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Publications and source records attributed to K M Crofton.
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Use of dermal or inhalation routes of maternal exposure during the postnatal period in rodent developmental neurotoxicity evaluations would be most practical if dams could be separated from their pups during the exposure period. However, this procedure raises questions concerning the effects of mother-infant separation itself on neurotoxicity endpoints. In the present study, Sprague-Dawley rat pups were either maternally deprived in warm incubators for 6 hr each day (7:00 AM-1:00 PM) or left with their dams (control), from Postnatal Day 4-20 (PND4-20), and were tested on a range of endpoints commonly used in developmental neurotoxicology. These included motor activity (PND13, 17, 19, 21, 29, 60), olfactory learning (PND18) and retention (PND25), T-maze delayed alternation (PND23, 24), acoustic startle response (PND23, 62), and auditory thresholds (PND62). None of the behavioral measures were affected by daily separation. Apparently, interrupting the mother-infant interaction for 6 hr/day has little or no effect by itself on behavioral development, as assessed by these measures.
Following a pilot study which revealed olfactory epithelial degeneration induced by beta,beta'-iminodipropionitrile (IDPN), dose-response and time-course analyses were undertaken to further characterize the effects of IDPN on the olfactory system. Male rats were sacrificed at multiple time points ranging from 24 hr after a single dose to 56 days after three consecutive daily doses of IDPN (0-400 mg/kg i.p.). Nasal cavities were fixed, decalcified and embedded in paraffin; 5 microns sections were stained with hematoxylin and eosin, middle neurofilament protein antibody or olfactory marker protein antiserum. Olfactory bulbs were removed for slot blot analyses of glial fibrillary acidic protein, synapsin I and p38. Another group of rats was treated with saline or IDPN and perfused 6 hr or 1, 2, 3, 7, 14 or 28 days after the last dose. Olfactory bulb axonal degeneration was visualized using a modified Gallyas technique. Twenty-four hours after treatment with 200 or 400 mg/kg IDPN, there was severe, highly site-specific mucosal degeneration in the dorsal-medial nasal cavity; regeneration was incomplete 8 weeks later. IDPN increased olfactory bulb glial fibrillary acidic protein, peaking 7 days after three daily 400 mg/kg doses, and remaining significantly elevated 8 weeks after treatment. Olfactory bulbs contained substantial silver deposition in afferent axon bundles in the glomerular layer, beginning 24 hr after the first dose and persisting for 14 days after dosing. Although only a portion of the olfactory epithelium was damaged by IDPN, all axon bundles entering the olfactory bulb were involved, suggesting the lack of a clear topographic arrangement of sensory endings in the olfactory bulb.
2,4-Dithiobiuret (DTB) exposure causes a delayed onset muscle weakness in rats that has been attributed to depressed neuromuscular transmission. The present study compares the effects of DTB on both sensory and motor function in rats. Adult male Long-Evans hooded rats were exposed to saline, 0.25, 0.5, or 1.0 mg/kg/day DTB, ip, for 5 consecutive days (Days 1-5). Body weights were monitored throughout the experiment. Motor activity was measured for 1 hr in figure-eight mazes on Days 0, 6, 13, and 27. Forelimb and hindlimb grip strength were assessed on Days 6, 13, and 27. Auditory thresholds were determined for 5- and 40-kHz tones using reflex modification of the startle response on Days 0, 7, 14, and 28. Visual function was examined on Day 6 in animals exposed at 0.5 mg/kg/day using flash- and pattern-elicited visual evoked potentials (FEPs and PEPs, respectively). Thermal sensitivity was measured using the hot plate procedure. All motor endpoints were decreased in a dosage- and time-dependent manner; the higher the dosage the longer the effects lasted. There were no effects on any measure of sensory function with the exception of peak N2 of the FEP. Both the amplitude and latency of FEP N2 were altered by DTB exposure. Decreases in body weight were maximal on Day 9 at 1.0 mg/kg/day (20% from control), but recovered by Day 22. Motor activity was suppressed on Day 6 only, whereas grip strength measures were decreased on both Days 6 and 13. Auditory thresholds were not significantly altered; however, baseline startle amplitude was decreased at the highest dosage on Days 7 and 14, but recovered by Day 28. Hot plate latencies were not altered by DTB treatment. These data demonstrate that DTB produces a reversible impairment of motor function, without altering auditory, thermal, or pattern visual function. FEP N2, which is thought to arise from activity generated in the superficial layers of visual cortex, was diminished by DTB treatment, indicating that DTB can alter the function of the CNS, although effects on the motor system are more pronounced.
