Localization of[3H]-2-deoxyglucose in single molluscan neurones

Mapping of odor-related neuronal activity using a fluorescent derivative of glucose

Activity labeling was applied to the olfactory systems of the terrestrial slug Limax valentianus using 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-2-deoxyglucose (2-NBDG), a fluorescent derivative of glucose. 2-NBDG was incorporated into cultured Limax olfactory interneurons, and this was partially blocked by the presence of a high concentration of glucose in the medium, indicating that a part of the uptake of 2-NBDG is mediated by glucose transporters. Next, in order to map odor-related neuronal activity in the primary olfactory center, tentacular ganglion, we injected 2-NBDG into the body cavities of slugs and exposed them to odors or clean air (control). In the odor-stimulated animals, the cell mass region was strongly stained. The digit-like extensions and the neuropil region were also stained in some animals. The control animals showed no staining. The neurons in the cell mass are thought to be involved in generating oscillating activities in the tentacular ganglion, and their activation may imply modulation of oscillatory activity during odor processing. Our results show that 2-NBDG is useful for mapping neuronal activity in vivo.

High-resolution mapping of neuronal activity by thallium autometallography

Different methods are available for imaging neuronal activity in the mammalian brain with a spatial resolution sufficiently high to detect activation patterns at the level of individual functional modules such as cortical columns. Severe difficulties exist, however, in visualizing the different degree of activity of each individual neuron within such a module, and mapping neuronal activity with a spatial resolution of single axons has remained impossible thus far. Here, we present a novel method for mapping neuronal activity that is able to visualize activation patterns with light and electron microscopical resolution. The method is based on the tight coupling of neuronal activity and potassium (K(+)) uptake. We have injected Mongolian gerbils with the K(+) analogue thallium (Tl(+)), stimulated the animals with pure tones of different frequencies and analyzed, by an autometallographic method, the Tl(+) distribution in the auditory cortex (AC). We find tonotopically organized columns of increased Tl(+)-uptake in AC. Within columns, the spatial patterns of neuronal activity as revealed by thallium autometallography are highly elaborated. Tl(+)-uptake differs in different layers, sublayers, and cell types, being especially high in large multipolar inhibitory interneurons in layer IV. A prominent feature of the columnar activation pattern is the presence of vertical modules of minicolumnar dimensions. Clusters of layer Vb pyramidal cells and their apical dendrite bundles are clearly visible in the center of the columns.

Selective uptake of [14C]2-deoxyglucose by neurons and astrocytes: high-resolution microautoradiographic imaging by cellular 14C-trajectography combined with immunohistochemistry

At the moment, there is no direct in vivo evidence of the relative amount of glucose taken up and metabolized by glial cells and neurons, respectively. Therefore, we developed a specific high cellular resolution beta-trajectory approach that allows recording and identification of individual tracks of electrons emitted during disintegrations of 14C. We used [14C]2-deoxyglucose (2DG), which is an analog of glucose and is not metabolized further than the first phosphorylation by hexokinase; this property allows localization of the tracer within the cell type where it is phosphorylated. The present technical approach associated a method of cellular trajectography mainly characterized by the high thickness of the emulsion (15 microm), which permits following of the trajectory of individual electrons. This technique was improved to preserve the in vivo label of diffusible compounds such as 2DG and 2DG-6P and associated with immunohistochemical detection of neurons and astrocytes. beta-Track counting of labeled compounds was performed in 5 microm glial fibrillary acidic protein (GFAP)- and microtubule-associated protein (MAP)2-immunolabeled paraffin adjacent sections. Of 3,075 counted beta-tracks, 53.0% were localized in astrocytes on GFAP-labeled sections and 60.1% in neurons on MAP2-labeled sections. These data represent the first in vivo evidence of the compartmentation of uptake and metabolism of glucose in neurons and astrocytes.

Oscillatory dynamics and information processing in olfactory systems

Oscillatory dynamics is a universal design feature of olfactory information-processing systems. Recent results in honeybees and terrestrial slugs suggest that oscillations underlie temporal patterns of olfactory interneuron responses critical for odor discrimination. Additional general design features in olfactory information-processing systems include (1) the use of central processing areas receiving direct olfactory input for odor memory storage and (2) modulation of circuit dynamics and olfactory memory function by nitric oxide. Recent results in the procerebral lobe of the terrestrial slug Limax maximus, an olfactory analyzer with oscillatory dynamics and propagating activity waves, suggest that Lucifer Yellow can be used to reveal a band-shaped group of procerebral neurons involved in the storage of an odor memory. A model has been constructed to relate wave propagation and odor memory bands in the procerebral lobe of L. maximus and to relate these findings to glomerular odor representations in arthropods and vertebrates.

