Local Cerebral Glucose Utilization in Hypothermic and Hyperthermic Rats

Abstract: Local rates of glucose utilization in 38 regions of the CNS were measured in conscious, lightly restrained rats during normothermia (rectal temperature, 37.4 ± 0.1°C), hypothermia (31.8 ± 0.1°C), and hyperthermia (40.2 ± 0.3°C). In 34 of the 38 regions examined (the four exceptions being primary auditory nuclei in the lower brainstem), a significant relationship could be demonstrated between the rate of glucose utilization and body temperature. The magnitude of temperature-related alterations in glucose use displayed considerable regional heterogeneity. In hypothermic rats the reductions in glucose use were proportionately most marked (reduced 35–50% from normothermic) in thalamic nuclei, extrapyramidal and motor areas, septohippocampal formation, and some areas of neocortex and white matter; they were least pronounced in anterior hypothalamus (reduced by 13%), habenula (by 16%), and amygdala (by 22%). In hyperthermic rats, significantly increased glucose utilization was observed in only 16 of the 38 areas examined (e.g., hypothalamus, hippocampus, extrapyramidal system, and raphe nucleus), whereas in a number of major areas (such as the neocortex and thalamus) glucose use was minimally altered with hyperthermia. The regional heterogeneity in the alterations in glucose utilization suggests that caution must be exercised in the interpretation of autoradiographic 2-deoxyglucose investigations in which body temperature disturbances occur.     

Differential effects of chloral hydrate- and ketamine/xylazine-induced anesthesia by the s.c. route

The proper use of anesthetics in animal experimentation has been intensively studied. In this study we compared the use of chloral hydrate (500 mg kg(-1)) and ketamine (167 mg kg(-1)) combined with xylazine (33 mg kg(-1)) by the s.c. route in male Wistar rats. Chloral hydrate and ketamine/xylazine produced a depth of anesthesia and analgesia sufficient for surgical procedures. The decrease of systolic and diastolic blood pressure was of a higher magnitude in rats anesthetized with chloral hydrate than with ketamine/xylazine. The initial microvascular diameter and blood flow velocity did not differ between both agents. On the other hand, ketamine/xylazine reduced the heart rate more intensively than chloral hydrate. Both anesthetics promoted an increase in arterial pCO(2) and a decrease in pH levels compared to unanesthetized animals. The blood glucose levels were of a higher magnitude in rats after ketamine/xylazine anesthesia than after chloral hydrate. In mesenteric arterioles studied in vivo, ketamine/xylazine anesthesia reduced the constrictive effect of noradrenaline and the dilator effect of bradykinin. However, both anesthetics did not modify the vasodilator effect promoted by acetylcholine. Based on our data, we concluded that both anesthetics alter metabolic and hemodynamic parameters, however the use of chloral hydrate in studies of microvascular reactivity in vivo is more appropriate since ketamine/xylazine reduces the responses to vasoactive agents and increases blood glucose levels.     

Differential Effects of Chloral Hydrate and Pentobarbital Sodium on a Cocaine Level and Its Catecholamine Response in the Medial Prefrontal Cortex: A Comparison with Conscious Rats

Abstract: Adult male Sprague-Dawley rats anesthetized with chloral hydrate and pentobarbital sodium were used as two different treatment groups. Conscious rats were used as a control group. By using baseline (precocaine) concentration as 100%, after cocaine administration (3.0 mg/kg i.v.), the maximal dopamine (DA) increase occurring at the first microdialysis collection period (20 min) in the medial prefrontal cortex was 299 ± 46% for the chloral hydrate group, 168 ± 12% for the pentobarbital sodium group, and 325 ± 23% for the conscious group. At the same time, norepinephrine (NA) increases reached a maximum and were 162 ± 20%, 100 ± 5%, and 141 ± 17%, respectively. The maximal changes of DA and NA in the chloral hydrate group and in the control group were both significantly higher than that in the pentobarbital sodium group. Meanwhile, the cocaine concentration was higher over a 100-min period of time in the chloral hydrate group when compared with the pentobarbital group and the control group. The peak cocaine concentration in dialysate occurred in the same time slot of maximal DA and NA responses, which were 0.65 ± 0.08, 0.30 ± 0.02, and 0.41 ± 0.05 µ M , respectively. Anesthetics suppress the pharmacologic response of neurons, which may explain the difference in catecholamine response between the pentobarbital sodium and the conscious groups. Conversely, because there was no significant difference in DA and NA response between the chloral hydrate group and the conscious group, it may possibly be due to the balancing effect between the higher existing cocaine concentration and the anesthetic suppression on pharmacological response of neurons in the chloral hydrate group. The effect of guide cannula implantation on the cocaine-induced catecholamine response was also evaluated.     

