[3H]2-Deoxy-D-glucose capture in the hippocampus and dentate gyrus of ketamine-anesthetized rat

Receptor mechanisms and circuitry underlying NMDA antagonist neurotoxicity

NMDA glutamate receptor antagonists are used in clinical anesthesia, and are being developed as therapeutic agents for preventing neurodegeneration in stroke, epilepsy, and brain trauma. However, the ability of these agents to produce neurotoxicity in adult rats and psychosis in adult humans compromises their clinical usefulness. In addition, an NMDA receptor hypofunction (NRHypo) state might play a role in neurodegenerative and psychotic disorders, like Alzheimer's disease and schizophrenia. Thus, understanding the mechanism underlying NRHypo-induced neurotoxicity and psychosis could have significant clinically relevant benefits. NRHypo neurotoxicity can be prevented by several classes of agents (e.g. antimuscarinics, non-NMDA glutamate antagonists, and alpha(2) adrenergic agonists) suggesting that the mechanism of neurotoxicity is complex. In the present study a series of experiments was undertaken to more definitively define the receptors and complex neural circuitry underlying NRHypo neurotoxicity. Injection of either the muscarinic antagonist scopolamine or the non-NMDA antagonist NBQX directly into the cortex prevented NRHypo neurotoxicity. Clonidine, an alpha(2) adrenergic agonist, protected against the neurotoxicity when injected into the basal forebrain. The combined injection of muscarinic and non-NMDA Glu agonists reproduced the neurotoxic reaction. Based on these and other results, we conclude that the mechanism is indirect, and involves a complex network disturbance, whereby blockade of NMDA receptors on inhibitory neurons in multiple subcortical brain regions, disinhibits glutamatergic and cholinergic projections to the cerebral cortex. Simultaneous excitotoxic stimulation of muscarinic (m(3)) and glutamate (AMPA/kainate) receptors on cerebrocortical neurons appears to be the proximal mechanism by which the neurotoxic and psychotomimetic effects of NRHypo are mediated.

Hippocampal and entorhinal glucose metabolism in relation to cholinergic theta rhythm

Hippocampal and entorhinal cortex glucose metabolism were studied by 14C-2-deoxyglucose (2-DG) autoradiography in anesthetized rats with and without continuous theta rhythm (theta). 2-Deoxyglucose changes in specific cytoarchitectonic regions were precisely assessed by n innovative approach. In the absence of theta there were areas with a higher glucose metabolism corresponding to neuropile regions at CA3, dentate gyrus, and subiculum, while the cellular layers always showed lower values. In the presence of theta, provoked by intraventricular injections of anticholinesterases (i.e., physostigmine) or curarimimetics (i.e., d-tubocurarine), 2-DG uptake showed two opposite significant changes in relation to controls: a) it increased in the outer zone of the molecular layer (inner blade) of the dentate gyrus, and in the stratum lacunosum-moleculare of CA3, suggesting an increase in perforant path input during theta rhythm; b) it decreased in the hilar dentate region. This noteworthy decrease in metabolic activity probably reflects an hilar inhibition by local circuits during theta rhythm generation.

The effect of the excitatory amino acid receptor antagonist dizocilipine maleate (MK-801) on hemispheric cerebral blood flow and metabolism in dogs: modification by prior complete cerebral ischemia

