The reproductive effects of dietary heptachlor in mink (Mustela vison)

Adult female mink were fed diets containing 0 (control), 6.25, 12.5, and 25 ppm (micrograms/g) technical grade heptachlor prior to and throughout the reproductive period (181 days) to evaluate the effects of heptachlor consumption on reproduction and offspring viability and to assess the extent of placental and mammary transfer of heptachlor epoxide to mink offspring. Feeding 12.5 and 25 ppm resulted in significant reductions in feed consumption and body weights of female mink. Mortality was 0, 8, 67, and 100% for the control, 6.25, 12.5, and 25 ppm groups, respectively. All females in the 25 ppm group died within 88 days. Mink fed the two higher heptachlor diets displayed clinical signs indicative of central nervous system involvement just prior to death. Females were mated with males on the same dietary treatments. Whelping success rates were 67, 83, 27, and 0% for the control, 6.25, 12.5, and 25 ppm groups, respectively. High mortality in the 12.5 and 25 ppm groups accounted for the lack of reproductive success. Gestation length, litter size and birth weight of kits were not significantly affected by adult female consumption of 6.25 ppm heptachlor while kits helped by females on the 12.5 ppm diet weighed significantly less than control kits at birth. Survival of kits in the 12.5 ppm group from birth to three weeks of age was also adversely affected. At three and six weeks of age, kit body weights in both the 6.25 and 12.5 ppm groups were significantly less than body weights in control kits.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of hydrated sodium calcium aluminosilicate in reducing the toxicity of dietary zearalenone to mink

Ovariectomized mink were fed diets containing zearalenone (ZEN) at concentrations of 0, 10 or 20 ppm with or without 0.5% hydrated sodium calcium aluminosilicate (HSCAS) for 24 days. Zearalenone at 10 and 20 ppm caused a significant increase in uterine weights, while 20 ppm ZEN resulted in significantly higher vulva swelling scores when compared to controls. The presence of HSCAS in the diet did not alter these hyperestrogenic effects of ZEN. In a second experiment, female mink were provided diets containing 20 ppm ZEN, 20 ppm ZEN plus 0.5% HSCAS or a control diet from 1 January 1989 through whelping (25 April to 15 May 1989). The females were given an opportunity to mate with untreated proven breeder males beginning on 1 March (day 59 of exposure). ZEN did not have an effect on the number of females whelping but there was a significant increase in gestation length, a decrease in litter size and an increase in kit mortality from birth to 3 weeks of age when compared to the control group and the group receiving the combination of ZEN and HSCAS. These results suggest that HSCAS can alleviate some of the reproductive effects of ZEN which are not related to its estrogenic action.

Neuropathological effects of triphenyl phosphite on the central nervous system of the hen (Gallus domesticus)

The neurotoxic effects of single subcutaneous injections of 1000 mg triphenyl phosphite (TPP)/kg body weight were investigated in White Leghorn hens. At 7 days postexposure, birds began to show signs of mild to moderate ataxia that progressed to severe ataxia and paralysis at 21 days. Inhibition of whole brain neuropathy target esterase was 85% at 48 hr and 73% by 21 days postexposure. After postexposure periods of 7, 14, and 21 days, hens were killed and their brains and spinal cords were examined for degenerating axons and terminals using the Fink-Heimer silver impregnation method. A small amount of degeneration was noted at 7 days. By 21 days, dense degeneration was noted in the spinal gray matter and funiculi. Degeneration was also present in the granular cell layer of cerebellar folia I-VI and in nuclei and fiber tracts of the medulla. Moderate to dense degeneration was also seen in several forebrain and midbrain areas including the paleostriatum, ansa lenticularis, the dorso-intermediate thalamic nucleus, lateral spiriform, pedunculopontine tegmental, and lateral mesencephalic nuclei and in the deeper layers of the optic tectum. These results indicate that, in addition to affecting the spinal cord and brainstem, exposure to TPP also damages higher order centers responsible for processing and integrating sensorimotor, visual, and auditory information.

Toleration of high concentrations of dietary zinc by mink

Adult and kit male and female natural dark ranch mink (Mustela vison) were fed a conventional diet supplemented with 0, 500, 1,000, or 1,500 ppm zinc, as ZnSO4.7H2O, for 144 days. No marked adverse effects were observed in feed consumption, body weight gains, hematologic parameters, fur quality, or survival. Zinc concentrations in liver, kidney, and pancreas of the mink increased in direct proportion to the zinc content of the diet. Histopathologic examination of the livers, kidneys, and pancreata revealed no lesions indicative of zinc toxicosis. The results indicate that mink can tolerate at least 1,500 ppm dietary zinc, as ZnSO4.7H2O, for several months without apparent adverse effects.