The consequences of 3,3'-iminodipropionitrile (IDPN) exposure in animals merits attention both because of its unique neurotoxic effects and as a potential model compound of human dyskinetic disorders. An important question that remains to be determined is whether IDPN itself or a putative active metabolite is responsible for the neurotoxic actions of the chemical in vivo. The present work tested the hypothesis that IDPN must be metabolized by the liver to an active metabolite to become neurotoxic. Thus a reduction in IDPN neurotoxicity would be expected when liver function is compromised. Male Long-Evans rats were given ip injections of saline, 100 (IDPN1) or 200 (IDPN2) mg/kg of IDPN for three days. Half of the animals in each IDPN dose group received corn oil po and the other half 1 g/kg of the hepatotoxicant carbon tetrachloride (CCl4) for three days, starting one day before IDPN administration. Body weights were obtained regularly after exposure. Horizontal and vertical motor activity, and acoustic startle response were monitored prior to, and 1,3,9 and 16 weeks after IDPN exposure. An observational rating score was obtained at 1, 3 and 9 weeks. Auditory thresholds for 5- and 40-kHz tones were estimated by reflex modification procedures at 10 weeks. Animals receiving IDPN2 alone displayed the overt behavioral signs characteristic of IDPN intoxication (postural disturbances, head dyskinesias, backward walking, circling, increased motor activity, and decreased startle response). They also showed weight loss, hyperactivity, a transient rearing deficit, decreased startle amplitudes and elevated auditory thresholds for low- and high-frequency tones. None of these symptoms were observed in the animals treated with CCl4 alone, and only a mild transient effect on the observational rating score was shown by the IDPN1 alone animals. In contrast, IDPN1/CCl4 resulted in the same or higher toxicity than the IDPN2 treatment. IDPN2/CCl4 resulted in severe toxicity (38% mortality over a two-week period) and enhanced body weight and behavioral effects compared to IDPN2 alone group. Impairment of xenobiotic biotransformation was confirmed by elevated pentobarbital sleeping time in animals under the same CCl4 dosing regimen. In conclusion, pretreatment with hepatotoxic dosages of CCl4 leads to increased toxicity of IDPN. This suggests that hepatic transformation of the chemical is not required for the manifestation of IDPN-induced neurotoxicity, but instead may be involved in the detoxification of this compound.
Rats were examined using a learning and memory test battery 4 weeks following exposure to 3,3'-iminodipropionitrile (IDPN). Initial testing revealed deficits in olfactory discrimination and passive avoidance (PA) conditioning. In order to dissociate learning and performance effects, additional tests were conducted. First, to rule out the possibility that IDPN reduced the aversiveness of foot shock, rats were tested in a simple shock sensitivity paradigm. The results indicated no change in shock sensitivity produced by IDPN. Second, to determine if the hyperactivity produced by IDPN was responsible for deficits in conditioning, several additional tests were conducted including (a) repeated-trials active avoidance (AA) and PA conditioning, (b) a PA study which included both a 1- and 24-hr training-testing interval, and (c) long-delay flavor-aversion conditioning. Rats treated with IDPN required more conditioning trials to reach criterion on both AA and PA procedures suggesting that they were capable of performing the required response but acquired those responses at a much slower rate. The deficits in PA conditioning were similar at both the 1- and 24-hr training-testing interval. Finally, the effects of IDPN on flavor-aversion conditioning depended on the delay separating flavor intake and lithium administration during conditioning. Rats treated with IDPN demonstrated robust flavor aversions when trained with a 30-min but not with a 6-hr delay. In summary, the neurotoxic profile of effects produced by IDPN must be expanded to include a prominent cognitive component characterized by protracted deficits in learning and memory capacity. The present experiment illustrates how chemically induced disruption of learning and memory produced by IDPN can be experimentally dissociated from associate neurological symptoms using a simple, routine battery of neurobehavioral tests.