The effect of the N-methyl-D-aspartate (NMDA) receptor antagonist dizociplipine maleate (MK-801) on cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), intracranial pressure and systemic variables was examined in 6 normal dogs (Group I). In 6 additional dogs (Group II), the effects of a prior 11 min episode of complete cerebral ischemia on the response to dizocilipine was studied. CBF was measured with a sagittal sinus outflow technique and CMRO2 was calculated as the product of CBF and the arterial to sagittal sinus O2 content difference. Dizocilipine was administered as a 150 micrograms/kg i.v. bolus followed by a 75 micrograms.kg-1.h-1 infusion for 90 min. Plasma dizocilipine levels were greater than 25 ng/ml for the duration of the infusion. The CSF levels were approximately half the plasma levels. Five minutes after initiation of dizocilipine treatment, Group I dogs experienced a 63% increase in heart rate (P less than 0.01) and an 8% decrease in the mean arterial blood pressure (P less than 0.05). Over the same time interval. CBF increased by 85% (P less than 0.01) and intracranial pressure nearly doubled (P less than 0.05). In addition, dizocilipine treatment in all Group I animals resulted in EEG quasiperiodic bursts of delta-waves and polyspikes on a background of beta-activity. With the exception of the intracranial pressure, the above changes in systemic and cerebral variables persisted for the duration of the drug infusion. Intracranial pressure was no longer significantly elevated after 80 min of drug infusion. Hemispheric CMRO2 was unchanged by dizocilipine in Group I dogs. There was a decrease in the cortical glucose level at the end of the study, but no significant change in phosphocreatine, ATP, lactate, or energy charge when compared with 6 laboratory normals. An identical dose of dizocilipine administered after an 11 min episode of complete cerebral ischemia resulted in no significant changes in either cerebral or systemic variables. The absence of systemic effects in Group II dogs suggests that dizocilipine administration in normal dogs results in a centrally mediated activation of the peripheral sympathetic nervous system. The uncoupling of CBF and CMRO2 observed following dizocilipine treatment is similar to that reported for two other known NMDA antagonists, ketamine and phencyclidine. If administration of dizocilipine results in improved histopathological and neurological outcome following an episode of complete cerebral ischemia, this improvement is unrelated to changes in postischemic CBF or hemispheric CMRO2.

Effects of NMDA antagonists, MK-801 and CPP, upon local cerebral glucose use

The effects upon cerebral glucose utilisation of (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801, a non-competitive N-methyl-D-aspartate (NMDA, receptor antagonist) and 3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP, a competitive NMDA receptor antagonist) were examined in conscious, lightly restrained rats. Cerebral glucose utilisation was assessed quantitatively in 74 brain regions with [14C]2-deoxyglucose autoradiography. The intravenous (i.v.) administration of MK-801 (0.05-5 mg/kg) induced heterogeneous patterns of altered cerebral glucose utilisation with statistically significant increases being observed in 21 brain areas and statistically significant decrease in 8 brain regions. Pronounced dose-related increases in glucose use were observed after MK-801 in the subicular complex, hippocampus molecular layer, dentate gyrus, limbic system (posterior cingulate cortex; mamillary body; anteroventral thalamic nucleus), olfactory areas and substantia nigra (pars reticulata). Glucose use in the neocortex and inferior colliculus was particularly sensitive to reduction by MK-801 administration. The pattern of altered glucose use after administration of CPP (3-30 mg/kg, i.v.) differed markedly from that observed after MK-801 treatment. Statistically significant increases in glucose use after CPP were noted in 11 brain areas and statistically significant decreases in 5 of the regions examined. Regions in which increases were noted after CPP included hippocampus molecular layer, olfactory areas, cochlear nucleus, vestibular nucleus, cerebellar nucleus, superior olives and substantia nigra (pars reticulata). These data indicate that widespread, anatomically organised alterations in cerebral function are associated with the administration of NMDA receptor antagonists despite the minor role normally ascribed to these receptors in conventional fast synaptic transmission. The distinct patterns of response to competitive and non-competitive antagonists may be a reflection of the differential responses of the two modes of receptor blockade to increased glutaminergic transmission.

Regulation of glycogen in the dentate gyrus of the in vitro guinea pig hippocampus; effect of combined deprivation of glucose and oxygen

Mammalian brain glycogen is adequate to support oxidative metabolism for several minutes. The present studies were done primarily to develop the guinea pig hippocampal slice as a model for studying the function and regulation of that glycogen. Slice glycogen falls to 6 nmol/mg dry wt. during the first hour of incubation at 36 degrees C but during the next 3 h recovers to 20 nmol/mg dry wt., similar to in situ values. Glycogen concentration in the dentate gyrus molecular layer is double its value in the whole hippocampal slice, suggesting its distribution is related to metabolic demand. When both glucose and oxygen are removed from the medium, glycogen and ATP fall to 50% within 6 min. The glycogen fall is unaffected by prolonged calcium depletion or by 3-isobutyl 1-methylxanthine, an adenosine antagonist. It is markedly slowed by preincubating the slice with creatine, which also slows the fall in ATP. It is concluded that ATP breakdown and subsequent increased 5'-AMP is activating glycogen mobilization in this in vitro model of ischemia.

