dopamine (DA) from corpus striatum is affected by the endocrine state of the animal being progesterone suggested as a potential hormonal modulatory signal. Most of its actions have been described on endogenous DA release induced by amphetamine. However the release of DA and the mechanism of the drug effect have been shown to be highly complexes. Considering that DA recently incorporated and/or synthetized is preferentialy used we have characterized the effect of progesterone in vitro on the K +-induced release of 3H-dopamine ( 3H-DA) from rat corpus striatum slices. These were obtained during the estrous cycle or under conditions of high or low levels of endogenous progesterone (pregnant and ovariectomized rats). The release of 3H-DA was independent of the cycle. However, progesterone in vitro modified the induced release in a cycle-dependent way. Low concentrations of the hormone (100–200 mM) reduced the K + (30 mM) effect while higher doses (300–500 mM) were facilitatories. After 7 days of ovariectomy, the induced release of 3H-DA was unchanged while in pregnant rats it was found decreased. In both cases the inhibitory effect of the hormone dissapeared. Both progesterone (200 nM) and omission of Ca ++ from the superfusion medium did not modified tyramine (20 uM) or K + induced release, respectively. Data suggest that the pool of DA, related to exocytotic mechanism of release, could be specifically affected by progesterone, in a bimodal way, probably through independent genomic and non-genomic influences.

Prolonged in vitro exposure of rat brain slices to adenosine analogues: Selective desensitization of adenosine A 1 but not A 2 receptors

Agonist-induced desensitization of adenosine A 1 and A 2 receptors was studied in rat striatum slices maintained in carbo-oxygenated Krebs buffer. Slices were exposed to adenosine analogues (either cyclo-penlyl-adenosine or N-ethyl-carboxamido-adenosine) for selected time periods (15–60 min) and repeatedly washed at the end of agonist exposure. Agonist-induced changes of adenosine receptors were then evaluated in P2 fractions prepared from slices by measuring A 1 and A 2 rcccptor-regulated adenylatc cyclase. A 1 receptors were rapidly desensitized by agonist exposure, as shown by a gradual loss of A 1 receptor-mediated inhibition of basal cyclase activity and cAMP formation, which was evident within 15–30 min after addition of the adenosine analogue. Agonist-induced desensitization of A 1 receptors was dose- and time-dependent, and seemed quicker in onset with cyclo-pentyl-adenosine, according to the higher A 1 selectivity of this receptor agonist, with respect to N-ethyl-carboxamido-adenosine. Binding of the A 1-sclective agonist [ 3H]cyclo-hexyl-adenosine was unaffected by the desensitization procedure at any of the exposure periods utilized, suggesting that an uncoupling of A 1 receptors from their transduction system is indeed responsible for the loss of functional activity. Loss of A 1 receptor function was accompanied by a time-dependent amplification of A 2 receptor-mediated stimulation of adenylete cyciase activity, likely due to an ‘unmasking’ of A 2 stimulatory receptor function as a consequence of the desensitizalion of A 1 inhibitory receptors. All these effects could be completely counteracted by the concomitant exposure to an adenosine receptor antagonist, and specifically involved the coupling mechanisms of adenosine receptors with their effector system. It is therefore concluded that the prolonged exposure of brain slices to adenosine analogues rapidly and selectively desensitizes A 14 receptors in the absence of any loss of A2 receptor function. These receptor adaptive changes might be relevant to brain pathological conditions characterized by over-exposure to endogenous adenosine.

