Levels of norepinephrine and dopamine in mouse brain regions following microwave inactivation--rapid post-mortem degradation of striatal dopamine in decapitated animals

Evidence for Noncanonical Neurotransmitter Activation: Norepinephrine as a Dopamine D2-Like Receptor Agonist

The Gαi/o-coupled dopamine D2-like receptor family comprises three subtypes: the D2 receptor (D2R), with short and long isoform variants (D2SR and D2LR), D3 receptor (D3R), and D4 receptor (D4R), with several polymorphic variants. The common overlap of norepinephrine innervation and D2-like receptor expression patterns prompts the question of a possible noncanonical action by norepinephrine. In fact, previous studies have suggested that norepinephrine can functionally interact with D4R. To our knowledge, significant interactions between norepinephrine and D2R or D3R receptors have not been demonstrated. By using radioligand binding and bioluminescent resonance energy transfer (BRET) assays in transfected cells, the present study attempted a careful comparison between dopamine and norepinephrine in their possible activation of all D2-like receptors, including the two D2R isoforms and the most common D4R polymorphic variants. Functional BRET assays included activation of G proteins with all Gαi/o subunits, adenylyl cyclase inhibition, and β arrestin recruitment. Norepinephrine acted as a potent agonist for all D2-like receptor subtypes, with the general rank order of potency of D3R > D4R ≥ D2SR ≥ D2L. However, for both dopamine and norepinephrine, differences depended on the Gαi/o protein subunit involved. The most striking differences were observed with Gαi2, where the rank order of potencies for both dopamine and norepinephrine were D4R > D2SR = D2LR >> D3R. Furthermore the results do not support the existence of differences in the ability of dopamine and norepinephrine to activate different human D4R variants. The potency of norepinephrine for adrenergic α2A receptor was only about 20-fold higher compared with D3R and D4R across the three functional assays.

Dopac distribution and regulation in striatal dopaminergic varicosities and extracellular space

DOPAC, the major intermediate metabolite of dopamine, is found in the cytosolic compartment of dopaminergic terminals/varicosities and in the extracellular space. It has been proposed that extracellular DOPAC is derived from newly synthesized dopamine rather than from dopamine in the signaling pool. On the basis of literature data supporting such a concept, we hypothesize a DOPAC synthesis/secretory complex producing extracellular DOPAC and use a computational simulation model of dopaminergic varicosities to estimate the distribution of DOPAC between cytosolic and extracellular compartments, amount of newly synthesized dopamine entering the DOPAC synthesis/secretory complex, and potential regulatory processes in the complex. Results suggest that about two-thirds of DOPAC is in the extracellular space. Approximately one-third of newly synthesized dopamine is immediately processed to DOPAC, which is then secreted into extracellular space. Extracellular DOPAC concentration is approximately 300 times higher than extracellular dopamine, and cytosolic DOPAC is ∼18-fold higher than cytosolic dopamine. We suggest that the high levels of extracellular DOPAC coupled with evidence for its production from newly synthesized dopamine imply the existence of an as yet undiscovered regulatory/signaling role for DOPAC.

Microwave applications in neuromorphology and neurochemistry: safety precautions and techniques

In science, the introduction of a new method is never easy, not even if it concerns the use of a simple microwave oven. Most scientists do not realize the numerous applications of microwave techniques. This paper gives a broad overview of the application of microwave techniques in neuromorphology and neurochemistry, starting with a historical overview ranging from the introduction of microwave techniques as a scientific method in the 1970s to present. Organizations and publication rules are highlighted in the next part. The effect of microwave irradiation is discussed in two sections relating to microwave effects on the whole organism and on the neuron. The main body of the paper discusses the application of microwave techniques in the fields of neuromorphology and neuropathology. The paper then presents aspects of microwave irradiation as applied to ELISA techniques. In addition, cell fusion and cell reproduction under microwave irradiation are discussed.

