Inhalation studies with the Göttingen minipig

A method for inhalative exposure of minipigs to aerosols and gases has been developed. Minipigs are exposed via mask inhalation to the test substance using a computer-controlled exposure system that permits simultaneous exposure of groups of four animals in parallel to different controlled dose levels. We studied inhalation treatment of verapamil, a cardiovascular drug, and show good absorption and favorable pharmacokinetics when compared with iv drug application. The results shown in this study encourage inhalation studies with the Göttingen minipig.

Time course of brain temperature and caudate/putamen microdialysate levels of amphetamine and dopamine in rats after multiple doses of d-amphetamine

Brain temperature monitoring and microdialysis were performed simultaneously in the caudate/putamen (CPu) of conscious, freely moving rats dosed with d-amphetamine (AMPH). The brain temperature was determined via a thermistor inserted through a microdialysis guide cannula located in the left CPu, while the microdialysis probe was positioned in the right CPu. The peak AMPH and dopamine (DA) levels were reached 40 to 60 min after dosing, while peak brain temperature was not achieved until 20 to 40 min thereafter in rats becoming moderately hyperthermic. Those rats becoming severely hyperthermic (temperatures above 41.0 degrees C) had microdialysate concentrations of AMPH and DA almost 2-fold higher than those with moderate hyperthermia after the second dose of 5 mg/kg AMPH. However, these peaks were not reached until 60 to 80 min after dosing. This was probably due, in part, to the longer half-life of AMPH in the severely hyperthermic group. The changes in brain temperature observed after exposure to neurotoxic doses of AMPH closely paralleled core body temperature changes previously reported during AMPH exposure. Temperature plays an important role in many types of neurotoxicity, and monitoring brain temperature during microdialysis studies can be done continuously, and with less chance of damage to the microdialysis equipment than most of the traditional methods used to measure core body temperature.

Preweaning experience as a modifier of prenatal drug effects in rats and mice--a review

The effects of preweaning experience in rats and mice on neuroendocrine and behavioral end points and their implications for prenatal drug effects are reviewed. The hypothalamo-pituitary-adrenal axis and the dopaminergic system were shown to be affected. Behavior related to hippocampal, adrenocortical functions and to the benzodiazepine receptor system was also modified. Other paradigms (nociception, conditioned taste aversion) exhibited susceptibility to such preweaning manipulations also. The effects of these early experiences seem to be mediated through complex factors including neuroendocrine responses of the pup to hypothermia and a permanent alteration of mother-infant interactions, with subsequent effects on neuroendocrine functions that are important for postnatal brain organization. Studies of interactions between prenatal drug effects and preweaning manipulations have been performed only with ethanol. When extending this work to other compounds, the systems and functions described above may provide some guidance in looking for possible interactions. In most cases the preweaning manipulations alleviated the effects of prenatal ethanol exposure. These findings may have important implications regarding the controversy about environmental influences affecting the outcome of exposure to neurobehavioral teratogens.

d-Fenfluramine produces neuronal degeneration in localized regions of the cortex, thalamus, and cerebellum of the rat

d-Fenfluramine is a potent serotonin (5-HT) reuptake inhibitor/releaser and, until its recent recall, was prescribed as an anoretic agent. This study demonstrates that 10 mg/kg d-fenfluramine i.p., when administered to rats in a warm (27 degrees C) environment, produces neuronal degeneration within select brain regions. Degeneration was detected and localized using a recently developed fluorescent marker of neuronal degeneration, Fluoro-Jade. The most extensive cortical damage was in the anterior cingulate region. In the medial thalamus, degeneration was frequently seen within the intralaminar nuclei, and somewhat less frequently observed within the paraventricular nucleus, the mediodorsal nucleus, and the gelatinosis nucleus. Cerebellar damage occurred primarily in medial Purkinje cells and occasionally in granule cells or basket cells. Degeneration was not observed in either saline-injected control animals or in rats given even higher doses of 25 mg/kg d-fenfluramine but kept in a cooler environment (23 degrees C). The degeneration was clearly most prominent in animals with body temperatures of 41 degrees to 42 degrees C, but this degeneration was not seen in animals given saline that became extremely hyperthermic in a 37 degrees C environment. Behavioral signs such as tremors, myoclonus, rigidity, and splayed legs were seen in all animals with extensive neurodegeneration. The areas damaged by d-fenfluramine, when hyperthermia occurs, could play a role in the expression of the serotonin syndrome. Elevated extracellular 5-HT levels alone are probably not sufficient for neurotoxicity, and additional factors such as hyperthermia, regional specificity of 5-HT receptor subtypes, blood flow, and/or neuronal networks may be involved.