Phencyclidine-induced desensitization of striatal dopamine release

Increased release of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) from slices of striatum of DBA/2J mouse in response to administration of phencyclidine (PCP) in vitro has been observed to be transient, despite continued exposure to PCP. To determinewhether this transient response was a result of depletion of releasable pools, toxicity or an adaptice response (desensitization), the recovery of the response to PCP was evaluated. Slices in the control condition were exposed to PCP (300 μM) during test-exposure only. Slices in the PCP pre-exposure condition, were exposed first to PCP (30 μM; pre-exposure) and subsequently to PCP (300 μM; test-exposure). During a washout period (0, 30, 60 or 120 min) between exposures to PCP, the slices were superfused in the absence of PCP. Pre-exposure to PCP diminished the subsequent response to test-exposure to PCP (49 and 37% of control for DA and DOPAC, respectively) after 0 min washout. Overflow of DA evoked by PCP returned towards control values but remained decreased (66% of control) after up to 120 min washout. However, overflow of DOPAC did return to control values after 60 min washout. Thus, the diminished dopaminergic response, resulting from continued exposure to PCP was not due to depletion of the releasable pool or cytotoxicity but rather to a dynamic adaptive response of the dopaminergic neuron to PCP.

Amygdala kindling does not alter the [formula omitted] receptor-channel complex which modulates dopamine release in the rat striatum and amygdala

Kindling is suggested to be critically associated with enhancement of N- methyl- d-aspartate (NMDA) type excitatory amino acid synaptic transmission. The present study examined effects of kindling on NMDA-induced dopamine (DA) efflux from slices of the rat striatum and amygdala. When assayed 5–7 days after the last evoked seizure, no difference was observed between kindled and non-kindled striatum in the ability of NMDA to induce DA release, or in the effect of MK-801 or 7-chlorokynurenic acid to inhibit the amino acid induced transmitter release. The present study revealed that NMDA receptors are also involved in the modulation of DA release in the amygdala. However, no difference was observed between kindled and non-kindled amygdala in the ability of NMDA to induce DA release. These results suggest that amygdala kindling does not alter activity of the NMDA receptor-channel complex modulating DA release in the striatum and amygdala.

GABA B receptor activation partially inhibits N-methyl-D-aspartate-mediated tyrosine hydroxylase stimulation in rat striatal slices

The effect of the GABA B agonist, (±)-baclofen, on the N-methyl-D-aspartate (NMDA)-mediated stimulation of tyrosine hydroxylase activity was investigated in slices of rat striatum. Tyrosine hydroxylase activity was stimulated by NMDA in a concentration-dependent manner (EC 50, 1.3 ± 0.3 μM; maximum stimulation 194 ± 7% of basal activity). The action of NMDA was reversed by the NMDA antagonist, 2-amino-5-phosphonovalerate (AP-5). (±-Baclofen (100 μM) decreased the maximum effect of NMDA by 24 ± 2% without significantly modifying its EC 50. The IC 50 for the inhibitory action of (±)-baclofen was 4.2 ± 1.2 μM. These results show that GABA B receptor activation modulates NMDA-stimulated tyrosine hydroxylase activity, further supporting the possibility of a role of GABA in the regulation of striatal dopaminergic neurotransmission.

Effect of phencyclidine on spontaneous and [formula omitted] (NMDA)-induced efflux of dopamine from superfused slices of rat striatum

Phencyclidine (PCP) acts as an indirect dopamine (DA) agonist by inhibiting the neuronal reuptake of DA, while it also works as a N- methyl- D-aspartate (NMDA) antagonist. Aiming to investigate characteristics of these two properties of PCP in the same experimental system, the effects of PCP on spontaneous and NMDA-induced efflux of DA from superfused slices of the striatum of the rat were examined. Dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in the samples of superfusate were extracted by alumina extraction and measured by high-performance liquid chromatography with electrochemical detection (HPLC-EC). Phencyclidine at concentrations greater than 1μM, produced a concentration-dependent increase of the spontaneous efflux of DA. The efflux of DOPAC was also concentration-dependently increased by PCP. However, PCP inhibited the efflux of DA induced by NMDA, even at a small concentration (0.1μM), which did not alter the spontaneous efflux of the transmitter. The mode of the inhibition by PCP was shown to be noncompetitive, with an estimated IC 50 value of 280 nM. These results suggest that PCP, at small concentrations, reduces the synaptic levels of DA by blocking the facilitating effect of endogenous glutamate on the release of DA and, at slightly greater concentrations, the drug also works as an indirect DA agonist, to increase the levels of the transmitter in the synaptic clefts. The clinical significance of the dual effects of PCP is discussed in relation with the unique schiophrenomimetic property of PCP.

