Increase in dopamine release from the nucleus accumbens in response to feeding: a model to study interactions between drugs and naturally activated dopaminergic neurons in the rat brain

The aim of the present study was to investigate the interactions between the in vivo release of dopamine and certain drugs, during conditions of increased dopaminergic activity. Dopaminergic neurons in the nucleus accumbens were activated by feeding hungry rats. 48-96 h after implantation of a microdialysis probe 30 min food ingestion by hungry rats induced an immediate eating response that was accompanied with a reproducible and long-lasting increase in extracellular dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC). The effect of various drugs (infused into the nucleus accumbens via the microdialysis probe), on the extracellular levels of dopamine and DOPAC were recorded, and the effect of eating was determined. Infusion of 5 mumol/l nomifensine and 3.4 mmol/l calcium increased dopamine release respectively 5.4 and 2-fold but did not modify the eating related increase in dopamine and DOPAC release. Infusion (1 mumol/l) as well as intraperitoneal administration (20 mg/kg) of sulpiride induced an increase in basal dopamine release to 220 and 195% of controls, respectively. Both routes of sulpiride pretreatment enhanced the eating related increase in extracellular dopamine and DOPAC. The results of the sulpiride experiments indicate that a behaviorally induced stimulation of dopamine release is modified by autoinhibition.     

Effects of lead-arsenic combined exposure on central monoaminergic systems

Lead acetate (116 mg/kg/day), arsenic (11 or 13.8 mg/kg/day as sodium arsenite), a lead-arsenic mixture or vehicle were administered to adult mice through gastric intubation during 14 days. Then, the regional content of norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4 dihydroxyphenyl-acetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA), arsenic, and lead were quantified. Compared with the accumulation after single element exposures, the mixture elicited a higher accumulation of lead and a lower arsenic accumulation in the brain. Compared to controls, lead induced only an augmentation of DOPAC (200%) in the hypothalamus. By contrast, the mixture provoked increases of DOPAC in the hypothalamus (250%), DA and 5-HIAA in the striatum (67 and 187%, respectively) and NE decreased in the hypothalamus (45%). Although these alterations were similar to those produced by arsenic alone, the mixture provoked a 38% decrease of NE in the hippocampus and increases of 5-HT in midbrain and frontal cortex (100 and 90%, respectively) over control values, alterations that were not elicited by either metal alone. These results demonstrate an interaction arsenic/lead on the central monoaminergic systems of the adult mouse.     

Gonadotropin and gonadal steroid release in response to a gonadotropin-releasing hormone agonist in Gqalpha and G11alpha knockout mice

In this study, we used mice lacking the G11alpha [G11 knockout (KO)] or Gqalpha gene (Gq KO) to examine LH release in response to a metabolically stable GnRH agonist (Buserelin). Mice homozygous for the absence of G11alpha and Gqalpha appear to breed normally. Treatment of (5 wk old) female KO mice with the GnRH agonist Buserelin (2 microg/100 microl, sc) resulted in a rapid increase of serum LH levels (reaching 328 +/- 58 pg/25 microl for G11 KO; 739 +/- 95 pg/25 microl for Gq KO) at 75 min. Similar treatment of the control strain, 129SvEvTacfBr for G11 KO or the heterozygous mice for Gq KO, resulted in an increase in serum LH levels (428 +/- 57 pg/25 microl for G11 KO; 884 +/- 31 pg/25 microl for Gq KO) at 75 min. Both G11 KO and Gq KO male mice released LH in response to Buserelin (2 microg/100 microl of vehicle; 363 +/- 53 pg/25 microl and 749 +/- 50 pg/25 microl 1 h after treatment, respectively). These values were not significantly different from the control strain. In a long-term experiment, Buserelin was administered every 12 h, and LH release was assayed 1 h later. In female G11 KO mice and control strain, serum LH levels reached approximately 500 pg/25 microl within the first hour, then subsided to a steady level (approximately 100 pg/25 microl) for 109 h. In male G11 KO mice and in control strain, elevated LH release lasted for 13 h; however, LH levels in the G11 KO male mice did not reach control levels for approximately 49 h. In a similar experimental protocol, the Gq KO male mice released less LH (531 +/- 95 pg/25 microl) after 13 h from the start of treatment than the heterozygous male mice (865 +/- 57 pg/25 microl), but the female KO mice released more LH (634 +/- 56 pg/25 microl) after 1 h from the start of treatment than the heterozygous female mice (346 +/- 63 pg/25 microl). However, after the initial LH flare, the LH levels in the heterozygous mice never reached the basal levels achieved by the KO mice. G11 KO mice were less sensitive to low doses (5 ng/per animal) of Buserelin than the respective control mice. Male G11 KO mice produced more testosterone than the control mice after 1 h of stimulation by 2 microg of Buserelin, whereas there was no significant difference in Buserelin stimulated testosterone levels between Gq KO and heterozygous control mice. There was no significant difference in Buserelin stimulated estradiol production in the female Gq KO mice compared with control groups of mice. However, female G11 KO mice produced less estradiol in response to Buserelin (2 microg) compared with control strain. Although there were differences in the dynamics of LH release and steroid production in response to Buserelin treatment compared with control groups of mice, the lack of complete abolition of these processes, such as stimulated LH release, and steroid production, suggests that these G proteins are either not absolutely required or are able to functionally compensate for each other.     