Effects of chronic neuroleptic treatment on dopamine release: insights from studies using 3-methoxytyramine

Antipsychotic medications appear to exert their therapeutic effects by blocking D2 receptors. While D2 blockade occurs rapidly, reduction in psychotic symptoms is often delayed. This time discrepancy has been attributed to the relatively slow development of depolarization inactivation (DI) of dopaminergic neurons. The reduced firing rates associated with DI has been hypothesized to reduce dopamine release and thus psychotic symptoms. Studies assessing changes in dopamine release during chronic neuroleptic treatment, using microdialysis and voltammetry, have been inconsistent. This may be due to methodological differences between studies, the invasive nature of these procedures, or other confounds. To investigate the effects of DI on dopamine release, 3-MT accumulation, an index of dopamine release that does not involve disruption of brain tissue, was measured during acute and chronic neuroleptic treatment. These results are compared with those using other techniques. 3-MT levels remained elevated after chronic treatment, suggesting that DI does not markedly reduce release. Regulation of dopamine release during DI was examined using two techniques known to block dopamine neuronal impulse flow. 3-MT levels were markedly reduced by both, implying that DI does not alter the portion of dopamine release mediated by neuronal impulse flow. Overall, studies to date suggest that the delayed therapeutic effects of neuroleptics are not due to reductions in impulse dependent dopamine release. Recent studies using a neurodevelopmental animal model of schizophrenia have pointed to altered pre- and post-synaptic indices of dopamine neurotransmission. The results suggest that neuroleptics may exert their therapeutic effects, in part, by limiting the fluctuations in dopamine release, and raise new issues for future research.

Effects of anticholinergic-antiparkinsonian drugs on striatal neurotransmitter levels of rats intoxicated with soman

Antimuscarinic drugs possessing antiparkinson activity that were effective in preventing convulsions induced by the organophosphorus cholinesterase (ChE) inhibitor soman were studied for their effects on spinal cord ChE activity and striatal levels of acetylcholine (ACh) and catecholamines in soman-intoxicated rats. Either biperiden (BPR) or trihexyphenidyl (THP) was administered to rats at an anticonvulsant dose (0.125 mg/kg, IM) in the presence or absence of soman (100 micrograms/kg, SC). The time course (up to 2 h) for ChE activity and levels of ACh and catecholamines were measured after soman, BPR, THP, soman and BPR, or soman and THP treatment. Soman rapidly inhibited ChE activity (65-75%; 15-120 min) and increased ACh levels (35%; at 30 min). It did not affect norepinephrine or dopamine (DA), but elevated at later time points (60-120 min) levels of the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), thus indicating increased DA turnover. BPR and THP alone reduced striatal ACh level from control, but did not affect any other neurochemical parameters studied. THP and BPR each reversed the effects of soman on DOPAC and HVA levels, but neither affected ChE activity nor ACh level induced by soman. Thus, our findings suggest that the anticonvulsant effects of BPR and THP in soman poisoning may be attributed to their earlier reported muscarinic receptor blocking properties.

Use of microwaves for rapid fixation of tissues in vivo

Accurate knowledge of the concentration in the central nervous system of neurochemicals undergoing rapid enzymatic destruction or synthesis is sparse because of the difficulty in stopping the rapid reactions while causing only minimal adverse changes in the neurochemistry and structure. Microwave heating can be effectively used to rapidly stop enzyme activity in the central nervous system with minimal adverse changes. This rapid inactivation of the enzymes increases the validity of the sample that is taken for analysis of the concentration of the enzyme's substrate.