Extracellular Brain Glucose Levels Reflect Local Neuronal Activity: A Microdialysis Study in Awake, Freely Moving Rats

The relationship between brain extracellular glucose levels and neuronal activity was evaluated using microdialysis in awake, freely moving rats. The sodium channel blocker tetrodotoxin and the depolarizing agent veratridine were administered through the dialysis probe to provoke local changes in neuronal activity. The extracellular glucose content was significantly increased in the presence of tetrodotoxin and decreased sharply following veratridine application. The systemic injection of a general anaesthetic, chloral hydrate, led to a large and prolonged increase in extracellular glucose levels. The brain extracellular glucose concentration was estimated by comparing dialysate glucose efflux over a range of inlet glucose concentrations. A mean value of 0.47 mM was obtained in five animals. The results are discussed in terms of the coupling between brain glucose supply and metabolism. The changes observed in extracellular glucose levels under various conditions suggest that supply and utilization may be less tightly linked in the awake rat than has previously been postulated.     

水合氯醛、乌拉坦及其1:1 混合液在SD 大鼠麻醉中的效果比较及应用

目的:比较水合氯醛、乌拉坦及其1:1混合液在SD大鼠麻醉中的效果并进一步在大鼠模型制备的麻醉中检验其效果。方法:分别采用不同剂量的水合氯醛和乌拉坦及其1:1混合液进行麻醉实验,比较其麻醉起效时间、维持时间和死亡率,并将相同剂量的1:1混合液应用于SD大鼠模型制作时的麻醉中,比较其与非模型组之间的差异。结果:水合氯醛和乌拉坦混合液麻醉大鼠的起效时间2.5±1.5分钟,与单用水合氯醛无差异(P>0.05),比单用乌拉坦起效时间短(P<0.05);维持时间107.4±4.1分钟,比单用水合氯醛、乌拉坦长(P<0.01);麻醉死亡率比单用水合氯醛低,总死亡率比单用水合氯醛、乌拉坦低。模型组大鼠的麻醉起效时间2.9±1.6分钟,维持时间108.9±4.4分钟,零麻醉死亡率,总死亡率为2.5%;与1:1混合液非模型组的麻醉效果没有明显差异。结论:水合氯醛+乌拉坦1:1混合液麻醉效果好、起效快、死亡率极低,适合用于2小时左右的SD大鼠手术或模型制作。     

水合氯醛、乌拉坦及其1：1混合液在SD大鼠麻醉中的效果比较及应用

目的：比较水合氯醛、乌拉坦及其1：1混合液在SD大鼠麻醉中的效果并进一步在大鼠模型制备的麻醉中检验其效果。方法：分别采用不同剂量的水合氯醛和乌拉坦及其1：1混合液进行麻醉实验,比较其麻醉起效时间、维持时间和死亡率,并将相同剂量的1：1混合液应用于SD大鼠模型制作时的麻醉中,比较其与非模型组之间的差异。结果：水合氯醛和乌拉坦混合液麻醉大鼠的起效时间2.5±1.5分钟,与单用水合氯醛无差异（P〉0.05）,比单用乌拉坦起效时间短（P〈0.05）;维持时间107.4±4.1分钟,比单用水合氯醛、乌拉坦长（P〈0.01）;麻醉死亡率比单用水合氯醛低,总死亡率比单用水合氯醛、乌拉坦低。模型组大鼠的麻醉起效时间2.9±1.6分钟,维持时间108.9±4.4分钟,零麻醉死亡率,总死亡率为2.5%;与1：1混合液非模型组的麻醉效果没有明显差异。结论：水合氯醛＋乌拉坦1：1混合液麻醉效果好、起效快、死亡率极低,适合用于2小时左右的SD大鼠手术或模型制作。     

