Biomedical subjects

B Hoskins

Publications and source records attributed to B Hoskins.

At least 73 records · Page 4Linked to original sources

PubMed1987

Effects of cold stress on brain regional calcium content in rats and mice.

The calcium levels of striatum, cerebellum, cortex, medulla and diencephalon from rat brain were significantly reduced after 30 minutes of cold exposure at 8 degrees C even though body temperatures were no different from pre-cold exposure values. Calcium content remained significantly depressed in striatum, cerebellum and diencephalon after 2 hours of cold exposure, at which time body temperatures were significantly depressed. A similar effect of short-term cold stress on calcium content in these brain regions from mice was observed. These results are consistent with a role of calcium in the maintenance of temperature and in adaptive responses to cold environments.

Animals↗

PubMed1987

Sensitivity difference to hepatotoxicity of cocaine in spontaneously hypertensive and Wistar Kyoto rats.

Experiments were conducted to determine the hepatic damage of cocaine in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) rats in terms of serum glutamic-oxaloacetic transaminase (SGOT) activity, liver weight/body weight ratio and hepatic microsomal enzyme activity, i.e., N-demethylase activity or UDP-glucuronyltransferase (GT) activity. In subacute experiments, 2, 4 and 10 daily cocaine treatments elevated the level of SGOT activity and reduced the liver weight/body weight ratio in SHR rats. The ethylmorphine N-demethylase activity and the cocaine N-demethylase activity in SHR rats were significantly greater (31% and 26%, respectively) than those in WKY rats. Ten daily treatments with cocaine diminished the ethyl morphine N-demethylase activity and the cocaine N-demethylase activity in SHR and WKY rats. However, attenuation of 4-nitrophenol GT activity was only observed in SHR rats. In acute experiments, a single dose of cocaine, 40 mg/kg, elevated the SGOT activity in SHR rats and reduced the 4-nitrophenol GT activity in SHR rats, but it did not affect the activities of SGOT and 4-nitrophenol GT in WKY rats. A higher dose of cocaine, 60 mg/kg, elevated the SGOT activity and reduced cocaine N-demethylase activity and 4-nitrophenol GT activity in both SHR and WKY rats. The present studies suggest that N-demethylation of cocaine plays an important role in the hepatotoxicity of cocaine in animals.

Animals↗

PubMed1986

The role of dopamine in behavioral supersensitivity to muscarinic antagonists following cholinesterase inhibition.

The role of brain dopamine (DA) in the enhancement of muscarinic antagonist-induced hyperactivity was investigated. The effects of atropine and scopolamine on the concentrations of DA and its metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), following DFP administration were determined. In control animals, atropine and scopolamine decreased the concentration of DA and increased the ratios of DOPAC/DA and HVA/DA in the striatum, but not in the N. accumbens - T. olfactorium (mesolimbic) area. Following a single dose of DFP, the two antimuscarinic drugs caused decreases of DA and further increases of the above ratios in both brain regions. However, following repeated DFP treatment for 2 weeks, these antimuscarinic drug-induced changes were observed only in the mesolimbic area, but not in the striatum. It is suggested that an increased DA turnover, indicated by elevated DOPAC/DA and HVA/DA ratios, underlies the muscarinic antagonist-induced hyperactivity. The well-known occurrence of muscarinic receptor down-regulation after DFP administration, could be responsible for the enhancement of the actions of muscarinic antagonists in DFP-treated animals. The observed differential effect on DA turnover in the two broad areas may involve both muscarinic and DA receptors.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1986

Lack of effect of dynorphin on consummatory behaviors in obese and normal rats.

