Biomedical subjects

T N Smolen

Publications and source records attributed to T N Smolen.

At least 19 recordsLinked to original sources

PubMed1993

Alterations in regional brain GABA concentration and turnover during pregnancy.

During pregnancy, mice are more susceptible to flurothyl-induced seizures than are nonpregnant control mice. The potential role of brain GABA in mediating this behavior was examined in the present study. GABA concentrations in the cerebellum, hippocampus, striatum, midbrain, and cortex from individual control, pregnant (days 17-18) and delivery-day Heterogeneous Stock mice were assayed using a fluorometric method. Turnover of GABA was assessed by inhibiting metabolism with aminooxyacetic acid and measuring GABA accumulation over the next 2 h. Steady-state GABA concentrations decreased significantly from control in all brain regions during pregnancy. Reductions in GABA concentrations were approximately 25-30% in the affected regions. At parturition, GABA concentrations in the cerebellum and cortex returned to control levels, but hippocampal, striatal, and midbrain GABA levels remained significantly depressed. All the indices of GABA turnover--first-order rate constant, half-life, initial rate of synthesis, and turnover rate (product of first-order rate constant and initial concentration)--showed a significant reduction in pregnancy, which was continued through the time of delivery in all brain regions except the hippocampus. Half-life values for GABA increased nearly fourfold in the cerebellum and cortex. These results show that there is a significant alteration in GABAergic systems during pregnancy and parturition. We suggest that the reduction in GABA turnover is a compensatory anticonvulsant mechanism to offset the inherent seizure susceptibility brought about by the reduced level of the major inhibitory neurotransmitter in the brain.

Aminooxyacetic Acid↗

PubMed1993

Testosterone modulation of N-acetylation in mouse kidney.

N-acetylation participates in the biotransformation of hydrazine drugs and arylamine carcinogens to cytotoxic and carcinogenic products. Differences in acetylation capacity expressed in several mammalian species, including humans and mice, are associated with differences in toxicity and carcinogenicity from these chemicals. The present study examines the influence of genotype, age and sex on kidney N-acetyltransferase (NAT) activity in C57BL/6J (B6) and A/J inbred mouse strains using p-amino-benzoic acid (PABA) as a substrate. There were no strain differences in kidney PABA NAT activity. However, within these strains, males have greater kidney NAT activity than females. A 2-fold increase in kidney NAT activity of males was evident by 30 days postnatally and persisted into maturity (> 200 days after birth), whereas the kidney NAT activity of females remained unchanged. Castration reduced male kidney NAT to female levels, whereas testosterone replacement restored original levels of activity. Ovariectomized females exhibited the same enzyme activity as intact females. Testosterone increased kidney NAT activity in females, but not in intact males. Estradiol decreased kidney NAT in males, but had no effect on female NAT activity. The data suggest that the increase in kidney NAT activity in male mice that accompanies development is under androgenic control. This idea is further supported by our finding that the kidney NAT activity of androgen-insensitive tfm/y mice is significantly less than the activity of either females or males sharing the same genetic background. These observations may explain, in part, the higher susceptibility of male mice to 2-acetylaminofluorene mutagenicity and carcinogenicity.

4-Aminobenzoic Acid↗

PubMed1990

Strain, sex and developmental profiles of cocaine metabolizing enzymes in mice.

Cocaine is a potent hepatotoxin in laboratory mice, although the cocaine-induced hepatotoxicity (CIH) is due to the action of a metabolite of cocaine. Cocaine can be hydrolyzed by serum cholinesterase (ChE) to inactive products, or be oxidized by hepatic cytochrome P-450 and FAD-containing monooxygenase (FADM). The oxidative pathway is thought to be responsible for production of the hepatotoxic metabolite of cocaine, presumably norcocaine nitroxide. Female mice are much more resistant to CIH than males of the same strain. We have found that immature male mice are as resistant as females to the development of CIH. Males did not show any CIH until the onset of puberty (30 days of age), indicating that the development of CIH in males was under hormonal control. To determine if the major cocaine-metabolizing enzymes were responsible for the regulation of CIH, we measured the activities of ChE, cocaine N-demethylation (CND) and FADM as a function of sex in C57BL/6Ibg and DBA/2Ibg mice 20-21, 30 +/- 1 and 65 +/- 5 days of age. There was a significant sex difference in ChE activity (females higher than males) but no effect of age. Cocaine N-demethylation increased in both males and females with age, but there was no consistent sex difference. Activity of FADM declined in males as a function of age, but remained constant in females. The lack of a consistent correlation between enzyme activities and sex-, strain-, and age-dependent differences in susceptibility to CIH, do not support a regulatory role for ChE, CND or FADM in mediating the hepatotoxic response.

