Alpha- and beta-adrenoreceptor blockers have opposite effects on energy metabolism of the central auditory system

Distinct Cellular Profiles of Hif1a and Vegf mRNA Localization in Microglia, Astrocytes and Neurons during a Period of Vascular Maturation in the Auditory Brainstem of Neonate Rats

Defining the relationship between vascular development and the expression of hypoxia-inducible factors (Hifs) and vascular endothelial growth factor (Vegf) in the auditory brainstem is important to understand how tissue hypoxia caused by oxygen shortage contributes to sensory deficits in neonates. In this study, we used histology, molecular labeling, confocal microscopy and 3D image processing methods to test the hypothesis that significant maturation of the vascular bed in the medial nucleus of the trapezoid body (MNTB) occurs during the postnatal period that precedes hearing onset. Isolectin-B4 histochemistry experiments suggested that the MNTB vasculature becomes more elaborate between P5 and P10. When combined with a cell proliferation marker and immunohistochemistry, we found that vascular growth coincides with a switch in the localization of proliferating cells to perivascular locations, and an increase in the density of microglia within the MNTB. Furthermore, microglia were identified as perivascular cells with proliferative activity during the period of vascular maturation. Lastly, combined in situ hybridization and immunohistochemistry experiments showed distinct profiles of Hif1a and Vegf mRNA localization in microglia, astrocytes and MNTB principal neurons. These results suggest that different cells of the neuro-glio-vascular unit are likely targets of hypoxic insult in the auditory brainstem of neonate rats.

Arousal-induced cortical activity triggers lactate release from astrocytes

It has been suggested that, in states of arousal, release of noradrenaline and β-adrenergic signalling affect long-term memory formation by stimulating astrocytic lactate production from glycogen. However, the temporal relationship between cortical activity and cellular lactate fluctuations upon changes in arousal remains to be fully established. Also, the role of β-adrenergic signalling and brain glycogen metabolism on neural lactate dynamics in vivo is still unknown. Here, we show that an arousal-induced increase in cortical activity triggers lactate release into the extracellular space, and this correlates with a fast and prominent lactate dip in astrocytes. The immediate drop in astrocytic lactate concentration and the parallel increase in extracellular lactate levels underline an activity-dependent lactate release from astrocytes. Moreover, when β-adrenergic signalling is blocked or the brain is depleted of glycogen, the arousal-evoked cellular lactate surges are significantly reduced. We provide in vivo evidence that cortical activation upon arousal triggers lactate release from astrocytes, a rise in intracellular lactate levels mediated by β-adrenergic signalling and the mobilization of lactate from glycogen stores.

β-adrenergic modulation of discrimination learning and memory in the auditory cortex

Despite vast literature on catecholaminergic neuromodulation of auditory cortex functioning in general, knowledge about its role for long‐term memory formation is scarce. Our previous pharmacological studies on cortex‐dependent frequency‐modulated tone‐sweep discrimination learning of Mongolian gerbils showed that auditory‐cortical D_1/5‐dopamine receptor activity facilitates memory consolidation and anterograde memory formation. Considering overlapping functions of D_1/5‐dopamine receptors and β‐adrenoceptors, we hypothesised a role of β‐adrenergic signalling in the auditory cortex for sweep discrimination learning and memory. Supporting this hypothesis, the β_1/2‐adrenoceptor antagonist propranolol bilaterally applied to the gerbil auditory cortex after task acquisition prevented the discrimination increment that was normally monitored 1 day later. The increment in the total number of hurdle crossings performed in response to the sweeps per se was normal. Propranolol infusion after the seventh training session suppressed the previously established sweep discrimination. The suppressive effect required antagonist injection in a narrow post‐session time window. When applied to the auditory cortex 1 day before initial conditioning, β₁‐adrenoceptor‐antagonising and β₁‐adrenoceptor‐stimulating agents retarded and facilitated, respectively, sweep discrimination learning, whereas β₂‐selective drugs were ineffective. In contrast, single‐sweep detection learning was normal after propranolol infusion. By immunohistochemistry, β₁‐ and β₂‐adrenoceptors were identified on the neuropil and somata of pyramidal and non‐pyramidal neurons of the gerbil auditory cortex. The present findings suggest that β‐adrenergic signalling in the auditory cortex has task‐related importance for discrimination learning of complex sounds: as previously shown for D_1/5‐dopamine receptor signalling, β‐adrenoceptor activity supports long‐term memory consolidation and reconsolidation; additionally, tonic input through β₁‐adrenoceptors may control mechanisms permissive for memory acquisition.