Triadimefon, a triazole fungicide, has been observed to increase locomotion and induce stereotyped behavior in rodents. The present experiments designed to characterize the stereotyped behavior induced by triadimefon used a computer-supported observational method, and tested the hypothesis that these observed effects involved central dopaminergic systems. Adult male and female Sprague-Dawley rats were injected with triadimefon (0, 50, 100, and 200 mg/kg) in corn oil (2 ml/kg ip) 4 hr prior to behavioral assessment. The two lowest doses of triadimefon increased the frequency of locomotion and rearing, while the highest dose induced highly stereotyped behaviors, including backward locomotion, circling, and head weaving. Immediately after behavioral testing, the rats were sacrificed, and the striata and olfactory tubercles, terminal fields of the nigrostriatal and mesolimbic dopamine systems, respectively, were removed. Steady-state concentrations of the monoamines dopamine and serotonin and their metabolites were determined by HPLC-EC. In independent experiments, the direct effects of triadimefon on dopamine (D1 and D2) receptor binding and dopamine-sensitive adenylate cyclase activity were assessed in vitro using rat striata. Dopamine concentrations were increased in olfactory tubercles, but decreased in striatum. Concentrations of 5-hydroxyindoleacetic acid (the major metabolite of serotonin) were increased only in striatum, and only in animals treated with 200 mg/kg triadimefon. In vitro, triadimefon neither competed with D1 or D2 dopaminergic radioligands nor affected dopamine-stimulated adenylate cyclase activity. Together these behavioral and biochemical data lend support to the hypothesis that triadimefon may have actions similar to those produced by indirect-acting dopamine agonists.
Trimethyltin (TMT) is a neurotoxicant known to alter auditory function. The present study was designed to compare TMT-induced auditory dysfunction using behavioral, electrophysiological, and anatomical techniques. Adult male Long-Evans hooded rats (n = 9-12/group) were acutely exposed to saline, 3, 5, or 7 mg/kg TMT. Auditory thresholds were determined 11 weeks postdosing for 5- and 40-kHz tones using reflex modification of the auditory startle response (ASR). Brainstem auditory evoked response (BAER) thresholds were determined for 5-, 40-, and 80-kHz tonal stimuli 9 weeks postdosing. Cochlear histology was assessed at 13 weeks postdosing. Functional endpoints demonstrated a high-frequency hearing loss. ASR thresholds for 40-kHz tones were elevated 25-35 dB in all dosage groups. BAER thresholds for 40- and 80-kHz tones were elevated 30-50 dB in the 5 and 7 mg/kg groups. Organ of Corti surface preparations revealed a pattern of damage suggesting classical ototoxicity. That is, outer hair cells died preferentially in regions associated with high-frequency hearing, in a dosage-dependent manner from base to apex. These data demonstrate the utility of the ASR and BAER in detecting functional alterations in audition and indicate that TMT-induced high-frequency hearing loss is associated with cochlear damage.
Pyrethroid insecticides have recently been purported to possess strong proconvulsant potential. The seizure-inducing properties of two pyrethroids were assessed by pentylenetetrazol (PTZ) seizure models (repeated ip, suprathreshold ip, and iv), and electrical kindling of the amygdala. The efficacy of po versus ip routes of deltamethrin administration was compared using iv-PTZ administration and tests of locomotor activity in a figure-eight maze. Both po and ip deltamethrin produced comparable decreases in motor activity indicating the effectiveness of both of these exposure routes on biological activity. The Type I pyrethroid, cismethrin (15 mg/kg, po), produced a 17% reduction in the threshold dosage of ip-PTZ required to induce a seizure, while delaying the onset of generalized seizure activity. The Type II pyrethroid, deltamethrin (10 mg/kg, po), failed to alter threshold or latency to seizure onset, but did increase seizure duration. No differences were revealed between po (0, 10, 15 mg/kg) or ip (0, 1, 10 mg/kg) administered deltamethrin on seizure thresholds or durations following iv-PTZ. Seizure severity, however, was enhanced by pyrethroids administered po in the iv-PTZ and suprathreshold-ip PTZ tests, ip deltamethrin was without effect. Cismethrin (0, 8, 15 mg/kg) and deltamethrin (0, 6, 10 mg/kg) administered po daily, 2 hours prior to electrical kindling stimulation facilitated amygdala kindling to a minimal but equivalent degree at the highest dosage. This dosage also evoked strong behavioral signs of toxicity. Deltamethrin also induced spontaneous seizures in partially kindled animals in the absence of stimulation. Thus strong evidence of proconvulsant activity of pyrethroids was not evident. The primary effects were limited to an enhancement of seizure severity in response to PTZ (tonic seizures) and the provocation of spontaneous seizures in partially kindled animals.