The possible role of dynorphin, an endogenous opioid peptide, in the regulation of appetite was studied in male genetically-obese (Zucker) rats and their litter mates of normal weight. Eighteen pairs were divided into 3 treatment groups: control, acutely dynorphin-treated (5 mg/rat), and implanted with Alzet mini-osmotic pumps containing 2 mg dynorphin to be delivered at a rate of 10 micrograms/hr. Body weights and food and water consumption were determined daily for 7 days. Body weights were not significantly changed from initial values for any treatment group. Food and water consumption per 24 hours were generally the same for obese rats and their normal littermates, but in terms of consumption per 100 g body weight, the obese rats generally consumed less food and water. Neither acute nor continuous dynorphin administration affected consummatory levels.

Animals↗

PubMed1986

Correlation of muscarinic receptor density and acetylcholinesterase activity in repeated DFP-treated rats after the termination of DFP administration.

Following chronic exposure to DFP, both AChE activity and muscarinic receptor density were markedly depressed in the rat striatum. The rate of recovery of AChE activity was 5.2% per day within 7 days, while the density of muscarinic receptor recovered at the rate of 1.94% per day. The correlation between 2 parameters was very high (R = 0.99). Thus, it is suggested that the muscarinic receptor density was intimately related to AChE activity.

Acetylcholinesterase↗

PubMed1986

Selective inhibitory effect of organophosphates on UDP-glucuronyl transferase activities in rat liver microsomes.

The effects of acute and subacute administration of diisopropylfluorophosphate (DFP) and acute administration of Soman, Sarin and Tabun on UDP-glucuronyltransferase (GT) activity towards 4-nitrophenol, 4-methylumbelliferone, phenolphthalein and testosterone in rat liver microsomes were investigated. Twenty-four hours after a single injection of DFP, the activity of GT towards 4-nitrophenol and 4-methylumbelliferone was inhibited, and the inhibitory effect continued for 3 days. The activity had recovered by 7 days after injection. The activity of GT towards phenolphthalein and testosterone was not affected at any time after injection. Soman, Sarin and Tabun showed the same effect as DFP after a single injection. After daily DFP injections, the activity of GT towards 4-nitrophenol and 4-methylumbelliferone was decreased to the same level as found following acute treatment with DFP. The in vitro addition of DFP to liver microsomes did not affect GT activity towards 4-nitrophenol. It is suggested that these changes are not due to a direct effect of DFP. Furthermore, the effects of two enzyme inducers on GT activity in the presence and absence of DFP were investigated. In the 3-methylcholanthrene (MC) pretreatment group, DFP inhibited only the GT activity towards 4-nitrophenol and 4-methylumbelliferone. On the other hand, in the phenobarbital (PB) pretreatment group, DFP did not inhibit the GT activity towards 4-nitrophenol and 4-methylumbelliferone. It was also demonstrated that MC pretreatment increased the mortality in the DFP-treated rats but that PB pretreatment suppressed it. These results suggest that DFP and other organophosphorus agents may be useful agents for studies on the heterogeneity of GT.

Androsterone↗

PubMed1986

Effects of maturation and aging on calmodulin and calmodulin-regulated enzymes in various regions of mouse brain.

Components of the calmodulin system (i.e., calmodulin levels and activities of the following calmodulin-dependent enzymes: Ca2+ + Mg2+-ATPase, adenylate and guanylate cyclases, cyclic AMP and cyclic GMP phosphodiesterases, and Ca2+-dependent protein kinase were studied in the following brain regions from immature (25-day-old), mature (3-month-old) and aged (22-month-old) mice: striatum, cortex, cerebellum, diencephalon and medulla + pons. Both maturation and advanced aging were associated with significant changes in calmodulin content and in enzyme activities. The study provides evidence for important changes in the activity of this fundamental cell regulatory system in the brain during the processes of maturation and aging.

Aging↗

PubMed1986

Differences in morphine-induced antinociception and locomotor activity in mature adult and aged mice.