Long-term effects of amphetamine neurotoxicity on tyrosine hydroxylase mRNA and protein in aged rats

Four injections (intraperitoneal) of 3 mg/kg amphetamine (2 hr apart) produced pronounced hyperthermia and sustained decreases in dopamine levels and tyrosine hydroxylase (TH) protein levels in the striatum of 15-month-old male rats. A partial recovery of striatal dopamine levels was observed at 4 months after amphetamine. In contrast, TH mRNA and TH protein levels in the midbrain were unaffected at all time points tested up to 4 months after amphetamine treatment. The number of TH-immunopositive cells in the midbrain was also unchanged at 4 months after amphetamine, even though the number of TH-positive axons in the striatum remained dramatically decreased at this time point. Interestingly, TH-immunopositive cell bodies were observed 4 months after amphetamine in the lateral caudate/putamen, defined anteriorly by the genu of the corpus collosum and posteriorly by the junction of the anterior commissures; these striatal TH-positive cells were not observed in saline- or amphetamine-treated rats that did not become hyperthermic. In addition, low levels (orders of magnitude lower than that present in the midbrain) of TH mRNA were detected using reverse transcription-polymerase chain reaction in the striatum of these amphetamine-treated rats. Our results suggest that even though there is a partial recovery of striatal dopamine levels, which occurs within 4 months after amphetamine treatment, this recovery is not associated with increased TH gene expression in the midbrain. Furthermore, new TH-positive cells are generated in the striatum at this 4-month time point.

Fenfluramine and norfenfluramine levels in brain microdialysate, brain tissue and plasma of rats administered doses of d-fenfluramine known to deplete 5-hydroxytryptamine levels in brain

The relationship between dose, frontal cortex (brain) microdialysate and brain tissue levels of fenfluramine (FEN) and norfenfluramine (NF), as well as the effect that these levels have on body temperature, was determined after systemic d-FEN. FEN and NF levels were monitored continuously in the microdialysate of adult male Sprague-Dawley rats dosed with 3 x 5 mg/kg s.c. (spaced 2 hr apart), 1 x 2 mg/kg s.c. or 1 x 10 mg/kg i.p. d-FEN (at ambient temperatures of either 23 degrees C or 27 degrees C). Drug concentrations in plasma and brain regions were also determined 1 hr after one or three doses of 5 mg/kg of d-FEN and 1 and 8 hr after 10 mg/kg d-FEN, and the levels of 5-hydroxytryptamine and 5-hydroxyindole acetic acid in the frontal cortex of FEN and controls were determined 4 days after dosing. Peak microdialysate FEN levels, occurring between 40 and 60 min after the first dose, were 0.24 +/- 0.07 microM after 2 mg/kg, 0.33 +/- 0.04 microM after 5 mg/kg and 1.65 microM after 10 mg/kg. After multiple doses of 5 mg/kg FEN the time-to-peak level was greater than 80 min with peaks of 0.68 +/- 0.04 microM after the second dose and 1.20 +/- 0.07 microM after the third dose. There was a positive correlation between combined (FEN + NF) peak levels in microdialysate and the increase in body temperature after 10 mg/kg d-FEN at 27 degrees C; however, the group mean and peak levels of FEN and NF in microdialysate were statistically the same at either 23 degrees C or 27 degrees C. The indole-depleting effect of d-FEN at 4 days after dosing was exacerbated at 27 degrees C when hyperthermia occurred. Thus, hyperthermia does not affect the pharmacokinetics of d-FEN but pharmacokinetics can influence the degree of hyperthermia in a 27 degrees C environment. Plasma levels, brain extracellular and brain levels of approximately 1 microM, 2.5 microM and 50 microM FEN (respectively), or greater, result from 5-hydroxytryptamine-depleting doses of 5 mg/kg s.c. FEN.