β-adrenoreceptor activation in brain, lung and adipose tissue, measured by microdialysis in pig

PURPOSE

The aim of this study is to investigate the effect of local activation of β-adrenoreceptor by Isoprenaline on metabolism in brain, fat and lung measured by microdialysis.

METHODS

We used 8 healthy pigs under general anaesthesia and placed microdialysis catheters in brain, fat, lung and artery. We performed a direct measurement of glucose, lactate, pyruvate and glycerol. The stimulation was performed by one-hour infusion of Isoprenaline, a β-adrenoreceptor agonist.

RESULTS

The infusion of isoprenaline did not affect the glucose in any tissue. The levels of lactate (p=0.008) and pyruvate (p=0.011) decreased significantly in lung after isoprenaline infusion. There was a significant increase in L/P ratio in fat tissue (p=0.001) while no significant changes could be found in brain (p=0.086) and lung (p=0.679). The most pronounced and significant change was observed in glycerol in fat (p<0.001) that increased by 95%.

CONCLUSION

The prominent increase in glycerol in fat proved to be a good measure of β-adrenoreceptor activation and a measure of lipolysis. This can be used to online monitor β-adrenoreceptor activation by glycerol measurement in patients.

Behavioral and biochemical studies in rats following prenatal treatment with beta-adrenoceptor antagonists

Increased motor activity and poor performance in the active avoidance test were observed in the offspring of rats treated with dl-propranolol or sotalol during pregnancy, but not with atenolol and d-propranolol. All substances were administered in drinking water from days 8-22 of gestation. A significant increase in the density of muscarinic acetylcholine receptors in the hippocampus was found for dl-propranolol and sotalol, at 35 and 20 days of age, respectively. Twenty-day-old pups born to dl-propranolol-treated rats exhibited a non-significant decrease in the number of beta-adrenoceptors in the frontal cortex. Assuming that all the beta-adrenoceptor antagonists tested had access to the developing fetal brain, the effect of dl-propranolol and sotalol on behavior could stem from central beta 2-adrenoceptor blockade. In view of the lack of behavioral changes after atenolol, a beta 1-selective adrenoceptor antagonist, it is suggested that the clinical use of beta 1-selective adrenoceptor antagonists during pregnancy might be safer for the fetus than beta 2-adrenoceptor antagonists.

The effects of chronic serum sickness on albumin distribution and glucose utilization in rat brain

The level of cerebrospinal fluid (CSF) protein is elevated in diseases and disease models that are associated with circulating immune complexes such as serum sickness. Circulatory immune complexes are known to deposit in the basal lamina of fenestrated capillaries and may, as a result, affect both capillary bed and parenchymal function. Since the brain has both fenestrated and unfenestrated capillaries and immune complexes deposit to a varying extent in the fenestrated capillaries in chronic serum sickness, cerebral capillary permeability to protein may be altered in some brain areas and lead to the elevation of CSF proteins. In addition various other cerebrovascular and metabolic functions may also be affected by this condition. In this study either radio-iodinated serum albumin (RISA) or 2-[14C]deoxyglucose (14C-2DG) was intravenously injected into control Wistar rats and Wistar rats with chronic serum sickness; subsequently the tissue levels of radioactivity were measured by quantitative autoradiography in 4 brain areas with fenestrated capillaries and 11 brain areas with unfenestrated capillaries. The 2-min distribution of RISA, which demarcates the volume of circulating plasma in perfused microvessels and is generally proportional to local plasma flow, was the same in control and experimental rats. The passage of RISA from blood into brain over 30 min was negligible in both groups; thus cerebral capillary permeability to albumin was not detectably increased in any of these 15 brain areas by chronic serum sickness. The rate of local cerebral glucose utilization, an indicator of local metabolic and neural activity, was calculated from the 14C-2DG data and was virtually identical in control and experimental rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain-stem auditory evoked potentials in squirrel monkey (Saimiri sciureus)