Participation of type A monoamine oxidase in the activated deamination of brain monoamines shortly after reperfusion in rats

Changes in monoamine levels during and after ischemia and effects of RS-8359, a type A monoamine oxidase (MAO-A) inhibitor, were studied in the cerebral cortex, hippocampus, and striatum of rats killed by microwave irradiation. The patterns of the changes in norepinephrine (NE), dopamine (DA), and serotonin (5HT) levels were similar during ischemia: All these monoamines decreased in all three regions. After reperfusion, however, the three monoamines showed different patterns of changes: NE, except in the striatum, decreased further; DA increased over the controls; 5HT remained suppressed in all three regions. With regard to the metabolites of the monoamines, the changes during and after reperfusion were almost similar in all regions: O-methylated metabolites, normetanephrine and 3-methoxytyramine, markedly increased during ischemia; After reperfusion, the elevated levels of normetanephrine and 3-methoxytyramine returned to normal, while deaminated metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid, homovanillic acid (HVA), and 3-methoxy-4-hydroxy-phenylethyleneglycol clearly increased. RS-8359 pretreatment (30 mg/kg, p.o.) at an hour prior to ischemia elevated the levels of NE in the cortex and hippocampus during ischemia and inhibited the increases in DOPAC and HVA levels and the decrease in 3MT levels at 30 min after reperfusion. These results suggest that deamination of NE, DA, and 5HT is activated by the increases in the substrates for MAO in all three regions, except the noradrenergic system in the striatum, and that MAO-A participates in the activated deamination after reperfusion.

Behavioral sensitization following subchronic apomorphine treatment--possible neurochemical basis

Subchronic treatment with the dopamine agonist apomorphine produces a sensitization to the stereotypic effects of subsequent apomorphine challenge. The present study investigated the effects of this subchronic treatment on apomorphine induced stereotypic behavior and striatal dopamine synthesis, release, metabolism, and D2 receptor binding. The pretreatment, which enhanced the behavioral response to apomorphine challenge, also elevated basal dopamine synthesis and metabolism, but left the ability of a challenge dose of apomorphine to inhibit dopamine synthesis and metabolism unaltered. Thus, ongoing dopamine synthesis and extracellular levels of metabolites would be higher following apomorphine challenge in animals treated subchronically with the agonist. In contrast, neither synaptosomal dopamine release in response to depolarizing stimuli nor the density of D2 dopamine receptors was altered by the treatment. Overall, the results suggest that, while we did not find evidence of autoreceptor desensitization per se, apomorphine treatment may result in enhanced extracellular dopamine levels following dopamine agonist challenge to provide a greater stimulation of an intact dopamine receptor system.

Biochemical analysis of caudate nucleus biopsy samples from parkinsonian patients

Biochemical analyses of caudate nucleus biopsy samples from patients with Parkinson's disease undergoing autologous adrenal transplantation were performed. Activity of the dopamine biosynthetic enzyme tyrosine hydroxylase, and concentrations of dopamine and its primary metabolite homovanillic acid were significantly greater than anticipated on the basis of previously published postmortem values. These data suggest that postmortem changes in various biochemical parameters of dopamine function are more rapid than has been generally appreciated. Further analysis of striatal biopsy samples may reveal predictive relationships between striatal indices of dopamine function and therapeutic response to adrenal transplantation.

Stress-related activation of cerebral dopaminergic systems

The changes in dopamine catabolites in various regions of mouse brain have been studied following a variety of behavioral treatments. In confirmation of the results of many others, we find that treatments such as footshock or restraint result in a pronounced activation of dopaminergic systems in the prefrontal cortex, as determined by increases in the content of DOPAC (3,4-dihydroxyphenylacetic acid). However, we also find small but statistically significant increases of DOPAC in the hypothalamus and brain stem even with mild treatments. With restraint and more intense footshock we observe increases of DOPAC in all regions studied, including nucleus accumbens, olfactory tubercle, amygdala, and the striatum. Thus in contrast to previous reports, we find that the DA response in stress is global like that of norepinephrine [as determined by increases of 3-methoxy,4-hydroxyphenylethyleneglycol, (MHPG)], and not specific to the prefrontal cortex. The activation of prefrontal cortex DA metabolism is associated with an activation of the synthetic enzyme tyrosine hydroxylase. The response pattern of catecholamine metabolites is similar following a variety of stressors, including conditioned footshock, training with one footshock in passive avoidance behavior, performance of passive avoidance behavior, and even following exposure to an apparatus in which mice have been shocked previously. Injection of mice with Newcastle disease virus increases plasma corticosterone, and DOPAC and MHPG in the hypothalamus and brain stem, but not the prefrontal cortex. Thus a virus infection can be considered a stressor. Furthermore, intracerebroventricular (ICV) injection of corticotropin-releasing factor (CRF) produces stresslike increases in DOPAC and MHPG concentrations, suggesting that the release of CRF in the brain during stress may mediate the changes in catecholamine metabolism.