Changes in local cerebral glucose utilization associated with Parkinson's syndrome induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the primate

The quantitative 2-[14C]deoxyglucose autoradiographic method was used to map the pattern of alterations in local cerebral glucose utilization associated with the Parkinsonian syndrome induced by the administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), to rhesus monkeys. Monkeys treated with the neurotoxin exhibited both behavioral symptoms (e.g. akinesia, rigidity, flexed posture, and eyelid closure) and neuropathological changes (degeneration of the cells of the substantia nigra pars compacta) that closely paralleled those in human Parkinson's disease. Glucose utilization was significantly reduced in the pars compacta of the substantia nigra and in the subthalamus, and increased in the external segment of the globus pallidus. Outside the basal ganglia reductions in glucose utilization were limited to the mediodorsal nucleus of the thalamus, frontal eye fields, and ventral tegmental area. The results of these studies indicate that the profound functional and behavioral deficits in MPTP-induced Parkinson's syndrome are the consequences of highly selective functional changes in a few cerebral structures, mainly within the basal ganglia.     

Regional distribution of glucose in mouse brain

After rapid inactivation of the enzymes responsible for glucose metabolism by microwave irradiation, concentrations of glucose in 20 regions of the mouse brain were estimated with combined gas chromatography-mass spectrometry (GC-MS). The highest concentrations of glucose were found in the periventricular nuclei of the hypothalamus and nucleus preopticus (P<0.05). The septum and nucleus amygdaloideus showed significantly higher glucose concentration compared with the cerebral neocortex, olfactory bulb, corpus striatum, cingulum, fornix, colliculus inferior, cerebellar cortex, corpus geniculatum laterale, substantia nigra, and nucleus ruber (P<0.05). The glucose concentration in the substantia nigra and nucleus ruber was significantly lower than in the other regions (P<0.01).     

Kinetic Constants for Blood—Brain Barrier Amino Acid Transport in Conscious Rats

The kinetic constants for large neutral amino acid (LNAA) transport across the blood-brain barrier (BBB) of conscious rats were determined in four brain regions: cortex, caudate-putamen, hippocampus, and thalamus-hypothalamus. Indwelling external carotid artery catheters allowed for single-bolus (200 microliters) injections directly into the arterial system of unanesthetized and lightly restrained animals. Our results showed lower brain uptake index values for conscious rats compared to previous reports for anesthetized animals which are consistent with higher rates of cerebral blood flow in the conscious animals. Km values were lower in the conscious animals and ranged from 29% to 87% of the Km values in pentobarbital-anesthetized animals whereas the KD values were about twofold higher in the conscious animals. No apparent regional differences were observed. Influx rates were determined which take into consideration flow rates and plasma amino acid concentrations. Our results showed an average amino acid influx value of 5.2 nmol/min/g, which is 53% higher than the average influx in pentobarbital-anesthetized animals. The present results in conscious animals regarding the low Km of LNAA transport across the BBB lend further support to the importance of fluctuations in plasma amino acid concentrations and LNAA transport competitive effects on brain amino acid availability.     

Tolerance to diazepam and methyl-beta-carboline-3-carboxylate measured in substantia nigra of benzodiazepine tolerant rats

The spontaneous activity of neurons in the pars reticulata of substantia nigra (SNpr) was studied in chloral hydrate anesthetized rats. As a function of dose, intravenous diazepam decreased, and methyl-beta-carboline-3-carboxylate (beta CCM) increased discharge frequency. Two days after terminating a one week treatment with flurazepam (FZP), both diazepam and beta CCM showed decreased ability to alter SNpr neuronal activity. Neither residual FZP nor down-regulation of benzodiazepine receptors can account for these results. In contrast, behavioral testing revealed no change in the ability of i.v. beta CCM to cause convulsions, suggesting that sites other than the SNpr are of prime importance in expressing the convulsant actions of systemically injected beta CCM.     

