Scanning-integrating cytophotometric analyses of brain neuronal RNA and acetylcholinesterase in acute soman toxicated rats

Effect of soman intoxication on the organization of rat brain ribosomes and the translational activity of mRNA in a cell-free system

The effect of soman on rat brain ribosomes organization and translational activity of mRNA in cell-free system was studied in rats exposed to 1.3 LD50 soman (120 micrograms/kg body weight) and in rats repeatedly injected with 0.4 LD50 soman (35 micrograms/kg). Fifteen minutes after the injection of 1.3 LD50 soman the heavy polyribosomal fraction from rat brain was found to be enriched and translational activity of mRNA was enhanced. In rats administered five injections of 0.4 LD50 soman at 24-h intervals, the low density ribosomes appeared as the predominant fraction whereas the activity of mRNA in all cell-free system was significantly impaired. It is concluded that soman intoxication expresses a stimulatory or inhibitory effect on the processes of protein synthesis in the rat brain, depending on the dose schedule of soman administration.

Effects of oxotremorine on neuronal RNA and chromatin in thalamic cholinoceptive sites

Neuronal nucleic acid responses were examined within the rat thalamic ventrobasal nuclear complex (VBC) and nucleus reticularis (NR) following single intraperitoneal injections of the central muscarinic-cholinergic (M2) receptor agonist oxotremorine (0.1, 0.7, or 1.0 mg/kg). After stoichiometric azure B and Feulgen staining of brain sections, scanning-integrating cytophotometry was used to quantify azure B-ribonucleic acid (RNA) content, Feulgen-DNA levels, and changes in the susceptibility of chromatin to Feulgen acid hydrolysis (F-DNA yield) of neurons on an individual basis. Changes in neuronal nucleolar volume were also determined histometrically. Within the VBC, oxotremorine produced marked dose-dependent elevations in neuronal RNA content and nucleolar volume with increased F-DNA yield (chromatin activation) in a proportion of VBC neurons. In contrast, within the NR, oxotremorine elicited reductions in RNA levels, F-DNA yield and nucleolar volume. The data demonstrate that oxotremorine-induced central muscarinic receptor stimulation is associated with metabolic correlates of thalamic VBC neuroexcitation and NR neuron depression. The overall study lends further credence to the hypothesis that muscarinic-cholinergic mechanisms are operative within the mammalian thalamus.

Brain neuronal chromatin responses in acute soman intoxicated rats

Male Sprague-Dawley rats (200 g) were injected subcutaneously with soman, a potent neuronal acetylcholinesterase (AChE) inhibitor, at doses of 0.5, 0.8 and 1.0 LD50 (1 LD50 = 135 micrograms/kg) before decapitation at 1 and 24 h post-exposure. Correlative data were obtained on the severity of brain AChE inactivation and physicochemical changes in nuclear chromatin of cerebrocortical (layer V) and striatal neurons using Feulgen-DNA (F-DNA) cytophotometry and ocular filar micrometry. Decreased lability of neurons to F-DNA acid hydrolysis (reduced F-DNA yield), nuclear shrinkage and chromatin aggregation (decreased chromophore area) were used as indices of suppression of genomic template activity; conversely, increases in F-DNA yield and chromophore area signify enhanced neuroexcitation. At 1 hr post-soman there was a dose-dependent inactivation of AChE with a moderate increase in chromatin activation, i.e., nuclear hypertrophy and chromatin dispersion. At 24 hr post-soman there was a partial restoration of AChE activity, notably in striatal neurons, with a suppression in chromatin template activity. These data indicate that actions of soman on neuronal functioning are time-dependent. The absence of any dose-related neuronal chromatin changes may signify existence of non-cholinergic mediated events.

