Dorothy E. Woolley

Morphometric effects of postnatal lead exposure on hippocampal development of the 15-day-old rat.

Neurotoxic sequelae of developmental lead exposure suggest that the hippocampus may be affected. Therefore, rats received low-level exposure via the milk of dams drinking 0.2% lead acetate beginning at parturition, and mid-dorsal sections of the hippocampus and dentate gyrus (DG) from 15-day-old pups were examined by light and electron microscopy. Lead exposure did not reduce body weight nor produce obviously abnormal vascularity or signs of cytotoxicity in the hippocampal formation, and total numbers per section of dentate granule cells or CA3 pyramidal cells were not reduced. On the other hand, lead exposure reduced neuropil development as evidenced both by reduced areas of the dentate hilus and dentate infrapyramidal stratum moleculare and by increased number of hilar CA3 pyramidal cells per unit area. Also, lead exposure reduced numbers of several types of synaptic profiles per unit area in the suprapyramidal mossy fiber zone. Complex invaginated (CI) profiles, assumed to be mature mossy fiber boutons, were characterized by multiple membrane densities and deep invaginations around dendritic spines of pyramidal cells. Complex noninvaginated (CN) boutons exhibited bag-like profiles with multiple membrane densities. Smaller, less numerous, simple (S) profiles contacted either dendritic trunks (ST) or spines (SS). Lead exposure reduced the numerical density of any of the profiles in the deep (close to stratum pyramidale) part of the proximal (close to DG) region of the suprapyramidal mossy fiber zone, but did not alter the numerical density of any of the profiles in the superficial (distal to stratum pyramidale) parts of either proximal or distal (close to CA1) regions. Average size of CN profiles in the distal region was increased by lead exposure. The pattern of effects suggests that low-level lead exposure during development preferentially affects later developing structures within the hippocampal formation, rather than affecting mature structures.

Acute and subacute parathion treatment: Effects on cholinesterase activities and learning in mice☆☆☆

The effects of parathion, an organophosphate insecticide, on the learning and memory of a one-trial passive-avoidance task and on blood and brain true cholinesterase (AChE) and pseudocholinesterase (ChE) activities were tested in mice. An acute dose of 6 mg/kg po was given to mice at various times either prior to the learning trial or the retest trial 24 hr later. A second group of animals was used to determine blood and brain AChE and ChE activities following parathion administration. In another study, various doses (1–4 mg/kg) of parathion were administered sc to mice for 6 days prior to the learning trial. The results of acute administration indicate that parathion given before the learning trial is effective in blocking learning. The maximum effect occurs when parathion is given within the first hour before the learning trial and correlates with maximum changes in enzyme activities. Subacute treatment with parathion results in marked depression of AChE and ChE activities, yet has no effect on learning. These results indicate that parathion disrupts learning upon acute exposure, but that compensation occurs to the prolonged depression of AChE.

Distribution of DDT, DDD, and DDE in tissues of neonatal rats and in milk and other tissues of mother rats chronically exposed to DDT.

Abstract Female rats were chronically exposed to 25, 100, or 200 μg/g dietary DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane] during pregnancy and lactation. In offspring sacrificed within 1 hr after birth before suckling had occurred, DDT concentrations in the whole rat averaged from 1.3 to 2.2 μg/g fresh tissue, and DDD [1,1-dichloro-2,2-bis(p-chlorophenyl)ethane] and DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene] concentrations were 1.0 μg/g or less in the 3 groups. Average concentrations of DDT and metabolites were higher in liver (1.3–4.3 μg/g) than in brain (0.9–2.5 μg/g). In neonatal rats, sacrificed about 10 hr after birth, after suckling had occurred and stomachs were full of milk, concentrations of DDT in the liver were about 5-fold greater than in the littermates sacrificed 1 hr after birth. The results indicate that the retention of DDT in tissues of the neonate during the lactational period was greater than in fetal tissues during gestation. DDT concentrations were 33 μg/g fresh tissue in milk from dams on 25 μg/g dietary DDT, 92 μg/g in milk from dams on 100 μg/g dietary DDT and 174 μg/g in milk from dams on 200 μg/g dietary DDT, showing that the level of output of DDT in the milk may be higher than the level of DDT intake on the lower levels of dietary DDT. In the maternal tissues, fat contained by far the highest concentrations of DDT and metabolites. Liver, kidneys, the various brain areas and spinal cord had approximately similar levels of DDT. Average plasma levels of DDT were low, ranging from 0.7 to 1.7 μg/ml among the 3 groups. Liver was the only tissue in which DDD concentrations were as high or higher than DDT concentrations. DDD concentrations in liver were higher than DDE concentrations, whereas the reverse was true for all other tissues.