To more fully characterize brain-stem auditory evoked potentials (BAEPs) in non-human primates, BAEPs were recorded from chronically implanted epidural electrodes in 10 squirrel monkeys (Saimiri sciureus). The effects of stimulus intensity, repetition rate, and anesthesia (ketamine 20 mg/kg i.m.) on peak latencies and inter-peak intervals were evaluated. Monkey wave forms consisted of approximately 7 peaks (I-VII), each exhibiting similar latencies across sessions, with later peaks exhibiting greater variability. In some subjects, additional peaks (IIa, IIIa) and slow potentials were recorded. The slow potentials provided a substratum for peaks IV through VII. As with human, monkey peaks exhibited systematic changes in latency with changes in stimulus intensity or repetition rate. These shifts included significant decreases in latency with increasing intensity for peaks I-IV and increases in latency with increases in repetition rate for peaks III, V, and VI. Inter-peak intervals were similar to those observed in human. Furthermore, ketamine anesthesia significantly delayed the latencies of most peaks (except I, V, and VII). Some differences between monkey and human BAEPs were evident in the relative amplitude of specific peaks. For example, peak V is typically most prominent in human, while this was true for peak III in monkey. The similarities between unanesthetized monkey and human inter-peak intervals suggest that the times required for impulses to reach particular brain-stem areas are conserved across primate species that vary in brain size. This supports the hypothesis that comparably numbered BAEP peaks in monkey and human index homologous processes. The data also suggest that the differences between animal and human BAEPs commonly reported may result from the use of anesthetics. In summary, unanesthetized monkey BAEPs resemble human BAEPs in morphology, number of peaks, polarity, latency variability, inter-peak intervals, slow potentials superimposed on the high-frequency peaks, and variations in morphology, amplitude, and resolution of peaks as a function of recording site. Thus, unanesthetized monkey BAEPs may be an excellent model for investigating the neural substrates of human BAEP or for determining species differences in acoustic processing among primates.

Altered peripheral and brainstem auditory function in aged rats

A technique for conducting free-field brainstem auditory evoked potential (BAEP) audiometry in unanesthetized, unrestrained rats revealed a non-recruiting 18 dB elevation of click threshold in aged rats. BAEPs were first recorded in young and aged rats to clicks of equal intensity (80 dB SPL). Compared to the young group, aged animals exhibited longer wave I and wave IV latencies with no difference seen in the I-IV central conduction time. The prominent negative wave (No) following wave IV was also delayed and the I-No and IV-No conduction times increased in the aged group. When BAEPs were recorded to clicks with intensities adjusted to 35 dB above individual threshold, no differences in wave I or wave IV latencies or in the I-IV central conduction time were found between groups. However, the No component was delayed and the I-No and IV-No conduction times remained prolonged in the aged group. The results suggest that in addition to changes in peripheral auditory structures, changes in the rostral auditory brainstem accompany age-related hearing loss in rats.

Preferential blood flow increase to the brain stem in moderate neonatal hypoxia: reversal by naloxone

Previous studies have shown that severe neonatal asphyxia and hypoxia lead to a redistribution of cerebral blood flow (CBF) with a preferential perfusion of the brain stem. The present study shows that this mechanism is operative also in moderately hypoxic newborn lambs (oxygen saturation 32.7-65.2) with a threshold of about 25% reduction in oxygen saturation. In hypoxia, the mean increase in total CBF, brain stem and telencephalic blood flow was 44%, 68% and 43%, respectively (five lambs). We found that naloxone reverses this redistribution, and that the effects of naloxone on telencephalic perfusion and cerebral metabolic rate of oxygen (CMRO2) were proportional. In hypoxia + naloxone (1 mg/kg), a further increase in total CBF, brain stem, and telencephalic blood flow of 30%, 7% and 31% was noted. We therefore suggest that the redistribution of CBF is an important opioid-mediated homeostatic mechanism, which diminishes the metabolic requirements of the newer part of the brain in hypoxia and allows a preferential perfusion of the vital structures of the brain stem.

alpha-Adrenergic receptors in cerebral microvessels of normotensive and spontaneously hypertensive rats