The dopamine metabolite 3-methoxytyramine is not a suitable indicator of dopamine release in the rat brain

It has been postulated that changes in the concentration of 3-methoxytyramine (3-MT) in the brain might reflect changes in the release of 3,4-dihydroxyphenylethylamine (DA, dopamine) and, therefore, might be used as an index of dopaminergic activity in the brain. 3-MT is known to accumulate rapidly after death. Killing by microwave irradiation (MWR) is considered to be the method of choice to obtain "undisturbed" 3-MT concentrations. We measured striatal 3-MT concentrations even lower than those following MWR when the brains were excised and frozen in dry ice very rapidly (typical time between decapitation and freezing of the brain 22 s). There was a linear increase in striatal 3-MT concentration when the time between decapitation and freezing was varied between 13 and 300 s. Extrapolation to time zero indicated negligible amounts of 3-MT at the time of decapitation. In addition, it was observed that DA, 3,4-dihydroxyphenylacetic acid, and homovanillic acid decompose during the cooling phase after heating the brain by microwave. It is concluded that MWR induces artifactual changes in the postmortem levels of DA and metabolites. Consequently 3-MT cannot be considered to be a reliable indicator of DA release in the rat brain.

Catecholamine, adenosine triphosphate, and P-creatine levels in decapitated whole mouse brain

The levels of norepinephrine, epinephrine, dopamine, adenosine triphosphate, and P-creatine were measured in whole mouse brain collected under two conditions: 1) the decapitated head was immediately plunged into liquid nitrogen (nonanoxic tissue); or 2) the tissue was allowed to remain anoxic before the quick-freezing procedure. The substrate levels were significantly decreased in brain anoxic for only 30 sec. The catecholamine levels in nonanoxic mouse brain appear to be higher than levels previously reported in brains collected with microwave irradiation or by decapitation with rapid dissection of tissue before it was frozen.

Maintenance of regional chemical integrity for energy metabolites in microwave heat inactivated mouse brain

A method is described in which brain tissue from microwave heat inactivated mouse brain is prepared for microregional energy metabolite analysis. This method permits the sectioning of the tissue into sections 40 microns thick in which layers can be visualized and dissected. Results show no movement or leaching of metabolites from one microregion to another. This method therefore, permits the combined use of the two powerful neurochemical techniques of microwave irradiation for sacrifice and microregional analysis for energy metabolite determination.

Study of the use of the microwave magnetic field for the rapid inactivation of brain enzymes

A new model of a microwave device was developed with a power of 10 kW at 2450 MHz. In order to accomplish even distribution of heating with minimum trauma and with a maximum certainty about enzyme inactivation, a modified magnetic field distribution was utilized rather than the conventional electric field. An integrated tuning system was used to increase efficiency and distribution of microwave energy absorption. This increased the ability of the instrument to properly inactivate the enzymes in the brain of both mice and large rats. In general, the time of irradiation for the rat was 600 to 900 msec and for the mice, 100 to 330 msec. The animal chambers used were designed so as not to impair breathing or too severely restrict movement. The effects of these improvements on microwave irradiation were confirmed by 1) observation of brain appearance, 2) effects on succinic dehydrogenase and cholinesterase activity, 3) measurement of regional temperatures in the animal's brain, 4) thermograms of the brain, 5) electron microscopic examination of brain tissue and 6) measurement of endogenous acetylcholine and catecholamines.