[14C]deoxyglucose labelling of functional activity in the cephalopod central nervous system

For the first time, the [14C]deoxyglucose radioautographic technique has been successfully used to map physiological activity in cephalopod brains. In unilaterally blinded octopus and cuttlefish, the optic lobe of the deprived side showed a decreased uptake of the labelled tracer. This suggests that the uptake is related to functional activity. The potential of the [14C]deoxyglucose technique as a powerful tool in studying the functional organization of cephalopod brains is discussed.

Selective labeling of [3H]2-deoxy-D-glucose in the snake trigeminal system: basal and infrared-stimulated conditions

[3H]2-Deoxy-D-glucose (2-DG) and high-resolution autoradiography were employed to investigate labeling patterns of the trigeminal and infrared sensory system in a crotaline snake, the pit viper (Trimeresurus flavoviridis). Following intracardiac injection of 9.25 MBq [3H]2-DG, neurons in the nucleus of the lateral descending trigeminal tract (LTTD), nucleus reticularis caloris (RC), nucleus trigemini mesencephalicus, nucleus trigemini motorius, and trigeminal ganglia were labeled in various degrees after the pit organ had been removed (basal condition). This revealed that a higher rate of glucose utilization occurred in these nuclei than in the common sensory trigeminal nuclei, which lacked labeling entirely. When a pit was stimulated periodically with an infrared stimulus for 45 min, the difference in percentage of labeled cells was ipsilaterally increased by 12.84% in large cells of the LTTD and by 7.55% in the RC, as compared with the contralateral, basal-condition side. These slight changes indicate a small increase of glucose consumption during infrared reception. On the other hand, the small cells in the LTTD showed labeling that did not change with stimulation, suggesting that 2-DG uptake in inhibitory interneurons is relatively constant.

Alterations in neurotransmitter receptors and glucose use after unilateral orbital enucleation

Serotonin (5-hydroxytryptamine; 5-HT), acetylcholine and gamma-aminobutyric acid (GABA) are neurotransmitters in the rat visual system. Using quantitative autoradiography, the effect of unilateral orbital enucleation on [3H]5-HT, [3H]ketanserin, [3H]quinuclidinyl benilate (QNB) and [3H]muscimol binding to 5-HT1, 5-HT2, muscarinic and GABAA receptors has been examined within anatomical components of the visual pathway at 4 time points up to 20 days after the lesion. The functional deficit was assessed in the same animals using quantitative [14C]2-deoxyglucose autoradiography. At 1 day after unilateral orbital enucleation, there were no significant alterations in ligand binding although local cerebral glucose use was reduced in primary visual structures in the visually deprived hemisphere. At 5 days post-enucleation, however, [3H]5-HT binding was significantly reduced in both the visually deprived superior colliculus (by 17%) and dorsal lateral geniculate body (DLG) (by 33%). There were similar alterations in the binding of this ligand in these primary retinal projection areas at 10 and 20 days after orbital enucleation, but there were no changes in secondary areas (e.g. visual cortex) at any time point. [3H]Muscimol binding was significantly reduced in the visually deprived DLG (30%) and visual cortex (21%) only at 20 days post-lesion, whilst [3H]ketanserin and [3H]QNB were not altered in any region in the visually deprived hemisphere at any time point post-enucleation. At 10 and 20 days post-enucleation, the degree of [3H]5-HT, and [3H]muscimol binding deficits in visually deprived structures correlated significantly with the level of reduced metabolic activity in these areas (r = 0.700 and r = 0.543 respectively). The specificity and regional and temporal heterogeneity of neurotransmitter receptor binding alterations provides evidence of selective adjustments within visual system components in response to orbital enucleation.

Glial (Müller) cells take up and phosphorylate [3H]2-deoxy-D-glucose in mammalian retina

[3H]2-Deoxy-D-glucose-6-PO4 ([3H]2DG-6P) was visualised at the level of single cells in freeze-dried guinea pig retinal sections by in vitro light microscopic autoradiography after incubation with [3H]2-deoxy-D-glucose ([3H]2DG). In the dark, autoradiographs revealed heterogeneous labeling within individual retinal layers. Labeling, representing [3H]2DG-6P, was preferentially located over Müller (glial) cells. Labelling over identified neurones in the inner nuclear layer, in contrast, was scarce and over ganglion cells was exceptional. Our observations indicate that Müller cells in the mammalian retina phosphorylate [3H]2DG to [3H]2DG-6P, the first step in glycolysis.

Receptor autoradiography and 2-deoxyglucose techniques in neuroscience

The use of the receptor autoradiography and 2-deoxyglucose (2-DG) techniques in neuroscience are reviewed. Receptors and other binding sites can be visualized autoradiographically in microtome tissue sections after labelling with radioligand in vivo or in vitro. Autoradiograms are generated by apposition of the labelled tissue to photographic emulsions. Combined with computerized image analysis, this technique can be used to analyse and quantify the microscopic distribution of receptors and receptor alterations associated with lesions or disease in human and animal tissues. The 2-DG technique permits microscopic analysis of modifications in brain glucose utilization induced by physiological and pharmacological manipulations. Limitations of these techniques and attempts to optimize their resolution are also discussed.