Modulation of release of acetylcholine from the striatum by a proposed excitatory amino acid antagonist U-54494A: Comparison with known antagonists, diazepam and phenytoin

The effect of (U-54494A) cis-3,4-dichloro- N-methyl- N-[2-(1-Pyrrolidinyl)-cyclohexyl] benzamide monohydrochloride, an excitatory amino acid antagonist, on N- methyl- d-aspartic acid (NMDA)- and K +-evoked release of [ 3H]acetylcholine ([ 3H]ACh) from slices of striatum was investigated. For the purpose of comparison, MK 801, PCP, CGP 37849, CPP, phenytoin and diazepam were investigated under identical conditions. Both U-54494A and the excitatory amino acid antagonists blocked NMDA-evoked release of [ 3H]ACh but these compounds failed to inhibit K +-evoked release of this neurotransmitter. Phenytoin blocked both NMDA and K +-evoked release of [ 3H]ACh, whereas diazepam was ineffective under similar conditions. These observations indicate that excitatory amino acid antagonists, including U-54494A, may mediate their anticonvulsant effect by blocking the activity of NMDA receptors, diazepam by activating the benzodiazepine receptors and phenytoin by inhibiting the activity of various depolarizing agents.

Evaluation of a cholinomimetic drug, 9-amino-2,3,5,6,7,8-hexahydro-1h-cyclopenta [b] quinoline (NIK-247), as an enhancer of endogenous efflux of acetylcholine from brain slices

Basal and high K +-stimulated efflux of endogenous ACh from slices of brain was measured to evaluate the cholinomimetic effect of 9-amino-2,3,5,6,7,8-hexahydro-1H-cyclopenta[b] quinoline monohydrate HC1 (NIK-247) on the central nervous system. The drug NIK-247 dose-dependently accelerated the efflux of ACh from slices of striatum. The maximum increase produced by 1.0 × 10 −4 M of NIK-247 was 329% in basal and 1332% in 30 mM K +-stimulated efflux. This drug was nearly twice as potent as THA (9-amino-l,2,3,4-tetrahydroacridine HC1) but had the same potency as physostigmine, in enhancing basal efflux, although there was no significant difference between the efficacy of these drugs in enhancing the K +-stimulated efflux. Both basal and 50 mM K +-stimulated efflux of ACh were increased by NIK-247, not only from the striatum but also from slices of frontal cortex and hippocampus. The activity was more effective in the striatum than in other tissues, and more effective on K +-stimulated than on basal efflux, regardless of the region of the brain. These effects of NIK-247 may be a result mainly of its inhibition of cholinesterase and its other biological characteristics, such as K + channel blockade, capable of modulating release of ACh, may not be of major importance.

Subpopulations of GABA-mediated synaptic potentials in slices of rat dorsal striatum are differentially modulated by presynaptic GABA B receptors

γ-Aminobutyric acid (GABA)-mediated synaptic potentials in rat dorsal striatum in vitro were reduced in amplitude by the GABA B receptor agonists baclofen and 3-aminopropyl-(methyl)-phosphinic acid (SK&F 97541), without any detectable postsynaptic effect. Synaptic potentials in 40% of neurones were distinctly multiphasic, the components of which exhibited a differential sensitivity to GABA B agonists. One population of GABA-releasing neurones within the striatum had presynaptic GABA B autoreceptors, whereas others were not directly affected by GABA B agonists.