Dopamine autoreceptors in rat nucleus accumbens modulate prepulse inhibition of acoustic startle

Dopamine and 3,4-dihydroxy phenylacetic acid (DOPAC) levels in discrete regions and apomorphine- or (-)-sulpiride-induced changes in electrically evoked dopamine release from nucleus accumbens slices were assessed after testing prepulse inhibition of acoustic startle (PPI) in rats. Dopamine and DOPAC levels in the nucleus accumbens, but not in the striatum, correlated well with PPI (r = -0.64 for dopamine, r = -0.48 for DOPAC). Evoked dopamine release from the nucleus accumbens did not differ between the high-PPI (more than 60%) and the low-PPI (less than 40%) group. When slices were superfused with 1 microM apomorphine, the S2/S1 ratio in rats showing high PPI was 0.77 +/- 0.02 (mean +/- SEM, 66% of control), significantly smaller than in the low-PPI group (S2/S1 ratio = 0.97 +/- 0.08, 94% of control, p < 0.05). Moreover, (-)-sulpiride-induced increase in evoked dopamine release from the nucleus accumbens in the high-PPI group was inclined to be greater than in the low-PPI group. The results suggest that PPI differences between individuals may reflect the sensitivity of release-modulating dopamine autoreceptors in the nucleus accumbens.     

Angiotensin-converting enzyme modulates dopamine turnover in the striatum

The effect of chronic inhibition of the angiotensin-converting enzyme on dopamine content and release in the striatum was investigated using in vivo microdialysis in awake, freely moving rats. Rats were treated for 1 week with the angiotensin-converting enzyme inhibitor perindopril (1 mg/kg) via the drinking water, whereas the controls were given water alone. One week after perindopril treatment, striatal dopamine dialysate levels in the treated group were markedly elevated compared with control values: control, 233 +/- 43 pg/ml; perindopril, 635 +/- 53 pg/ml (p < 0.001). These results were confirmed by a complementary study in which dopamine content was measured in striatal extracts (3.5 +/- 0.4 micrograms of dopamine/g of tissue for controls compared with 9.2 +/- 2.4 micrograms of dopamine/g of tissue for the treated group; p < 0.05). In the rats that were dialyzed, angiotensin-converting enzyme levels in the striatum were decreased by 50% after perindopril treatment. Levels of dopamine D1 and D2 receptors and of preprotachykinin and tyrosine hydroxylase mRNAs were unchanged after angiotensin-converting enzyme inhibition. A small, but significant, increase was detected in striatal preproenkephalin mRNA levels in the angiotensin-converting enzyme inhibitor-treated group. These results indicate that peripherally administered angiotensin-converting enzyme inhibitors penetrate the blood-brain barrier when given chronically and modulate extracellular dopamine and striatal neuropeptide levels.     