The pyrethroid insecticides have been divided into two classes on the basis of their biochemical actions and behavioral indices of toxicity. Both types of pyrethroids have effects on sodium conductance, and Type II pyrethroids have been reported to antagonize gamma-aminobutyric acid (GABA) by interacting with the t-butyl-bicyclophosphorothionate (TBPS)/picrotoxinin binding site. The dentate gyrus of the hippocampus is equipped with GABAergic recurrent inhibitory circuits. The present experiment was designed to demonstrate dissociation in the biochemistry of pyrethroids by activating the perforant path with pairs of stimulus pulses and monitoring the recurrent inhibition in this circuit. Antagonism of GABA leads to a reduction in inhibition, measured as an increase in the size of the population spike in response to the second pulse of the pair. The GABAergic properties of the pyrethroids were assessed by examining paired pulse inhibition before and after oral treatment with 20 mg/kg of cismethrin (Type I), 20 mg/kg of fenvalerate, or 10 mg/kg of deltamethrin (Type IIs). Input/output (I/O) functions revealed a reduction in excitatory postsynaptic potential (EPSP) following cismethrin and deltamethrin. Population spike height was unaffected. Fenvalerate had no effect on I/O functions. In contrast to the prediction of reduced inhibition following treatment with Type II pyrethroids, deltamethrin and fenvalerate increased inhibition up to 500 and 150 ms interpulse intervals, respectively. Cismethrin was without effect on paired pulse inhibition. These findings fail to provide evidence of GABA antagonistic properties of Type II pyrethroids and may be best explained by a differential effect of these three pyrethroids on sodium channel kinetics.
Triadimefon is a triazole fungicide that produces hyperactivity in both mice and rats similar to that seen following administration of compounds with catecholaminergic activity (e.g., d-amphetamine). To determine whether the triadimefon-induced hyperactivity is due to an action on CNS catecholaminergic systems, we evaluated the effects of combined treatment of triadimefon with either the tyrosine hydroxylase inhibitor d,l-alpha-methyl-p-tyrosine methyl ester HCl (alpha MPT) or the amine depletor reserpine. Adult male Long-Evans hooded rats, approximately 70 days of age were used. Dosage-effect functions were determined for alpha MPT (0-200 mg/kg IP), reserpine (0-2.5 mg/kg IP), d-amphetamine (0-3 mg/kg IP), and methylphenidate (0-40 mg/kg IP). Motor activity was measured as photocell interruptions in figure-eight mazes. The interaction between triadimefon and alpha MPT was determined with the following groups: 1) vehicle control; 2) 200 mg/kg triadimefon PO; 3) 100 mg/kg alpha MPT; and 4) both alpha MPT and triadimefon. A similar design was used to determine the interaction between triadimefon and reserpine (0.62 mg/kg), alpha MPT and d-amphetamine (1.5 mg/kg), and reserpine and methylphenidate (5.0 mg/kg). In the first experiment alpha MPT did not block the increased motor activity produced by triadimefon (i.e., both triadimefon alone and alpha MPT in combination with triadimefon produced significant increases in motor activity). alpha MPT did, however, block d-amphetamine-induced hyperactivity. Since alpha MPT did not antagonize the effect of triadimefon, these data suggest that increased motor activity produced by triadimefon is not mediated through release of newly synthesized catecholamines.(ABSTRACT TRUNCATED AT 250 WORDS)
The results of a series of screening tests to determine the potential teratogenicity and neurotoxicity of developmental exposure to TBTO in rats are presented in this paper. For prenatal exposure, pregnant Long Evans rats were intubated with 0-16 mg/kg/day bis(tri-n-butyltin)oxide TBTO from Days 6 to 20 of gestation (GD 6-20). For postnatal exposure, rat pups were intubated with 0-60 mg/kg TBTO on Postnatal Day 5 (PND 5). Following prenatal exposure, dams were allowed to litter and pups were evaluated using a postnatal teratology screen. Postnatal evaluation for both exposures included motor activity (PND 13-64), the acoustic startle response (PND 22-78), growth, and brain weight. The maximally tolerated dose (MTD) in pregnant rats was 5 mg/kg/day, which is one-third the MTD in nonpregnant rats. There were decreased numbers of live births, and decreased growth and viability at dosages greater than or equal to 10 mg/kg/day. Cleft palate was found in 3% of the 12 mg/kg/day group. There was mortality following postnatal exposure to 60 mg/kg and all prenatal dosages greater than or equal to 10 mg/kg/day. Preweaning body weight was significantly decreased for all postnatal dosages, and all prenatal dosages greater than 2.5 mg/kg/day. Body weight reductions persisted to the postweaning period only in the high dose groups (10 mg/kg/day and 60 mg/kg). Behavioral evaluation demonstrated transient alterations in motor activity development (prenatal exposure only) and the acoustic startle response (postnatal exposure only). Persistent behavioral effects were observed only at dosages that produced overt maternal toxicity and/or postnatal mortality. The demonstration of the teratogenic and neurotoxic potential of TBTO in rats is confounded by associated maternal toxicity and/or pup mortality.