Mature adult (3-6 months old) and aged (24-27 months old) male ICR mice were injected with 10 to 100 mg/kg morphine, SC. The ED50 values for locomotor behavior representing 5 times control activity were 7.5 mg/kg for aged mice and 17.8 mg/kg for the mature adults. There were striking age- and dose-dependent differences in both intensities and durations of morphine-induced locomotor activity. The ED50 values for antinociception 1 hour after morphine administration were 70 mg/kg for the aged mice and 13 mg/kg for the mature adults. One hour after injecting 30 and 100 mg/kg morphine tagged with 3H-morphine, 0.13 and 0.14 percent of the doses appeared in brains of aged and mature adult mice, respectively. Distribution of morphine among brain regions was the same for both age groups. The results suggest that the differences in response to morphine by the two age groups were due to age-related differences in affinities, numbers and/or functioning of opioid receptors and not to pharmacokinetic differences.

Aging↗

PubMed1986

Relationship between the neurotoxicities of Soman, Sarin and Tabun, and acetylcholinesterase inhibition.

Acetylcholinesterase (AChE)-induced chewing movements, tremors, convulsions and hind limb abduction at doses of 50-85% LD50 in rats were monitored in order to determine whether the severity of these different signs would correlate with brain AChE levels and the time course of such a relationship. 30 min after subcutaneous (s.c.) injection of Soman, the intensities of toxic signs were significantly correlated with the degree of striatal AChE inhibition. In the case of Sarin, the corresponding r-values were not significant except for tremors. For Tabun-induced chewing, tremor and hind-limb abduction, the r-values were significant. The neurotoxicity was most intense between 15 min to 2 h after treatment, but at 2 or 6 h, the r-values were well below 0.5. The inhibition of brain AChE was maximal by 30 min and was still high at 24 h.

Animals↗

PubMed1986

Hypersensitivity to antimuscarinic agents following brief exposure to Soman and Sarin.

Behavioral responses to atropine in rats exposed to the potent anticholinesterase agents Soman and Sarin were studied. Atropine itself produced limb-shakes and certain stereotyped activities, in a dose-dependent manner. The neurotoxicity elicited by Soman and Sarin was antagonized by atropine, while at the same time the responses induced by the latter were attenuated. In contrast, where rats were challenged with atropine 6-72 h after giving single doses of Soman or Sarin, the limb-shake myoclonus was markedly enhanced. The atropine-induced stereotypies were not, however, significantly affected, except for an increase seen at 24 h after Sarin treatment. Repeated treatment with Soman for 3 wk also led to similar supersensitivity of atropine-induced responses. The peripheral muscarinic receptor antagonist, methylatropine, produced no such hyperactivity on its own or at any time after anticholinesterase exposure. The rapid occurrence of hypersensitivity to antimuscarinic compounds following exposure to these anticholinesterases, therefore, suggests the need for observation of subjects who are poisoned with such agents and treated with antimuscarinics, for adverse reactions such as myoclonus during the critically sensitive period, especially if repeated antimuscarinic therapy is carried out.

Animals↗

PubMed1986

Acute effects of Soman, Sarin, and Tabun on cyclic nucleotide metabolism in rat striatum.

Rats were injected sc with 120 micrograms/kg Soman, 120 micrograms/kg Sarin or 240 micrograms/kg Tabun. At 15 min, 2 h, or 6 h after administration, animals were decapitated along with saline-treated controls, and striatal activities of nucleotide cyclases and phosphodiesterases and striatal cyclic nucleotide levels were determined. All three agents had two similar effects on rat striatal cyclic nucleotide systems: they all increased cyclic GMP levels 15 min after their administration, and they all decreased guanylate cyclase activity 2 h after administration. There were also some different effects elicited by these three organophosphorus compounds. Different effects of Soman and Sarin seem to be mainly due to their different potencies, which in turn influence the time course of their actions. Tabun is quite different from Soman and Sarin in several respects: it rarely causes convulsions at sub-lethal doses, it has no effects on striatal cyclic AMP levels, and it affects enzyme activities 6 h after its administration. These differences may be due to the presence of cyanide instead of fluoride in its structure: i.e., this may be responsible for the different effects of Tabun on striatal cyclic nucleotide systems, and perhaps other biochemical effects. These results also indicate that other neurotransmitter systems, in addition to the cholinergic system, may be involved in organophosphate-induced toxicity.