Aging↗

PubMed1990

Developmental expression of cocaine hepatotoxicity in the mouse.

Cocaine may be metabolized either by ester hydrolysis to inactive products or by oxidation via a cytochrome P-450 and FAD-monooxygenase pathway to a hepatotoxic metabolite, presumably norcocaine nitroxide. Mice are the species most susceptible to cocaine-induced hepatotoxicity (CIH), and marked strain differences in response have been found. Female mice are very resistant to CIH, whereas males are susceptible, indicating that hormonal factors may be involved. We treated mice of 5 inbred strains with cocaine at three ages: 20 days (weanling), 30 days (adolescent) and 60 days (adult). The CIH response was assessed by measurement of plasma alanine aminotransferase (ALT) activity 18 hours later. For each of the strains females of all three age groups were resistant to CIH, and males did not begin to develop CIH until approximately 30 days of age. The degree of CIH in 30-day-old males was intermediate between the levels found in 20-day-old males and adult males. These data suggest that the enzyme, or enzymes, responsible for the production of the toxic metabolite are absent, or at very low levels, in female and immature male mice, and that they are either inducible by androgens or are repressed by estrogens or progestins. It is possible that these enzymes may be involved in the production of toxic metabolites of compounds other than cocaine.

Aging↗

PubMed1989

Reproducibility of ethanol elimination rates in long-sleep and short-sleep mice.

Ethanol metabolism was measured in long-sleep (LS) and short-sleep (SS) mice on two occasions separated by 1 week to test for repeatability. Mice were injected intraperitoneally with either 1.5 or 4.0 g/kg ethanol and the linear decline of blood ethanol level was measured. The parameters measured in each animal were linear ethanol elimination rate (EER), peak blood ethanol level, volume of distribution and Widmark ratio (r). Reproducibility was assessed using two statistical methods, paired t tests and Pearson correlations. Paired t tests indicated good reproducibility since the two replicate determinations did not differ significantly from each other. The other widely used indicator of reproducibility, the correlation coefficient (Pearson r) between the two measurements, was nonsignificant in almost every case, indicating poor reproducibility. This occurs because the range of values of EER is fairly narrow; thus, an individual is likely to fall anywhere within that narrow range from one day to the next, and the rank ordering of the individuals may not be maintained. Although parameters such as EER and volume of distribution appear to be reproducible for populations, they may have little or no utility as covariates in genetic analyses of individual differences in response to ethanol.

Animals↗

PubMed1987

Alterations in brain catecholamines during pregnancy.

During pregnancy mice are more susceptible to flurothyl-induced seizures than are non-pregnant controls. The potential role of brain catecholamines in mediating this behavior was examined in the present study. The concentration and turnover of norepinephrine (NE) and dopamine (DA) were measured in hippocampus, striatum, midbrain and cortex in control, pregnant and delivery-day mice. There were no significant changes from control in DA levels during pregnancy and parturition. The turnover of DA was not altered during pregnancy, except for a small increase in turnover rate in the hippocampus. The concentration of NE decreased during pregnancy, and rose at parturition. This effect was most striking in the hippocampus. The turnover of NE was markedly depressed during pregnancy, with the hippocampus again being most affected. These data imply a role for NE, but not DA in the mediation of increased seizure susceptibility during pregnancy.

Animals↗

PubMed1987

Genetic variation in paraoxonase activity and sensitivity to diisopropylphosphofluoridate in inbred mice.