Recent data have demonstrated that the in vivo effects of low dosages of two pyrethroids, cismethrin and deltamethrin, can be differentiated. Two behavioral tests, locomotor activity and the acoustic startle response (ASR), were utilized to separate the behavioral actions of Type I and II pyrethroids using permethrin, RU11679, cypermethrin, RU26607, fenvalerate, cyfluthrin, flucythrinate, fluvalinate and p,p'-DDT. Dosage-effect functions for all compounds were determined for both figure-eight-maze activity and the ASR in the rat. All compounds were administered po in 1 ml/kg corn oil 1.5-3 hr prior to testing. All compounds produced dosage-dependent decreases in locomotor activity. The Type I compounds, permethrin and RU11679, along with p,p'-DDT, increased amplitude and had no effect on latency to onset of the ASR. In contrast, the Type II pyrethroids, cypermethrin, cyfluthrin, and flucythrinate, decreased amplitude and increased the latency to onset of the ASR. Fenvalerate increased the amplitude, had no effect on latency, but unlike the other compounds tested, increased ASR sensitization. Fluvalinate had no effect on any measure of the ASR. These data provide further evidence of the differences between the in vivo effects of low dosages of Type I and II pyrethroids, and extend the findings of our previous work to other representatives of the two classes of pyrethroids.
Triadimefon is an agriculturally important triazole fungicide. The present experiments were conducted to characterize the effects of triadimefon on a measure of motor activity. Dosage-effect, time-effect, and the effect of repeated dosing (7 days) were determined following triadimefon exposure. Male Long Evans hooded rats, approximately 70 days old, received triadimefon po in 2.0 ml/kg corn oil. Motor activity testing was conducted for 1 hr in figure-eight mazes. For the dosage-effect determination, triadimefon (50-400 mg/kg) was administered 1 hr prior to testing. In the time-course study, triadimefon (200 mg/kg) was administered either 0.5, 1, 2, 4, 8, or 24 hr prior to testing. In the repeated dosing experiment animals received triadimefon (100 mg/kg) daily for 7 days and were tested 24 hr after the last exposure. Triadimefon produced significant hyperactivity following dosages of 100 and 200 mg/kg. This hyperactivity was rapid in both onset (0.5 hr) and recovery (8.0 hr). Repeated dosing with 100 mg/kg/day revealed no cumulative effects nor tolerance. These results indicate that triadimefon produces a transient hyperactivity at dosages 17 to 33% of the reported LD50.
Radioligand binding displacement studies were conducted to determine the effects of Type I and II pyrethroids on [3H]flunitrazepam (FLU), [3H]muscimol (MUS), and [35S]t-butylbicyclophosphorothionate (TBPS) binding. Competition experiments with [3H]FLU and [3H]MUS indicate a lack of competition for binding by the pyrethroids. Type I pyrethroids failed to compete for the binding of [35S]TBPS at concentrations as high as 50 microM. Type II pyrethroids inhibited [35S]TBPS binding to rat brain synaptosomes with Ki values ranging from 5-10 microM. The data presented here suggest that the interaction of Type II pyrethroids with the gamma-aminobutyric acid (GABA) receptor-ionophore complex is restricted to a site near the TBPS/picrotoxinin binding site.