Adrenocorticotropic hormone influences the development of adaptive changes in dopamine autoreceptors induced by chronic administration of desipramine

The influence of adrenocorticotropic hormone (ACTH) in the adaptive changes on central dopamine (DA) autoreceptors following chronic administration of desipramine (DMI) as been examined in rats. Dopamine had an inhibitory effect on basal and K +-induced release of [ 3H]DA from slices of striatum and n. accumbens of rats treated chronically (10 days) with ACTH (50 IU/kg, s.c.), DMI (10 mg/kg, i.p.) or the combination of ACTH and DMI. In slices of n. accumbens, but not in slices of striatum of rats exposed to the combined treatment of ACTH and DMI, a significant decrease in the inhibitory effect of exogenous DA on stimulated release of [ 3H]DA was observed. Chronic administration of ACTH or DMI alone had no effect. The effect of the combined treatment with both agents, on the reactivity of these DA receptors was evaluated by means of apomorphine-induced hypoactivity. The administration of ACTH and DMI (5 mg/kg, i.p.) reduced the hypoactivity induced by apomorphine, as compared to hypoactivity in rats treated with ACTH or DMI alone. Experiments with ACTH 4–10 revealed that the peptide modified biochemical and behavioural parameters of dopaminergic function, which may implicate a direct action of the peptide on the brain, rather than on the release of adrenal hormones. These findings suggest that ACTH accelerates the onset of DMI-induced adaptive changes on dopamine in the mesolimbic area. However, because the effect of ACTH 4–10 on release of adrenocortical hormone was not investigated, the possibility cannot be disregarded that the effect of the peptide was secondary to an enhancement of release of adrenal hormone.

Effects of calmodulin antagonists on sodium-dependent high-affinity choline uptake

The effects of calmodulin (CaM) antagonists were investigated on the sodium-dependent high-affinity choline uptake (SDHACU) as assessed by the specific binding of [3H]hemicholinium-3 ([ 3H]HCh-3) and high-affinity [ 3H]choline uptake. Potassium depolarization caused a significant 2-fold increase in the specific binding of [ 3H]HCh-3 in slices of rat striatum in vitro. CaM antagonists, including trifluoperazine (TFP), W-5, W-7, promethazine and haloperidol, dose-dependently inhibited potassium depolarization-stimulated [ 3HCh-3 binding with IC 50s of 20, 40, 70, 30 and 48 (μM), respectively. Scatchard analysis revealed that the inhibitory effect of TFP resulted from a decrease in B max but no change in K d of [ 3H]HCh-3 binding. Potassium depolarization of slices also stimulated high-affinity [ 3H]choline uptake, which was completely inhibited by 10 μM TFP. These results are discussed in relation to the regulatory mechanisms of SDHACU.

Alterations in Catecholamine Release in the Central Nervous System of Spontaneously Hypertensive Rats.

The aim of the present study was to investigate alterations in catecholamine release in the central nervous system of spontaneously hypertensive rats. Slices of hypothalamus, medulla oblongata and striatum were prepared from spontaneously hypertensive rats (SHR: 9-10 weeks old) and age-matched Wistar Kyoto rats (WKY). The slices were incubated with (3H)norepinephrine (NE) or (3H)dopamine (DA), superfused with Krebs-solution in vitro, and the release of the catecholamines was compared between the two strains. The basal release of hypothalamic (3H)NE did not differ between SHR and WKY slices. However, stimulation (1 Hz)-evoked (3H)NE release was significantly greater in SHR than in WKY (percent fractional release of total tissue NE: WKY 0.494 +/- 0.019%, n = 6, SHR 0.730 +/- 0.053%, n = 6, p less than 0.05). The stimulation-evoked (3H)NE release from the medulla oblongata did not differ significantly between SHR and WKY slices. Finally stimulation-evoked release of striatal (3H)DA was significantly depressed in SHR (percent fractional release of total tissue DA: WKY 2.048 +/- 0.24%, n = 6, SHR 1.460 +/- 0.068%, n = 6, p less than 0.05). These results indicate that the release of hypothalamic NE and striatal DA are altered in SHR. It is suggested that enhanced hypothalamic noradrenergic activity and reduced striatal dopaminergic activity can increase sympathetic outflow to the periphery, which may play a role in the pathogenesis of this form of hypertension.