Sulfate conjugation of dopamine in rat brain: regional distribution of activity and evidence for neuronal localization

Brain tissue contains at least two forms of phenolsulfotransferase that are involved in the sulfate conjugation of biogenic amines and their metabolites. Two apparent Km values were obtained for p-nitrophenol at pH 7.4 (0.6 microM and 0.3 mM) but only one enzyme had the capacity to conjugate dopamine (Km = 130 microM). Dopamine sulfotransferase activity was found to vary 17-fold in different brain regions, with the highest levels in diencephalon, hippocampus, and striatum. To determine the cellular localization of the enzymes, phenolsulfotransferase activity was measured in striatum following selective destruction of striatal neurons by stereotaxic injection of 2 micrograms kainic acid. Fourteen days after injection the catecholamine sulfotransferase activity in the lesioned striatum was reduced to approximately 40-50% of that in the control contralateral striatum. There was a statistically significant correlation between the ratio of lesioned to control activity for the sulfotransferase and the neuronal marker enzymes glutamate decarboxylase and neuron-specific enolase. p-Nitrophenol sulfotransferase activity was also decreased in the lesioned striatum. These results suggest that PST activity is present within the kainic acid-sensitive neurons of the striatum. The regional variation in activity, together with the results of the kainic acid studies, suggest that sulfate conjugation of biogenic amines and their metabolites in brain may take place within specific types of neurons.

Age-correlated changes in dopaminergic nigrostriatal perikarya of the C57BL/6NNia mouse

Alterations in neurotransmitter systems of the basal ganglia have been postulated to contribute to the disruption of motor function and balance associated with aging. This study examined nigrostriatal (A9) and mesolimbic (A10) dopamine neurons for qualitative age-correlated changes using fluorescence histochemistry for catecholamines and immunocytochemical techniques for the catecholamine-synthesizing enzyme, tyrosine hydroxylase. Results from this study suggest that age-correlated morphological changes in A9 but not all A10 neurons in the midbrain are present in mature adult (10-month) C57BL/6NNia mice and show a progressive increase in severity until at least 30 months of age. These changes are characterized by a progressive accumulation of lipofuscin in dopamine-containing perikarya, a markedly reduced dopamine content per cell as determined visually by histofluorescence, and an increase in the number of large, fluorescent axonal dilations in dopamine-containing fibers of the mesolimbic and nigrostriatal systems. These data suggest that heterogeneous morphological aging patterns exist within dopamine-containing neurons of the midbrain and that based upon their terminal projection sites, various regions of the striatum and cortex may be differentially affected in the aged brain. In addition, these findings support the belief that age-related changes in neural structure are not generalized to an entire brain nucleus or cell type but are selective for individual cells within an affected area.

Simultaneous measurement of tyrosine, tryptophan and related monoamines for determination of neurotransmitter turnover in discrete rat brain regions by liquid chromatography with electrochemical detection

Concomitant measurement of monoamine neurotransmitter turnover in discrete rat brain areas with the use of radiolabeled amino acid precursors permits simultaneous evaluation of interacting transmitter systems. [3H]Tyrosine and [3H]tryptophan were administered via indwelling catheters to unrestrained rats. Content and specific activity of norepinephrine, dopamine, 5-hydroxytryptamine, and the metabolites dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindoleacetic acid in addition to tyrosine and tryptophan were quantified by liquid chromatography with electrochemical detection and liquid scintillation counting. The method employs a simple extraction procedure without prior cleanup for chromatography. Neurotransmitter turnover rates that incorporated tyrosine- or tryptophan-specific activities were found to be two to four times greater than those that did not include them.

