Stimulus-dependent changes of extracellular glucose in the rat hippocampus determined by in vivo microdialysis

Neuronal activity is tightly coupled with brain energy metabolism; and glucose is an important energy substrate for neurons. The present in vivo microdialysis study was aimed at investigating changes in extracellular glucose concentrations in the rat ventral hippocampus due to exposure to the elevated plus maze. Determination of basal hippocampal glucose and lactate/pyruvate ratio in male Wistar rats was conducted in the home cage using in vivo microdialysis. Rats were exposed to the elevated plus maze, a rodent model of anxiety-related behaviour, or to unspecific stress induced by white noise (95dB) as a control condition. Basal hippocampal levels of glucose, as determined by zero-net-flux, and the basal lactate/pyruvate ratio were 1.49+/-0.05mmol/l and 13.8+/-1.1, respectively. In rats without manipulation, glucose levels remained constant throughout the experiment (120min). By contrast, exposure to the elevated plus maze led to a temporary decline in hippocampal glucose (-33.2+/-4.4%) which returned to baseline level in the home cage. White noise caused only a non-significant decrease in extracellular glucose level (-9.3+/-3.5%). In all groups, the lactate/pyruvate ratio remained unchanged by the experimental procedures. Our microdialysis study demonstrates that exposure to the elevated plus maze induces a transient decrease in extracellular hippocampal glucose concentration. In contrast, an unspecific stimulus did not change hippocampal glucose. The latter suggests that only specific behavioural stimuli increase hippocampal glucose utilization in the ventral hippocampus.

Muscle relaxant use for tracheal intubation in pediatric anaesthesia: a survey of clinical practice in Germany

OBJECTIVES

Aim of this Germany-wide study was to evaluate the use and application customs of neuromuscular blocking drugs (NMBDs) for tracheal intubation in children of age 5 years or younger.

MATERIAL AND METHODS

In the year 2005, a total of 3260 questionnaires were sent out to all heads of anesthesia departments at all types of hospitals as well as ambulatory anesthesia centers in Germany. The fields covered by the questionnaire were regarding institutional size, amount of general anesthesia and specifically pediatric cases, number of intubations and NMBDs used, frequency of use of the individual relaxants and techniques utilized when administering muscle relaxants.

RESULTS

Of the sent-out questionnaires 66.9% could be analyzed: 82% of hospitals use 1-3 muscle relaxants in children; 91% of the ambulatory anesthesia centers use a repertoire of 1-2 neuromuscular blockers for pediatric cases. However, general anesthesia with tracheal intubation in children is often induced without using any NMBD at all. Mivacurium is the predominantly used NMBD for pediatric intubation in Germany. In contrast, the use of succinylcholine is far less in ambulatory anesthesia centers than in hospitals. Despite controversial discussion, precurarization, priming, and timing are still utilized in German anesthesia practice.

CONCLUSION

In Germany, mivacurium, with its favorable pharmacologic profile for short cases, is the predominantly used NMBD for pediatric tracheal intubation. Despite the known adverse effects of intubation without muscle relaxation, this technique is also wide-spread, especially among German anesthetists in ambulatory anesthesia centers. Surveys like these are important to determine a status quo of use and application customs of NMBDs in pediatric anesthesia and provide a basis for numerous other studies.

Repeated anaesthesia with isoflurane and xylazine/levomethadone/fenpipramide premedication in female Beagle dogs: Influence on general health and wellbeing

Summary

Beagle dogs continue to be used in experimental studies and preclinical and clinical trials, many of which address the usage of anaesthesia. In order to reduce the number of animals, researchers tend to conduct several experiments on a single animal. The question arises, however, as to whether or not this frequent usage involves more than simply additional stress and discomfort for the individual animal. Within the framework of an existing study involving six female Beagle dogs, we investigated the effects of repeated (5) isoflurane anaesthesia with xylazine/levomethadone/fenpipramide premedication carried out at short intervals (2 weeks) and compared these with the effects of two treatments intermitted by a longer resting period (8 weeks). To verify our hypothesis that frequent anaesthesia affects the dog's wellbeing more than the occasional anaesthesia, the following parameters were measured at regular intervals: body weight, body temperature, respiratory rate, blood pressure, reflexes and heart rate, both at rest and during a treadmill exercise. In addition, recovery behaviour subsequent to anaesthesia was monitored for one hour. Our observations indicate that the anaesthetic effects are most prominent 24 h after the anaesthetic treatment. However, crossover analysis of our data cannot show that there is no statistical difference of whether dogs were anaesthetized occasionally or frequently. In our study, it appears that frequent anaesthesia within a two-week period did not affect the wellbeing and general health of Beagle dogs in a super-additive manner and that a minimum of two-week testing-free period is sufficient to ensure complete recovery from the unwanted effects induced by anaesthesia.

