Cyclic AMP in brain areas: effects of amphetamine and norepinephrine assessed through the use of microwave radiation as a means of tissue fixation

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.

Methodological variables during analysis of in vivo cerebellar cyclic GMP, an indirect marker of nitric oxide release

In light of the recent recognition of the physiological significance of nitric oxide, there is considerable interest in the methodological variables that can confound the results of the cerebellar cGMP analysis from in vivo experiments. In this study, using male Swiss Webster mice, the effect of such methodological variables as 1) weight of the animals; 2) tissue extraction procedures used in radioimmunoassay for cGMP; and 3) the commercial source of the assay kit on, harmaline-, pentylenetetrazole- or SNAP-induced increase in cerebellar cGMP in vivo were evaluated. Results indicate that mice in the 15- to 19-g weight range are most sensitive and best suited for in vivo drug effects on cerebellar cGMP. Furthermore, for the extraction of cerebellar cGMP, use of ice-cold 0.5N hydrochloric acid and subsequent dilution of the sample in assay buffer is the simplest and fastest method. Present data also indicate that the source of the radioimmunoassay kit has a significant effect on the cerebellar cGMP results. Based on the present results, the protocol developed and the guidelines drawn are timely and of high practical significance for research in the area of pharmacology of nitric oxide.

Effects of acute and continuous administration of morphine on the cyclic AMP response induced by norepinephrine in rat brain slices

Pre-incubated cortical brain slices from adult male Sprague Dawley rats when challenged by exogenous norepinephrine (NE) exhibited a dose-dependent increase in the level of endogenous cyclic 3',5' adenosine monophosphate (cyclic AMP), with the maximal response elicited at 50 microM NE concentration. The administration of 50 mg/kg sub-cutaneous (Sub-Q) morphine 5 minutes before sacrifice significantly increased the responsiveness of the brain slices to the NE-induced cyclic AMP response at 0.5, 5.0, and 50.0 microM NE. Sustained administration of morphine from the subcutaneously implanted morphine pellet (75 mg morphine base) attenuated the potentiated cyclic AMP response to NE in the brain slices of the rats exposed to a single challenge dose of 50 mg/kg (Sub-Q) morphine 5 minutes before sacrifice. This tolerance or attenuated response is first observed 24 hours after morphine pellet implantation with maximal tolerance observed at 48 hours after the pellet implantation. A complete reversal of attenuated NE-induced cyclic AMP response was observed when the 3 day morphine implanted rats were injected with a challenge dose of naloxone (4 mg/kg, Sub-Q) at 10 minutes prior to the acute administration of 50 mg/kg Sub-Q injection of morphine 5 minutes before sacrifice. These results suggest that both acute and prolonged administration of morphine alters NE-induced cyclic AMP response of the brain slices, and that naloxone, an opioid antagonist, reverses this response. This is perhaps due to morphine-induced alterations in the availability of NE in the CNS.

Calcium regulation of pigment transport in vitro

Calcium has been implicated in the regulation of many cellular motility events. In this study we have examined the role of different Ca2+ concentrations on the in vitro transport of pigment within cultured chromatophores. Cells treated with Brij detergent for 1-2 min were stripped of their plasma membranes, leaving their cytoskeleton and associated pigment granules exposed to the external milieu. We found that retrograde pigment transport (aggregation) is induced upon addition of 1 mM MgATP2- with 10(-7) M free Ca2+, while an orthograde transport (redispersal) of pigment results from lowering the concentration of free Ca2+ to 10(-8) M while maintaining 1 mM MgATP2-. These Ca2+-regulated movements are ATP dependent but are apparently independent of cAMP and insensitive to calmodulin inhibitors. The observations reported here provide novel evidence that the concentration of free Ca2+ acts to regulate the direction of intracellular organelle transport.

Possible mechanism of rubidium-induced hyperactivity in the rat

This study suggests that replacement of intracellular potassium by rubidium ions might lower the resting membrane potential. Thus rubidium-treated rats were more responsive to depolarizing influences and generated more cyclic AMP in the brainstem and consequently the behavioral changes.

Dopamine diffusion after microwave fixation at 986 MHz

It has been previously demonstrated by us that microwave irradiation at 2450 MHz causes diffusion of dopamine from rat brain regions of high dopamine concentration to contiguous regions low in dopamine. Because we have found that the heating pattern at 986 MHz is opposite to that seen at 2450 MHz, we attempted in the present study to eliminate DA diffusion by heating at 986 MHz. However, dopamine levels were elevated in frontal and parietal cortex, remainder of cortex, and amygdala after sacrifice by microwave irradiation at 986 MHz. Norepinephrine levels were unaffected by sacrifice method. Microwave-induced diffusion of certain substances must be considered in the interpretation of regional neurochemical data.

Endogenous phosphorylation in vitro: differential effects of brain state (anesthesia, post-mortem) on electrophoretically separated brain proteins