Determination of picogram levels of brain catecholamines and indoles by a simplified liquid chromatographic electrochemical detection method

A simple and rapid method for the simultaneous determination of norepinephrine, epinephrine, dopamine, 5-hydroxytryptamine and 5-hydroxyindoleacetic acid in rat brain regions by high-performance liquid chromatography (HPLC) with electrochemical detection has been developed. Perchloric acid extracts of the tissue were directly analyzed in the HPLC system. Each of these compounds gave a linear response over the range of 10-320 ng/ml cerebellar homogenate (0.2-6.4 ng on column). Analytical recoveries of these compounds added to the homogenates were complete when compared with standards dissolved in perchloric acid. The average between-run coefficients of variation for all these compounds were lower than 6.7%, over the range of 10-320 ng/ml, whereas the within-run coefficients of variation at 10 ng/ml were lower than 6.9%. Under the present instrumental and mobile phase conditions, all compounds were readily oxidized at 0.72 V vs. a Ag/AgCl reference electrode. The present method has been applied to a study determining the basal levels of these compounds in several rat brain regions as well as levels after medium raphe lesions.

A method for dissection of discrete regions of rat brain following microwave irradiation

A simple microdissection technique for obtaining discrete areas from rat brains exposed to microwave irradiation is described and illustrated. Using the atlas of Pellegrino et al. [10] as a guide, stereotaxically defined areas were removed from coronal sections prepared with sectioning stages constructed from microscope slides. The dissection of sixteen discrete regions is shown in photographic and schematic form. This technique may prove useful for examining neurochemical processes in discrete areas of the rat central nervous system and may aid in establishing the distribution of pharmacological and toxicological agents at a neuroanatomical level.

Effect of microwave irradiation on monoamine metabolism in dissected rat brain

The effect of 5 kW microwave irradiation on monoamine metabolism was investigated in dissected regions of rat brain. Concentrations of intracerebral monoamines and their metabolites were simultaneously determined by means of high performance liquid chromatography with electrochemical detection. The concentrations of noradrenaline, dopamine and 5-hydroxytryptamine were reduced by a 0.5 s irradiation in comparison with those of decapitated animals. When the duration of irradiation was prolonged by 1.5 s, on the other hand, the levels of monoamines were increased. The changes of metabolite concentrations were generally opposite direction for those of parent transmitters. These findings suggest that the microwave irradiation affects those concentrations and that a 1.5 s irradiation is recommended in order to completely inactivate the corresponding enzyme prior to the simultaneous determination of monoamines' related substances in dissected brain regions.

Investigations of catecholamine metabolism using high-performance liquid chromatography: analytical methodology and clinical applications

High-performance liquid chromatography, particularly in its reversed-phase mode, coupled with electrochemical or fluorometric detection, is becoming increasingly popular as an analytical tool for metabolic profiling of substances of neurochemical interest, such as catecholamines and their metabolites. During the last decade, a continued effort has been made to improve and simplify the analytical methodology for routine use in clinical laboratories where this technique is tremendously needed. New developments in column technology, reliable detectors, simplified sample cleanup procedures, and particularly better understanding of the complex physicochemical phenomena underlying the operation of electrochemical detection, have resulted in a steady and encouraging progress. The purpose of this review was to describe the current analytical methodology and recent applications of HPLC in the field of catecholamine metabolism. Although this discussion is by no means detailed and complete, it, at least, hints at the impact of this technique on biochemical investigations and its future potential in clinical laboratories.

Catecholamines in head and body blood of eels and rats

1. When compared with other vertebrates, the circulating titers of norepinephrine and epinephrine of the yellow eel are very low. 2. The ratio of the catecholamine titers in the eel differs from that reported for other vertebrates. 3. Following decapitation, the titers of the catecholamines are higher in head blood than in body blood of both unanesthetized and anesthetized eels. In decapitated rats, only the dopamine titer is higher in head blood. 4. As in the lamprey, agitation stress causes a drop of circulating catecholamines. However, other forms of stress cause the expected increase. 5. It appears that many data on catecholamines in both brain and circulation of vertebrates in general have been influenced by stress effects.