Determination of D-fenfluramine, D-norfenfluramine and fluoxetine in plasma, brain tissue and brain microdialysate using high-performance liquid chromatography after precolumn derivatization with dansyl chloride

A HPLC method is described for the simultaneous determination of D-fenfluramine (FEN), D-norfenfluramine (NF) and fluoxetine (FLX) using fluorometric detection after precolumn derivatization with dansyl-chloride. The method has limits of quantitation of 200 fmol for FEN and NF, 500 fmol for FLX in brain microdialysate, and 1 pmol for NF and FEN, and 2 pmol for FLX in plasma. Brain tissue standards were linear between 5 and 200 pmol/mg for all three compounds. The inter-assay variability (relative standard deviation) was 6.6%, 6.9% and 9.3% for FEN, 4.6%, 3.7% and 7.9% for NF and 10.4%, 4.9% and 12.2% for FLX, for brain microdialysate (2 pmol/microl), plasma (2 pmol/ microl) and brain tissue (50 pmol/mg), respectively. Intra-assay variability was always lower, typically several times lower than inter-assay variability. Extraction recovery was 108% and 48% for FEN, 105% and 78% for NF and 94% and 45% for FLX, in plasma (2 pmol/microl) and brain tissue (5 pmol/mg), respectively. Due to the stability of the dansyl-chloride derivatives this method is well suited for an autoinjector after manual derivatization with dansyl chloride at room temperature for 4 h.

Effects of prenatal ethanol exposure and early experience on radial maze performance and conditioned taste aversion in mice

C57BL/6 mice were intubated on gestational days 14-18 twice daily with 1.58 g/kg ethanol, 4.2 g/kg sucrose, or remained untreated. Offspring of ethanol-treated or lab chow control groups were raised either by group-housed dams and weaned on postnatal day (PND) 28 (enriched condition), or by individually housed dams and weaned on PND 21 (standard condition). Offspring of the sucrose control group were raised by individually housed dams and weaned on PND 21. Groups did not differ in pup weight or litter size. Male and female offspring were assessed for performance in an unbaited radial maze (PND 45-52) and male offspring only were tested for conditioned taste aversion (PND 54-59). As hypothesized, mice prenatally exposed to ethanol and raised under standard conditions failed to develop the conditioned taste aversion response. In contrast, subjects with in utero ethanol exposure that were raised under enriched preweaning conditions developed the taste aversion response. Maze performance improved significantly over days, but no significant effects were detected for either prenatal treatment or preweaning rearing conditions. In conclusion, enriched preweaning rearing conditions abolished the detrimental effects of prenatal ethanol exposure on conditioned taste aversion, but radial maze performance remained unaffected by any treatment in this study.

Differential effects of communal rearing and preweaning handling on open-field behavior and hot-plate latencies in mice

On day 2 after delivery, dams of the DBA/1 mouse inbred strain (n = 20/group) with their litter were allocated to one of the following groups: NH21, nonhandling, housed 1 litter/cage, weaned on postnatal day (PND) 21;H21, handling, housed 1 litter/cage, weaned on PND 21; NH30, nonhandling, group-housed (5 litters/cage), weaned on PND 30; H30, handling, group-housed (5 litters/cage), weaned on PND 30. Two male pups of each litter were color marked on PND 2. From PND 8-21 they were removed from their cage, gently held in the experimenter's hand for 5 min/day. The two marked males of each litter were housed together after weaning, and tested in the open-field on PNDs 51-53, and one of each of these siblings was tested for hot-plate latencies on PND 54. Being raised in group-housing and weaned on PND 30 resulted in offspring exhibiting shorter latencies to initiate behavior and higher percentages of centerfield entries in the open field, hot-plate latencies, however, remained unaffected. Preweaning handling increased hot-plate latencies and the number of grooming episodes in the open field, and it decreased defecation, percent centerfield entries and open-field activity in general. It is concluded that the two forms of early experience have different effects on neurobehavioral endpoints 8 weeks after birth.

