William J. Pizzi

Effects of monosodium glutamate on somatic development, obesity and activity in the mouse.

Neonatal mice 1 and 5 days of age and older mice 25 days of age were injected with an increasing dose of monosodium glutamate (MSG) for a ten-day period and observed for at least 150 days. Both male and female animals in the 1- and 5-day age group treated with MSG showed large increases in weight over controls along with a shortened body length. The MSG group also showed decreases in locomotor and explatory behavior. The 25-day animals took much longer to show effects or failed to show any effects, indicating that the MSG-induced changes studied are age dependent. Possible methodological considerations accounting for conflicting reports in the MSG literature are discussed in light of the present findings.

Effects of prenatal diphenylhydantoin treatment on reproductive outcome, development, and behavior in rats

Pregnant Sprague-Dawley rats were administered sodium diphenylhydantoin (DPH) by gavage on gestation days 9-18 in doses of 0, 100, or 200 mg/kg. DPH-treated dams showed a dose-related decrease in weight gain throughout the drug treatment period. Offspring had significantly lowered birth weights, along with increased mortality through the first 30 days of life. In one of the experiments specifically designed to measure pup mortality, the rates were 41.4% and 60.7% respectively, for the 100 and 200 mg/kg DPH groups. Shortly after eye opening, many of the DPH-treated animals developed chromodacryorrhea, a condition that remained throughout the experiment. Aside from lowered body weights, no differences were observed in the attainment of several standard developmental landmarks. During the neonatal period, the pups exposed in utero to 100 mg/kg DPH showed a significant increase in pivoting locomotion on postnatal days 7 and 9. As adults, the animals exposed to 200 mg/kg DPH showed significant increases in locomotor activity measures. Both DPH groups developed a dose-related and highly abnormal spontaneous circling behavior. These results confirm a small but growing body of literature that demonstrates that DPH is a behavioral teratogen.

Differential effects of methylphenidate on the growth of neonatal and adolescent rats

Methylphenidate (MPH), the drug of choice in the treatment of Attention Deficit Disorders with Hyperactivity (ADD/H), has raised concern regarding its suspected potential for reducing body stature in growing patients. In a previous study we demonstrated that neonatal rats treated with MPH (35 mg/kg, SC, twice daily) showed an acute growth impairment followed by a rapid growth-rebound phenomenon. This report confirms our earlier findings in neonatal rats and extends the investigation of the growth suppressing effects of MPH to the periadolescent period of development in rats. Specifically, neonatal groups of male and female rats treated with higher and lower doses of MPH than in the original study confirmed the growth impairment and growth rebound phenomena reported earlier. Unlike neonatal rats, rats treated during the periadolescent period of development failed to show any growth impairment. These data suggest that the growth suppressing effects of MPH are the result of an acute toxicity which is readily reversible on discontinuation of the drug. Further, it is concluded that there is a low probability of long term effects on human body stature when the minimal therapeutic dose is used in clinical practice.

Muscimol and γ-hydroxybutyrate: Similar interactions with convulsant agents

Abstract Muscimol has been shown to be a potent GABA agonist in several preparations. After systemic administration, muscimol is rapidly metabolized in the periphery and little, if any, unchanged muscimol gains access to the brain. A major metabolite of muscimol may be structurally analogous to γ-hydroxybutyric acid. In this study it is shown that both muscimol and γ-hydroxybutyrate antagonize convulsions induced by 3-mercaptopropionate, an inhibitor of GABA synthesis, and strychnine, a glycinergic antagonist, while potentiating convulsions induced by bicuculline, a putative GABA antagonist, and pentylenetetrazol, a generalized excitant and possible GABA antagonist. Although these results apparently contradict previously reported data, it is proposed that these anomalies reflect differences dependent upon varying dose regimens of muscimol. The differential effects of low vs. high doses of muscimol may reflect differences in the accessibility to, or affinity of, morphologically distinct GABA receptors that mediate different pharmacological functions.

Methylphenidate and growth: demonstration of a growth impairment and a growth-rebound phenomenon.

Methylphenidate (MPH), the drug of choice in the treatment of attention deficit disorder with hyperactivity (ADD/H), has been shown to reduce the body stature of some patients. The present study was undertaken to determine if MPH suppresses growth in rats, and whether the clinical observation of a growth rebound phenomenon could be experimentally demonstrated. Our results demonstrate that neonatal rats treated with MPH show a reduction in femur length and a reduction in thyroid, pituitary, testis, adrenal gland, and brain weights immediately following drug cessation. However, a growth-rebound phenomenon occurs such that there are no differences between treated and control groups within 30 days of the last drug exposure. These data, along with those from the clinical literature, suggest that growth impairment is most likely a result of the acute effects of the drug. Further, these data suggest that when administered at therapeutic doses which avoid significant weight loss in the patient, MPH is not likely to cause growth impairment in children.