Changes in the brain serotonin satiety system in transgenic rats lacking brain angiotensinogen

In transgenic rats, TGR(ASrAOGEN)680, with reduced glial expression of angiotensinogen, changes in brain angiotensinogen are associated with reductions in serotonin (5-HT) content and/or 5-HT metabolism as determined in various brain regions, including the hypothalamus. These rats showed an anxious phenotype upon a first behavioural screen. The present study aimed to extend the search for functional consequences of changes in brain 5-HT with respect to feeding behaviour in these transgenic rats. In feeding experiments, rats were treated with the anorectic drug fenfluramine to probe for functional changes in the serotonergic satiety system. Fenfluramine (0.3 mg/kg, i.p.) reduced food intake in TGR(ASrAOGEN)680 rats whereas the minimal effective dose in wild-type rats was 3 mg/kg, i.p. Although, in the cortex, no differences were apparent in the expression of serotonin 5-HT(1A), 5-HT(1B), 5-HT(2C) receptor and 5-HT transporter mRNAs between TGR(ASrAOGEN)680 and wild-type rats, the expression of mRNAs for the 5-HT(2C) receptor and 5-HT transporter mRNA were significantly higher in the hypothalamus of TGR(ASrAOGEN)680 rats compared to wild-type rats. No differences were found in the mRNA levels for hypothalamic 5-HT(1A) and 5-HT(1B) receptors between TGR(ASrAOGEN)680 and wild-type rats. Taken together, these findings suggest that the transgenic effect on the brain 5-HT system is paralleled by functional changes of the serotonergic feeding system.

Changes in extracellular hypothalamic glucose in relation to feeding

The aim of the present in vivo microdialysis study was to investigate the relation between feeding and changes in glucose concentrations in the rat ventromedial hypothalamus (VMH). Absolute ambient glucose concentrations in VMH were 1.43 mm in non-deprived rats as compared to 0.94 mm after 24-h food deprivation. To examine whether feeding influences hypothalamic glucose, changes of glucose concentration over time were determined relative to a baseline. Experiments were conducted in relation to both, nutritional state (food-deprived rats vs. non-deprived rats) and feeding conditions throughout the experiment (freely feeding rats vs. rats without access to food). The results of this microdialysis study show clearly that glucose concentration in the VMH of rats increases significantly in relation to food intake. The data demonstrate that a 24-h food deprivation before the experiment further augments this increase (up to 350% from baseline) as compared to non-deprived conditions (up to 60% from baseline). However, the magnitude of food related increase in VMH glucose does not correlate with the individual amount of food eaten. In conclusion, the present study shows for the first time that VMH glucose concentrations increase with food intake in the early dark phase, indicating that such changes do not only occur after pharmacological treatment, but also under physiological feeding conditions. The results further indicate that the feeding related increase in VMH glucose depends on the nutritional state of the organism.

Muskelrelaxanzien in Deutschland 2005

Aim of this study was to evaluate application customs of muscles relaxants in hospitals compared to their use in private practice. Of the 3,260 questionnaires sent-out, 66.9% could be analyzed. Of these 54% were from anesthetists in private practice, 41% from heads of hospital anesthesia departments and 5% from heads of level one hospital anesthesia departments. The first difference between private practices and hospitals was the number of available muscle relaxants: 87% of private practices use 1-3 relaxants, whereas 79% of hospitals use 3-5. Another apparent difference was the relationship between general anesthesia and the number of intubations: 60% of private practices have over 80% of general anesthesia cases, but only 50% of these patients are intubated. On the contrary, two thirds of the hospitals have 50-80% general anesthesia cases and 60-70% of patients are intubated. The main wish for an ideal muscle relaxant was independent of private practice or hospital, short onset time, followed by fast recovery. In accordance 74% of anesthetists in hospitals and 72% of anesthetists in private practice voiced the wish for a non-depolarizing succinylcholine substitute. The results of this nationwide survey suggest that time pressure in combination with an increased specialization of anesthetists in private practice are the main factors for availability and use of muscle relaxants in routine anesthesia.