In rat cerebral microvessels, we characterized alpha 1- and alpha 2-adrenergic receptors, using [3H]prazosin and [3H]-p-amino-clonidine as radioligands. [3H]Prazosin binding to the cerebral microvessels was saturable and of high affinity (dissociation constant of 78 pM), with a maximum binding of 48 fmol/mg protein. [3H]Prazosin binding reached equilibrium within 15 minutes and was dissociated by the addition of 10 microM phentolamine. The inhibitory effects of isomers of norepinephrine and epinephrine on the binding showed that l-isomers were over 10 times more potent than d-isomers. [3H]-p-Amino-clonidine binding to the cerebral microvessels was saturable and of high affinity (KD = 0.61 nM) with a Bmax of 73 fmol/mg protein. The binding reached equilibrium within 30 minutes, and was dissociated by the addition of 100 microM l-norepinephrine. l-Isomers of norepinephrine and epinephrine were over 10 times more potent than d-isomers in displacing the binding. Thus, both [3H]prazosin and [3H]-p-amino-clonidine bindings to the cerebral microvessels were characterized by saturability, high affinity, reversibility, and stereo-specificity. Furthermore, the specificity of both binding sites was pharmacologically evaluated by the inhibitory effects of various adrenergic agonists and antagonists on the bindings. These data indicate the existence of alpha-adrenergic receptors in the cerebral microvessels and are consistent with the hypothesis that the cerebral microcirculation is regulated by adrenergic innervation. Furthermore, the receptors were measured in cerebral microvessels of spontaneously hypertensive rats and Wistar-Kyoto controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebrovascular responses to haemorrhagic hypotension in anaesthetized cats. Effects of alpha-adrenoceptor antagonists

Haemorrhagic hypotension induces the phenomenon of cerebrovascular autoregulation and, concomitantly, involves an activation of the sympathetic nervous system. As brain vessels in cats have an atypical adrenoceptor distribution we studied the effects of an alpha-adrenoceptor antagonist on the autoregulatory response to haemorrhage. Cortical blood flow was studied by the H2 technique in chloralose-anaesthetized cats subjected to a period of graded haemorrhage over 3 h. Three groups of cats were studied: control, i.e. those receiving saline (n = 10); yohimbine-treated (200 micrograms . kg-1 . h-1, n = 7); and prazosin-treated (50 micrograms . kg-1 . h-1, n = 6). In the control group, cortical blood flow remained relatively constant when mean arterial pressure was decreased from 102 +/- 1 mmHg (mean +/- SE) to approximately 50 +/- 1 mmHg; thereafter, blood flow decreased with decreasing perfusion pressure. In the arterial pressure range 64-55 mmHg, cortical blood flow was significantly higher in the yohimbine group (109 +/- 12 ml . 100 g-1 . min-1) compared to the control group (69 +/- 6 ml . min-1) and remained higher in the yohimbine-treated cats at more extreme levels of hypotension. Blood flow did not fall significantly in the yohimbine-treated cats until mean arterial pressures of 31 +/- 1 mmHg were attained. In the prazosin-treated cats, flow began to decrease at arterial pressures even greater than those observed in the control group. Thus, there is a sympathetic vasoconstriction of brain arteries that is primarily mediated by alpha 2-adrenoceptors in the feline cerebrovascular bed.

Acute administration of 1-N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a compound producing parkinsonism in humans, stimulates [2-14C]deoxyglucose uptake in the regions of the catecholaminergic cell bodies in the rat and guinea pig brains

A modification of the [2-14C]deoxyglucose (2-DG) autoradiographic technique of Sokoloff et al. was used to study the effects of acute administration of 1-N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (10 mg/kg, s.c.) in the rat and guinea pig brains. MPTP administration resulted in both species in a dramatic increase in the 2-DG uptake in the substantia nigra pars compacta, ventral tegmental area and locus ceruleus, brain areas containing the cell bodies of dopaminergic and noradrenergic neurons. Many other brain areas were not affected. In the rat the effects were time dependent, being maximal between 1 and 2 h after drug administration. The effects of MPTP on 2-DG uptake differ from those of other dopaminergic or catecholaminergic drugs and suggest a specificity of the action of this drug on catecholaminergic neurons.