Pharmacokinetic and pharmacodynamic studies of L-dopa in rats. II. Effect of L-dopa on dopamine and dopamine metabolite concentration in rat striatum

The purpose of this investigation was to quantitatively describe the time courses of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) concentrations in the striatum after L-dopa injection using a constructed dopamine metabolism model. The time courses of dopamine, DOPAC and HVA concentration in the striatum of rats was determined before and after the rapid i.v. injection of 10, 50 and 100 mg/kg using the same animals as in the previous report. The endogenous dopamine, DOPAC and HVA concentrations in the striatum before L-dopa administration were 5.9 +/- 0.7 micrograms, 3.6 +/- 0.4 micrograms and 1.0 +/- 0.2 micrograms/g, respectively. The dopamine concentration in the striatum increased immediately after L-dopa injection, with the peak concentration (15.9 +/- 0.5 micrograms/g) occurring at 3 min; then it returned to the pre-medication level until 2 h at 100 mg/kg dosing. The time course of dopamine concentration in the striatum was analyzed on a constructed dopamine metabolism model which has a zero-order production rate for the production of dopamine (i.e. release from the dopamine neuronal terminals) and two apparent first-order clearance terms, one from L-dopa to dopamine, which was estimated in the previous report, and the other from dopamine to dopamine metabolites (DOPAC and HVA). However, the time course of dopamine concentration in the striatum could not be described by this model.(ABSTRACT TRUNCATED AT 250 WORDS)     

Injuries among domestic waste collectors

In a recent paper [R.R. Holson, J.F. Bowyer, P. Clausing, B. Gough, Methamphetamine-stimulated striatal dopamine release declines rapidly over time following microdialysis probe insertion, Brain Res. 739 (1996) 301-307] we reported that methamphetamine-stimulated striatal dopamine release declined rapidly over the first eight hours following microdialysis probe insertion. This decline was strictly a function of time post-probe implantation, and not due to tolerance or desensitization. To further examine this phenomenon, we subjected rats to three brief pulses of several DA-releasing compounds at 2, 4 and 6 h post-probe insertion, and compared these results to those caused by a single pulse 6 h post-insertion, or in some cases to pulses given more than 24 h post-insertion. We found that when buproprion, a dopamine reuptake blocker, was infused briefly into the striatum via the microdialysis probe, there was a pronounced drop in the amount of dopamine released at 6 h vs. 2 h post-insertion; this drop was not due to repeated exposure, since dopamine release at 6 h post-insertion was the same for a single pulse, or when preceded by two earlier pulses. Twenty-four hours later, buproprion-stimulated dopamine release was still lower, but did not appear to drop further thereafter. Potassium-stimulated dopamine release, on the other hand, dropped rapidly over the first 8 h post-insertion, and this decline continued throughout the 24-32 h interval post-insertion. Similarly, a single i.p. injection of 0.5 mg/kg haloperidol released three times as much dopamine when given two compared to six hours post-implantation. Both bupropion- and potassium-stimulated dopamine release were accompanied by declines in extracellular DOPAC concentrations, and these declines were the same 2 or 26 h post-insertion. In contrast, haloperidol exposure increased extracellular DOPAC, and this haloperidol-stimulated DOPAC increase was also greatly attenuated at 6 compared to 2 h post-insertion. We conclude that there is a general decline over time post-probe implantation in the ability of the striatal dopamine system to release dopamine, and perhaps to increase dopamine synthesis, in response to pharmacological challenges.     

Treatment of antecubital pterygium in the nail-patella syndrome

The effects of an aggressive biting response on stress-induced noradrenaline (NA) release in the rat amygdala and gastric ulcer formation were studied with an intracerebral microdialysis technique. Rats were exposed to a 60-min period of cold restraint stress with or without being allowed to bite a wooden stick. They were sacrificed 100 min after release from stress to investigate gastric ulcer formation. Cold-restraint stress increased NA release to 304 +/- 22.3 and 206 +/- 23.8% of basal levels (mean +/- SEM) in the nonbiting and biting groups, respectively. The stress-induced increases in NA release in the nonbiting group were significantly higher than those in the biting group. In the nonbiting group, significant increases in NA release continued for 80 min after release from stress; however, NA levels in the biting group recovered to basal levels immediately after the cessation of stress. Although many severe gastric lesions with bleeding were found in the nonbiting group, fewer gastric lesions without bleeding were found in the biting group. The cumulative length of gastric lesions in the nonbiting group and in the biting group was 26.2 +/- 7.4 and 6.8 +/- 3.9 mm (mean +/- SEM), respectively. The mean number of ulcers in the nonbiting group and the biting group was 11.8 +/- 1.3 and 1.8 +/- 0.7 (mean +/- SEM), respectively. Both the cumulative length of ulcers and the number of ulcers were significantly lower than those seen in the nonbiting group. These findings strongly suggest that expression of aggression during stress exposure attenuates not only stress-induced increases in NA release in the rat amygdala but also gastric ulcer formation consequent to stress.     