Single unit activity of dopaminergic neurons in freely moving cats

Single unit activity was recorded from the area of the substantia nigra in freely moving cats. A sub-population of these neurons had the following characteristics: long action potential durations (2–4 msec); relatively slow discharge rates (2–6 spikes/sec); firing as single spikes along with periods of bursting activity in which spike amplitude successively decreased; suppression of unit activity by systemic injection of apomorphine and increased activity after systemic injection of haloperidol. These characteristics are similar to those of identified dopamine neurons recorded in chloral hydrate anesthetized or peripherally paralyzed rats. Therefore, based upon these physiological and pharmacological similarities, this study represents the first systematic report providing evidence for recording the activity of dopaminergic neurons in freely moving cats. In addition, when these cells were studied across the sleep-waking cycle they displayed little variation in firing rates between waking, slow wave sleep and REM sleep.     

Responsiveness of nigral neurons to the stimulation of striatal dopaminergic receptors in the rat

The microinfusion of low doses of apomorphine into the striatum of anesthetized rats depressed the electrical activity of the neurons of the substantia nigra pars compacta while the infusion of bromocriptine had an excitatory or inhibitory effect. These data suggest that:1) the action of the two dopamine agonists on the striato-nigral pathway is different; 2) the striatum might contain dopaminergic receptors located on cells projecting to the substantia nigra with different roles in the feedback regulation of the latter; 3) the inhibitory action of systemically injected apomorphine is not simply due to a stimulation of dopamine “autoreceptors” but also to an action mediated by fibers descending from the striatum to the substantia nigra.     

Effect of injectable or inhalational anesthetics and of neuroleptic, neuroleptanalgesic, and sedative agents on tumor blood flow

Among other parameters, varying blood flow values may be responsible for tumor-to-tumor variabilities in the radiobiologically hypoxic cell fraction of experimental rodent tumors. To test whether changes in tumor blood flow may be caused by anesthetic agents often used in radiobiology, the effect of injectable and inhalational anesthetics and of neuroleptic, neuroleptanalgesic, and sedative agents on blood flow in subcutaneous DS-carcinosarcomas implanted in Sprague-Dawley rats has been investigated using the 85Kr clearance technique. In conscious rats, 20-100 min after animal instrumentation mean blood flow is 0.62 +/- 0.17 ml/g/min (mean +/- SD) in 0.75 +/- 0.15 g tumors at a mean arterial blood pressure of 125 +/- 12 mm Hg. In animals receiving thiobutabarbital, chloral hydrate, or methoxyflurane tumor blood flow is somewhat higher than that measured in conscious rats. Tumor blood flow in animals receiving etomidate, ketamine-xylazine, fentanyl-fluanisone, or urethane is significantly lower than that in the thiobutabarbital group and somewhat lower than in the conscious animals. Blood flow values observed with midazolam, ketamine-midazolam, fentanyl-droperidol, droperidol, diazepam, and pentobarbital are similar to those measured in conscious rats. Virtually no flow alterations with time are detectable in conscious rats and with most of the drugs used. In animals anesthetized with urethane or methoxyflurane, tumor blood flow increases and tumor vascular resistance diminishes slightly with time.     

No Effect of Hyperketonemia on Local Cerebral Glucose Utilization in Conscious Rats

Abstract: Local cerebral glucose utilization was measured by the [¹⁴C]2-deoxy- d -glucose method in conscious control and hyperketonemic rats. Hyperketonemia was induced by 3 days of starvation or by infusion of 3- hydroxybutyrate in fed rats. These treatments produced combined blood ketone body concentrations (acetoacetate + 3-hydroxybutyrate) of from 1.2 to 2.4 mM. Neither treatment significantly affected glucose utilization in any of the 15 brain regions studied. These observations indicate that hyperketonemia in resting, conscious rats does not interfere with brain uptake and phosphorylation of glucose.     