Identification of H1 visual interneuron in Drosophila by [3H]2-deoxyglucose uptake during stationary flight

High-resolution 2-deoxyglucose (2-DG) neuronal activity labeling is used to identify a visual interneuron in Drosophila by its stimulus-specific uptake of [3H]2-DG during stationary flight in a well-characterized behavioral situation. With a single rotating stripe as visual stimulus a neuron is heavily labeled that has not been described in Drosophila before but is homologous to the extensively studied H1 visual interneuron of larger diptera. Labeling of this cell is inconspicuous in Drosophila if the animal is stimulated with a rotating striped drum.

Auditory neural activity evoked by pure-tone stimulation as a function of intensity

The 2-deoxyglucose (2-DG) autoradiographic technique was employed to map activation of the central auditory pathway in the mongolian gerbil during stimulation with a 3.0 kHz tone at several intensities. In most auditory nuclei, the tone produced restricted areas in which 2-DG uptake was markedly higher than that of adjacent tissue, at locations consistent with the known tonotopic organization of the structure. The size of these regions changed relatively little with increasing stimulus intensity from 25 to 65 dB SPL (re 0.0002 dyne/cm2). At higher intensities, evoked uptake spreads into locations which represent frequencies above 3.0 kHz. In the inferior colliculus, relative 2-DG uptake decreased with increasing stimulus intensity in bands on either side of the 3.0 kHz region. These bands of reduced uptake became wider with increasing stimulus intensity from 25 to 85 dB SPL. The optical densities of auditory structures were normalized by the density of non-auditory white matter to derive optical density ratios. In the cochlear nuclei, optical density ratios in the 3.0 kHz region increased monotonically with increasing stimulus intensity, to a plateau at 45 dB SPL. In higher auditory nuclei, relative 2-DG uptake increased to a peak at 45 dB SPL and then declined at higher intensities.

Reduction in [3H]glutamate binding in the visual cortex after unilateral orbital enucleation

Glutamate is a major neurotransmitter in the rat visual system. The effect of lesion-induced functional deficit on [3H]glutamate binding sites within anatomical components of the visual pathway has been examined using quantitative autoradiography. In the same animals, the magnitude and extent of the functional deficit was assessed with quantitative [14C]-2-deoxyglucose autoradiography. At 24 h after orbital enucleation, significant reductions (approx. 25%) in glutamate binding were present throughout the visual cortex but there were no significant alterations in glutamate binding in the two principal projections of the retina, the superior colliculus or lateral geniculate body. Function-related glucose use was significantly reduced throughout the visual pathway after orbital enucleation. Thus, alterations in the number of glutamate binding sites occur in some, but not all, of the regions in a polysynaptic pathway in which activity is altered.

Ultrastructural metabolic activity following quick-freezing and freeze-substitution in tetrahydrofuran in the superior cervical ganglion

A method of quick-freezing and freeze-substitution has been developed for localizing diffusible substances such as 2-deoxyglucose-6-phosphate (2-DG-6-P) ultrastructurally in neural tissue. Quick-freezing under pressure provides well preserved tissue down to 30-35 microns from the surface. This allows blocks of neural tissue to be quick-frozen and analysed for diffusible substances in areas removed from the freezing face. Freeze-substitution in tetrahydrofuran following quick-freezing was found to dissolve and remove 2-deoxyglucose (2-DG) but not 2-DG-6-P. Consequently, this technique extends the ability to analyse localization of glucose utilization to postsynaptic as well as presynaptic sites. We have applied the technique to isolated superior cervical ganglion while provoking selective increases in energy metabolism. Exposure to an elevated extracellular potassium (12 mM) concentration produced a pattern of metabolic activity with enhanced neuropil labelling (neuronal and glial processes). With antidromic stimulation of the external carotid nerves, deoxyglucose uptake in neuronal and glial soma in the caudal portion of the ganglion was enhanced more than neuropil labelling. This caudal region corresponds to the region of origin of the cell bodies of the external carotid nerve. Results from this technique suggest that the contribution of glia to overall rate of energy metabolism may be significant and that this is a promising method for correlating the relationship between functional activity and cellular electrical activity.