Catecholamine levels and turnover during aging in brain regions of male C57BL/6J mice

A radioenzymatic assay is described for measuring brain catecholamines (CA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the same tissue extract. The [3H]-methylated products are differentially extracted and then acetylated by acetic anhydride, followed by thin layer chromatography in non-basic solvents. Routine sensitivity is 3-5 pg per sample. This assay gave CA levels in brain regions which generally agreed with previous reports. CA levels/mg protein and turnover (after injection of a-methyl-p-tyrosine) were measured in male C57BL/6J mice at various ages between 4 and 30 months, the average lifespan of male C57BL/6J mice. No region showed progressive age changes in levels or turnover, or changes before midlife, 8-12 months. Brain regions with no evidence of age changes include globus pallidus, zona incerta, substantia nigra, cerebellum, and olfactory bulbs. Small changes (10-25%) were detected in only some regions of mice aged greater than or equal to 24 months; few changes were statistically significant. CA levels and turnover decreased in some samplings of striatum and median eminence-arcuate nucleus. In contrast, DA levels increased in anterior pituitary and possibly in medial preoptic region. DOPAC levels (measured only in rostral striatum) decreased by 20% at 28 months. These results diverge from the larger, progressive decreases of DA reported in human striatum during aging.

Alteration of acetylcholine synthesis in mouse brain cortex in mild hypoxic hypoxia

Acetylcholine synthesis in four brain regions (cerebral neocortex, hippocampus, septum and striatum) of the mouse during mild hypoxic hypoxia was measured by using [U-14C]glucose and [2H4]choline. At the same time, concentrations of norepinephrine and dopamine in four brain regions (cerebral neocortex, hippocampus, striatum and hypothalamus) were also estimated. During 12% O2 hypoxia, concentrations of acetylcholine in the striatum were significantly decreased (P less than 0.05), whereas [2H4]acetylcholine, lactate and glucose did not alter in any regions studied. During 12% O2 hypoxia, concentrations of choline and [2H4]choline were significantly increased in all regions examined (P less than 0.05), except the [2H4]choline inthe striatum. Radioactivity (dpm/100 mg protein) and specific activity (dpm/nmol) of acetylcholine were significantly decreased in the cerebral neocortex, hippocampus and septum (P less than 0.01) during 12% O2 hypoxia. A particularly marked decrease was found in the hippocampus, strongly suggesting that cholinergic terminals are particularly sensitive to hypoxia. In addition, these data also suggest that the acetylcholine synthesis from glucose might be more sensitive to hypoxia than that from choline. During 12% O2 hypoxia, concentrations of catecholamine did not alter in any regions examined, whereas during 9% O2 hypoxia dopamine was significantly decreased in the cerebral neocortex and hippocampus (P less than 0.05).

Effect of microwave irradiation on brain tissue structure and catecholamine distribution

Recently we reported regional levels of norepinephrine and dopamine in rat brain following microwave irradiation. In our report, we also compared these levels with those of norepinephrine and dopamine following decapitation. Catecholamine levels following exposure to microwave irradiation significantly increased in several areas. However, whether these increases resulted from compound transfer associated with tissue disruption due to high intensity microwave irradiation was not determined. Sections of corpus striatum and locus coeruleus were examined with a light microscope and the interface of the striatum and the cortex showed no trace of tissue breakdown. Transformed cells, vacuolation, and indications of pyknotic degeneration in the nucleus were found in locus coeruleus after irradiation, but the shapes of these cells were well-defined. Electron microscopic photographs of synapses in the same area showed membrane damage after exposure for 5 s at 1.3 kW, but synaptic vesicles were clearly defined. It was concluded that the increased catecholamine levels were not the result of tissue disruption following rapid heating of the brain by irradiation.