Methamphetamine-stimulated striatal dopamine release declines rapidly over time following microdialysis probe insertion

To investigate changes in striatal dopamine release over a series of brief methamphetamine (METH) exposures, METH was pulsed three times at 2-h intervals, with the first exposure occurring 2 h after microdialysis probe insertion. Whether METH was administered directly into the striatum via the microdialysate (20 microM of METH for 10 min), or via peripheral intraperitoneal (i.p.) injection (1 mg/kg METH, i.p.), the dopamine (DA) peak elicited by the third METH exposure was only 50% as large as that elicited by the first exposure, 4 h earlier. This decline in the magnitude of METH-induced DA release probably continued over at least 24 h, since the magnitude of a single peak 26 h after probe implantation was only one-seventh of that at 2 h. This reduction in the response to METH was a function of time post-probe insertion, and not of prior METH exposure. Thus, peak size was the same at 6 h post-implantation in animals which received two prior METH pulses or no prior METH pulses, and in both cases this 6-h peak was substantially lower than that at 2 h post-implantation. Circadian influences were also excluded as a factor, because size of the initial METH-induced DA peak did not vary as a function of time of probe implantation. It is concluded that METH-stimulated striatal DA release declines rapidly over time post-probe insertion. When METH exposures occur repeatedly at short intervals, this decline can mimic, but is not caused by, desensitization or depletion in response to prior METH exposure.

Individual differences in dopamine release but not rotational behavior correlate with extracellular amphetamine levels in caudate putamen in unlesioned rats

It has been postulated that differences in pharmacokinetics do not contribute to the well-known individual variability in response to amphetamine (AMPH), but this is yet to be investigated thoroughly. Therefore, rotational behavior of outbred rats (Sprague-Dawley, 4 months old) was recorded during microdialysis sessions and striatal microdialysate was analyzed concomitantly for AMPH and dopamine concentrations after a single injection of 2.5 mg/kg AMPH SC. Three hours later these rats received three doses of 5 mg/kg AMPH SC (spaced 2 h apart) and their brain temperature was recorded every 20 min. The most important findings were: 1) the increase in extracellular dopamine was highly correlated with the corresponding peak AMPH levels in the microdialysate; 2) the peak dopamine level in response to 2.5 mg/kg AMPH was predictive of the hyperthermic response observed during 3 x 5 mg/kg AMPH and 3) high versus low rotators differed neither in their AMPH nor in their dopamine extracellular striatal concentrations.

Central and peripheral neurochemical alterations and immune effects of prenatal ethanol exposure in rats

In contrast to the well known effects of prenatal ethanol exposure on the central nervous system, data about its peripheral effects are scarce. Here, Sprague Dawley rats were fed a liquid diet (gestational days 0-20) containing 36% ethanol-derived calories (EDCs, group H) or were pair-fed with 18% EDCs (group L) or 0% EDCs (group C). On postnatal day 20, one male and one female from each of 10 litters per group were killed. Norepinephrine (NE) was analyzed in the frontal cortex, spleen and thymus, and dopamine, 5-hydroxytryptamine (serotonin, 5-HT) and their metabolites 3,4-dihydroxyphenylacetic acid, homevanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) were analyzed in the striatum by high-performance liquid chromatography with electrochemical detection. Lymphocyte subpopulations in the spleen and thymus were also assessed in half of these litters. Significant decreases in splenic NE concentration were seen in both sexes of group H (males 27%, females 28%). Decreases in striatal 5-HT and 5-HIAA of group H subjects appeared to be sex specific (only females were significantly affected: 23% decrease in 5-HT, 37% decrease in 5-HIAA). Pronounced, dose-dependent reductions in T cell percentages were observed in both the thymus and spleen. Splenic CD8+ and CD4+ cell percentages were positively correlated with the splenic NE concentrations. It is concluded that the decreases seen in splenic T cell percentages subsequent to prenatal ethanol exposure may be caused, at least partially, by impaired noradrenergic control of this organ.