Elimination of PBBs in rats. Effect of mineral oil and/or feed restriction

Rats were fed polybrominated biphenyls (PBBs) at 0.1 to 100.0 ppm for 14 d and then treated to hasten the removal of PBBs with 0, 5, or 10% mineral oil (MO) and/or 0, 15, 30, or 45% feed restriction (FR) for 21 d. PBB body burdens were determined at d 14 and expressed on a log-log basis by Y = 0.91X + 2.179 (r2 = 0.974), where X = log of PBB concentration in diet (ppm) and Y = log of PBB body burden (micrograms). After 21 d withdrawal, body burdens were expressed by the equation Y = 0.787X + 2.218 (r2 = 0.95). The most effective withdrawal treatment was 10% MO + 45% FR producing a reduction of body burdens inversely related to prior body burdens (69% at 0.1 ppm to 23% at 100 ppm). Body weights and fat content were significantly (p less than or equal to .05) reduced by feed restriction, with fat content only 39% of controls at 21 d off. Mortality averaged 0, 13.6, and 35.8% for rats fed 0, 5, or 10% MO, and 25, 15, 8.6, and 3.7% for rats feed restricted at 0, 15, 30, and 45%, respectively. Histopathology of the dead and moribund rats indicated that the clinical signs were not characteristic of PBB toxicity. In a second experiment, safflower oil at 3.5% or excess vitamins prevented the mortality and clinical signs associated with MO during withdrawal from 100 ppm PBBs. Based on these data and those in the literature, PBBs interfere with vitamin utilization.

The effect of triorthocresyl phosphate, a delayed neurotoxin, on the testes of young broilers

Broiler chickens were raised in brooder batteries. At 6 weeks of age 10 chickens were given either a single oral dose of triorthocresyl phosphate (TOCP) at 500 mg/kg body wt. or corn oil as a vehicle. The testes of both groups were examined morphologically and histologically. Changes in characteristics of testicular atrophy in the TOCP-treated group were clearly evident. The results also suggest that TOCP, a delayed neurotoxin, may induce sterility in young male chickens by an unknown mechanism.

Exposure to triphenyl phosphite results in widespread degeneration in the mammalian central nervous system

Previous studies in mammals have found that exposure to triphenyl phosphite results in cellular and axonal degeneration in the spinal cord and medulla. However, the nature of concomitant clinical signs suggested that other areas of the central nervous system might also be affected. In this study, the brains of ferrets receiving single subcutaneous injections of triphenyl phosphite were examined 8-12 days after dosing. Widespread areas of axonal, terminal, and somatic degeneration were seen in medullary, pontine, and thalamic nuclei. Extensive axonal and terminal degeneration were also noted in the cerebellar granule cell layer and in the cerebral cortical primary visual and sensorimotor areas. These data indicate that triphenyl phosphite exerts a potent neurotoxic effect, not only in the medulla and spinal cord, but also in the cerebellum, thalamus, and cerebral cortex.

Effect of beta-naphthoflavone on o-tolyl saligenin phosphate-induced delayed neuropathy in two lines of chickens

The effect of the microsomal enzyme inducer beta-naphthoflavone (beta NF) on the development of organophosphorus-induced delayed neuropathy (OPIDN) was examined in two laboratories (VPI and MSU), utilizing two strains of White Leghorn hens. A single intraperitoneal injection of beta NF at 80 mg/kg body weight 48 h prior to administration of o-tolyl saligenin phosphate (TSP), the neuroactive metabolite of tri-o-tolyl phosphate (TOTP), caused a significant increase in hepatic microsomal cytochrome P-450 concentrations and aniline hydroxylase activities after 72 h in both strains. Hepatic carboxylesterase and cholinesterase activities were not affected by beta NF treatment in either strain. Administration of TSP in single subcutaneous doses of 20 and 25 mg/kg body weight (VPI) or 30 and 60 mg/kg body weight (MSU) caused significant inhibition of whole-brain neuropathy target esterase (NTE) activity 24 h postdosing, and hens subsequently developed clinical signs characteristics of OPIDN. beta NF had no significant effect on NTE inhibition or on initiation or severity of OPIDN clinical signs. However, OPIDN clinical signs were less severe in the strain of bird (MSU) with the higher intrinsic hepatic carboxylesterase activity and the higher beta NF-induced cytochrome P-450 concentration. The study indicates that microsomal enzyme induction, which has been shown to alleviate TOTP-induced delayed neuropathy, could not alleviate OPIDN resulting from exposure to TSP. This study also suggests that strain may affect susceptibility to TSP-induced delayed neuropathy.