Quantitative cytophotometric analysis of brain neuronal RNA and protein changes in acute T-2 mycotoxin poisoned rats

Male Sprague-Dawley rats (200 g) injected intraperitoneally with T-2 toxin, a trichothecene mycotoxin protein synthesis inhibitor, at dosages of 0.75, 1.0, 1.5 and 6.0 mg/kg (1 LD50 = 0.9 mg/kg) were decapitated at 8 hr post-exposure. Data were obtained on changes in neuronal (perikaryal) RNA levels, protein contents and nucleolar volumes in cerebrocortical (layer III) and striatal (caudate-putamen) brain regions using quantitative azure B-RNA and Coomassie-protein cytophotometry and ocular filar micrometry. Correlative observations were made on changes in brain cytomorphology. Reductions in neuronal RNA/protein contents and nucleolar volume were used as indices of impaired perikaryal functioning. At 8 hr after T-2 toxin poisoning the following results were obtained in cerebrocortical and striatal brain compartments: neuronal RNA contents were generally maintained at control values in both brain regions, however, moderate RNA depletion was evidenced in the cerebral cortex with 1.5 mg/kg T-2 and in the striatum with a 6.0 mg/kg dose; neuronal protein levels were suppressed in a dose-dependent fashion within the cerebrocortex, while in the striatum there was no direct correspondence between protein loss and T-2 dosage; neuronal nucleolar volumes were typically maintained at control levels in both neuronal compartments. Microscopic observations revealed no gross evidence of T-2-induced brain cytopathology. These data indicate that T-2 toxin does not elicit direct cytopathic actions in these two brain regions, thus indicating that cerebrocortical and striatal compartments do not represent primary target sites of T-2 toxicant action.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of HI-6 and pralidoxime on neuronal RNA in thalamic cholinergic sites

Quantitative azure B-RNA cytophotometry was employed to compare effects of the oximes HI-6 and pralidoxime (2-PAM) to those of atropine sulfate (AS) on neuronal RNA metabolism in the thalamic ventrobasal nuclear complex (VBC) and nucleus reticularis (NR). The ability of these compounds to mitigate soman (pinacolyl methylphosphonofluoridate)-induced neuronal RNA alterations (i.e., VBC-RNA depletion/NR-RNA elevation) in these muscarinic cholinergic sites was also determined. Generally, HI-6 (125 mg/kg, i.p.) and 2-PAM (43.2 mg/kg, i.m.) elicited similar patterns of neuronal RNA changes, i.e., diminution of VBC-RNA and NR-RNA with oximes alone; partial amelioration of soman (1.5 LD50, s.c.)-induced VBC-RNA loss; and slight or no effect on soman induced NR-RNA accumulation. HI-6 produced more severe RNA reduction than 2-PAM in both brain regions of non-poisoned rats, whereas 2-PAM was more effective in reversing the effects of soman in these two regions. The muscarinic antagonist, AS, also produced VBC-RNA depletion and partially counteracted the VBC-RNA loss in soman intoxicated rats. Unlike the oximes, however, AS resulted in NR-RNA accumulation and it also antagonized soman induced NR-RNA elevation. Neither oxime reactivated soman inhibited brain acetylcholinesterase but HI-6 did reactivate appreciable plasma cholinesterase. The overall data suggest that HI-6 and 2-PAM do exert pharmacologic actions on cholinergic neurons in the rat CNS. However, the greater effectiveness of HI-6 over 2-PAM in countering lethal actions of soman does not appear to be correlated with oxime mediated restoration of neuronal RNA levels in these two cholinergic regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocortical metabolism and plasma corticosterone in soman intoxicated rabbits

The organophosphate neurotoxin soman produced impairments in adrenocortical RNA and protein metabolism. Fasciculate and reticular cell RNA and protein contents were suppressed with sublethal to acutely lethal dosages (20, 30 and 40 micrograms/kg, s.c.) during the acute excitatory phase of intoxication and at 6-8 h post injection. All three dosages produced ca 90% inactivation of plasma cholinesterase. A transient elevation of plasma corticosterone occurred with 20 micrograms/kg soman whereas there was a protracted increase with 30 micrograms/kg. Corticosterone was not significantly elevated with 40 micrograms/kg, but death occurred at 13 +/- 4 min. Thus, the magnitude and/or nature of soman-induced metabolic impairments does not appear to prevent adrenal activation.