Parenterally administered 3-nitropropionic acid and amphetamine can combine to produce damage to terminals and cell bodies in the striatum

The combined effects of amphetamine (AMPH) and 3-nitropropionic acid (3-NPA) were investigated to determine how the energy depletion proposed to be produced by AMPH interacts with an inhibitor of mitochondrial respiration to produce striatal neurotoxicity. Neither two doses (2 h apart) of 3.75 mg/kg AMPH alone nor a single dose of 30 mg/kg 3-NPA i.p. produced neurotoxicity in the striatum or lowered striatal dopamine content in rat. Administration of 40 mg/kg of 3-NPA alone almost invariably produced either lethality or did not produce neurotoxicity in the striatum of surviving animals. However, 30 mg/kg of 3-NPA administered along with 2 doses of 3.75 mg/kg AMPH to 47 animals produced striatal damage in the 31 survivors with 15 of the surviving rats showing muscle rigidity/catatonia for several days after dosing, along with decreased food consumption. Thirteen of these 15 rats showed degeneration of axons and cell bodies in the medial caudate-putamen with minimal damage to the globus pallidus. However, two rats exhibited hindlimb paralysis and signs of axonal and neuronal soma degeneration in the thalamus and cerebellar nuclei as well as striatum. Sixteen of the rats given both AMPH and 3-NPA exhibited only torpidity and loss of muscle tone 1-3 h after dosing. Such rats showed no signs of neuronal cell degeneration in the striatum, but did show significant dopamine depletions (60% of control) and reductions in tyrosine hydroxylase immunoreactivity at 14 days postexposure. The mitochondrial dysfunction produced by 3-NPA combined with activation of neuronal pathways by AMPH may have predisposed terminals, axons and cell bodies in striatum to degeneration.

Effects of prenatal ethanol exposure and early experience on home-cage and open-field activity in mice

-C57BL/6 mice were intubated from gestational day 14-18 twice daily with 1.58 g/kg ethanol, 4.2 g/kg sucrose, or remained untreated. Offspring of ethanol treated or lab chow control groups were raised either by group-housed dams and weaned on postnatal day (PND) 28 or by individually housed dams and weaned on PND 21. Offspring of the sucrose control group were raised by individually housed dams and weaned on PND 21. Groups did not differ in pup weight or litter size. Offspring were assessed for home-cage activity (PND 36-38) and open-field behavior (PND 40-42). Mice prenatally exposed to ethanol showed increased activity in their home cages, whereas open-field behavior was generally not different from that of control groups. Conversely, different preweaning rearing conditions had affected open-field behavior, but not home-cage activity. In conclusion, home-cage behavior was a sensitive paradigm for detecting hyperactivity subsequent to a relatively low dose of prenatal ethanol in mice, and communal nesting/late weaning vs. individual nesting/ standard weaning may be a useful preweaning environmental manipulation to study possible modifications of prenatal neurobehavioral effects.

Nitric oxide regulation of methamphetamine-induced dopamine release in caudate/putamen

A possible role for NO modulation of dopamine (DA) release in the caudate/putamen (CPU) during methamphetamine (METH) exposure was investigated using in vivo microdialysis in rats. Inclusion of the nitric oxide synthase (NOS) inhibitors NG-nitro-L-arginine (NOARG), NG-nitro-L-arginine methyl ester (L-NAME) or D-NAME (less potent inhibitor) in the microdialysis buffer prior to METH minimally affected basal levels of DA, DOPAC or HVA in CPU microdialysate. However, L-NAME and NOARG produced concentration-dependent decreases of up to 64% (100 microM) in CPU DA levels in microdialysate during exposure to four doses of METH (5 mg/kg i.p./2 h), with lesser effects on DOPAC or HVA. Reversal of the NOARG inhibition was produced by inclusion of 500 microM of either L-arginine or L-citrulline in the microdialysate. D-NAME (100 microM) minimally affected levels of DA or metabolites. Paradoxically, inclusion of from 20 to 2 microM of the NOx generators isosorbide dinitrate (ISON) or sodium nitroprusside (SNP) in the microdialysis buffer decreased DA and DOPAC levels in microdialysate during METH exposure. This paradox might result from the concentrations of NOx produced by SNP or ISON being great and not regionally specific resulting in inhibition of DA release and/or synthesis while the NO generated endogenously during METH exposure may have localized and site-specific actions. Alternatively, NOx may inhibit NOS or other enzymes in the NO synthesis pathway, thereby reducing levels of an intermediate (other than NO) which potentiates DA release. In their entirety, our results indicate that NO generation in the CPU may augment the release of DA during METH exposure.