Protection against influenza after annually repeated vaccination: a meta-analysis of serologic and field studies

We report the effects of a tyrosine (and phenylalanine)-free amino acid mixture on tyrosine levels, ex vivo catecholamine synthesis and in vivo catecholamine release in brain regions of the rat. Administration of a tyrosine-free amino acid load reduced tissue levels of tyrosine (-50% after 2 h) in all brain regions examined (frontal cortex, hippocampus, striatum). The tyrosine-free amino acid mixture also reduced DOPA accumulation: this effect was most marked in striatum (-44%) and nucleus accumbens (-34%), areas with a predominantly dopaminergic innervation. Smaller decreases (-20-24%) were detected in other areas (cortex, hippocampus and hypothalamus). The effect on DOPA accumulation was prevented by supplementing the mixture with tyrosine/phenylalanine. The tyrosine-free amino acid mixture did not alter 5-HTP accumulation in any region. In microdialysis experiments, the tyrosine-free amino acid mixture did not consistently alter striatal extracellular dopamine under basal conditions but markedly, and dose-dependently, reduced the release of dopamine induced by amphetamine. In contrast, the tyrosine-free amino acid mixture did not alter either basal or amphetamine-evoked release of noradrenaline in hippocampus. Overall, these studies indicate that administration of a tyrosine-free amino acid mixture to rats depletes brain tyrosine to cause a decrease in regional brain catecholamine synthesis and release. Dopaminergic neurones appear to be more vulnerable to tyrosine depletion than noradrenergic neurones.     

In vivo comparison of the effects of inhibition of MAO-A versus MAO-B on striatal L-DOPA and dopamine metabolism

Utilizing the cerebral microdialysis technique, we have compared in vivo the effects of selective MAO-A, MAO-B, and nonselective MAO inhibitors on striatal extracellular levels of dopamine (DA) and DA metabolites (DOPAC and HVA). The measurements were made in rats both under basal conditions and following L-DOPA administration. Extracellular levels of dopamine were enhanced and DA metabolite levels strongly inhibited both under basal conditions and following L-DOPA administration by pretreatment with the nonselective MAO inhibitor pargyline and the MAO-A selective inhibitors clorgyline and Ro 41-1049. The MAO-B inhibitor deprenyl had no effect on basal DA, HVA, or DOPAC levels. Nevertheless, deprenyl significantly increased DA and decreased DOPAC levels following exogenous L-DOPA administration, a finding compatible with a significant glial metabolism of DA formed from exogenous L-DOPA. We conclude that DA metabolism under basal conditions is primarily mediated by MAO-A. In contrast, both MAO-A and MAO-B mediate DA formation when L-DOPA is administered exogenously. The efficacy of newer, reversible agents which lack the "cheese effect" such as Ro 41-1049 are comparable to the irreversible MAO-A inhibitor clorgyline. The possible relevance of these findings for the treatment of Parkinson's disease is discussed.     