Freeze-mount microautoradiographic study in the mouse hippocampus after intravenous injection of tritiated 2-deoxyglucose and glucose

Differences in the uptake of tracers from radioactive 2-deoxyglucose ([1,2-3H] and [2,6-3H]), and glucose ([1-3H], [3-3H]) into hippocampal regions were investigated by freeze-mount microautoradiography after 45 min for 2-deoxyglucose, and after 15 and 45 min for glucose. Silver grains were assessed quantitatively by an image analyser. (1) The radioactivity (silver grains/mm2) in the stratum lacunosum-moleculare of Ammon's horn from 2-deoxyglucose autoradiograms was significantly higher than that in other hippocampal regions (P less than 0.01), while lowest in the hilus fascia dentata (P less than 0.01). (2) Autoradiograms of [1-3H]glucose and 15 min of [3-3H]glucose showed the radioactivity in the dentate molecular layer to be significantly higher than that in other regions, excepting the stratum lacunosummoleculare (P less than 0.05). (3) The 2-deoxyglucose and 45-min glucose autoradiograms showed intensely labeled perikarya of pyramidal cells in the CA3a sector. (4) Radioactivity in the dentate granular layer from the 45-min autoradiogram of [3-3H]glucose was significantly higher than that in the molecular layer (P less than 0.05). The results imply that the metabolic fate of glucose, i.e. whether it is mainly used for energy production or amino acid synthesis, depends on each structure of the hippocampus.

Local cerebral glucose utilization in the Ammon's horn and dentate gyrus of the rat brain

The local cerebral glucose utilization (LCGU) was measured in different regions and layers of the Ammon's horn and dentate gyrus in the conscious rat. The LCGU was determined by quantitative [14C]2-deoxyglucose autoradiography using a computerized image processing system. In the hippocampus, the various regions and layers exhibited different glucose consumptions, the lowest values being found in the alveus and the highest ones in the lacunosum-molecular layers of the sectors of the Ammon's horn and the molecular layer of the dentate gyrus' external limb. Additionally, in many layers, the LCGU values of the left hemispheres were found to be higher compared with the right hemispheres. The analysis of LCGU changes in rostrocaudal direction revealed, that in sector 1 of Ammon's horn and in the dentate gyrus the glucose consumption decreased from rostral to caudal levels, whereas in sector 3 of Ammon's horn an increase was found.

The determination of the local cerebral glucose utilization with the 2-deoxyglucose method

In the adult mammalian brain, the energy metabolism is almost entirely dependent on glucose. Furthermore, a close relationship between the energy metabolism and the functional activity could be shown. Thus, the functional activity of the brain or parts thereof can be quantified by measuring the cerebral metabolic rate for glucose. Studying in vivo the fate of a radioactive labeled analogue of glucose, the 2-deoxy-D-[1-14C]glucose, and using quantitative autoradiographic techniques, it is possible to estimate the cerebral glucose utilization of every discrete brain region. The advantage of the 2-deoxyglucose method is, that the local cerebral glucose utilization represents a "metabolic encephalography" (Sokoloff 1982).

Ketamine effects on local cerebral blood flow and metabolism in the rat

The effects of an anesthetic dose (100 mg/kg) of ketamine, a phencyclidine derivative, on local rates of cerebral glucose utilization (LCGU) and CBF (LCBF) have been investigated by the quantitative [14C]2-deoxy-glucose and [14C]iodoantipyrine techniques in the unparalyzed, spontaneously breathing rat. In ketamine-injected animals, LCGU was significantly increased in some limbic structures and decreased in inferior colliculus, vestibular, and cerebellar nuclei. The degree and spatial distribution of drug-induced changes was similar for local blood flow rates, LCBF being increased in limbic regions and decreased in the inferior colliculus. Although Paco2 values were higher in anesthetized animals, the pattern of LCBF/LCGU ratios was not significantly affected by ketamine in the 36 brain regions examined in this study. So, at least in the rat and at the anesthetic level studied here, a net vasodilatory in vivo effect was not observed. These results support the hypothesis that CBF changes induced by the drug in animals and man are primarily related to the metabolic effects exerted by ketamine on cerebral structures.