New high-resolution 2-deoxyglucose method featuring double labeling and automated data collection

A new approach to high-resolution 2-deoxy-D-glucose (2DG) emulsion-autoradiography which combines improved retention of 2DG labeling, staining with immunohistochemical and other specific markers, and automated data collection and analysis of local silver grain and stain densities is described. The Durham et al. (J. Neurosci. 1:519-526, '81) procedure for fixation of 2DG with periodate-lysine-paraformaldehyde (PLP, McLean and Nakane: J. Histochem. Cytochem. 22:1077-1083, '74) was adapted to increase retained label roughly tenfold. Phenobarbital anesthesia is induced 45 minutes after 2DG injection. Barbiturate anesthesia increases brain glycogen (Nelson et al.: J. Neurochem. 15:1271-1279, '68) and presumably increases the incorporation of intracellular 2DG from 2DG-6P into brain glycogen and other molecules (Nelson et al.: J. Neurochem. 43:949-956, '84; Pentreath et al.: Neuroscience 7:759-767, '82). Iodoacetate is added to cold fixative to prevent glycogen breakdown (Cammermeyer and Fenton: Histochemistry 76:339-356, '82). This high-resolution 2DG protocol is directly compatible with many other neuroanatomical techniques. We demonstrate 2DG emulsion autoradiography combined with cytochrome oxidase (CO) histochemistry, markers for axonal pathway tracing, plastic embedding for semithin sections, and immunohistochemical staining for glutamate decarboxylase (GAD). The method should be compatible with antibodies for other antigens and with other neuroanatomical stains. To collect the data directly from microscope slides, a computer-controlled microscope was integrated with image-processing software to eliminate the need for manual counting and scoring of autoradiograms. Regions of interest are scanned automatically at high resolution to map regional labeling and/or stain density. There is excellent correspondence between computer-enhanced two-dimensional maps of the data and the original autoradiograms. Automated counts for five specimens were compared to counts of labeled cells by trained observer. The correlation between the two sets of measurements is high (r = .93). Automated data collection has been generalized to measure regional stain densities on the autoradiographed sections for direct comparison with silver grain density. The method is extremely flexible, especially since new image-processing strategies can be developed in software to extract the desired information from materials labeled by other methods (e.g., HRP).(ABSTRACT TRUNCATED AT 400 WORDS)

A low-priced computer-assisted densitometer and analysis software for quantitative autoradiography

A computer-assisted densitometer which consists of a darkroom enlarger, a black-and-white exposure meter, an amplifier, an analog-to-digital converter, and a microcomputer with a monitor and a graphic printer can be utilized for the quantitative analysis of autoradiograms. QUANTAR, a computer program written in BASIC, records the density measurements and stores the data in a file that can be easily retrieved by commercially available spreadsheet software. A spreadsheet template was designed to convert the digital readings into concentration of ligand in tissue. A variety of spreadsheet templates can be created to analyze data for a standard curve, a Scatchard plot, or a binding competition curve. This system, which is easy to assemble, may be useful to the frugal investigator with a modest equipment budget.

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).

Microscopic imaging of cells

The microworld was revealed to investigators through a glass bead or a hanging water droplet long before optics was understood. The cellular structure of plants was well resolved by such simple magnifying glasses, van Leeuwenhoek, the Dutch merchant and amateur microscopist, was the first to report to the English Royal Society his observations of bacteria with his single-lens microscope in 1665.

Effects of antidromic stimulation of the ventral root on glucose utilization in the ventral horn of the spinal cord in the rat

Electrical stimulation of the proximal stump of the transected sciatic nerve increased glucose utilization in the ventral horn of the spinal cord, with the greater increase in Rexed's lamina IX. Antidromic stimulation of the ventral root, however, did not change glucose utilization in the ventral horn. These results suggest that the axon terminals and not the cell bodies are the sites of enhanced metabolic activity during increased electrical activity in these elements.

Quantitative analysis of glucose after transient ischemia in the gerbil hippocampus by light and electron microscope radioautography

Changes in glucose uptake in the gerbil hippocampus were studied by high-resolution [3H]2-deoxyglucose radioautography under sham and postischemic conditions. Sections of dorsal hippocampi were fixed by chemical fixatives or rapid-freezing and freeze-substitution techniques. Light and electron microscope radioautograms showed that the cell soma of each CA1 neuron subjected to transient ischemia revealed various degrees of glucose uptake. In the neuropil of the CA1 stratum radiatum, glucose uptake was higher in the thin dendrites of the ischemic group. Cell damage due to transsynaptic stimulation is suggested by these results.

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.