The mechanism underlying genetic variation in the acute and chronic responses of mice to diisopropylphosphofluoridate (DFP) are unknown. We investigated whether variation in metabolism of organophosphates by A-esterase, as exemplified by the enzyme paraoxonase, was correlated to the degree of sensitivity to DFP in four inbred mouse strains. LD50s and plasma paraoxonase were measured in each strain. We observed genetic variation in both of these measures, but there was no significant correlation between the two measures. We conclude that plasma paraoxonase activity does not underlie genetic variation in sensitivity to the lethal effects of DFP in mice since it does not determine the degree of sensitivity or resistance to DFP.

Animals↗

PubMed1987

Cross-tolerance between muscarinic agonists: role of muscarinic receptors.

In order to explore the relationship between response to muscarinic agonists and brain muscarinic receptors, two mouse strains that differ in acute sensitivity (DBA and C3H) were injected chronically with DFP or infused with oxotremorine. Chronic DFP-treated DBA mice were not tolerant to DFP's effects on any measure, but they were cross-tolerant to the effects of oxotremorine on heart rate and body temperature. DFP-treated C3H mice were not tolerant to DFP or cross-tolerant to oxotremorine on any measure. Oxotremorine infusion resulted in tolerance to oxotremorine in both mouse strains, and chronically infused DBA mice were cross-tolerant to DFP on five of the six measures. Oxotremorine-infused C3H mice were cross-tolerant to DFP on two of the measures. These results suggest that genetic factors influence the development of tolerance or cross-tolerance. These genetic factors do not seem to be related to changes in brain QNB binding. Both mouse strains showed comparable changes in QNB binding following chronic DFP and oxotremorine with DFP eliciting reductions in QNB binding in striatum and hippocampus and oxotremorine eliciting reductions in nearly every brain region. However, tolerance and cross-tolerance did not seem to correlate with changes in binding which suggests that the relationship between receptor changes and responses to muscarinic agonists must be examined further.

Animals↗

PubMed1987

Sex differences in the recovery of brain acetylcholinesterase activity following a single exposure to DFP.

Male and female C57BL, DBA, and C3H mice were injected intraperitoneally with a single 6.33 mg/kg dose of diisopropylphosphofluoridate (DFP). The time course of recovery of acetylcholinesterase (AChE) activity as well as effects on choline acetyltransferase (ChAT) activity and brain muscarinic and nicotinic receptors were measured. DFP treatment did not affect ChAT activity or the muscarinic and nicotinic receptors. Near control levels of AChE activity were regained in female mice within the first 20 days. However, levels of whole brain AChE activity remained depressed for as long as 40 days following a single dose of DFP in male mice. An analysis of the recovery of AChE activity in several brain regions indicated that control activity was regained in striatum, hindbrain, and hippocampus, but not in cortex, midbrain, and hypothalamus. These data are discussed in terms of potential neurotoxicity induced by a single dose of DFP.

Acetylcholinesterase↗

PubMed1987

Relationship between acute ethanol-related responses in long-sleep and short-sleep mice.

Long sleep (LS) and short sleep (SS) lines of mice were derived from a heterogeneous stock of mice (HS) and have been selectively bred on the basis of the time the animals were devoid of the righting reflex (sleep time) following acute ethanol administration. We have tested a large group of the HS mice for sleep time response to ethanol. Animals were then selected from the extremes of the HS sleep time response and designated short sleep (HS-SS) or long sleep (HS-LS). The ED50 value for loss of righting reflex was compared between these mice (HS-SS and HS-LS) and animals that had undergone 25 generations of selection (SS and LS mice). The ED50 value was not significantly different for the HS-LS (1.9 g/kg) and LS (2.17 g/kg) mice but was markedly different between HS-SS (3.02 g/kg) and SS (4.21 g/kg) mice. The ED50 values for the eight inbred strains that constituted the HS stock ranged only from 2.33 to 2.78 g/kg. The value for LD50 one hour after ethanol administration was found to be 9.03 g/kg and for SS mice 6.94 g/kg for LS mice, in contrast to our previous findings of no difference in LD50 values between SS and LS mice when ascertained 24 hr after the ethanol dose. Since the two lines were selected only for a sleep time difference, a differential sensitivity to other consequences of acute ethanol exposure, such as the lethal dose, would not be expected unless the effects shared a common genetic mechanism of action with ethanol sleep time.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Demonstration of a threshold concentration for ethanol at the time of regaining the righting response in long-sleep and short-sleep mice.