Cerebral metabolic mapping at the cellular level with dry-mount autoradiography of [3H]2-deoxyglucose

The uptake and retention of radioactivity from [3H]2-deoxyglucose [( 3H]2-DG) was assessed in certain regions of the rat brain under basal conditions using dry-mount autoradiography, a procedure which affords the best available conditions to accurately localize diffusable radiolabeled compounds at cellular and subcellular levels. The overall amount of radioactivity accumulated in neuropil and in neuronal cell bodies was similar in most brain regions examined. Of the regions assessed, the CA3 pyramidal cell field of the hippocampus was the only region in which the radioactivity in cell bodies was notably greater than that of neuropil. In the somatosensory cortex and in the lateral hypothalamus, a wide range of radioactivity was found among individual neurons and among different areas of neuropil. In all brain regions examined, a subpopulation of small cells, with morphological characteristics of glial cells, accumulated [3H]2-DG to a much greater extent than other glial cells or neurons. That finding suggests that certain glial cells are in a markedly higher metabolic state than other brain cells.

Differential metabolic activity in the brain during deep halothane anesthesia. A qualitative study using [3H]deoxyglucose

Alteration of metabolic activity during deep halothane anesthesia (3%) was analyzed qualitatively in the rat using a modified 2-deoxyglucose technique using the tritiated compound. The grey matter exhibited a homogeneous low level of metabolic activity in most places but some nuclei or subnuclear structures showed a much higher activity. These included in particular the locus coeruleus, the dorsal raphé, the substantia nigra pars compacta, the CA3 region of the hippocampus and the nucleus reticularis thalami. In the nucleus reticularis thalami, the use of 2-deoxy-[3H]glucose allowed us to demonstrate a high cellular metabolic activity, which is in agreement with several electrophysiological studies which showed a high rate of spontaneous activity under the same anesthetics.

Peripheral sympathetic ingrowth can alter metabolic activity within the hippocampal formation

After cholinergic denervation of the hippocampal formation, peripheral sympathetic fibers arising from the superior cervical ganglia grow into the dentate gyrus and CA3 region; the functional significance of sympathetic ingrowth into the hippocampal formation is unknown. Utilizing electrical stimulation of the preganglionic trunk in combination with 2-deoxy-D-[3H]-glucose fine-grained autoradiograms, we demonstrated an alteration of hippocampal glucose metabolism, suggesting that this neuronal rearrangement makes functional connections within the hippocampus.

High resolution autoradiographic determination of the topographic distribution of radioactivity in the hippocampal formation after injection of [1-14C]glucose or 2-deoxy[14C]glucose

Using high resolution autoradiography, the accumulation of radioactivity after intravenous injection of [1-14C]glucose was measured in the corpus callosum, hippocampus, dorsal hippocampal commissure, somatosensory cortex, inferior colliculus and pontine periaqueductal grey. Autoradiograms were prepared by thaw-mounting 4 micron frozen sections on nuclear emulsion-coated slides, and were evaluated quantitatively with a computer-assisted video system for automated counting of silver grains. In all brain regions examined, silver grain densities were greater in rats killed 30 min after injection of [1-14C]glucose compared to rats killed 10 min after injection. After intravenous injection of [1-14C]glucose or 2-deoxy[14C]glucose, the relative uptake and retention of radioactivity in different hippocampal subregions was compared. Striking differences were found in the hippocampus between 2-deoxy[14C]glucose and [1-14C]glucose autoradiograms. After injection of 2-deoxy[14C]glucose, there were large variations in the uptake and retention of radioactivity among different pyramidal cell fields. The CA 3 pyramidal cell field retained considerably more radioactivity than other pyramidal cell fields after injection of 2-deoxy[14C]glucose, while after injection of [1-14C]glucose, the retention of radioactivity was similar in all pyramidal cell fields. After [1-14C]glucose injection, the dentate gyrus contained relatively high levels of radioactivity and more 14C accumulated in the granular layer, compared to the molecular layer. In contrast, after 2-deoxy[14C]glucose injection, there was uniformly less radioactivity throughout the dentate gyrus when compared to rats injected with [1-14C]glucose and there was no preferential accumulation of 2-deoxy[14C]glucose in the granular layer compared to the molecular layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic influences on hippocampal glucose metabolism