Effects of diazepam on soman-induced brain neuronal RNA depletion and lethality in rats

Studies were conducted to determine effects of the benzodiazepine anticonvulsant diazepam on soman induced brain neuronal RNA depletion and lethality in rats. Quantitative azure B-RNA cytophotometry was used to monitor RNA responses of cerebrocortical (layer V) and striatal neurons following dosages of 0.5, 0.9 and 1.5 LD50 soman (LD50 = 135 micrograms/kg, sc), whereas mean time of death and 24-h survival following 0.8, 1.2 and 1.5 LD50 were used to assess the antidotal efficacy of diazepam (2.2 mg/kg, im) pretreatment. Soman produced dose-dependent RNA depletion in both brain regions. This RNA impairment was almost completely prevented by diazepam, although neuronal RNA contents were generally slightly lower than corresponding control values. However, diazepam pretreatment was not associated with any change in mean time of death or in 24-h survival. The overall data suggest that excessive neural activity per se may underlie the genesis of soman-induced central metabolic impairments, but also appear to effectively dissociate epileptiform activity from lethal actions of soman.

Effects of HI-6 on brain neuronal RNA and acetylcholinesterase: metabolic responses during acute soman intoxication

Quantitative cytochemical techniques were used to monitor effects of the bis-pyridinium oxime HI-6 with and without atropine sulfate (AS) on soman-induced cerebrocortical (layer V) and striatal neuron RNA and acetyl-cholinesterase (AChE) impairments. In addition, plasma cholinesterase (ChE) activity was measured to determine the extent of peripheral enzyme reactivation. Antidotal pretreatment effected complete (HI-6) or partial (AS) amelioration of neuronal RNA depletion evidenced following 1.5 LD50 (195 micrograms/kg) soman, whereas combined HI-6 + AS treatment only partially restored (cortical) or did not change (striatal) neuron RNA contents. HI-6 produced appreciable plasma ChE reactivation but brain AChE activity was not significantly altered. In rats treated only with antidotes, HI-6 or AS alone significantly reduced neuronal RNA in both brain regions. These data indicate that HI-6 influences the metabolic status of central cholinergic compartments and can completely protect against soman-induced neuronal RNA depletion. However, there are no precise relationships among RNA restitution, AChE reactivation or the protective potency of antidotal treatments. Effects of HI-6 on neuronal RNA may signify central cholinolytic activity in vivo, but indirect effects mediated by peripheral mechanisms can not be excluded at present.

Cytophotometric analyses of thalamic neuronal RNA in soman intoxicated rats

Quantitative azure B-RNA cytophotometry was used to monitor metabolic responses of individual neurons within the ventrobasal nuclear complex (VBC) and nucleus reticularis (NR) of the rat thalamus following administration of soman (0.5, 0.9 or 1.5 LD50, sc). A dose-dependent depression in brain acetylcholinesterase (AChE) was evidenced. With respect to thalamic RNA responses, a complex pattern of RNA alterations was evidenced, with these two regions generally exhibiting opposite patterns of dose-related RNA changes. With sub-lethal dosages of soman, RNA accumulation was evidenced in the acetylcholine (ACh) mediated excitatory VBC region and RNA depletion in the ACh mediated inhibitory NR neurons. With a lethal dose, an opposite RNA response pattern was observed in both thalamic regions. It is postulated that the observed RNA response pattern with sub-lethal dosages of soman is what one would anticipate with cholinergic brainstem reticular formation activation. The absence of such a response with lethal doses strongly suggests some disruption of functional excitatory cholinergic activity and perhaps also an impairment of inhibitory cholinergic synaptic activity.

Soman toxication in hypoxia acclimated rats: alterations in brain neuronal RNA and survival