Two behavioral tests, motor activity and the acoustic startle response (ASR), were used to test for dose-addition of cismethrin, a Type I, or deltamethrin, a Type II pyrethroid, with compounds active at the gamma-aminobutyric acid (GABAA) receptor complex (picrotoxin, muscimol and chlordiazepoxide). Additivity was assessed using a simplified version of isobolographic analysis using chlorpromazine and haloperidol as positive controls for dose-additivity. Dosage-effect functions for all compounds were determined for both motor activity and the ASR. The effects of various combinations of chlorpromazine (0.5-4.0 mg/kg) and haloperidol (0.05-0.2 mg/kg) on motor activity indicate dose-addition. To test for dose-addition of pyrethroids and GABAergic compounds, cismethrin (3-18 mg/kg) or deltamethrin (2-6 mg/kg) were administered 90 min before testing, either alone, or before treatment with picrotoxin (0.25-2.0 mg/kg), muscimol (0.6-2.5 mg/kg) or chlordiazepoxide (2.5-10 mg/kg) administered 20 to 30 min before testing. All compounds produced dosage-dependent decreases in motor activity. Muscimol and picrotoxin decreased ASR amplitude, increased ASR latency and reduced ASR sensitization to increasing background noise levels. Chlordiazepoxide had no effect on any measure of the ASR. Results from the interaction studies indicate dose-addition of the effects of picrotoxin and deltamethrin on motor activity and the ASR. Additivity of dose was not seen with any other combination. These data suggest that the in vivo effects of the Type II pyrethroid deltamethrin may be due in part to interaction with the picrotoxinin binding site of the GABAA receptor-ionophore complex. In addition, these results are consistent with reported differential effects of the two classes of pyrethroids on the GABAA receptor complex.
Pregnant Sprague-Dawley rats were exposed to either 3500 or 7000 mg/m3 p-xylene from days 7-16 of gestation. Dams were allowed to give birth, and litters were counted, weighed, and observed for external malformations on postnatal days (PD) 1 and 3. Litters were normalized to 8 pups (4 males and 4 females +/- 1) on PD4. On PD21 animals were weaned and littermates housed by sex. Body weights were recorded weekly until weaning and once every 2 weeks thereafter. Central nervous system (CNS) development was evaluated by acoustic startle response on PD13, 17, 21, and 63 as well as figure-8 maze activity on PD22 and 65. Maternal weight gain during the treatment period was significantly less in the high-dose group. No effects were seen on litter size or weight at birth or on PD3. There were no effects of xylene exposure on growth rate. There were no treatment-related effects on acoustic startle response or figure-8 maze activity. Thus, p-xylene as administered in this study does not appear to be a selective developmental toxicant in the rat.
Pyrethroid insecticides have been divided into Types I and II based on behavioral profiles of toxicity produced by life-threatening dosages. In order to assess potential alterations in acquired (operant) behavior, acute dosage-effect and time-course determinations for permethrin (Type I) and cypermethrin (Type II) were made. Long-Evans rats responded for food according to a multiple schedule consisting of four different variable-interval schedules. Permethrin (100-400 mg/kg) and cypermethrin (7.5-60 mg/kg) were administered PO 1.5 hr pre-session and their effects on response rates and between-component response patterning determined. Permethrin reduced responding in a manner which was independent of the baseline response rate, while the rate reductions following cypermethrin administration showed a dependence on the baseline levels of responding, with low response rates showing differential sensitivity to disruption. When select dosages of each compound were delivered at various pre-session times, onset of and recovery from the rate-decreasing effects were more rapid with cypermethrin, with rates returning to baseline levels by 12 hr post-dosing. Responding was maximally suppressed 24 hr after administration of permethrin and returned to baseline levels 48 hr after administration. The disruption of response patterning following cypermethrin was maximal at 1.5 hr after administration, with complete recovery 12 hr post-dosing. Differential effects on response patterning, in potency, and in the time-course of effects of permethrin and cypermethrin suggest a type-specificity for pyrethroid effects on schedule-controlled behavior at dosages far below those producing lethality in rats.