2-Deoxy-D-[3H]glucose autoradiography was employed to investigate the effects of acute cholinergic manipulations on hippocampal glucose metabolism. In general, manipulations designed to reduce cholinergic activity (medial septal ablation, atropine treatment) reduced hippocampal glucose metabolism. Maximal decrements were found in the terminal fields of the septohippocampal projection after medial septal lesions, while maximal deficits after atropine treatment correlated with muscarinic receptor binding. Electrical stimulation of the medial septum resulted in increased glucose utilization in some terminal fields of the septohippocampal projection and decreased utilization in the terminal fields of the perforant pathway. Our data clearly indicate that acute alterations in cholinergic activity can affect hippocampal glucose metabolism but the distribution, direction and degree of these changes is dependent on the specific treatment.

Cholinergic denervation of the hippocampal formation does not produce long-term changes in glucose metabolism

Decreased glucose metabolism is found in Alzheimer's disease associated with a loss of cholinergic neurons. The relationship between the chronic cholinergic denervation produced by medial septal lesions and glucose metabolism was studied using 2-deoxy-D-[3H]glucose in the rat hippocampal formation. Hippocampal glucose metabolism was increased 1 week after medial septal lesions. Three weeks after lesions, glucose metabolism was profoundly suppressed in all regions. By 3 months, intraregional hippocampal glucose metabolism had returned to control values. Our results demonstrate that chronic cholinergic denervation of the hippocampal formation does not result in permanent alterations of metabolic activity.

Altered metabolic activity in the cerebral cortex of rats exposed to ketamine

Uptake of the metabolic marker, [3H]2-deoxy-D-glucose (2DG) was compared in rats given subanesthetic (50--100 mg/kg, i.p.) or anesthetic (200 mg/kg, i.v.) doses of ketamine with that in normal, unanesthetized rats. All doses of ketamine caused a relative increase of 2DG labeling in limbic regions, including the hippocampus, dentate gyrus, and cingulate, piriform, and entorhinal cortices. Striking 2DG-dense zones were confined to the molecular layer in the hippocampus, dentate gyrus, and entorhinal cortex. Subanesthetic doses of ketamine produced a relative reduction of 2DG uptake in layers I--IV of granular somatosensory cortex while sparing uptake in layer Va; therefore, the peak of dense uptake shifted from layer IV to layer Va. In regions of the somatosensory cortex which display a dysgranular layer IV, vertical columns of relatively dense 2DG uptake extended through all cortical layers. Columns of 2DG label also occurred outside of S1, in visual and auditory areas. In the primary visual cortex, this dose of ketamine decreased 2DG uptake relative to secondary visual cortex. Alteration of 2DG uptake in various cortical regions might be the consequence of a ketamine-induced activation of specific neuronal pathways with special neurochemical features. During subanesthetic ketamine administration, peak 2DG uptake shifts from cortical layer IV, which receives specific thalamocortical input, to layer Va, which receives projections via intrinsic cortical circuits. The ketamine-induced shift in the laminar focus of sensory cortical metabolism may reflect a functional disconnection from peripheral sensory input and/or enhanced internal (corticocortical) processing.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of apomorphine upon local cerebral glucose utilization in conscious rats and in rats anesthetized with chloral hydrate