Degeneration patterns in the chicken central nervous system induced by ingestion of the organophosphorus delayed neurotoxin tri-ortho-tolyl phosphate. A silver impregnation study

Exposure to certain organophosphorus compounds results in a neurological condition known as organophosphorus-induced delayed neurotoxicity (OPIDN). OPIDN is characterized clinically by an initial post-exposure delay period of 8-14 days after which signs of progressively developing ataxia and paralysis of the hindlimbs are observed. Although several studies have reported the presence of degeneration induced by organophosphorus delayed neurotoxins in specific central nervous system (CNS) structures, none have systematically examined CNS changes seen in the most frequently studied animal model for OPIDN--the domestic fowl. In the present study, we assessed the location and extent of anterograde degeneration in the chicken CNS following exposure to tri-o-tolyl phosphate (TOTP). All birds were dosed with 500 mg TOTP/kg body weight and killed after post-exposure periods of 1, 2, 3, or 4 weeks. The brains and spinal cords were processed with Fink-Heimer and Nissl stains. In the spinal cord, axon degeneration was noted in the fasciculus gracilis at cervical levels two weeks after exposure to TOTP. At 3 weeks, degeneration was also present in the cervical part of the dorsal spinocerebellar tract, in the lumbar part of the medial pontine-spinal tract, and in lamina VII in the lumbar ventral horn. In the medulla, moderate amounts of terminal and preterminal degeneration appeared at two weeks in the lateral vestibular, gracile, external cuneate, and lateral cervical nuclei. Lesser amounts of degeneration were noted in the solitary, inferior olivary, and raphae nuclei, in the medial, descending and lateral vestibular nuclei, and in the lateral paragigantocellular, gigantocellular, and lateral reticular nuclei. Fiber degeneration was also present in the medullary portions of the dorsal and ventral spinocerebellar tracts and spinal lemniscus. In the cerebellum, moderate amounts of terminal degeneration appeared in the deep cerebellar nuclei at one week while moderate mossy fiber degeneration was first noted in the granular layers of cerebellar folia I-V at 3 weeks. These results indicate (1) that, in the CNS, axonal and terminal degeneration resulting from TOTP intoxication appears to be confined to the spinal cord, medulla and cerebellum, (2) that the time of onset of degeneration in different fiber tracts and nuclei ranges from one to three weeks post-exposure, and (3) that the delay in the appearance of clinical signs of OPIDN is consistent with the delayed onset of degeneration in many of the affected CNS fiber systems.

Effect of route of administration on the development of organophosphate-induced delayed neurotoxicity in 4-week-old chicks

The poor absorption of organophosphate delayed neurotoxins through the gastrointestinal tract has been suggested as a reason why young chickens are not susceptible to organophosphate-induced delayed neurotoxicity (OPIDN). In the present study, 4-wk-old White Leghorn chickens were administered a single dose of 500 mg tri-o-tolyl phosphate (TOTP)/kg body weight or 100 mg o-tolyl saligenin phosphate (TSP)/kg body weight via the oral, intramuscular, or intraperitoneal route. In addition, TOTP TSP were administered intravenously at 250 and 50 mg/kg body weight, respectively. Forty-eight hours after dosing, half the birds in each group were killed for subsequent determination of whole-brain and sciatic nerve neurotoxic esterase (NTE) activity while the remaining 5 birds per group were observed daily from d 7 through d 21 for development of OPIDN clinical signs. TOTP administered by the 4 routes generally resulted in whole-brain and sciatic nerve NTE inhibition in excess of 85%. TSP given via the different routes resulted in 75-84% inhibition of whole-brain NTE activity and 66-79% inhibition of sciatic nerve NTE activity. No birds displayed clinical signs typical of OPIDN during the 21-d test. Thus, the resistance of the young chicken to the delayed effects of organophosphate compounds is due to factors other than the poor absorption of the compound through the gastrointestinal tract or the inability of the bird to convert TOTP to its neuroactive metabolite, TSP.