Presynaptic modulation by VIP, secretin and isoproterenol of somatostatin release from enriched enteric synaptosomes: role of cAMP

The release of somatostatin-like immunoreactivity was studied in isolated synaptosomes. A significant release of somatostatin-like immunoreactivity was observed in the presence of vasoactive intestinal polypeptide (VIP) (10(-6) M: 53.0 +/- 12.4 pg/mg, basal: 14.3 +/- 1.7 pg/mg, n = 5, P < 0.05), secretin (10(-6) M: 56.1 +/- 3.8 pg/mg, basal: 25.8 +/- 1.6 pg/mg, n = 6, P < 0.01) and isoproterenol (10(-5) M: 54.0 +/- 13.4 pg/mg, basal: 20.0 +/- 3.4 pg/mg, n = 8, P < 0.05). Forskolin, an unspecified activator of the adenylate cyclase, caused a significant release of somatostatin-like immunoreactivity (10(-6) M: 57.3 +/- 13.2 pg/mg, basal: 30.0 +/- 5.8 pg/mg, n = 13, P < 0.01) which was further augmented in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX 10(-4) M) (77.0 +/- 17.8 pg/mg, n = 13, P < 0.01). 3-Isobutyl-l-methylxanthine and N6, 2'-O-dibutyryladenosine-3',5'-cyclic monophosphate mimicked at effect of forskolin and VIP. The release of somatostatin was paralleled by an increase of cAMP immunoreactivity in the presence of VIP (10(-6) M: 37.1 +/- 9.4 pmol/mg, basal: 19.8 +/- 4.2 pmol/mg, n = 10, P < 0.05), isoproterenol (10(-5) M: 42.4 +/- 9.8 pmol/mg basal: 16.7 +/- 2.4 pmol/mg, n = 12, P < 0.01) and forskolin (10(-6) M: 47.1 +/- 12.4 pmol/mg, basal: 19.8 +/- 4.2 pmol/mg, n = 10, P < 0.01). The effect of nitric oxide (NO) which acts as an inhibitory neurotransmitter in the enteric nervous system was studied. NO is known to activate guanylate cyclase to induce transmitter release. The NO-generating compound sodium nitroprusside and bromoguanosine-3',5'-cyclic monophosphate (8-Br-cGMP) had no effect on the release of somatostatin-like immunoreactivity. These data demonstrate the stimulatory effect of VIP, secretin and isoproterenol on release of somatostatin-like immunoreactivity from enteric synaptosomes, which is presumably mediated by cAMP-dependent mechanisms. cGMP-dependent mechanisms seem to be of minor relevance.     

Effect of hemorrhagic hypotension on cortical oxygen pressure and striatal extracellular dopamine in cat brain

This study investigated the relationships between blood pressure, cortical oxygen pressure, and extracellular striatal dopamine in the brain of adult cats during hemorrhagic hypotension and retransfusion. Oxygen pressure in the blood of the cortex was measured by the oxygen dependent quenching of phosphorescence and extracellular dopamine, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) by in vivo microdialysis. Following a 2 h stabilization period after implantation of the microdialysis probe in the striatum, the mean arterial blood pressure (MAP) was decreased in a stepwise manner from 132 +/- 2 Torr (control) to 90 Torr, 70 Torr and 50 Torr, holding the pressure at each level for 15 min. The whole blood was then retransfused and measurements were continued for 90 min. As the MAP was lowered there was a decrease in arterial pH, from a control value of 7.37 +/- 0.05 to 7.26 +/- 0.06. The PaCO2 decreased during bleeding from 32.3 +/- 4.8 Torr to 19.6 +/- 3.6 Torr and returned to 30.9 +/- 3.9 Torr after retransfusion. The PaO2 was 125.9 +/- 15 Torr during control conditions and did not significantly change during bleeding. Cortical oxygen pressure decreased with decrease in MAP, from 50 +/- 2 Torr (control) to 42 +/- 1 Torr, 31 +/- 2 Torr and 22 +/- 2 Torr, respectively. A statistically significant increase in striatal extracellular dopamine, to 2,580 +/- 714% of control was observed when MAP decreased to below 70 Torr and cortical oxygen pressure decreased to below 31 Torr. When the MAP reached 50 Torr, the concentration of extracellular dopamine increased to 18,359 +/- 2,764% of the control value. A statistically significant decrease in DOPAC and HVA were observed during the last step of bleeding. The data show that decreases in systemic blood pressure result in decrease in oxygen pressure in the microvasculature of the cortex, suggesting vascular dilation is not sufficient to result in a full compensation for the decreased MAP. The decrease in cortical oxygen pressure to below 32 Torr is accompanied by a marked increase in extracellular dopamine in the striatum, indicating that even such mild hypoxia can induce significant disturbance in brain metabolism.     