The effect of antidepressant drugs on regional cerebral glucose utilization in the rat

The 2-deoxyglucose (2-DG) technique is a potentially powerful method for assessing the effect of centrally acting drugs on local neuronal function in the brain. Since little is established on the effect of antidepressant drugs on local functional activity throughout the brain, we have employed this technique to study the effects of desmethylimipramine (DMI), a tricyclic antidepressant, and assessing the effect of centrally acting drugs on local neuronal function in the brain. Since little is established on the effect of antidepressant drugs on local functional activity throughout the brain, we have employed this technique to study the effects of desmethylimipramine (DMI), a tricyclic antidepressant, and assessing the effect of centrally acting drugs on local neuronal function in the brain. Since little is established on the effect of antidepressant drugs on local functional activity throughout the brain, we have employed this technique to study the effects of desmethylimipramine (DMI), a tricyclic antidepressant, and phenelzine, a monoamine oxidase inhibitor used clinically as an antidepressant, on local glucose utilization. The drugs were administered either as an acute dose, or repeatedly for 7 days, or chronically for 28 days. The local metabolic rate of glucose was determined in 30 regions of rat brain. Acute DMI increased glucose utilization in 11 regions whereas, in contrast, chronic DMI decreased glucose utilization in 7 regions of rat brain. Many of the areas affected are those of the telencephalon and diencephalon that receive prominent noradrenergic innervation. This is consistent with the notion that acute DMI treatment leads to enhanced and chronic DMI treatment leads to reduced noradrenergic functioning in the CNS. In contrast to these effects with DMI, phenelzine had little effects on glucose utilization either after acute or chronic dosing.

Effect of propranolol treatment in pregnant rats on motor activity and avoidance learning of the offspring

Rats born to mothers treated with propranolol, during days 8-22 of gestation, displayed hyperactivity in the open field which lasted up to 60 days of age and an impairment of avoidance in the shuttle box which was more marked in the male rats. Females exhibited hyperactivity in the open field but developed impaired avoidance learning only when exposed prenatally to both propranolol and hypoxia. Propranolol administration during the last term of pregnancy (days 18-22) affected mostly shuttle box performance. In contrast, hyperactivity could be induced by treatment during various stages of pregnancy, (days 8-22, 8-18, or 18-22) with the duration of hyperactivity being directly related to the length of treatment of the mothers. The possible mechanism of the disruptive effect of propranolol in the fetus and newborn is discussed.

Lateral inhibition in the anteroventral cochlear nucleus of the cat: a microiontophoretic study

The spontaneous firing rates of non-prepotential (NPP) units of the anteroventral cochlear nucleus are quite low so it has not been possible to determine whether side band tones are inhibitory when presented alone. Microiontophoretically-applied excitatory amino acids can be used to excite non-spontaneous cells directly. Using this technique it can be shown that side band tone bursts 1/2 to 3/4 octave above the characteristic frequency (CF) of a NPP unit inhibit the amino acid-induced firing. Side band tones which inhibited the amino acid-induced firing were beyond the tuning curve. Side band tones within the tuning curve produced excitation. Both, however, usually reduced the activity evoked by a CF tone burst (i.e., two-tone interaction). The data suggests that lateral inhibition and two-tone interactions are separate phenomena in the auditory system and that lateral inhibition may play a critical role in determining the shape of the tuning curve of NPP units.

No effect of hyperketonemia on local cerebral glucose utilization in conscious rats

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.

Th central noradrenergic system in the rat: metabolic mapping with alpha-adrenergic blocking agents

Rates of cerebral glucose utilization were measured by means of the autoradiographic 2-deoxy-D-[14C]glucose technique in 73 normal, awake rats treated with different doses of the alpha-adrenergic blockers, phenoxybenzamine, phentolamine and yohimbine. Three types of responses were elicited by the administration of these drugs. The predominant effect observed after administration of all alpha-blockers was a widespread depression of glucose utilization, particularly within the neocortex. The effect was most pronounced with phenoxybenzamine. In a few structures (locus coeruleus, interstitial nucleus of the stria terminalis, medial forebrain bundle, periventricular nucleus and some medullary and hypothalamic nuclei associated with the regulation of blood pressure) marked increases in glucose utilization were observed. Administration of phentolamine resulted in increased glucose utilization in all the central components of the auditory system (cochlear n., superior olivary n., n. lateral lemniscus, inferior colliculus, medial geniculate body and auditory cortex). Phenoxybenzamine and yohimbine tended to decrease glucose utilization in the auditory system. Alternating columns with higher and lower rates of local glucose consumption were observed in most of the neocortical areas and in the cerebellar vermis. The significance of these columns is not clear.