Adenylyl Cyclases↗

PubMed1986

Acute effects of soman, sarin, and tabun on microsomal and cytosolic components of the calmodulin system in rat striatum.

Two hours after administration of Soman (120 micrograms/kg, s.c.), Sarin (150 micrograms/kg, s.c.), or Tabun (240 micrograms/kg, s.c.), microsomes and cytosol were prepared from rat striata. Microsomal and cytosolic calmodulin (CaM) levels, microsomal adenylate and guanylate cyclase activities, protein kinase activities, and Ca2+ + Mg2+-ATPase activities were determined while cytosolic phosphodiesterase (PDE) activities were determined. CaM levels in both cell fractions were significantly increased by Soman and Sarin. Cyclic AMP-PDE and adenylate cyclase activities were decreased by Soman and Sarin. All three agents decreased activities of cyclic GMP-PDE and guanylate cyclase. Sarin and Tabun administration caused significant increases in microsomal protein kinase activity and none of the agents affected activity of divalent cation ATPases. The intensity of effects of the three organophosphates roughly paralleled their observed neurotoxic potencies. The results indicate that components of the CaM system are implicated as either causative or adaptive changes induced by these agents.

Adenylyl Cyclases↗

PubMed1986

Regional and subcellular calmodulin content of rat brain.

Calmodulin contents of cortex, cerebellum, striatum, diencephalon, and medulla + pons and of subcellular fractions of each region were determined by radioimmunoassay. The diencephalon had the highest level of calmodulin (48.87 +/- 4.56 micrograms/mg protein), whereas medulla + pons had the lowest level (8.01 +/- 0.84 micrograms/mg protein). In all brain regions, the mitochondrial fraction was richest in calmodulin (from 71 to 227 micrograms/mg protein) whereas other areas contained from 6 to 66 micrograms/mg protein.

Animals↗

PubMed1985

Rapid induction of supersensitivity to muscarinic antagonists-induced motor excitation by continuous stimulation of cholinergic receptors.

Following single or repeated treatment with the irreversible anticholinesterase, DFP or, during infusion of the muscarinic receptor agonist, oxotremorine, and the reversible anticholinesterase physostigmine, effects of challenges with muscarinic antagonists were studied in rats. The antagonists, atropine, scopolamine, benztropine, orphenadrine and trihexyphenidyl induced, to a low degree, limb-shakes (myoclonus) and stereotyped behaviors in normal rats. However, within 24-72 hr after the above pretreatments, this myoclonus was significantly enhanced. The anticholinergic-stereotypies were also increased but only by severe cholinergic pretreatment and at a time later than that for the myoclonus. Myoclonus and stereotypies are known to be produced by treatments which directly enhance serotonergic and dopaminergic activities, respectively. It is suggested that during prolonged cholinergic stimulation, the cholinergic-monoaminergic balance in the brain can be altered depending upon the degree of stimulation. This could be responsible for the observed differential onset of changes in the anticholinergic-behavioral responses, which could, in turn, be mediated by different monoaminergic (serotonin and dopamine) systems.

Animals↗

PubMed1985

Effects of aging and morphine administration on calmodulin and calmodulin-regulated enzymes in striata of mice.

Male ICR mice, young (25-days old), mature (3-months old), and old (22 months), were injected with morphine sulfate (10 mg/kg, s.c.) or were implanted with morphine pellets (75 mg). Controls received saline injections or placebo pellets. One hour after injections and 72 h after pellet implantations, the mice were decapitated and striatal regions were removed for the following analyses: calmodulin (CaM) levels via radioimmunoassay and activities of cyclic nucleotide phosphodiesterases, adenylate and guanylate cyclases, and Ca2+, Mg2+-ATPase. Acute morphine treatment produced the following: (1) increases in calmodulin levels in the young and old mice while having no effect on mature levels; (2) increases in activities of guanylate cyclase of mature mice while decreasing those of the old mice; (3) no effects on activity of adenylate cyclase; (4) decreased activity of cyclic AMP-phosphodiesterase in young mice only; (5) decreased activity of Ca2+, Mg2+-ATPase in the old mice only. The only changes found in striata from morphine-tolerant mice when compared with age-matched controls were elevations in cyclic GMP-phosphodiesterase activities in all three age groups. Differences in control values of the three age groups were as follows: CaM levels, mature greater than old greater than young; Ca2+, Mg2+-ATPase activity, old greater than mature-young. The results indicate age-induced changes in cellular regulation and biochemical responses to morphine.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1985