Effects of DDT on brain electrical activity in awake, unrestrained rats

Abstract The effects of 50 and 100 mg/kg DDT per os on the spontaneous electrical activity (SEA) of 10 brain areas were investigated in awake, unrestrained rats chronically implanted with electrodes. After DDT changes in SEA occurred before clinical symptoms, such as tremoring, were evident. The most marked change was the great increase in amplitude of the high frequency waves in the SEA of the cerebellar vermis and neocerebellum, probably caused both by increased proprioceptive input to the cerebellum and by excitatory effects of DDT on cerebellar neurons. Changes in the SEA of the cerebellum occurred sooner and were greater than changes in other brain areas investigated simultaneously. Many of the changes in SEA were characteristic of arousal, e.g., disappearance of the occasional slow waves and continous appearance of low amplitude, high frequency waves in the electrical activity of the dorsal (frontal, parietal, and occipital) cortex, reticular formation, and cerebellum; increased occurrence, amplitude and sometimes frequency of the fast sinusoidal waves in the olfactory bulb and prepyriform cortex; and increased occurrence of the 7/sec theta waves and fast waves in the hippocampus. These changes suggested that DDT stimulates the reticular activating system and may explain the hyperirritability caused by DDT. In addition, the increased frequency and amplitude of the respiratory waves in olfactory SEA are evidence that low doses of DDT stimulate respiration, whereas high doses are known to produce death by respiratory paralysis.

Dopaminergic agonists increase [3H]estradiol binding in hypothalamus of female rats, but not of males

Specific nuclear binding of [3H]estradiol in the hypothalamus was increased by acute dopaminergic treatment in female, but not in male, gonadectomized-adrenalectomized rats. In the female this increase could be blocked by the dopaminergic receptor blocker perphenazine and was noted from 1 to 3 hours after injection of [3H]estradiol. Binding was not different in male and female rats in the absence of dopaminergic treatment. These results suggest that acute dopaminergic stimulation may modulate estradiol binding in neural areas known to be important in endocrine function.

Demonstration of nuclear 3H-estradiol binding in hypothalamus and amygdala of female, androgenized-female, and male rats.

The subcellular distribution of radioactivity in female, androgenized female, and male rats 1 hour after the iv administration of tritiated estradiol was examined. High regional specificity among nucle ar fractions of brain areas was seen with the preoptic-anterior hypothal amic area (POA-AH), median eminence-basal hypothalamus (ME-BH), and amygdala having much higher nuclear binding than other brain areas. Nuc lear binding was receptor-mediated in POA-AH, ME-BH, amygdala, dorsal hypothalamus, and the prehypothalamic area in all groups, as demonstrate d by competetive inhibition with diethylstilbestrol (DES). At this time period no differences between male and female rats in DES-blockable radioactivity levels of either nuclear or supernatant fractions in any brain area or pituitary were observed. Androgenized females had lower DES-blockable, nuclear radioactivity levels in POA-AH, ME-BH, and uteri but the % of total tissue radioactivity in the nuclei did not differ between groups for any tissue. These results demonstrate that males and females have similar estradiol uptake systems that are capable of high levels of nuclear binding in various brain areas.