Monitoring norepinephrine levels by microdialysis in the white adipose tissue of spontaneously hypertensive rats

1. To investigate whether microdialysis is suitable to monitor catecholamine in white adipose tissue of conscious rat and to assess eventual differences in norepinephrine (NE) interstitial levels, two groups of 12 male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, 14-16 weeks old, were compared. 2. A flexible microdialysis probe was implanted subcutaneously in the parascapular region, and perfused with Ringer solution (flow rate: 2.0 mu L/min). After a 20 min equilibration period, NE levels were monitored over a 120 min period; then, tyramine hydrochloride (0.1 nmol/min) was perfused for 80 min. Dialysates from each 20 min collection period were analysed by HPLC with electrochemical detection for NE. 3. Basal levels of NE (adjusted for the recovery) were higher in SHR compared to WKY (1210.0 +/- 140.5 pg/mL dialysate vs 573.3 +/- 75.8 pg/mL dialysate; P < 0.001, ANOVA). In both strains tyramine perfusion increased NE concentration in dialysates; the net (i.e. baseline subtracted) NE output was lower (76.3 pg/h, s.e.m. 22.3) in SHR compared with that shown by WKY rats (201.0 pg/h, s.e.m 18.4, P < 0.01). 4. The increased basal levels of NE observed in SHR are associated with a blunted response to tyramine challenge. Since tyramine is known to cause NE release from the cytosol but not from vesicle stores, such a blunted response is consistent with an increased turnover rate of NE or with an accelerated uptake in pre-synaptic vesicles which, together with the higher basal levels, would suggest increased noradrenergic activity.     

Quantitative microdialysis of neuropeptide Y

The feasibility of using the difference method of quantitative microdialysis to measure neuropeptide Y (NPY) was evaluated in vitro and in vivo. The accuracy of this method was tested in vitro under steady-state conditions for 3 test solutions containing known concentrations of NPY. The estimated concentrations of NPY were 1.2 +/- 0.6, 3.7 +/- 0.9, and 15.1 +/- 0.7 pg/microliter (mean +/- SEM) in agreement with the actual concentrations of NPY in the test solutions which were 1.1 +/- 0.8, 4.6 +/- 0.6, and 14.6 +/- 0.5 pg/microliter (mean +/- SEM of solution samples), respectively. The responsiveness of the estimated NPYext measure to changes in the external concentration of NPY was also evaluated in vitro. An accurate estimate of NPYext was obtained within the first sampling period (within 15 min) after a 2-3-fold increase in the test solution concentration of NPY and within 2-3 sampling periods (15-45 min) in response to a 2-3-fold decrease in the test solution concentration of NPY. In vivo, the estimated basal concentration of NPY in dialysis samples from probes in the medial basal hypothalamus of anesthetized female rats (n = 4) was 4.0 +/- 1.6 pg/microliters and increased to 9.5 +/- 0.3 pg/microliter during K+ stimulation. Relative recovery was 22% in vivo under steady-state conditions and ranged from 14% to 30% during dynamic conditions. These results demonstrate that the difference method of quantitative microdialysis accurately estimates picomolar concentrations of NPY in vitro, and is sufficiently sensitive to detect basal and increasing concentrations of NPY in vivo.     

A hemagglutinin-based multipeptide construct elicits enhanced protective immune response in mice against influenza A virus infection