In vitro phosphorylation of rat cerebral cortex synaptosomes was measured in animals that had been acutely treated with sodium pentobarbital. [32P]Labelled phosphoproteins were separated by SDS-slab gel electrophoresis, and the autoradiographs were analyzed by densitometry. We report here that Band F of our previous reports can be separated into two components, F1 and F2, using an improved gel system. This separation is particularly relevant in this report since these components appear to be differentially sensitive to the manipulations used. Specifically, we found that while F1 phosphorylation was markedly diminished by deep barbiturate anesthesia, F2 was relatively stable. While phosphorylation of F2 was also stable 24 h post-mortem, Band F1 phosphorylation was no longer detectable. Finally, while osmotic shock treatment of synaptosomes reduced phosphorylation of F2 somewhat, it eliminated the in vitro phosphorylation of Band F1. We found that under light barbiturate anesthesia, just at the time when the animals lost the righting reflex, the in vitro phosphorylation of Bands D (MR 78,000--80,000 daltons), F1 (MR 47,000--49,000) and F2 (MR 40,000--45,000) increased relative to unanesthetized controls. The in vitro labelling of Bands D and F1 was depressed in tissue prepared from animals that were deeply comatose. These effects of pentobarbital were more pronounced when animals were sacrificed by liquid nitrogen immersion, rather than by decapitation. Cyclic AMP-dependent phosphorylation of Band D exhibited remarkable stability 24 h post-morten (7 days in one case), even when brain tissue was left at room temperature (21--23 degrees C). Phosphorylation of Band F1, however, was not detectable in post-mortem tissue. The results of these studies indicate that phosphorylation of Band F1 is: (1) sensitive to pentobarbital, and (2) unstable post-mortem. Previous findings from our laboratory suggest that Band F1 is: (3) increased in phosphorylation in liquid nitrogen P2 preparations, and may be (4) cAMP-independent, (5) rapidly turning over its phosphate in vivo, and (6) altered by a training experience. Other evidence suggests that: (7) Band F1 phosphorylation may be Ca2+-dependent and that: (8) its phosphorylation is sensitive to osmotic lysis of synaptosomes. The results suggest an important and perhaps unique role for Band F1 in neuronal function.

A simple method for sampling murine pulmonary and cardiac tissues for analysis of cyclic nucleotide levels

A simple method for the rapid removal and freezing of mouse cardiac and pulmonary tissues is described. Samples thus obtained were judged to be suitable for valid estimation of in vivo levels of cyclic AMP and cyclic GMP based on the following findings: (a) the samples could be obtained and frozen in the very short time period of a few seconds; (b) no indication of adverse effects of the collection procedure was found upon examination of chemical indicators of energy metabolism; (c) the apparent rates of change of cyclic AMP and cyclic GMP levels during the first seconds after tissue isolation could produce small, but acceptable errors; and (d) dose-dependent elevations of pulmonary cAMP levels consistent with known effects in vitro were found after in vivo administration of isoproternol.

Rapid microwave fixation of rat brain

A new microwave device which inactivates brain enzymes rapidly and uniformly is described. From the results obtained with microwave irradiation at two power levels (0.8 kW and 4.5 kW), it has been demonstrated that the high power microwave irradiation has several advantages over the low power irradiation. In its application to neurochemical studies, significant increase in the DOPAC level was found in the irradiated brain, while there were no statistical differences in the levels of NE, DA, 5-HT and 5-HIAA between microwave irradiation and decapitation. Significant increase in the Ach level and marked reduction of the choline level were observed after microwave irradiation. There were no significant differences in the level of cyclic GMP in the brain between the two methods of sacrifice, while significant reduction of the cyclic AMP level was observed in the irradiated brain.

Changes in receptor sensitivity of the cerebral cortex and liver during chronic ethanol ingestion and withdrawal

The evidence was reviewed supporting the noradrenergic sub- and supersensitivity hypothesis of ethanol withdrawal pathogenesis. New data indicates that the cAMP generating system linked to noradrenergic receptor sensitivity is in a steady state in the brain during ethanol withdrawal since the cAMP levels were not different from controls in vivo. Propranolol blocking experiments indicated the beta-adrenergic receptor is a necessary link in the increased cAMP response induced by ethanol withdrawal. The changes in sensitivity observed in the ethanol withdrawn rats were reproduced by acute and chronic reserpinization.

Effects of narcotic analgesic drugs on the cyclic adenosine 3',5'-monophosphate-adenylate cyclase system in rat brain

1. The concentrations of cyclic adenosine 3',5'-monophosphate (cyclic AMP), measured in discrete brain areas removed from rats killed by microwave irradiation, rose transiently in most areas after the administration of morphine. The most pronounced changes, however, were found 2 h after doses of either 10 or 60 mg/kg morphine when cyclic AMP levels declined significantly in the hypothalamus, medulla and cerebellum. In morphine-tolerant rat brains there were no decreases in cyclic AMP levels. 2. Basal adenylate cyclase activity in crude nerve-ending fractions from discrete areas of rat brain was unaffected by the addition of active analgesic agonists, antagonists or inactive isomers to the assay medium in vitro, except for a nonspecific inhibition at drug concentrations of 1 mM. 3. The acute administration of morphine or levorphanol, but not dextrorphan produced transient increases in basal cyclase activity of crude nerve-ending preparations from midbrain and striatum. In morphine-tolerant rats, these changes in basal adenylate cyclase activity were no longer seen.

Effects of arecoline and cholinesterase inhibitors on cyclic guanosine 3',5'-monophosphate and adenosine 3'.5'-monophosphate in mouse brain

In mice, Arecoline in vivo dose-dependently increased the cGMP concentrations of the cerebellum and the "cereberum" (= parts of cortex, hippocampus, hypothalamus, thalamus, striatum and midbrain) without influencing thecAMP levels. The cholinesterase inhibitors paraoxon and physostigmine caused an elevation only in "cerebrum", whereas the cGMP content of the cerebellum even decreased. Pretreatment with atropine prevented the rise in cGMP levels as well as the symptoms of cholinergic stimulation elicited by arecoline or paraoxon. Diazepam reduced cGMP levels below control values and blocked the effect of arecoline, while typical symptoms due to arecoline, e.g., tremor and salivation remained unaffected. The tripeptide prolyl-leucyl-glycinamide (MIF) had no effect on either cGMP values or the peripheral signs of cholinergic stimulation elicited by arecoline. The results show that elevation of cGMP in the central nervous system caused by cholinomimetic agents can be prevented not only by cholinolytics, blocking muscarinic receptors but also by influencing other mechanisms to be discussed.