Chronic toxicity of dietary fluorine to mink

Seventy-two 3-mo-old pastel mink were fed diets that contained 0, 33, 60, 108, 194 or 350 ppm supplemental fluorine (F), as NaF, for 382 d to assess its effects on growth, fur quality, reproduction and survivability. The basal diet contained 35 ppm F as fed. No significant differences were observed in body weight gains or fur quality between the controls and any of the F-treated groups (P greater than .05). Some males fed 350 ppm supplemental F for a 4-mo period prior to pelting had weakened frontal, parietal and femoral bones that fractured during the pelting process. The F treatments had no measurable adverse effects on breeding, gestation, whelping or lactation, although only 14% of the kits whelped by females fed 350 ppm F survived to 3 wk of age. The survivability of the adult mink was adversely affected only at 350 ppm supplemental F. At the termination of the study, no differences were observed in hematologic parameters or serum calcium concentrations between the controls and treated mink (P greater than .05), but serum alkaline phosphatase activities were increased (P less than .05) by the two highest dietary F levels. Serum F levels were elevated (P less than .01) only in mink fed 194 and 350 ppm F, and urinary and femoral F concentrations in the treated animals were generally greater (P less than .05; P less than .01) than control values and were closely related with dietary F levels. Femoral ash contents of the 194 and 350 ppm F-treated mink were less than the control values (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicological manifestations of 2,4,5,2',4',5'-, 2,3,6,2',3',6'-, and 3,4,5,3',4',5'-hexachlorobiphenyl and Aroclor 1254 in mink

Adult female mink were fed diets that contained 2.5 ppm Aroclor 1254, 0.1 or 0.5 ppm 3,4,5,3',4',5'-hexachlorobiphenyl (345 HCB), 2.5 or 5.0 ppm 2,4,5,2',4',5'-hexachlorobiphenyl (245 HCB) or 2,3,6,2',3',6'-hexachlorobiphenyl (236 HCB), or a control diet from 1 mo prior to breeding through parturition. All mink fed 0.5 ppm 345 HCB died within 60 d, while those fed 0.1 ppm showed 50% mortality after 3 mo exposure. Only one stillborn kit was whelped in the Aroclor 1254 group. No adverse reproductive effects were observed in the animals fed 236 HCB or 245 HCB. Plasma progesterone concentrations were significantly depressed by Aroclor 1254 and significantly elevated by 0.1 ppm 345 HCB. 17 beta-Estradiol concentrations were not significantly altered by any of the dietary treatments. Hepatic microsomal cytochrome P-450 concentrations were significantly elevated by all treatments except 236 HCB, with the largest increases occurring in mink exposed to Aroclor 1254 and 345 HCB. Aminopyrine N-demethylase activity was elevated by 5.0 ppm 245 HCB. Aroclor 1254 caused significant elevations in both benzo[a]pyrene hydroxylase and ethoxyresorufin O-deethylase activities. Benzo[a]pyrene hydroxylase activities were also significantly elevated in mink fed 245 HCB and 345 HCB. Aroclor 1254 caused a significant elevation in cerebellar and hypothalamic norepinephrine concentrations and a significant elevation in hypothalamic dopamine concentrations. Cerebral dopamine was elevated by 0.1 ppm 345 HCB, while midbrain dopamine levels were depressed. Norepinephrine concentrations were significantly elevated by 5.0 ppm 236 HCB in the midbrain and by 5.0 ppm 245 HCB in the medulla.

Mating behavior and brain biogenic amine concentrations in chickens treated with parachlorophenylalanine (PCPA)

Four experiments were conducted to determine the effect of parachlorophenylalanine (PCPA) on the male mating behavior of a line of chickens genetically selected for low mating frequency and to determine the effect on brain concentrations of 5-hydroxytryptamine, dopamine (DA) and norepinephrine (NE). Mating behavior was not affected by moderate levels (less than 64 mg/kg) of PCPA, and decreased significantly when higher levels (100 mg/kg) of the drugs were administered. Results suggest that elevated brain serotonin titers were not causing the low mating frequency associated with the selected line. Birds receiving higher levels of PCPA exhibited a lethargy which persisted for approximately ten days after withdrawal of the drug. Serotonin, DA, and NE were all significantly reduced in the brains of birds receiving PCPA (30 mg/kg).