The effect of the muscarinic antagonist, scopolamine, was examined for a change in the increase in extracellular dopamine, dihydroxyphenyl acetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindolacetic acid (5-HIAA), induced by haloperidol or clozapine in the striatum and nucleus accumbens of anaesthetised and awake rats, monitored using in vivo cerebral microdialysis. Rats received scopolamine (1 mg kg(-1); s.c.) or vehicle followed by haloperidol (1 mg kg(-1); s.c.) or clozapine (20 mg kg(-1); s.c.). Dopamine, DOPAC, HVA and 5-HIAA overflow into striatal or accumbens perfusates was determined using high performance liquid chromatography with electrochemical detection (HPLC-ECD). Scopolamine failed to modify the clozapine- or haloperidol-induced efflux of dopamine or its metabolites in either the striatum or nucleus accumbens following systemic administration in anaesthetised or awake rats. Although pretreatment with scopolamine tended to produce a smaller increase in the clozapine-induced efflux of DOPAC in striatal perfusates than following clozapine treatment alone, this was not statistically significant. Furthermore, local infusion of scopolamine (100 microM) with clozapine (1 mM) via the microdialysis probe did not attenuate the elevated efflux of dopamine observed following clozapine alone, in either the striatum or nucleus accumbens, in anaesthetised rats. This treatment did prevent the clozapine-induced increase in DOPAC and HVA in the striatum but not the nucleus accumbens. Carbachol (50 microM) infused into the dorsolateral striatum or nucleus accumbens raised extracellular dopamine levels 200% and 150%, respectively above baseline. Our data suggest that the increased efflux of dopamine and its metabolites in the rat basal ganglia following clozapine administration is not significantly dependent upon the interaction of clozapine with muscarinic receptors.     

Alteration in L-DOPA evoked dopamine and DOPAC output under conditions of impaired vesicular dopamine storage

We examined the effect of L-dihydroxyphenylalanine (L-DOPA) infusion in vitro upon dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) output from superfused corpus striatum of vehicle and reserpine or tetrabenazine (TBZ) treated male rats. Specifically, we tested the effects of two 20-min infusions of L-DOPA (5 uM) upon DA and DOPAC output (pg/mg/min) in reserpine (5 mg/kg, i.p., 24 hours before sacrifice; n=11), TBZ (30 mg/kg, i.p. 1 hour before sacrifice; n=8) or vehicle (n=21) treated rats. There was an overall significantly higher L-DOPA evoked DA output from the vehicle (12.22+/-1.74) versus reserpine (4.39+/-2.40) (p < 0.05), but not TBZ (9.16+/-2.81) treated rats. In addition, the DA response to the second L-DOPA infusion was significantly increased over that of the first response in the vehicle (9.40+/-2.11 vs. 15.04+/-2.78) (p < 0.05), but not reserpine or TBZ treated rats. The overall DOPAC outputs did not achieve a statistically significant difference among all treatment groups. However, the DOPAC outputs following the second L-DOPA infusion were significantly reduced in reserpine (41.15+/-6.10 vs. 20.27+/-4.54) and TBZ (21.38+/-4.41 vs. 10.87+/-2.36) (both p < 0.05), but not vehicle (28.99+/-4.00 vs. 24.91+/-4.78) treated rats. We conclude that: 1) the storage capacity of DA neurons is one of the important elements involved in affecting L-DOPA's effects upon DA and DOPAC output, 2) the shunting of storage to metabolism may represent a common characteristic in impaired nigrostriatal dopaminergic system, and 3) TBZ may operate differently from reserpine in the nigrostriatal dopaminergic system.     

Identification and characterization of CDS2, a mammalian homolog of the Drosophila CDP-diacylglycerol synthase gene

The technique of intracranial microdialysis was used to investigate the effects of aging on the striatal dopaminergic system of the anesthetized Fischer 344 rat. Microdialysis probes were implanted into the striatum of young (2-8 months) and aged (24-28 months) urethane anesthetized rats. Striatal dialysate levels were analyzed for dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and serotonin (5-HT) by high performance liquid chromatography with electrochemical detection. As compared to the young animals, basal extracellular levels of DA and DOPAC were significantly decreased in two groups of aged animals. Stimulation with excess potassium added through the microdialysis probe produced a robust overflow of DA in the young and aged rat striatum, but the evoked overflow of DA was not diminished in the aged rat striatum as compared to young animals. In contrast, d-amphetamine-evoked overflow of DA was again robust in young and aged animals, but was greatly decreased in the aged rat striatum as compared to the signals recorded in the young rats. Taken together with previous reports, these data support the hypothesis that a major change in the regulation of DA release that occurs in aging involves changes in the function of the neuronal uptake of DA, which may be a compensatory property of DA neurons in senescence.     