Effects of hyperprolactinemia on plasma prolactin and glucose and on local cerebral glucose utilization

Elevated blood levels of prolactin increase the synthesis, turnover, and release of 3,4-dihydroxyphenylethylamine (dopamine) from the tuberoinfundibular dopaminergic neurons, which project to the median eminence. The present study examined whether hyperprolactinemia also increases local cerebral glucose utilization, as determined by the 2-deoxy-D-[1-14C]glucose method, in the median eminence and other brain structures. Adult male rats were given ovine prolactin (4 mg/kg) subcutaneously every 8 h for 48 h. This treatment exerted an autoregulatory feedback effect on endogenous rat prolactin secretion, as evidenced by decreased circulating levels of rat prolactin. Ovine prolactin treatment also decreased plasma glucose concentrations. However, in both partially immobilized and free-ranging rats, glucose utilization in brain structures containing tuberoinfundibular dopaminergic cell bodies (the arcuate nucleus) and terminals (the median eminence) was not affected by ovine prolactin treatment. Hyperprolactinemia was, however, associated with decreased glucose utilization in the medial forebrain bundle and the CA subfield of the dorsal hippocampus. The lack of a significant effect of prolactin treatment on glucose utilization in the median eminence indicates that the resolution of the deoxyglucose technique, as used here, is not adequate to detect the ovine prolactin-induced increase in tuberoinfundibular dopaminergic neuronal activity, that the median eminence does not utilize glucose as its primary energy substrate, or that ovine prolactin treatment causes a counterbalancing decrease in the activity of other neurons projecting to the median eminence.

Autoradiographic measurement of tritiated agmatine as an indicator of physiologic activity in Hermissenda visual and vestibular neurons

[3H]Agmatine (amino-4-guanidobutane) has been shown to be potentially useful for identifying and assessing the ACh sensitivity of specific neurons. Small cationic amines are able to permeate ACh-activated ion channels in sympathetic neurons and vertebrate endplates. Sensory neurons of the photic pathway in the nudibranch mollusc Hermissenda crassicornis are cholinergic and the synaptic interactions between the photic and vestibular systems have been well characterized electrophysiologically. We have therefore tested the feasibility of using autoradiography with [3H]agmatine, (a) to identify known ACh-responsive postsynaptic cells and (b) to examine its ability to serve as an indicator of physiologic activity within the photic and vestibular pathways under conditions of darkness and light stimulation. Scintillation counting revealed that approximately 70% of the radioactivity was associated with the CNS while approximately 30% was found in the processing fluids, indicating that routine glutaraldehyde-osmium fixation and subsequent processing for epoxy embedding allows retention of substantial amounts of the radiolabel. The autoradiographic results consistently demonstrated that the uptake patterns for [3H]agmatine did reflect some of the known neuronal interactions under the experimental conditions of light and dark. The accuracy extended to the second order cells of the optic ganglion and to putative interneurons along the photic tract in the cerebropleural ganglion. Since all the neurons in these pathways are unipolar with their synaptic interactions occurring only at the terminal endings, the radiolabel accumulated in the somata resulted from retrograde axonal transport. In the photic-vestibular pathways, the highest silver grain densities were found over structures (cell bodies or axon tracts) with increased synaptic activity coupled with higher levels of cellular activity (i.e. increased excitatory postsynaptic potentials or increased spontaneous impulse activity). Slightly less label was found in cells which received increased numbers of inhibitory postsynaptic potentials that produced hyperpolarization and a transient cessation of impulse activity under conditions of illumination. Therefore, the uptake levels of [3H]agmatine as revealed by autoradiography appear to reflect not only changes in sensitivity or density of ACh-activated channels but also changes in cellular activity as indicated by increased amounts of retrograde transport. These results represent the first example of the effective use of this radiolabel as an indicator of synaptic activity in invertebrates and in sensory systems.

Differential effects of electrical stimulation of sciatic nerve on metabolic activity in spinal cord and dorsal root ganglion in the rat

Electrical stimulation of the proximal stump of the transected sciatic nerve produces a frequency-dependent activation of glucose utilization, measured with the autoradiographic deoxy [14C]glucose method, in the dorsal horn of the spinal cord but produces no change in glucose utilization in the dorsal root ganglion cells. These results suggest that axon terminals and not the cell bodies are the sites of enhanced metabolic activity during increased functional activity of this pathway.

High-resolution 2-deoxyglucose autoradiography in quick-frozen slabs of neonatal rat olfactory bulb

We have used rapid freezing and freeze-substitution fixation to permit electron microscopic study of [3H]2-deoxyglucose autoradiographs. The techniques minimize diffusion of label into processing fluids and, by inference, migration of label within tissue. Slabs of olfactory bulbs from 12-day-old rats were quick-frozen after one hour of exposure to physiological olfactory stimuli. In light microscopic autoradiographs at low magnification, the neuropil of individual olfactory glomeruli appeared uniformly labeled with different levels of labeling in different glomeruli. At higher magnification, glomerular neuropil labeling consisted of small unlabeled regions surrounded by label clusters, suggesting greater deoxyglucose uptake by olfactory nerve terminals as compared with their postsynaptic dendrites. Periglomerular neurons were labeled differentially. Some microglia and glia precursor cells were heavily labeled in all bulbar laminae. The ultrastructure of cells and neuropil in all bulbar laminae was well-preserved. Cell processes and organelles could be identified in both stained sections and unstained electron microscopic autoradiographs. These experiments demonstrate the feasibility of combining quick-freezing with freeze substitution, in order to extend the resolution of studies using diffusable tracers such as 2-deoxyglucose. The results suggest that this is a promising method for assessing several controversies concerning deoxyglucose incorporation and neuronal and glial metabolism.