The effect of hepatic mixed-function oxidase enzyme inducers on the development of tri-o-tolyl phosphate-induced delayed neurotoxicity

Adult White Leghorn hens were divided into 15 groups of 10 birds each. Five groups received the prototype mixed-function oxidase (MFO) enzyme inducer phenobarbital (PB) at a dosage of 50 mg/kg body weight for 3 consecutive days by intraperitoneal (i.p.) injection, 5 groups received the MFO enzyme inducer beta-naphthoflavone (beta NF) at 20 mg/kg body weight for 2 consecutive days by i.p. injection, while the remaining 5 groups did not receive an inducer. At 24 h after the last injection, the birds received a single oral dose of tri-o-tolyl phosphate (TOTP) (an organophosphate that produces delayed neurotoxicity after metabolic activation by the MFO system) in doses of 62.5, 125, 250, or 500 mg/kg body weight. Corn oil served as the vehicle control. At 48 h after the administration of TOTP, half the birds in each of the 15 groups were killed for determination of whole-brain neurotoxic esterase (NTE) activity. The remaining birds were observed for the subsequent 19 d for onset of clinical signs characteristic of delayed neurotoxicity. Birds receiving beta NF prior to TOTP were protected by the inducer when compared to birds receiving PB + TOTP or TOTP alone. This was indicated by less severe clinical signs as well as less inhibition of whole-brain NTE activity. The protective effect offered by beta NF may be due to induction of enzymes responsible for the inactivation of the neurotoxic metabolite.

Grouping in Japanese quail. 1. Agonistic behavior during feeding

Agonistic behavior in male Japanese quail, shown by aggressive pecking after feed restriction, was potentiated in unstable groups (a visitor bird moved to a new cage containing an unfamiliar resident each 24-hr period) but not in stable (a pair that was never changed once the birds were placed in cages) groups. The resident quail were more aggressive than either visitors or individuals of the stable groups. Ambivalent behavior (behavior characterized by an aggressive action followed immediately by a submissive posture) during feeding competition was observed in both the unstable and stable groupings. The ambivalent behavior appeared to be a conditioned response and was probably a result of the motivation to feed after a period of feed deprivation. During the experimental period the stable pairs of quail gained 28% of their initial body weight, but the resident and visitor quail, which were in the unstable grouping, gained only 15 and 13%, respectively. The differences in percentage weight gain were significant. Paired testes weights of the resident and visitor quail were significantly less than those of the stable birds.

Microsomal enzyme induction, egg production, and reproduction in three lines of Japanese quail fed polybrominated biphenyls

The sensitivity of three genetic lines of Japanese quail to polybrominated biphenyls (PBBs) was evaluated using criteria of egg production, reproduction, and induction of the hepatic microsomal mixed-function oxidase (MFO) system. Two genetic lines of quail, developed to diverge in their plasma cholesterol response to exogenous adrenocorticotropin (ACTH) (a "Low" line and a "High" line), were compared to a random-bred line ("Random"). ACTH administration caused increases in plasma cholesterol in the Low line that were 15 and 39% below the Random-line values in males and females, respectively, while High-line values were 31% higher in males and 36% higher in females when compared to the respective Random-line values. Hepatic activities of aryl hydrocarbon hydroxylase (AHH) and hexobarbital hydroxylase (HxH) were not significantly influenced by ACTH administration or by genetic line in either sex. PBBs fed at 40 or 80 mg/kg diet for 5 wk resulted in significant increases in hepatic AHH and aminopyrine N-demethylase (APND) activities and cytochrome P-450 concentrations. The induction of AHH, APND, and cytochrome P-450 was significantly less in Low-line males in comparison to Random- and High-line males, while the induction of AHH was less in Low-line females when compared to females from the other two lines, based on covariance analysis. In terms of reproductive parameters, there was a greater adverse effect on egg production at 80 ppm PBBs in Low-line females when compared to the Random and High lines. These data indicate an example in which the biological toxicity of a compound and the induction of a 3-methylcholanthrene-type hepatic enzyme are not directly correlated.