Conditioned taste aversion is a confound in behavioral studies that report a reduction in the reinforcing effects of drugs

Pharmacologic agents with a potential to attenuate the reinforcing properties of drugs of abuse may have an important role in the treatment of drug addiction. The reduction of drug self-administration and sweet solution intake are two common animal models employed to screen for promising therapeutic agents. When these agents are effective in suppressing the behavior maintained by drugs of abuse, the cause is usually attributed to a neuronal mechanism such as the modification of neurotransmitters that subserve reinforcement. These experiments present data for an alternate interpretation which suggest that some of these agents produce a conditioned taste aversion (CTA) that acts as a confounding variable in the screening of potential therapeutic agents. Both carbamazepine and isradipine were shown to establish a CTA at doses reported to attenuate the reinforcing properties of drugs of abuse. It is concluded that CTA represents a potential experimental confound in studies of pharmacologic agents that appear to attenuate the reinforcing properties of drugs. These results suggest that screening for a CTA is necessary in any paradigm that measures the suppression of consummatory behavior in response to pharmacologic intervention.

Developmental and behavioral effects of prenatal primidone exposure in the rat

Pregnant Sprague-Dawley rats were administered primidone (PRM) by oral gavage on gestation days 8-17 in doses of 0.40, and 80 mg/kg. Although these doses of PRM did not produce significant differences in litter size, birth weight, mortality, date of attainment of developmental landmarks or measures of preweaning reflex and motor development, there were a number of significant differences that developed as the animals approached and entered adulthood. When tested as adults, the 80 mg/kg male rats showed a deficit in the performance of an eight-arm radial maze task. These same animals showed a significant reduction in open field activity when tested as adults. In addition, both male and female PRM-treated animals showed reduced body weights at different periods corresponding to onset of sexual maturation during development. These findings are consistent with the larger body of literature reporting on the neurobehavioral teratology of phenobarbital, including its ability to produce lesions in the hippocampus and endocrine dysfunction resulting in reproductive deficits. These results suggest that PRM produces its adverse effects as a result of its metabolism to phenobarbital, which in turn affects the limbic system.

Somatic, behavioral, and reproductive disturbances in mice following neonatal administration of sodium L-aspartate.

Sodium L-aspartate (ASP) was administered to neonatal mice according to an increasing dose schedule from Days 2--11 after birth. Adult ASP-treated animals showed large increases in body weight over controls along with stunted body length. The ASP group also showed decreases in locomotor and exploratory behavior. Reproductive dysfunction occurred in both female and male ASP-treated animals. Among treated animals, females had fewer pregnancies and smaller litters while males showed reduced fertility. Evidence of multiple endocrine dysfunction in ASP-treated animals was reflected by decreased pituitary, thyroid, ovaries and tested weights, along with delayed onset of puberty in females. These results demonstrate that sodium L-aspartate produces a syndrome similar to that seen following the administration of monosodium L-glutamate.

Primidone-induced embryolethality and DRL deficits in surviving offspring.

Pregnant Sprague-Dawley rats were administered primidone (PRM) by oral gavage on gestation days 8-20 in doses of 0 or 120 mg/kg. This dose did not produce body weight differences in the dams during the dosing period nor were there differences in the birth weights of the offspring. PRM was embryolethal with only 43% of drug-treated dams maintaining their pregnancies, whereas 100% of the pregnant controls produced offspring. An analysis of resorption sites in PRM-treated dams that did not deliver showed a nearly identical number of implantation sites (12.6) compared to the litter size of controls (12.8) that delivered pups. There were no overall differences in exploratory activity levels between PRM-treated and control animals. However, in the PRM-treated females there was an absence of the sexually dimorphic increase in activity seen in control females when compared to control males. The PRM-treated males showed an impairment in the acquisition of a DRL-20 (differential reinforcement of low rates) operant schedule over a 9-week acquisition period. There were no differences in the total response rates between the groups, suggesting that this is a specific learning deficit and not a performance deficit. The results of these experiments provide evidence that prenatal PRM exposure can be embryolethal and also impair behavior in the surviving rat offspring.

Unified reversed-phase method for the determination of di (2-ethylhexyl) phthalate and its major metabolite, mono (2-ethylhexyl) phthalate, in biological samples

Abstract A UV detector at 235 nm and an Alltech Altima C18 column (150×4.6 mm and 5 micron) were used to develop a high performance liquid chromatographic method to determine Di (2‐ethylhexyl) phthalate [DEHP] and its metabolite mono (2‐ethylhexyl) phthalate [MEHP] in biological samples. A gradient time of 8 min and a gradient range of 60–100% acetonitrile (ACN) at pH 3.0, with a segmented flow rate gradient, were found to be optimum conditions. These conditions resulted in retention times of 4.2 and 7.1 min for MEHP and DEHP, respectively. The estimated limits of detection (LOD) and quantitation (LOQ) for DEHP were 1.37 and 4.8 µg/mL, respectively. For MEHP, LOD, and LOQ were 0.57 and 2.4 µg/mL, respectively. The developed method was applied to determine DEHP and its metabolite MEHP in blood plasma, liver, kidney, brain, and testis samples.