Prenatal ethanol exposure in rats: long-lasting effects on learning

Pregnant Sprague-Dawley rats were fed a liquid diet containing either 0% (group C), 18% (group L), or 36% (group H) ethanol-derived calories (EDC) from gestational day 1 to 20. Male offspring were assessed under a conditioned taste aversion paradigm (PND 35-45), in a complex maze (PND 68-80), and for operant behavior (temporal response differentiation and motivation to work for food, PND 140-198). Although conditioned taste aversion was fully acquired by all groups, retention of the conditioned taste aversion response was impaired in group H animals. Importantly, deficits in the acquisition of timing behavior were found in group H (group L not tested), confirming that this operant task is quite sensitive in detecting prenatal drug effects and demonstrating that neurological effects of prenatal ethanol exposure persist into late adulthood.

Amphetamine levels in brain microdialysate, caudate/putamen, substantia nigra and plasma after dosage that produces either behavioral or neurotoxic effects

Extracellular levels of d-amphetamine (AMPH) in caudate/putamen were determined using microdialysis and HPLC quantitation after s.c. doses that produced increased motor activity (1 mg/kg), stereotypic behavior (2.5 mg/kg) or dopamine depletion in the caudate/putamen (4 x 5 mg/kg). In 6-mo-old rats exposed to neurotoxic doses of AMPH sulfate (4 x 5 mg/kg in a 23 degrees C environment), extracellular caudate/putamen AMPH rose to levels of 7.9 +/- 0.9 microM after the first dose and peaked at 15.1 +/- 2.5 microM after the third dose with no further increases after the fourth dose. After one or three doses of 5 mg/kg, peak plasma and tissue levels of AMPH were 1.7 +/- 0.2 and 2.9 +/- 0.3 microM in plasma, 36 +/- 6 and 73 +/- 10 in substantia nigra and 25 +/- 4 and 50 +/- 8 in caudate/putamen, respectively. Caudate/putamen extracellular AMPH levels were about three times higher (in either 6- or 12-mo-old rats) after 4 x 15 mg/kg in a 10 degrees C environment and tissue levels in caudate/putamen and substantia nigra were three to five times higher after three doses of AMPH. However, these higher levels did not produce dopamine depletion in the caudate/putamen, while the lower doses (4 x 5 mg/kg) given at 23 degrees C did. Estimated caudate/putamen extracellular AMPH levels of 2.5 to 5 microM after single doses (1 and 2.5 mg/kg) that caused hyperactivity and stereotypic behavior are compatible with the 2 to 10 microM AMPH concentrations reported to be necessary to produce pronounced dopamine release in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of d-amphetamine in biological samples using high-performance liquid chromatography after precolumn derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid

An HPLC method is described for the determination of amphetamine using fluorometric detection after derivatization with o-phthaldialdehyde and 3-mercaptopropionic acid. This procedure is more sensitive (detection limit 370 fmol in microdialysate buffer standards, 1.5 pmol in extracted plasma and tissue samples) than most of the previous methods described for the determination of amphetamine with HPLC-fluorescence detection. Due to the stability of the derivative it is also suitable for autosampling after manual derivatization. Investigators currently using o-phthaldialdehyde derivatization and fluorometric detection for amino acid determination should be able to rapidly implement this method.

Social isolation modifies the response of mice to experimental Mengo virus infection