Metabolic activation of specific postsynaptic elements in superior cervical ganglion by antidromic stimulation of external carotid nerve

Using the rat superior cervical ganglion in vivo as a model of the central nervous system, we have sought to determine whether postsynaptic elements as well as terminal processes are metabolically activated during impulse activity. The rate of glucose utilization in the ganglion was found to be stimulated by antidromic stimulation of the external carotid nerve. This stimulation was frequency-dependent and was confined only to the region in the caudal portion of the ganglion corresponding to the location of the cell bodies of origin of the external carotid nerve.

Freeze-substitution of Drosophila heads for subsequent [3H]2-deoxyglucose autoradiography

High resolution of [3H]2-deoxyglucose labelling was obtained in autoradiographs of Drosophila brains after freeze-substitution in anhydrous acetone at -76 degrees C. This method was applied to preparations which received visual, olfactory and mechanosensory stimulation. The autoradiographs were compared to those obtained after freeze-drying. Freeze-substitution, which has proved to be technically simple, rapid and inexpensive, yields a good quality of tissue preservation and hence is recommended for tissue dehydration prior to autoradiography.

An inexpensive microcomputer-based image-analysis system: novel applications to quantitative autoradiography

We describe a relatively inexpensive, yet versatile and powerful microcomputer-based image-analysis system, and its applications to processing of deoxyglucose autoradiographic data. Images are acquired via a video camera mounted on a light microscope or a light box, and digitized in 40 ms to 512 X 512 picture elements with 8-bit resolution (256 gray levels). The bit-mapped image analysis hardware can provide up to 256 colors for pseudo-color coding, and virtually instantaneous readout of brightness values for densitometry. The system is controlled by an 8-bit S-100 bus microcomputer, providing flexibility and ease of expansion. In addition to pseudo-color coding and densitometry, we have developed programs for averaging of successive sections, image subtraction and quantitative reconstruction of different planes of section from serial autoradiograms.

Attempts to combine 2-deoxyglucose autoradiography and tyrosine hydroxylase immunohistochemistry

The possibilities were analysed to combine the 2-deoxyglucose technique and indirect immunofluorescence histochemistry using tyrosine hydroxylase antiserum, with the aim to study functional activity in immunohistochemically characterized single neurons. Since the product measured with the 2-deoxyglucose method is water soluble and since immunohistochemistry requires that sections repeatedly run through aqueous media, the 2-deoxyglucose method was carried out before fixation and immunohistochemistry. The routine rapid thaw-mounting at + 60 degrees C of sections for 2-deoxyglucose autoradiography was found not to be compatible with immunohistochemistry. Instead a new mounting technique based on "gluing" the sections on to the object slide with a mixture of a standard mounting medium (Permount) and xylene was used to avoid diffusion at this stage. Two procedures were outlined, both starting with unfixed brains cut on a cryostat. In Method I autoradiographic sheet film was used. After autoradiographic exposure, the section was immersion-fixed in formalin, processed for immunohistochemistry, analysed and photographed in a fluorescence microscope and the results compared with the autoradiographic distribution patterns on the film. However, only the low resolution of the routine 2-deoxyglucose technique was obtained, which did not allow analysis of activity in single cells. In Method II, liquid emulsion applied by the loop technique was used. After exposure, autoradiographic developing and fixation, dehydration, mounting, analysis and photography of autoradiographs in the light microscope, the cover-slip was removed, the sections rehydrated and processed for indirect immunofluorescence histochemistry. With this procedure single autoradiographically labeled cells were observed, some of which contained tyrosine hydroxylase. Thus, with Method II it may in the future be possible to monitor functional activity in single immunohistochemically identified neuronal cell bodies. In order to obtain a useful and reliable method for this purpose, however, further extensive work with regard to, for example, quantification will be required.

Identification of [3H]deoxyglucose-labelled interneurons in the fly from serial autoradiographs

Using the [3H]deoxyglucose technique we find in the third visual ganglion of the fly, Musca domestica, a number of neuronal profiles whose labelling strongly depends on the direction of visual movement. By reconstruction from serial autoradiographs of semithin sections the three-dimensional morphology of the labelled profiles, we demonstrate that cell bodies, neurites, axons and arborizations of two interneurons are labelled whose homologues in Calliphora have been identified as movement-sensitive centrifugal horizontal cells ('CH-cells'). A set of three other cells whose homologues in Calliphora show similar electrophysiological responses to horizontal movement ('HS-cells') exhibit very little label on either side. It is suggested that the relation between deoxyglucose mapping and physiological activity can be investigated at the cellular level by using this system of fly interneurons.