Cerebral blood flow and oxygen consumption in the rat brain after lesions of the noradrenergic locus coeruleus system

The effect of lesions of the locus coeruleus neuron system on cerebral metabolic rate for oxygen (CMRO2) and blood flow (CBF) was evaluated in paralyzed and mechanically ventilated rats, using a 133xenon modification of the Kety-Schmidt inert gas technique. Bilateral electrothermic lesions of its ascending bundle caused no significant change in CBF or CMRO2. The 6-hydroxydopamine lesions did not influence the CBF and CMRO2 responses to hypercapnia and hypoxia. It is concluded that the locus coeruleus does not exert any resting tone on CBF and CMRO2 and that no influence on the CBF and CMRO2 responses to hypercapnia and hypoxia is mediated via its ascending projections.

Effect of propranolol on local cerebral blood flow under normocapnic and hypercapnic conditions

The effect of propranolol (2.5 mg kg-1, i.v.) on local cerebral blood flow (CBF) in normocapnia was studied in rats maintained artificially ventilated on 70% N2O and 30% O2. The method used was autoradiography with [14C]iodoantipyrine. Although a single dose of propranolol, given 30 min prior to CBF measurements, somewhat reduced mean CBF values in all of the 22 structures analysed, none of the changes were significant. The results confirm previous ones, in which overall CBF was measured, in showing that beta-adrenergic mechanisms have little effect on normal cerebrovascular tone. Following a single dose of propranolol, results obtained in hypercapnia were equally negative; neither did CBF fall significantly when propranolol was given by constant infusion during 15 min. Furthermore, local CBF did not differ between animals infused with dl-propranolol and d-propranolol. It is concluded that in the rat, propranolol has but small effects on the CBF response to hypercapnia, if any. The results reveal that local CO2 responsiveness, calculated as delta CBF/delta PCO2, varies with normocapnic flow rates.

Effects of naftidrofuryl on local cerebral glucose utilization in the rat

The effects of naftidrofuryl on local cerebral glucose utilization have been examined in 21 lightly restrained, conscious rats by means of the quantitative autoradiographic 2-deoxyglucose technique. Naftidrofuryl (15, 30, and 45 mg/kg, i.p.) did not significantly alter the rate of glucose utilization in any of the 29 gray matter or 4 white matter areas that were examined.

Intraperitoneal administration and other modifications of the 2-deoxy-D-glucose technique

Experiments were conducted to determine the optimal conditions necessary for implementing modifications of the 2-deoxyglucose (2-DDG) technique. Substitution of tritium-labeled 2-DDG with subsequent microdissection of selected brain regions and liquid scintillation counting produced results that were highly correlated with both [14C]radioautograms and glucose utilization values as obtained by Sokoloff et al. The route of administration of isotope was also varied. Whole brain uptake at maximal levels of incorporation was the same for both intravenously and intraperitoneally injected animals. Radioautograms from i.p. and i.v. injected animals were indistinguishable. Densitometric analyses of the i.p. radioautograms were highly correlated with glucose utilization values. Thus, relative indices of functional activity may be obtained when experimental circumstances preclude arteriovenous cannulations and restraint. The use of naive, unrestrained animals, therefore, makes the 2-DDG technique applicable to a broader range of studies.

Local cerebral glucose consumption in the artificially ventilated rat: influence of nitrous oxide analgesia and of phenobarbital anesthesia

The objectives of the present study, which concerns local glucose consumption (1-CMRgl) in the rat brain as measured with the 14C-deoxyglucose technique of Sokoloff et al. (1977), were (1) to provide data for 10CMRgl in nitroux oxide analgesia and in phenobarbital anesthesia, allowing a comparison with previous results on oxygen consumption, and (2) to test a recent proposal that 70% N2O markedly reduces 1-CMRgl in (mainly) cortical structures. Under 70% N2O, 1-CMRgl in frontal and parietal cortex was close to 0.7 mumol x g-1 x min-1. This value is in excellent agreement with previous values for "cortical" oxygen consumption. In phenobarbital anesthesia, 1-CMRgl was lower than that expected from oxygen consumption, probably reflecting the fact that barbiturate anesthesia is accompanied by consumption of endogenous substrates. Experiments on adrenalectomized animals that were given local anesthesia and protected from external stimuli failed to demonstrate that 70% N2O depresses 1-CMRgl. In fact, N2O was found to increase 1-CMRgl in many structures. It is concluded that if 1-CMRgl is lower in ventilated animals than in spontaneously breathing, conscious controls, the depression is more likely to be due to the neuromuscular blockade.