Differential sensitivity to the delayed neurotoxin tri-o-tolyl phosphate in several avian species

Adult white leghorn chickens, ring-necked pheasants, mallards, bobwhites, and Japanese quail were administered single oral doses of tri-o-tolyl phosphate (TOTP) at levels of 125, 250, 500, and 1000 mg/kg body weight. Corn oil served as the vehicle control. At 24 h after dosing, half the birds from each group were killed for determination of whole-brain neurotoxic esterase (NTE) activity. The remaining birds were maintained for 21 d. Daily observations for the development of clinical signs typical of delayed neurotoxicity were begun 7 d after dosing and continued for the subsequent 14 d. In both the Japanese quail and bobwhite, all doses of TOTP resulted in NTE inhibition in excess of 70%, yet no birds of either species developed ataxia or paralysis. However, in the mallard none of the doses of TOTP caused inhibition of NTE activity greater than 61% nor resulted in the development of clinical signs. In the pheasant, all doses of TOTP caused at least a 70% inhibition of whole-brain NTE activity, yet only birds receiving 500 and 1000 mg/kg developed clinical signs. In the chicken, all TOTP doses caused inhibition of NTE in excess of 80%, and all doses resulted in clinical signs typical of delayed neurotoxicity.

Neurochemical alterations induced by manganese chloride in neonatal rats

Male rats were exposed to manganese at doses of 1, 10, and 20 microg/g body weight/day from birth to day 24 post-partum. Animals were weighed and examined daily. The animals showed no visible signs of toxicity and exhibited normal weight gain. On day 25 the animals were killed by decapitation and the hypothalamic area and corpus striatum were removed and analyzed for several neurochemical components. Chronic manganese administration (10 and 20 microg/g) caused a significant reduction in the concentration of endogenous dopamine in the hypothalamic area. The concentration of endogenous norepinephrine in the hypothalamic area was unaffected at all levels of manganese administration. The depletion of dopamine induced by alpha-methyl-p-tyrosine was less in the hypothalamic area of chronic manganese-treated rats suggesting that dopamine turnover was reduced. No significant changes in neurochemical components occurred in the corpus striatum. Manganese at a dose of 20 microg/g caused a significant decrease in hypothalamic tyrosine hydroxylase activity and a significant increase in hypothalamic monoamine oxidase activity. The dosing regimen of 10 and 20 microg/g caused a significant elevation in tissue levels of manganese in both the hypothalamic area and corpus striatum. The results of this study indicate that minor alterations in the manganese content of the developing rat brain can lead to neurochemical alterations in specific brain regions.

An investigation into the effects of manganese and other divalent cations on tyrosine hydroxylase activity

The activity of tyrosine hydroxylase (TH) was measured in homogenates of hypothalamic tissue and corpus striatum obtained from 24 day old rats. The addition of manganese to the preparations had no direct effect on TH activity in either brain region. Similarly, the addition of calcium, magnesium and lead at concentrations of 1.0 mM did not affect TH activity. Cadmium and zinc (1.0 mM) significantly reduced TH activity in both the hypothalamic area and corpus striatum. Iron (1.0 mM) significantly stimulated TH activity in the corpus striatum but did not affect TH activity in the hypothalamic area. At conentrations of 1.0 mM, neither disodium ethylenediamine tetra-acetic acid (EDTA) nor ethylene glycol bis (beta-amino-ethyl ether)-N,N'-tetraacetic acid (ECTA) affected directly TH activity in either brain region. Cyclic adenosine 3',5'-monophosphate (cAMP) at a concentration of 1.0 mM did not affect TH activity in either the hypothalamic area or corpus striatum. Results from these in vitro studies show clearly that manganese does not inhibit directly TH activity and that manganese does not compete with other physiologically important divalent cations to cause the reduction in TH activity seen in vivo after chronic exposure.

Some aspects of brain neurochemistry after intrauterine exposure to tritium

Rats were continuously exposed to tritiated water (0, 1, 10 and 100 muCi HTO/ml body water) from conception to birth. Calculated, cumulative whole-body doses to the embryo and foetus were approximately 0, 6-6, 66 and 660 rad. The levels of several enzymes and established or presumptive central nervous system neurotransmitters were examined postnatally in whole brains. These were norepinephrine (NE), dopamine (DA), acetylcholinesterase (AChE) and monoamine oxidase (MAO). Intrauterine exposures to doses as low as 66 rad produced measurable and persistent decreases in brain weight and increases in NE concentrations at 21 and 45 days postnatally. No differences from control values were seen in the rate of turnover of NE or the concentrations of DA, AChE or MAO at 45 days. Exposure in utero to 6-6 rad produced no detectable postnatal effects on the brain neurochemical parameters measured.