The duration of loss of the righting response (sleep time) is often used to assess central nervous system sensitivity to ethanol. It has been assumed that there is a threshold concentration of ethanol at which an animal will regain the righting response, and that this level should not change with dose or route of administration of ethanol. Five hypnotic doses of ethanol were given to Long-sleep and Short-sleep mice by intraperitoneal injection. At the time of awakening, blood and brain ethanol levels were measured. It was found that within a line, the animals awoke at the same blood and brain ethanol concentration irrespective of the ethanol dose given. The threshold blood ethanol level was 265 mg% for Long-Sleep males and 484 mg% for Short-Sleep males. These results indicate that there is a threshold value for ethanol, and that this threshold is characteristic for a given mouse line.

Animals↗

PubMed1986

Genetic influence on increased seizure susceptibility in pregnancy.

In previous studies we have reported that flurothyl-induced clonic seizure threshold was significantly reduced in pregnant mice. In the present study eight strains of mice were tested for flurothyl seizure susceptibility during pregnancy in an effort to find one which lacked this trait. Latency to myoclonus, latency to clonus, and the interval between these seizures were measured. Two inbred strains, A/Ibg and BALB/cByJ, were resistant to the pregnancy-associated increase in seizure susceptibility. These strains will be used, along with others which show the increased seizure trait, to investigate the neurochemical mechanisms which underlie the increased seizure susceptibility in pregnancy.

Animals↗

PubMed1986

The effect of naloxone administration on pregnancy-associated seizures.

Pregnant mice are more susceptible to flurothyl-induced seizures than are non-pregnant controls. The possibility that the well-known increase in beta-endorphin concentration which accompanies pregnancy was involved in this effect was examined by testing whether naloxone administration could block the increased seizure susceptibility. Pregnant female, control female and male C3H mice were treated with 5-50 mg/kg naloxone 5 min before flurothyl seizure testing. Naloxone markedly increased clonic seizure susceptibility in all three groups at a dose of 50 mg/kg, but had little effect at lower doses. In contrast, naloxone had differential effects on myoclonic seizures in pregnant and control female mice, being anticonvulsant in the controls, but proconvulsant in the pregnant mice. A role for endogenous opiates is unlikely in mediating clonic seizures in pregnant mice, but may be involved in myoclonic seizures.

Animals↗

PubMed1986

Dissociation of decreased numbers of muscarinic receptors from tolerance to DFP.

Several studies have demonstrated that chronic treatment with organophosphates, such as DFP, elicits a decreased number of brain muscarinic receptors (measured by the binding of QNB) which has been presented as an explanation for tolerance to the organophosphates. The purpose of the studies presented here was to assess whether graded changes in QNB binding could be attained following different methods of chronic DFP treatment, and whether tolerance to DFP paralleled these changes. Male DBA mice were injected with DFP every 4 days or 2 days for 30 days or daily for 14 days. The animals were subsequently challenged with DFP or the muscarinic agonist, oxotremorine, and respiratory rate, heart rate, body temperature, Y-maze activity and rearing were recorded. Chronic DFP-treated animals were supersensitive to the effects of DFP on respiratory rate, heart rate, and body temperature whereas a modest tolerance to the effects of oxotremorine on respiratory rate, heart rate, and body temperature was seen. Neither tolerance nor supersensitivity were observed for the effects of DFP and oxotremorine on the Y-maze measures. Chronic DFP treatment elicited reduced binding of QNB in striatum, cortex, and hippocampus with the group that had been treated every other day exhibiting the greatest changes. The changes in drug response did not parallel changes in QNB binding which raises questions as to the cause of the reduction in binding.

Animals↗

PubMed1986

A strain comparison of physiological and locomotor responses of mice to diisopropylfluorosphosphate.