3H-Estradiol Distribution in Normal and Androgenized Female Rats Using an Improved Hypothalamic Dissection Procedure

The distribution of radioactivity in control and neonatally androgenized adult rats was determined 48 h after ovariectomy and 1 h after an i.v. injection of either 3H-estradiol or diethylst

Distribution of DDT in brain and spinal cord of the rat

Abstract The distribution of DDT in the neocortex, cerebellum, brain stem, remaining brain, spinal cord, liver, and plasma of the rat was determined 6, 12, and 24 hours after a single dose per os of 100 mg/kg DDT in oil. The results showed that lipids in central nervous system (CNS) areas which are mostly gray matter, such as neocortex and cerebellum, take up DDT rather rapidly and attain a relatively high maximal concentration. Lipids in areas which have a high myelin content, such as brain stem and spinal cord, take up DDT more slowly and reach a relatively lower maximal concentration. DDT concentrations in lipids of whole brain were twice as high as in the spinal cord lipids at 6 and 12 hours, but were about the same at 24 hours. When DDT concentrations were expressed per unit fresh weight, rather than per unit lipid weight, the concentrations were the same in brain and spinal cord at 6 and 12 hours, but were twice as high in the spinal cord as in the brain at 24 hours. One possible relation between the symptoms of DDT poisoning and the distribution of DDT in the CNS is discussed.

TOXICOKINETICS OF RO 5-4864, LINDANE AND PICROTOXIN COMPARED

The effects produced by IP administration of these three agents in the rat were compared because of in vitro evidence that each modulates the picrotoxinin site of the GABAA receptor. For each, hypothermia had the lowest threshold and convulsions the next, with hypophagia produced only by the highest dose of either Ro 5-4864 or lindane. Convulsant effects had a shorter latency and a shorter duration than did hypothermia. Hypophagia, when present, lasted the longest. Myoclonus was the seizure type with the lowest threshold for all three agents. At the highest dose, lindane produced a high incidence of maximal clonic (hopping) seizures, whereas Ro 5-4864 and picrotoxin produced a high incidence of maximal tonic seizures instead. On a mole/kg basis, picrotoxin was 40 times more effective than the other two agents and produced seizures which started later, peaked later, and persisted longest. Ro 5-4864 and lindane were effective at equimolar concentrations and, in combination, produced effects which suggested either dose-addition or synergism. The data are consistent with the hypothesis that the toxic effects of both Ro 5-4864 and lindane may be attributable, at least in part, to an action at a subpopulation of GABAA receptors.

Sex differences in [3H]-estradiol binding in brain and pituitary after acute dopaminergic treatment: in vivo studies in the rat

Responses to estrogen differ between the sexes, yet sex differences in specific binding of estradiol (E2) to its receptor are not observed consistently. Dopaminergic treatment has been shown to increase binding of 3H-E2 in selected brain areas and anterior pituitary in the female rat, and the dopaminergic system is sexually differentiated. In order to determine whether or not dopaminergic stimulation might induce sex differences in 3H-E2 binding, male and female gonadectomized-adrenalectomized rats were pretreated either with bromocriptine, a dopamine agonist, or with diethyldithiocarbamate (DDC), an inhibitor of dopamine beta-hydroxylase. DDC was used in order to increase endogenous release of dopamine. After such acute dopaminergic treatment, specific binding of 3H-E2 in nuclear and extranuclear fractions of 6 brain areas and pituitary in vivo was determined 1 h after intravenous injection of 3H-E2 (1 microgram/kg body weight). Administration of either bromocriptine or DDC increased specific 3H-E2 binding to nuclear and extranuclear fractions of basal hypothalamus and anterior pituitary from female but not from male rats, thus inducing sex differences in binding in these two tissues. Bromocriptine also increased specific binding in the pineal in females. Total binding was increased in a crude membrane fraction (P2) from pituitary of female but not of male rats after administration of DDC, but the percent of extranuclear specific binding found in the P2 fraction was decreased after DDC in both males and females. The findings suggest that dopaminergic stimulation may induce sex differences in 3H-E2 binding by increasing binding in some brain areas and anterior pituitary in females but not in males.