Tritiated 2-deoxy-D-glucose: a high-resolution marker for autoradiographic localization of brain metabolism

The technique for autoradiographic localization of 2-deoxy-D-glucose (2DG) uptake has become a useful method for observing alterations of functional brain activity resulting from experimental manipulation. Autoradiographic resolution is improved using tritiated ([3H]) rather than carbon-14 ([14C)]2DG, due to the lower energy and shorter path of tritium emissions. In addition, lower 2DG uptake by white matter relative to gray matter is exaggerated in the [3H]2DG autoradiographs due to the greater absorption of tritium emissions by lipids. Using [3H]2DG, it is possible to observe differential metabolic labeling in various individual nuclei or portions of nuclei that is unresolvable using [14C]2DG in the awake, normal animal. Heterogeneous patterns of 2DG uptake seen only with [3H]2DG are found in the nucleus accumbens, the anterior portion of the basolateral nucleus of the amygdala, specific nuclei of the inferior olivary complex, various hypothalamic regions, and a region straddling the border of the medial and lateral habenular nuclei. The lamination of differential 2DG uptake in the hippocampus is better localized using [3H]2DG. Autoradiographic resolution of labeled 2DG is further improved when the brain is perfused prior to frozen sectioning, due perhaps to selective fixation and retention of intracellular labeled 2-deoxy-glycogen. A series of [3H]2DG autoradiographs are presented together with views of the Nissl-stained sections that produced the autoradiographs.

Improved resolution of the 2-deoxy-D-glucose technique

It was attempted to improve the resolution of the 2-deoxyglucose method. Two principle changes in the procedure were introduced: the gluing of the sections on to the object slide at--20 degrees C and the application of the emulsion with the loop technique. With this approach autoradiographs with grain accumulations over single cell bodies could be observed in many brain regions in addition to a diffuse activity over neuropil.

Minireview: quantitative autoradiography of neurochemicals

Several new methods have been developed that apply quantitative autoradiography to neurochemistry. These methods are derived from the 2-deoxyglucose (2DG) technique of Sokoloff (1), which uses quantitative autoradiography to measure the rate of glucose utilization in brain structures. The new methods allow the measurement of the rate of cerebral protein synthesis and the levels of particular neurotransmitter receptors by quantitative autoradiography. As with the 2DG method, the new techniques can measure molecular levels in micron-sized brain structures; and can be used in conjunction with computerized systems of image processing. It is possible that many neurochemical measurements could be made by computerized analysis of quantitative autoradiograms.

Alterations in local cerebral glucose utilization during hemorrhagic hypotension in the rat

The alterations in local cerebral glucose utilization in 58 anatomically discrete regions which occur during a period of hemorrhagic hypotension have been investigated in conscious rats, using the quantitative autoradiographic 14C-deoxyglucose technique. Hemorrhagic hypotension (mean arterial pressure reduced by approximately 50 mm Hg) effected significant increases in glucose utilization in eight areas of the central nervous system, namely, the nucleus of the tractus solitarius (glucose utilization increased by 38%), the dorsal motor nucleus of the vagus (by 36%), locus coeruleus (by 38%), lateral habenular nucleus (by 40%), periventricular nucleus of the hypothalamus (by 41%), paraventricular nucleus of the hypothalamus (by 97%), supraoptic nucleus (by 86%), and the interstitial nucleus of the stria terminalis (by 84%). In five of these eight areas (nucleus of the tractus solitarius, dorsal motor nucleus of the vagus, paraventricular and supraoptic nuclei, and the interstitial nucleus of the stria terminalis), a significant relationship could be demonstrated between the level of glucose utilization and mean arterial blood pressure. In the majority of the CNS regions examined (neocortex, hippocampus, thalamus, extrapyramidal and motor areas), hemorrhagic hypotension was without significant effect upon local cerebral glucose utilization. The results provide direct evidence of the functional involvement of specific brain areas of conscious rats (thus obviating complicating anesthetic influences) in the response of the CNS to hemorrhagic hypotension.

2-deoxyglucose autoradiography of single motor units: labeling of individual acutely active muscle fibers

2-Deoxy-D-[l-14C]glucose (2DG) was given intravenously during repetitive stimulation of single motor units in adult cats and autoradiographs were made of frozen sections of the target muscles in order to evaluate methods designed to improve the spatial resolution of [14C]2DG autoradiography. With the modifications used, acutely active muscle fibers, independently identified by depletion of intrafiber glycogen, were associated with highly localized accumulations of silver grains over the depleted fibers. The results indicate that [14C]2DG autoradiography can successfully identify individual active muscle fibers and might in principle be used to obtain quantitative data about rates of glucose metabolism in single muscle fibers of defined histochemical type. The modifications may be applicable also to other tissues to give improved spatial resolution with [14C]-labeled metabolic markers.