The effects of acute treatment with the organophosphate, diisopropylfluorophosphae (DFP), were studied in three inbred mouse strains. C57BL, DBA and C3H. A battery of physiological and locomotor tests including respiratory rate, heart rate, body temperature, Y-maze activity and rotarod performance was used. Dose-response and time course studies were carried out. Approximately 15 min after injection the animals were markedly affected by the drug with maximal effects occurring approximately 2 hours after injection. Strain comparisons were made at the 2 hr time point. In all strains, males and females were affected about equally except for respiratory rate and rotarod performance in which females were slightly more affected. Strain comparisons revealed that for most of the tests the C57BL mice were most affected by the DFP and the C3H mice were least affected. For the heart rate test the DBA mice were the most sensitive. Previous studies from our laboratory have demonstrated a similar rank ordering of the strains in their responses to oxotremorine and nicotine. The strain differences in response to these agents is not easily explained by differences in number or affinity of brain muscarinic or nicotinic receptors. The genetic influence on cholinergic drug response may involve receptor coupling mechanisms.

Animals↗

PubMed1985

Genetically determined differences in acute responses to diisopropylfluorophosphate.

The acute effects of diisopropylfluorophosphate (DFP) were assessed in DBA/2Ibg, C57BL/6Ibg and C3H/2Ibg mice. The DFP was administered by intraperitoneal injection in saline. Brain acetylcholinesterase (AChE) activity was maximally inhibited within 5 min after injection. All mice showed signs of organophosphate intoxication including salivation, lacrimation, diarrhea, respiratory distress, tremor and, at high doses, seizures. The C57BL mice were most susceptible to these effects of DFP. The LD50 values for DFP were 8.0, 7.6, and 6.8 mg/kg for male DBA, C3H, and C57BL mice, respectively. The LD50 values for females were nearly the same. Body temperature and brain AChE activity decreased in a dose-dependent manner following injections of DFP of 3.17, 4.22, 5.28, and 6.33 mg/kg. Maximum temperature depression occurred 2 hours after DFP administration; by 24 hours temperatures had returned to normal except for C57BL mice treated with the highest dose of DFP. The C57BL strain was most susceptible to the DFP-induced hypothermia, the C3H strain was the most resistant, and the DBA strain was intermediate. Maximum temperature depression and residual AChE activity, as measured 24 hours after injection, were linearly related. These strain differences do not seem to be explained easily by a differential inhibition of AChE activity.

Animals↗

PubMed1985

Recovery of acetylcholinesterase activity after acute organophosphate treatment of CNS reaggregate cultures.

The effect of a single dose of diisopropylfluorophosphate on acetylcholinesterase (AChE) activity was examined in mouse CNS reaggregate cultures. At 17-24 days in culture, reaggregates were treated with 0.6 mg/liter DFP for 15 min. The recovery of AChE activity was examined in culture. After treatment, 5.4 +/- 1.19% of control AChE activity remained. By 24 hr, 31.6 +/- 6.4% of control activity had returned and the recovery of activity was essentially complete by 7 days after treatment. Recovery of AChE activity after DFP treatment required protein synthesis, since there was no recovery in the presence of cycloheximide. After treatment with the reversible inhibitor, physostigmine at 0.5 mg/ml, recovery of AChE activity was complete within 24 hr after treatment. These results indicate that CNS reaggregate cultures not only express differentiated functions of the CNS, but also have the capacity to turn over proteins, and thus may provide a good model system in which to examine mechanisms of toxicity.

Acetylcholinesterase↗

PubMed1984

Effects of ethanol and salsolinol on catecholamine function in LS and SS mice.

Long Sleep (LS) and Short Sleep (SS) mice differ in duration of ethanol-induced sleep time because of differences in brain sensitivity to the depressant effects of alcohols. These lines of mice also differ in their sensitivity to salsolinol, the condensation product of acetaldehyde with dopamine. Some of ethanol's acute effects may be due to salsolinol interactions with catecholamine systems. In the present study, the half-lives of salsolinol were found to be 12.8 min (LS) and 12.3 min (SS). Salsolinol administration resulted in a decrease in brain norepinephrine content in LS but not SS mice. Dopamine levels were not altered by salsolinol. Ethanol or salsolinol, in vitro, inhibited dopamine uptake by striatal synaptosomes. The IC50 values for ethanol were 491 mM (LS) and 514 mM (SS), and for salsolinol, 300 microM (SS). Thus, the mouse line which is most sensitive to the behavioral effects of salsolinol is also most sensitive to salsolinol's effects on norepinephrine levels and inhibition of dopamine uptake. However, much higher concentrations are required to alter dopamine uptake in vitro than are required to alter behavior in vivo.

Animals↗