Dopamine agonist pretreatment alters LSD's electrophysiological action from dopamine agonists to antagonist.

LSD (50 μg/kg, i.v.) significantly depressed the discharge rate of dopamine-containing neurons in the substantia nigra of chloral hydrate anesthetized rats. However, when this same dose of LSD was administered to rats whose nigral cell discharge had been reduced 45% below baseline by d-amphetamine (mean dose = 1.45 mg/kg, i.v.), the discharge rate was significantly increased (typically returning to the pre-amphetamine baseline). A similar pattern was observed when LSD was administered to apomorphine-pretreated animals. Brom-LSD also produced these reversal effects. These effects of LSD resemble those of classical central dopamine antagonists such as haloperidol. We hypothesize that the shift in LSD's action from that of dopamine agonist to antagonist by prior dopamine agonist treatment may be mediated by a conformational shift in the state of the dopamine receptor.     

Cerebral Metabolic Effects of Monoamine Oxidase Inhibition in Normal and 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Acutely Treated Monkeys

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces dopaminergic cell death in the substantia nigra pars compacta (SNpc) and clinical parkinsonism in humans and experimental animals. Pretreatment with monoamine oxidase inhibitors prevents this cell death and associated parkinsonism by blocking the oxidation of MPTP to a toxic intermediate. The 2-deoxyglucose method was used to study the acute effects of MPTP in the monkey brain and the effects of monoamine oxidase inhibition on local cerebral glucose utilization in both normal and MPTP-treated monkeys. MPTP administration alone caused a major increase in glucose utilization in the SNpc and smaller increases in some subnuclei within the ventral tegmental area in which eventual dopaminergic cell loss also occurs. Pretreatment with pargyline abolished these metabolic increases, a finding suggesting both that the oxidized product of MPTP generates the metabolic increases and that the increased glucose consumption may contribute to cell toxicity. On the other hand, in most cortical, thalamic, striatal, brainstem, and cerebellar areas MPTP alone caused reductions in glucose utilization, and pargyline failed to prevent these effects. Pargyline alone depressed metabolism in the locus coeruleus and a few other monoaminergic structures.     

Pharmacologic characterization and autoradiographic distribution of binding sites for iodinated tachykinins in the rat central nervous system

P-type, E-type, and K-type tachykinin binding sites have been identified in the mammalian CNS. These sites may be tachykinin receptors for which the mammalian neuropeptides substance P, neuromedin K, and substance K are the preferred natural agonists, respectively. In the present investigation, we have compared the pharmacology and the autoradiographic distribution of CNS binding sites for the iodinated (¹²⁵I-Bolton-Hunter reagent) tachykinins substance P, eledoisin, neuromedin K, and substance K. Iodinated eledoisin and neuromedin K exhibited an E-type binding pattern in cortical membranes. Iodinated eledoisin, neuromedin K, and substance K each labeled sites that had a similar distribution but one that was considerably different from that of sites labeled by iodinated substance P. CNS regions where there were detectable densities of binding sites for iodinated eledoisin, neuromedin K, and substance K and few or no sites for iodinated substance P included cortical layers IV–VI, mediolateral septum, supraoptic and paraventricular nuclei, interpeduncular nucleus, ventral tegmental area, and substantia nigra pars compacta. Binding sites for SP were generally more widespread in the CNS. CNS regions where there was a substantial density of binding sites for iodinated substance P and few or no sites for iodinated eledoisin, neuromedin K, and substance K included cortical layers I and II, olfactory tubercle, nucleus accumbens, caudate-putamen, globus pallidus, medial and lateral septum, endopiriform nucleus, rostral thalamus, medial and lateral preoptic nuclei, arcuate nucleus, dorsal raphe nucleus, dorsal parabrachial nucleus, parabigeminal nucleus, cerebellum, inferior olive, nucleus ambiguus, retrofacial and reticular nuclei, and spinal cord autonomic and somatic motor nuclei. In the brainstem, iodinated substance P labeled sites in both sensory and motor nuclei whereas iodinated eledoisin, neuromedin K, and substance K labeled primarily sensory nuclei. Our results are consistent with either of two alternatives: (1) that iodinated eledoisin, neuromedin K, and substance K bind to the same receptor site in the rat CNS, or (2) that they bind to multiple types of receptor sites with very similar distribution.     