Inhibition of monocyte leukotriene B4 production after aspirin desensitization

Aspirin-sensitive patients may be desensitized through a graded series of exposures to aspirin. We investigated the underlying mechanism of aspirin desensitization by measuring the release of leukotrienes B4 and C4 from calcium ionophore-stimulated peripheral blood monocytes. Compared with monocytes from normal volunteers (n = 5), monocytes from patients with aspirin-sensitive asthma (n = 10) released increased amounts of thromboxane B2 (1060 +/- 245 pg/ml vs 456 +/- 62 pg/ml), leukotriene B4 (861 +/- 139 pg/ml vs 341 +/- 44 pg/ml), and leukotriene C4 (147 +/- 31 pg/ml vs 56 +/- 6 pg/ml) at baseline. After aspirin desensitization, thromboxane B2 release was almost completely suppressed in both groups. Leukotriene B4 release was significantly decreased in the aspirin-sensitive group (484 +/- 85 pg/ml) but not in the normal subject group (466 +/- 55 pg/ml). The need for prednisone decreased significantly after patients were desensitized to aspirin (10.4 +/- 2.2 mg/day to 1.6 +/- 2.8 mg/day). These results demonstrate that desensitization to aspirin results in decreased monocyte leukotriene B4 release. On the basis of the bronchospastic and inflammatory potential of leukotrienes, the decrease in leukotriene release may contribute to the clinical improvement seen after aspirin desensitization.     

New Approach: Waste Materials as Sorbents for Arsenic Removal from Water

The sorption of inorganic arsenic species (arsenite and arsenate) from aqueous solutions onto steel-mill waste and waste filter sand, under neutral conditions, was investigated in this study. Additionally, the steel-mill waste material was modified in order to minimize its deteriorating impact on the initial water quality and to meet the drinking water standards. The influence of contact time and initial arsenic concentration was investigated using batch system techniques. To evaluate the application for real groundwater treatment, the capacities of the obtained waste materials were further compared to those exhibited by commercial sorbents, which were examined under the same experimental conditions. Kinetic studies revealed that waste slag materials are the most efficient in arsenic removal, reaching equilibrium arsenic sorption capacities in the range 47.6–55.2?μg/g, while waste filter sand exhibited capacities of 25.4–29.8?μg/g (for an initial arsenic concentration Co = 0.5?mg/L). The higher iron content in the slag materials was considered to be responsible for the better removal efficiencies, and the specific arsenic removal efficiency was estimated to be 220?μgAs/gFe. The specific arsenic removal efficiency of the second active substance found in waste filter sand, manganese, was estimated to be 115?μgAs/gMn. Equilibrium studies revealed the occurrence of both chemisorption and physical sorption processes. All the waste materials exhibited higher performances for As(V). The highest maximum sorption capacity was obtained by waste iron slag: 4040?μg/g for As(V). The waste materials reached the arsenic removal capacities of the examined commercial materials, suggesting the feasibility of their application in real groundwater treatment.     

Some experiences with hospital-based psychiatric aftercare over ten years

Smooth muscle cells represent a significant percentage of the total cells in the airway but their contribution to the inflammatory response seen in airway disease has not been studied. Hence, we have looked at the release of the cytokine granulocyte-macrophage colony stimulating factor (GM-CSF) in response to bacterial lipopolysaccharide (LPS) and the pro-inflammatory cytokines interleukin-1 beta (IL-1 beta), tumour necrosis factor alpha (TNF alpha) and interferon gamma (IFN gamma). Human airway smooth muscle (HASM) cells released GM-CSF under basal conditions (45.4 +/- 13.1 pg ml-1) that was significantly enhanced by IL-1 beta and TNF alpha with a maximal effect seen at 10 ng ml-1 (1.31 +/- 0.07 ng ml-1 and 0.72 +/- 0.16 ng ml-1, respectively). In contrast, neither LPS nor IFN gamma produced a significant increase in GM-CSF release. However, HASM cells exposed to IL-1 beta, TNF alpha and IFN gamma generated more GM-CSF than that evoked by any cytokine alone (2.2 +/- 0.15 ng ml-1). The release of GM-CSF elicited by the cytokine mixture was inhibited by cycloheximide and dexamethasone. These data suggest that HASM cells might play an active part in initiating and/or perpetuating airway inflammation in addition to controlling airway calibre.