Effects of 8-OH-DPAT on hippocampal NADH fluorescence in vivo in anaesthetized rats

Systemic administration of the 5-HT1A receptor agonist 8-OH-DPAT modifies 5-HT neuronal transmission via stimulation of presynaptic and postsynaptic receptors. Compared to the effects of presynaptic receptor stimulation, there are less data on the effects of postsynaptic 5-HT1A receptors and the net effects of a stimulation of pre- and postsynaptic 5-HT1A receptors available. We measured the neuronal activity in the rat hippocampus after systemic treatment with 8-OH-DPAT in doses (30-300 microg/kg) known to reduce 5-HT release and anxiety-like behavior in rodents. Neuronal activity was assessed by laser-induced fluorescence spectroscopy determining changes in nicotinamide adenine dinucleotide (NADH) fluorescence in the ventral hippocampus of anaesthetized rats in vivo. NADH, a co-substrate for energy transfer in the respiratory chain, mirrors mitochondrial activity. Increased NADH fluorescence signals lower consumption of NADH caused by neuronal inhibition. 8-OH-DPAT in a dose of 300 microg/kg, but not 100 microg/kg and 30 microg/kg, increased NADH fluorescence by maximal +27 +/- 3.5%, suggesting a decreased neuronal activity in the ventral hippocampus. The selective 5-HT1A antagonist WAY-100635 (3 mg/kg) prevented the increased NADH fluorescence after 8-OH-DPAT, but had no own effect. The results show that systemic administration of the 5-HT1A agonist 8-OH-DPAT dose-dependently affects neuronal activity in the ventral hippocampus. The dose of 300 microg/kg seemingly activates presynaptic and postsynaptic receptors with dominating inhibitory postsynaptic effects.

Clomipramine and selegiline: do they influence impulse control?

Anxiety disorders in dogs are often accompanied by loss of impulse control and can result in inappropriate behaviour such as destructiveness, excessive barking and aggression. The reduction of these undesirable actions is the focus of behaviour therapy. Clomipramine and selegiline have been approved for the treatment of separation anxiety in dogs, but there are anecdotal reports that they produce inconsistent therapeutic effect. Hence, the aim of this study was to verify the efficacy of clomipramine and selegiline for regulating impulse control by using a rat model based on the delay of reward procedure. The principle is that the animal has to decide between an immediate small food reward, normally preferred by impulsive animals, and a delayed large food reward. In this study, acute effects of clomipramine (0.3-10.0 mg/kg), selegiline (0.3-3.0 mg/kg), and diazepam (1.0-3.0 mg/kg) on the impulsive behaviour of two breeding lines of rats with different anxiety-related behaviour were investigated. Neither clomipramine nor selegiline had an effect on impulse control in either breeding line. However, motor activity was decreased by clomipramine and increased by selegiline. Diazepam led to an increase in impulsive behaviour of one rat line concomitant with an increase in motor activity. The results of this rat model for studying impulsive behaviour suggest that a single administration of selegiline and clomipramine has no influence on impulsive behaviour.

Anxiety but not arousal increases 5-hydroxytryptamine release in the rat ventral hippocampus in vivo