To investigate the effects of social isolation on host resistance male mice were housed either individually (IH) or in groups of four or five (GH). All animals were infected with MengoM,L virus. Incubation time (INCUB), duration of illness (ILL), death rate (DR), histopathological changes, and serum corticosterone levels (CORT) were recorded. First, the effect of IH starting 4 days prior to infection was studied in 5 different inbred strains. Next, the effect of different IH length was examined, and the role of T-cells was investigated by comparing euthymic (+/+) and athymic (nu/nu) NMRI mice. Finally, the effects of the infection on CORT in IH and GH mice were compared in C57BL/6 mice. The major findings were: 1. IH significantly increased ILL in all but the DBA/2 strain, whereas DR was not affected except in C57BL/6. 2. Longer IH (starting 35 [DBA/2] or 10 [NMRI] days prior to virus inoculation) significantly shortened INCUB and prolonged ILL, but IH starting on the day of virus inoculation [DBA/2] significantly prolonged INCUB and shortened ILL. 3. NMRI nude mice exhibited an unaltered DR accompanied by a tremendously prolonged INCUB. 4. Investigations in C57BL/6 mice revealed a significant rise of CORT after infection. This increase was higher in IH compared to GH mice. It is suggested that IH attenuates T-cell mediated inflammatory processes and/or increases macrophage activation, which in turn results in a prolonged course of the disease.

Cholinergic and adrenergic drugs affect delayed type hypersensitivity in C57BL/6 mice

The present study examined the influence of systemic administration of neuroactive drugs on delayed-type hypersensitivity (DTH) in C57BL/6 mice. The cholinergic agonist nicotine and the acetylcholinesterase inhibitor physostigmine decreased DTH, whereas the alpha-adrenergic agonist clonidine stimulated DTH. In contrast isoprenaline, a specific beta-adrenergic agonist suppressed DTH. It is concluded from these observations that the autonomic nervous system modulates those processes governing DTH. It seems that the alpha-adrenergic subsystem stimulates, whereas the beta-adrenergic subsystem and the parasympathicus inhibit DTH.

Variability of exposure measurements in environmental epidemiology

In studies in environmental epidemiology, exposure to harmful agents is often highly variable in time and space. It is not usually possible to measure the relevant, personal exposure of study subjects to these agents directly. Instead, exposure measurements are performed at fixed sites and/or for limited periods of time in many cases. Such measurements are imperfect in the sense that they only approximate the "true" personal exposure of study subjects. When measures of exposure are highly variable in time and space, single measurements approximate the true exposure only to a limited extent. The variability of measures of exposure can be investigated by repetition of the measurements in time and space. Analysis of variance techniques can be used to separate the within-subject or "error" variance from the between-subjects or true variance. Computation of the ratio between the error variance and the true variance is a useful technique to evaluate the potential bias in correlation and regression coefficients calculated with these measures of exposure. Using data from a number of different studies, the authors have estimated the variance ratio of lead exposure and nitrogen dioxide exposure variables. The results suggest that these ratios may be large. Empirical illustrations are given of bias in regression coefficients of childhood blood levels on different lead exposure variables. It is recommended that pilot studies be performed more routinely to estimate the magnitude of the variance ratios of exposure variables of interest in studies in environmental epidemiology.

A method for estimating soil ingestion by children

In recent years, many cases of soil pollution have been unearthed in the Netherlands. The ingestion of soil particles due to mouthing behaviour of young children is an important potential pathway of exposure and may constitute a health risk. For an assessment of these health risks, a reliable estimation of the daily inadvertent ingestion of soil particles is necessary. A method to estimate soil ingestion is the use of titanium (Ti), aluminium (Al) and acid insoluble residue (AIR) content of the soil as a tracer. By measuring these tracers in faeces of children and in soil, an estimate can be made of the amount of soil ingested. This method can be used if the following conditions are met: tracer intake by other routes (food) is low and not too variable; tracer absorption from soil in the gastro-intestinal (GI) tract is negligible; tracer concentrations in soil are high and not too variable. A small pilot study was conducted among 18 children visiting a nursery school and 6 hospitalized children without any possibility of soil contact. The results of the pilot study indicate that each tracer is present in faeces in highly variable amounts, but that a combination of these three tracers produces a useful picture of potential soil ingestion. Quantitatively, a difference between the two populations of 55 mg/d, expressed as soil ingestion, was found. Despite the small numbers involved, this difference was statistically significant as the population standard deviations were small. In a number of different soil types, tracer concentrations were found to be almost equal. Further studies are planned to test the validity of the assumptions, and to investigate larger child populations living in different circumstances.