The effects of the dopaminergic agonist apomorphine (1 mg . kg-1 i.v.) upon local cerebral glucose utilization in 43 anatomically discrete regions of the CNS were examined in conscious, lightly restrained rats and in rats anesthetized with chloral hydrate by means of the quantitative autoradiographic [14C]2-deoxyglucose technique. In animals anesthetized with chloral hydrate, glucose utilization was reduced throughout all regions of the CNS from the levels observed in conscious animals, although the magnitude of the reductions in glucose use displayed considerable regional heterogeneity. With chloral hydrate anesthesia, the proportionately most marked reductions in glucose use (by 40-60% from conscious levels) were noted in primary auditory nuclei, thalmaic relay nuclei, and neocortex, and the least pronounced reductions in glucose use (by 15-25% from conscious levels) were observed in limbic areas, some motor relay nuclei, and white matter. In conscious, lightly restrained rats, the administration of apomorphine (1 mg . kg-1) effected significant increased in glucose utilization in 15 regions of the CNS (e.g., subthalamic nucleus, ventral thalamic nucleus, rostral neocortex, substantia nigra, pars reticulata), and significant reductions in glucose utilization in two regions of the CNS (lateral habenular nucleus and anterior cingulate cortex). In rats anesthetized with chloral hydrate, the effects of apomorphine upon local glucose utilization were less widespread and less marked than in conscious animals. In only two of the regions (the globus pallidus and septal nucleus), which displayed increased glucose use following apomorphine in conscious rats, were significant increases in local glucose utilization observed with this agent in chloral hydrate-anesthetized rats. In the pars compacta of the substantia nigra, in which apomorphine increased glucose utilization in conscious animals, significant reductions in glucose utilization were observed following apomorphine in rats anesthetized with chloral hydrate. The profound effects of chloral hydrate anesthesia upon local cerebral glucose use, and the modification by this anesthetic regime of the local metabolic responses to apomorphine, emphasize the difficulties which exists in the extrapolation of data from anesthetized animals to the conditions which prevail in the conscious animal.

A potential error in modifications of the [14C]2-deoxyglucose technique

Although the technique developed by Sokoloff et al. employing [14C]2-deoxyglucose as tracer, provides measurements of local cerebral glucose utilization, various modifications of the original technique are presently in widespread use. We have examined the validity of a crucial simplifying assumption which is an integral feature of many of these modifications; namely, that all the radioisotope in the CNS at the moment of sacrifice is present as 2-deoxyglucose-6-phosphate. By employing the kinetic model developed by Sokoloff et al. and arterial plasma [14C]2-deoxyglucose and glucose histories, the proportion of total radioactivity present in the CNS as unphosphorylated 2-deoxyglucose was calculated and found to vary from 5 to 50% of the total amount of isotope present in the CNS under different experimental conditions. It can be shown to be dependent upon (a) the rate of cerebral glucose utilization, (b) the time which elapses from administration of the radioisotope until the sacrifice, (c) the route by which the isotope is administered, and (d) arterial plasma glucose levels. Thus, modifications of the original 2-deoxyglucose technique have introduced a potential source of error which is not a feature of the approach of Sokoloff and his associates.

Autoradiographic patterns of hippocampal metabolism during induced hypothermia

[14C]2-Deoxyglucose (2-DG) uptake in the hippocampal formation was studied in the ground squirrel subjected to induced hypothermia. Whereas the stratum lacunosum-molecular has the highest 2-DG uptake in the dorsal hippocampus during euthermia, 2-DG uptake in the stratum lacunosum-molecular and stratum radiatum are similar during hypothermia. This may indicate activation of a cholinergic input to the hippocampus during hypothermia.

Correlation of regional brain metabolism with receptor localization during ketamine anesthesia: combined autoradiographic 2-[3H]deoxy-D-glucose receptor binding technique

LKB film autoradiography of 2-]3H]deoxy-D-glucose uptake shows that ketamine, administered in anesthetic doses, alters the pattern of metabolic activity in rat hippocampus. The labeled metabolic marker can be washed out of the slide-mounted tissue sections by preincubation to permit in vitro autoradiography of drug and neurotransmitter receptors in the same animal. In this way, opiate and phencyclidine receptor distributions may be correlated with patterns of glucose utilization in adjacent sections. If the observed relative enhancement of 2-deoxy-D-glucose uptake in the stratum moleculare of hippocampus reflects elevated metabolism in nerve terminals there, then the binding of ketamine to phencyclidine receptors on neurons in distant afferent sites, such as entorhinal cortex, may initiate the physiologic and metabolic effects.