Uptake and localization of 3H-2 deoxy-D-glucose by retinal photoreceptors

Following dark incubation of isolated retinas of Xenopus laevis in Ringer solution supplemented with 3H-2-Deoxy-D-glucose (2DG), virtually all of the uptake of the label was by the inner segments and synaptic bases of the photoreceptor cells. Autoradiographs prepared from conventionally fixed tissue showed the same cellular distribution of label as those prepared from identically incubated, unfixed, freeze-dried retinas. However, fixation removed about 77% of the total counts. This fixation-labile, soluble fraction was identified as being primarily 2DG-6 phosphate by thin-layer chromatography. The remaining insoluble fraction corresponded in distribution to glycogen grains. In cones, glycogen is stored primarily in the paraboloid, whereas in rods it is distributed throughout the inner segment and synaptic base. EM autoradiographs illustrated that these were the sites over which fixation-resistant 2DG label was localized. Measurements of radioactivity associated with extracts of retinal glycogen following 2DG incubation demonstrated that a disproportionately high fraction of total counts were associated with the glycogen fraction. We conclude that in the amphibian retina 2DG may be incorporated into glycogen.

Mapping of odor-related neuronal activity in the olfactory bulb by high-resolution 2-deoxyglucose autoradiography

The spatial distribution of odor-induced neuronal activity in the olfactory bulb, the first relay station of the olfactory pathway, is believed to reflect important aspects of chemosensory coding. We report here the application of high-resolution 2-deoxyglucose autoradiography to the mapping of spatial patterns of metabolic activity at the level of single neurons in the olfactory bulb. It was found that glomeruli, which are synaptic complexes containing the first synaptic relay, tend to be uniformly active or inactive during odor exposure. Differential 2-deoxyglucose uptake was also observed in the somata of projection neurons (mitral cells) and interneurons (periglomerular and granule cells). This confirms and extends our previous studies in which odor-specific laminar and focal uptake patterns were revealed by the conventional x-ray film 2-deoxyglucose method due to Sokoloff and colleagues [Sokoloff, L., Reivich, M., Kennedy, C., DesRosiers, M. H., Patlak, C. S., Pettigrew, K. D., Sakurada, O. & Shinohara, M. (1977) J. Neurochem. 28, 897--916]. Based on results obtained by the two methods, it is suggested that the glomerulus as a whole serves as a functional unit of activity. The high-resolution results are interpreted in terms of the well-characterized synaptic organization of the olfactory bulb and also serve to illustrate the capability of the 2-deoxyglucose autoradiographic technique to map metabolic activity in single neurons of the vertebrate central nervous system.

High resolution analysis of [3H]2-deoxyglucose incorporation into neurons and glial cells in invertebrate ganglia: histological processing of nervous tissue for selective marking of glycogen

The 2-deoxyglucose (2-DG) autoradiographic technique, in conjunction with 3H-labelled 2-DG and glutaraldehyde fixation, was applied to the isolated ganglia of the leech and the snail in order to analyse its potential use for the understanding of energy utilization in these simple nervous systems. Approximately 50% of the label is retained in these tissues after histological processing, and the method can be satisfactorily applied at the subcellular level. In both species most neurons progressively accumulate radioactivity over 15 min-1 h, although to different extents. In the leech the glial cells showed greater uptake than the neurons. Paired homologous neurons in contralateral buccal ganglia of the snail were equally labelled. In all structures studied by electron-microscope autoradiography the label was positively associated with glycogen. Freshly extracted glycogen from ganglia previously exposed to 2-DG was significantly labelled (2-10% of total radioactivity in the ganglia); thus the glutaraldehyde fixation did not appear responsible for artifactual binding of the label. The significance of the glycogen labelling and the potential of the technique for metabolic mapping in these nervous systems are discussed.

[3H]-2-deoxyglucose autoradiography in a molluscan nervous system

We have used [3H]2-deoxyglucose autoradiography to correlate the labeling of individual neurons with electrical activity within the central nervous system of a terrestrial mollusc, Limax maximus. In an electrically quiescent control preparation where a single neuron is impaled with a glass microelectrode but not stimulated, several somata are uniformly labeled at 3-5 times background. In preparations where a single cell is impaled and stimulated, one or more somata are heavily labeled with [3H]2-deoxyglucose at 10-50 times tissue background. This technique may be useful for surveying metabolically active neurons during spontaneous and driven electrical activity.