Toxicokinetics of the herbicide dichlorprop and its leucinate and their action on liver mixed function oxidase in rats

The concentrations of dichlorprop and its leucine conjugate in serum and bile of rats have been determined at different periods after a single oral dosage of these compounds (30 or 300 mg/kg body weight). From the results it can be concluded that dichlorprop is excreted by active renal mechanisms resembling that described for 2,4,5-T. It is suggested that the leucinate is excreted more by the biliary route. Investigations of the liver demonstrate that both compounds are able to induce mixed function oxidases.

Differences in the distribution of methyl mercury in erythrocytes, plasma, and brain of Japanese quails and rats after a single oral dose

Distribution of a single oral dose of methyl mercury (10 mg Hg/kg body weight) was followed from 90 min up to 120 h in plasma, erythrocytes, and brain of Japanese quails and rats. Significantly higher Hg concentrations were observed in plasma and brain of quails and red blood cells of rats. Blood/brain ratio decreased in quails from 6 to 2 at 24 h and 120 h respectively, whereas it increased in rats. Erythrocyte/plasma ratio in quails was about three times lower and averaged 54. The differences in Hg distribution were accompanied by a more than 3-fold higher acute toxicity in quails under adequate experimental conditions.

Iron overload of spleen, liver and kidney as a consequence of hemolytic anaemia

Iron overload in spleen, liver and kidney induced by hemolytic anaemia due to a 90-day oral exposure of rats to diuron (N-3,4-dichlorphenyl-N,N-dimethylurea), an urea herbicide, was studied by histochemistry, transmission electronmicroscopy, morphometry and energy dispersive X-ray microanalysis. Increasing dosages of diuron provoked a hemosiderosis in the spleen followed by erythrocytic sequestration and the formation of haemopoietic foci coinciding with Kupffer cell siderosis of the liver. A strong enlargement of the spleen red pulp on the one hand faces an unchanged total white pulp volume as well as no alterations of the white pulp microscopic structure on the other. The electron dense bodies of the endothelial cells did not contain iron whereas hepatocytes possess two types of lysosomes, homogeneous iron containing ones at the sinusoidal site and complex structured ones without detectable iron at the biliary site. The formation of the homogeneous lysosomes is suggested to be due to the hepatocytic reception of hemoglobin-haptoglobin-complexes after intravascular hemolysis. The lysosomes of the biliary site seem to be engaged in hemoglobin degradation. A partial nephrohydrosis due to hemosiderotic events in succession of intravascular hemolysis including hemoglobin reabsorption from the primary urine could be observed. It is assumed that exocytosis might play a major role in hemosiderin removal from kidney tubule cells.

[Subchronic toxicity of gamma-Falisan-Universal dry dressing agent to rats]

Doses of 50 mg/kg, 100 mg/kg, and 400 mg/kg of Gamma-Falisan-Universal dry dressing agent (active ingredients including 20 per cent of Lindan and 2.5 per cent of phenyl-mercury acetate) were administered in agar suspension by stomach intubation to rats over 13 weeks, with five applications weekly. The following changes were produced: retardation in body weight, lymphopenia and leucopenia, rise of segment-nuclear neutrophils in peripheral blood, decrease of haematocrit and haemoglobin, as well as rise in activities of leucine aminopeptidase and serum glutamate oxalo-acetate transaminase. The males proved to be more sensitive in the context of their haematological parameters, while the females displayed higher sensitivity in terms of clinico-chemical values. Absolute weight increases were recorded from kidneys and liver of both males and females and from the adrenal gland of females, while weight loss was recorded from the pituitary gland of males. Changes of the same kind were expressed even more strongly, in the context of relative weights of organs. Histopathological changes were recorded from liver, kidneys, and adrenal gland of either sex, and they were histometrically confirmed. Retardation in body weight, rise in activity of leucine aminopeptidase, and weight changes of various organs were significant up to first dosage group. Analogous findings were obtained with regard to microscopic changes in kidneys. Hence, no-effect levels did not occur at all throughout the experiment.

Aspects of methodology employed in the investigation of combined chemical effects on acute oral toxicity

The evaluation of combined chemical effects should be based on the theoretical additive LD50 values which are derived from the LD25 values of the single substances rather than the 1/2 LD50 values. If the latter are used, misinterpretation of the character of the combined action (overestimation of antagonism/underestimation of potentiation) are not excluded, particularly in case of low slope functions.