Effects of prior hypoxia acclimation (14-day at 380 mm Hg) on soman (pinacolyl methylphosphonofluoridate) induced brain neuronal RNA and acetylcholinesterase (AChE) depletion and lethality were monitored in rats following their return to ambient oxygenation. Quantitative cytochemical techniques were used to measure RNA and AChE changes in individual cerebrocortical (Layer III) and striatal (caudate plus putamen) neurons. In ambient Po2 controls, soman eventuated in a moderate diminution of neuronal RNA in both brain regions and severe, dose-dependent suppression of AChE activity. Hypoxia acclimation per se induced RNA alterations as manifested in cortical RNA depletion and increased variability of striatal neuron RNA contents. In hypoxia acclimated rats, the extent of neuronal RNA depletion following soman injection was attenuated in both brain regions, yet there were no discernible differences in saline control AChE levels or in the extent of soman-induced AChE inhibition in ambient control versus hypoxia acclimated treatment groups. Hypoxia acclimated rats, however, were found to be even more susceptible to lethal actions of soman as assessed using 24- and 48-hour survival following a three-point treatment regimen. These data indicate that while compensatory systemic and central metabolic adjustments associated with 14d acclimation to reduced oxygen availability may retard soman-induced neuronal RNA depletion, resistance to lethal or near-lethal soman exposure is not enhanced. It is postulated that hypoxia acclimation is associated with complex adaptive and maladaptive neurophysiological alterations influencing CNS responsiveness to soman toxication, and that detrimental consequences exceed protection afforded by metabolic adaptation.

Nuclear chromatin changes in hepatocytes of soman treated rats

Cytochemical and morphometric indices of DNA metabolism and nuclear transcriptional-translational capabilities were used to monitor liver responses in Sprague-Dawley X Wistar rats subcutaneously injected with 0.9 LD50 soman, a highly toxic acetylcholinesterase-inhibiting organophosphate. Thirty minutes post-soman the following were evident: (1) increased polyploidization; (2) expansion of the nuclear envelope; and (3) elevated deoxyribonucleoprotein (DNP) complex lability to acid hydrolysis. Nuclear changes were accompanied by cytoplasmic correlates of impaired hepatocyte function, i.e., vacuolation and depressed basophilia. The overall data suggest that with acute soman toxication there are concomitant adaptive and maladaptive responses occurring within liver parenchymal elements. It is postulated that nuclear changes represent an early proliferative response and DNP activation to enhance detoxification capabilities, whereas cytoplasmic changes reflect the disruption of normal function and hepatotoxic injury.

Brain neuronal RNA metabolism during sustained low-level soman toxication

Quantitative azure B-RNA cytophotometry was used to monitor metabolic responses of cholinergic elements of the rat brain during sustained low-level administration of soman (0.25-0.50 LD50, sc). RNA contents of caudate and cerebrocortical (Layers III and V) neurons were measured 60 min following 1-5 soman dosages given at 24 h intervals. Marked and progressive RNA depletion was evidenced after 1-4 soman injections, whereas partial or complete restitution of RNA levels was observed following the fifth injection. These data indicate that repetitive soman toxication is associated with metabolic correlates of impaired rather than accentuated activation of CNS cholinergic systems, and that tolerance is developed to CNS actions of the agent. It is postulated that impaired neuronal activation is related to soman or ACh-induced transmission block, and that the same adaptive processes responsible for recovery during acute poisoning may underlie the development of tolerance during repetitive administration of organophosphates.

Brain neuronal RNA metabolism during acute soman toxication: effects of antidotal pretreatments

Effects of various antidotal treatments on neuronal RNA contents and on soman induced RNA and acetylcholinesterase (AChE) depletion were monitored using quantitative cytochemical techniques. In rats only with antidotes, atropine depressed whereas pralidoxime (2-PAM) elevated RNA contents of both caudate and cerebrocortical (Layer V) neurons. Soman produced a virtually complete inhibition of AChE activity and a moderate decline in neuronal RNA contents. Atropine pretreatment partially restored neuronal RNA levels. Atropine + 2-PAM prophylaxis eventuated in a complete restoration of RNA levels but no reactivation of AChE. Addition of physostigmine to the atropine + 2-PAM treatment regimen resulted in appreciable AChE reactivation but reduced RNA levels. The overall data indicate that: (1) soman-induced neuronal RNA depletion can be completely reversed by antidotal pretreatments; (2) no precise relationship exists between the extents of antidote-induced restoration of RNA and AChE levels; and (3) 2-PAM exerts marked effects on the brain neuronal network which are unrelated to AChE reactivation. It is postulated that effects of soman and antidotes on neuronal RNA metabolism may signify alterations in acetylcholine (ACh) sensitivity and that pharmacologic manipulation of ACh responsiveness during organophosphate cholinesterase poisoning may be a mechanism for additional therapeutic intervention.