Central serotonin [5-hydroxytryptamine (5-HT)] is involved in the aetiology of numerous disease states, including depression and anxiety disorders. Studies have shown that exposure of rats to animal tests of anxiety increases extracellular 5-HT in the cortex or hippocampus determined by in vivo microdialysis. To discriminate whether this increase is caused by the aversive conditions of an animal test for anxiety or by an unconditioned stressor evoking mainly arousal, the present study investigates the effects of an unconditioned acoustic stimulus and exposure to the elevated plus maze (X-maze), respectively, on the release of 5-HT in the ventral hippocampus compared with hippocampal 5-HT release in the home cage and in a non-aversive unfamiliar environment in freely moving rats. Our results showed a distinct pattern of 5-HT release in the ventral hippocampus depending on the stimulus used. Exposure to the X-maze for 20 min was accompanied by an 'anxious' behaviour in the rats and increased extracellular 5-HT to 165% of basal release, whereas exposure to a less aversive 'deactivated' plus maze (115+/-6%) or to white noise for 20 min in the familiar surroundings of the home cage (98+/-6%) did not change hippocampal 5-HT release significantly, despite similar behavioural activation indicated by increased locomotor activity. While both the X-maze and white noise may model anxiety and stress to a certain extent, it seems that the X-maze is more aversive. The results suggest a close relationship between anxiety-related behaviour, but not arousal/non-specific behavioural activation, and 5-HT release in the ventral hippocampus.

Transient overexpression of the 5-HT1A receptor impairs water-maze but not hole-board performance

Previously, we showed that mice that overexpress the 5-HT(1A) receptor transiently from embryonic to perinatal stages show reduced anxiety and changes in brain serotonin turnover as adults. Here, we investigated the long-term effects of the temporary overexpression of the 5-HT(1A) receptor during early embryonic and perinatal development on the performance in two memory tasks. In the hole-board test mice that were homozygous for the transgene showed similar behavioral habituation but increased locomotion compared to heterozygous mice. In contrast water-maze performance of homozygous mice was impaired compared to heterozygous mice. These results suggest that a transient overexpression of 5-HT(1A) receptor during embryonic and perinatal development has detrimental effects on water-maze performance at adult stages.

Effect of 5-HT1A receptor activation on hypothalamic glucose

The somatodendritic 5-HT1A agonist 8-OH-DPAT reduces serotonergic activity and stimulates feeding in freely feeding rats. Interactions between circulating glucose and 5-HT1A receptor expression related to feeding have been described. The aim of the present microdialysis study was to (1) describe the relation between feeding and glucose in the LH, (2) to investigate if peripherally administered 8-OH-DPAT itself has an effect on extracellular glucose in the lateral hypothalamus (LH) of conscious rats. Baseline glucose concentrations were significantly different in microdialysis samples obtained from food deprived rats compared to freely feeding rats. After re-feeding, a significant rise in glucose levels by 45% was observed in the formerly food deprived rats. In freely feeding rats, 8-OH-DPAT (0.3 mg/kg, i.p.) reduced glucose level in the LH significantly. The effect of 8-OH-DPAT on brain glucose was antagonized by pre-treatment with the 5-HT1A antagonist WAY 100635 (3 mg/kg i.p.) which had no effect on its own. The data indicate, therefore, that the effect of 8-OH-DPAT on hypothalamic glucose is mediated by 5-HT1A receptors. In contrast, the same dose of 8-OH-DPAT proven effective in the brain had no effect on peripheral glucose. Only a very high dose of the 5-HT1A agonist (1.8 mg/kg i.p.) had a hyperglycaemic effect in the periphery. In conclusion, the present results show for the first time, that glucose in the lateral hypothalamus increases with a meal. The data demonstrate furthermore 8-OH-DPAT-induced changes of hypothalamic glucose level, implicating 5-HT1A receptors being involved not only in the control of hypothalamic 5-HT as shown before, but also in the control of hypothalamic glucose.

Nucleus accumbens serotonin1A receptors control cocaine-induced hyperactivity but not local serotonin increase: an in vivo microdialysis study

The nucleus accumbens (Nac) is an important structure for cocaine-induced hyperactivity and receives a dense serotonergic (5-HT) innervation. Previous studies showed that a systemic activation of 5-HT(1A) receptors potentiates cocaine-induced hyperlocomotion, but attenuates the cocaine-induced 5-HT increase in the Nac. In order to address the role of Nac 5-HT(1A) receptors in the control of cocaine-induced and spontaneous behavioural activity and local 5-HT release, we used in vivo microdialysis in freely moving rats. The 5-HT(1A)-receptor agonist, 8-OH-DPAT (0, 1 and 10 microM), was applied locally into the Nac by reverse dialysis followed by a cocaine (10 mg/kg) or saline i.p. injection. The Nac 5-HT(1A)-receptor activation potentiated cocaine-induced hyperlocomotion, but attenuated rearing behaviour dose-dependently. Parallel to that, the cocaine-induced increase in Nac 5-HT dialysate level was unaffected, as were the decreases in 5-HIAA and DOPAC dialysate levels after cocaine. In saline treated rats, the local application of 8-OH-DPAT into the Nac affected neither spontaneous behavioural activity nor 5-HT, 5-HIAA or DOPAC dialysate levels in the Nac. These data suggest that Nac 5-HT(1A) receptors exert a bi-directional control of cocaine-induced hyperactivity, while not affecting spontaneous behaviour. Furthermore, accumbal 5-HT(1A) receptors do not appear to be directly involved in the acute effects of cocaine on 5-HT, 5-HIAA or DOPAC levels in the Nac.