Studies on low dose sub-acute administration of soman, sarin and tabun in the rat.

The effects of low-dose administration of the organophosphate cholinesterase inhibitors, soman, sarin and tabun, on growth rates over 85 days were studied in rats. Acetylcholinesterase (AChE) activity was determined in the striatum and the remainder of the brain 24 hrs following the last exposure to these agents. Further, the cumulative mortality of daily administration of several doses of soman, sarin and tabun for 25 days was studied. The animals treated with 25 micrograms/kg of soman or sarin for 85 days demonstrated reduced growth rates which returned to control levels after 30 days. The animals which received 50 micrograms/kg of sarin also grew at reduced rates which returned to control levels after 35 days, while the tabun-treated (100 micrograms/kg) animals required 38 days to return to control growth rates. The striatal AChE activity of the soman-treated group was reduced to 36% of control while the AChE activities of the high-dose sarin-treated group were reduced to 66% of control. The striatal AChE activity of the tabun-treated group was only 13% of control. It is suggested that growth rates may be used to monitor the development of tolerance to low-dose administration of organophosphate cholinesterase inhibitors.

Acetylcholinesterase↗

PubMed1985

Variability of neurotoxicity of and lack of tolerance to the anticholinesterases soman and sarin in the rat.

The neurotoxicity and lethality of Soman and Sarin, after single and repeated treatment at 50-60% of their LD50 doses in rats were investigated. Single treatment with Soman (100 micrograms/kg) and Sarin (120 micrograms/kg) produced severe tremors, convulsions and hypothermia, in some rats only, while the others did not show toxicity, i.e. an all or none effect. Soman and Sarin (100-120 micrograms/kg) caused, respectively, 89-93% and 26-48% inhibition of AChE at 6 hr and 56-68% and 17-39% inhibition at 24 h after single injections. Repeated treatment with Soman (90 micrograms/kg) and Sarin (100 micrograms/kg) at 4 day intervals caused variable incidences of neurotoxicity and increasing mortalities, and after ten injections the survival rates were 31 and 54%, and AChE inhibition was 86 and 75%, respectively. It is suggested, that the variable neurotoxicity of and the low tolerance to of these compounds are partly related to peripheral dispositional mechanisms. Furthermore, the profile of toxicity of these anticholinesterase agents should be differentiated from, but not generalized with, that of the other anticholinesterase organophosphates.

Animals↗

PubMed1984

Changes in activities of calmodulin-mediated enzymes in rat brain during aging.

Components of the calmodulin system, (i.e. calmodulin levels and activities of the following calmodulin-dependent enzymes: (Ca2+ + Mg2+)-ATPase, adenylate and guanylate cyclases, cyclic AMP and cyclic GMP phosphodiesterases, and Ca2+-dependent protein kinase) were studied in brains from rats of three different ages: 3 weeks old, 3 months old and 1 year old. With the exception of adenylate cyclase activity, all components measured were found to significantly decrease with increasing age. Adenylate cyclase activity was significantly higher in brains from the 3-month-old rats than in those from 3-week-old rats. Brains from year-old rats had adenylate cyclase activity that was intermediate between the two younger ages and was significantly different from both groups. The study provides evidence for important changes in the activity of this fundamental cell regulatory system in the central nervous system during the aging process.

3',5'-Cyclic-AMP Phosphodiesterases↗