Kinetics of Regional Blood-Brain Barrier Glucose Transport and Cerebral Blood Flow Determined with the Carotid Injection Technique in Conscious Rats

Anesthetics, particularly barbiturates, have depressive effects on cerebral blood flow and metabolism and likely have similar effects on blood-brain barrier (BBB) transport. In previous studies utilizing the carotid injection technique, it was necessary to anesthetize the animals prior to performing the experiment. The carotid injection technique was modified by catheter implantation in the external carotid artery at the bifurcation of the common carotid artery. The technique was used to determine cerebral blood flow, the Km, Vmax, and KD of glucose transport in hippocampus, caudate, cortex, and thalamus-hypothalamus in conscious rats. Blood flow increased two to three times from that seen in the anesthetized rat. The Km in the four regions ranged between 6.5 and 9.2 mM, the Vmax ranged between 1.15 and 2.07 mumol/min/g, and the KD ranged between 0.015 and 0.035 ml/min/g. The Km and KD in the conscious rat did not differ from the values seen in the barbiturate anesthetized rat. The Vmax, on the other hand, increased two- to three-fold from that seen in the anesthetized rat and was nearly proportional to the increase in blood flow seen in the conscious rat. The development of the external carotid catheter technique now allows for determination of BBB substrate transport in conscious animals.     

The role of 5-HT1B receptors in the regulation of serotonin cell firing and release in the rat brain

The release of 5-HT in terminal areas of the rodent brain is regulated by 5-HT1B receptors. Here we examined the role of 5-HT1B receptors in the control of 5-HT output and firing in the dorsal raphe nucleus (DR), median raphe nucleus (MnR) and forebrain of the rat in vivo. The local perfusion (30-300 microM) of the selective 5-HT1B receptor agonist CP-93,129 to freely moving rats decreased 5-HT release in the DR and more markedly in the MnR. Likewise, 300 microM CP-93,129 reduced 5-HT output in substantia nigra pars reticulata, ventral pallidum, lateral habenula and the suprachiasmatic nucleus. The effect of CP-93,129 was prevented by SB-224289, but not by WAY-100635, selective 5-HT1B and 5-HT1A receptor antagonists, respectively. SB-224289 did not alter dialysate 5-HT in any raphe nuclei. The intravenous administration of the brain-penetrant selective 5-HT1B receptor agonist CP-94,253 (0.5-2.0 mg/kg) to anesthetized rats decreased dialysate 5-HT in dorsal hippocampus and globus pallidus, increased it in MnR and left it unaltered in the DR and medial prefrontal cortex. SB-224289, at a dose known to block 5-HT1B autoreceptor-mediated effects (5 mg/kg), did not prevent the effect of CP-94,253 on MnR 5-HT. The intravenous administration of CP-94,253 (0.05-1.6 mg/kg) to anesthetized rats increased the firing rate of MnR, but not DR-5-HT neurons. The local perfusion of CP-94,253 in the MnR showed a biphasic effect, with 5-HT reductions at 0.3-3 microM and increase at 300 microM. These results suggest that 5-HT cell firing and release in midbrain raphe nuclei (particularly in the MnR) are under control of 5-HT1B receptors. The activation of 5-HT1B autoreceptors (possibly located on 5-HT nerve endings and/or varicosities within DR and MnR) reduces 5-HT release. The effects of higher concentrations of 5-HT1B receptor agonists seem more compatible with the activation of 5-HT1B heteroreceptors on inhibitory neurons.