NMDA-receptor antagonism via dextromethorphan and ifenprodil modulates graded anxiety test performance of C57BL/6 mice

The majority of N-methyl-D-aspartate receptors (NMDA-R) in the adult forebrain are di- or triheteromers composed of NR1, NR2A and NR2B subunits. Subunit non-selective NMDA-R antagonists produce anxiolytic-like effects together with motor and sensory side-effects. The graded anxiety test (GAT), permits the within-task distinction of drug effects on anxiety from those on activity and perception. By testing NMDA-R subunit selective agents in the GAT it might be possible to determine whether their effects on anxiety, activity and perception are interrelated, and whether separate NMDA-R subtypes are involved. Dextromethorphan (weakly NR2A-selective) (10 and 30 mg/kg, i.p.) and ifenprodil (highly NR2B-selective) (1, 3 and 5 mg/kg, i.p.) were tested in the GAT. Both drugs failed to induce anxiolysis devoid of side-effects. However, the 10 mg/kg dose of dextromethorpan showed an anxiolytic, whereas the 30 mg/kg dose showed an anxiogenic, behavioral profile. Since the selective blockade of the NR2B subunit by ifenprodil had no clear anxiolytic effect, the anxiolytic potential of NMDA subunit non-selective agents might involve NR2A-containing receptors.

Effects of xenon on mesenteric blood flow

BACKGROUND AND OBJECTIVE

The effects of xenon on mesenteric vascular resistance have not been investigated. Because human beings anaesthetized with xenon show good cardiovascular stability, we believed that the agent would have little or no effect on vascular resistance in the splanchnic bed. We determined the effects of different inhaled xenon concentrations on mesenteric blood flow and mesenteric oxygen consumption in pigs sedated with intravenous propofol.

METHODS

Twenty-three minipigs were instrumented with transit time flow probes around the pulmonary and superior mesenteric arteries as well as with pulmonary artery and portal venous catheters. A 14 h recovery was allowed followed by recordings of baseline values. Xenon was then randomly administered in 0.30, 0.50, and 0.70 end-tidal fractions.

RESULTS

The administration of xenon resulted in an 8% (not dose dependent) decrease in mean arterial pressure (from 99 +/- 15 to 91 +/- 19 mmHg; P < 0.05), a 20% decrease in calculated systemic oxygen consumption (from 0.23 +/- 0.07 to 0.19 +/- 0.04L min(-1); P < 0.01), a 20% reduction in mesenteric oxygen delivery (from 41 +/- 12 to 33 +/- 11 mL min; P < 0.001), a 37% reduction in mesentericmetabolic rate of oxygen (from 11.3 +/- 3.6 to 7.1 +/- 3.2 mL min(-1); P < 0.01) and an 8% decrease in mesenteric artery blood flow (0.22 +/- 0.07 to 0.20 +/- 0.07 L min(-1); P < 0.05) in a dose-dependent fashion. Heart rate, cardiac output, systemic vascular resistance, mesenteric vascular resistance, mesenteric oxygen extraction fraction and portal lactate concentration were not significantly altered by xenon.

CONCLUSIONS

Xenon inhalation in the propofol-sedated pig had no measurable effects on mesenteric vascular resistance. This finding may partly explain the well-known cardiovascular stability observed in patients anaesthetized with xenon. Although mesenteric artery blood flow and mesenteric oxygen delivery decreased during xenon administration, unchanged mesenteric oxygen extraction fraction and portal lactate suggest that metabolic regulation of the splanchnic circulation remained unaltered.