Effects of prenatal exposure to amphetamine in the medial prefrontal cortex of the rat

Prenatal methamphetamine exposure is associated with corticostriatal white matter changes in neonates

Diffusion tensor imaging (DTI) studies have shown that prenatal exposure to methamphetamine is associated with alterations in white matter microstructure, but to date no tractography studies have been performed in neonates. The striato-thalamo-orbitofrontal circuit and its associated limbic-striatal areas, the primary circuit responsible for reinforcement, has been postulated to be dysfunctional in drug addiction. This study investigated potential white matter changes in the striatal-orbitofrontal circuit in neonates with prenatal methamphetamine exposure. Mothers were recruited antenatally and interviewed regarding methamphetamine use during pregnancy, and DTI sequences were acquired in the first postnatal month. Target regions of interest were manually delineated, white matter bundles connecting pairs of targets were determined using probabilistic tractography in AFNI-FATCAT, and fractional anisotropy (FA) and diffusion measures were determined in white matter connections. Regression analysis showed that increasing methamphetamine exposure was associated with reduced FA in several connections between the striatum and midbrain, orbitofrontal cortex, and associated limbic structures, following adjustment for potential confounding variables. Our results are consistent with previous findings in older children and extend them to show that these changes are already evident in neonates. The observed alterations are likely to play a role in the deficits in attention and inhibitory control frequently seen in children with prenatal methamphetamine exposure.

Effects of postnatal exposure to methamphetamine on the development of the rat retina

Since the development of different cell types in the retina occurs at different rates, it is possible that exposure to an exogenous substance may produce effects during one time period, but not during another. This study aims to analyze the effects of methamphetamine (METH) in the growth pattern of an experimental model as well as neurochemical and immunohistochemical parameters of the dopaminergic system of the rat retina. The three development stages chosen in this study are key markers in rat eye development. Rats were given 15 mg/kg body weight per day of METH as subcutaneous injections in 0.9% saline (3 mL/kg weight/day) from the day after birth PND 1 to PND 6, PND 13, and PND 29. Each daily dose was split into two. The control group was injected subcutaneously with saline. Both the schedule and volume for injecting saline in the control group were the same as for the METH-treated group. There were no significant differences in the total number of offspring per litter among treatment groups. All offspring had similar body weight at birth. Analysis of body weight on PND 1, showed that animals treated with METH had similar body weights to control-treated animals and females had smaller weights than males. For growth evolution, only litters with a sex ratio of four males and four females were used. Animals treated with METH had smaller body weights than the control-treated animals for all ages studied (PND 7, 14, and 30). Within the control group at PND 30, a significant difference was found in the body weight of females, which was lower when compared with males. For the postnatal model, 7 deaths occurred for the METH-exposed group. No deaths occurred in the control group in a total of 16 saline-injected litters comprising 186 pups. Although the levels of dopamine (DA) was within normal values for the postnatally exposed METH group when compared with its respective control group at PND 7 and 30, at PND 14 this was not the case: in this experimental group, the level of DA was lower than in the control group for both females and males. Support for this result was not evident from the TH immunoreactivity studies, probably because the methodology lacks the sensitivity to distinguish any mild effects, such as that observed in the postnatal model at PND 14. The level of the DA metabolite 3, 4-dihydroxyphenylacetic acid (DOPAC) remained unaffected at all ages studied, for both females and males. The results obtained in this study support the view that, during the critical periods in which the catecholamines can influence the development of neurones, METH transiently affects the pattern of the dopaminergic system in the developing retina.

Myelination changes in the rat optic nerve after prenatal exposure to methamphetamine

The use of psychostimulants during adolescence and early adult life has increased in recent years. It is known that these substances affect the sensory systems, and the optic nerve has been shown to be a target tissue. This work was conducted to evaluate the effects of prenatal exposure to methamphetamine (MA) on the developmental pattern of the rat optic nerve. Pregnant female rats were given 5 mg/kg body weight/day MA, s.c., in 0.9% saline from gestational days 8 to 22. The control group was injected with an isovolumetric dose of 0.9% saline. Animal model parameters, such as gestational body weight evolution, food intake and pups parameters were registered. The offspring were sacrificed at postnatal days (PND) 7, 14 and 21. Morphometric analyses were performed at light and electron microscopic levels on optic nerve cross sections; parameters measured included optic nerve diameter and area, axonal density, total number of axons and myelin thickness. Myelin basic protein (MBP) was measured by western blotting in optic nerve samples at PND14 and PND21. The animal model parameters, such as maternal and pup weight, showed no significant differences between MA and control groups. Optic nerve diameter was smaller at PND7 in the male MA group and in both male and female MA groups at PND21. The mean cross-sectional area was smaller at PND14 in the male MA group and in both male and female groups at PND21. The total number of myelinated axons did not vary between groups at any of the studied ages. The myelin thickness of the axons in MA-treated females was thinner when compared with the respective control group at PND21. No other differences were found concerning myelin thickness. There was a reduction of MBP protein expression in MA-injected females at PND14 and PND21. The combined results suggest that prenatal exposure to MA affects the myelination process.

Methamphetamine and lipid peroxidation in the rat retina

BACKGROUND

The use of psychoactive drugs during adolescence and early adult life has increased in the last few decades. It is known that developmental exposure to psychostimulants affects the sensory systems, and the retina has been shown to be a target tissue. This work was conducted to evaluate the pattern of lipid peroxidation in the rat retina following prenatal exposure to methamphetamine (MA).

METHODS

Pregnant female Wistar rats were given MA (5 mg/kg of body weight/day; SC, in 0.9% saline) from GD 8 to 22. Offspring were sacrificed at postnatal days (PNDs) 7, 14, and 21. The retinas were homogenized, and both the total antioxidant and superoxide dismutase (SOD) activities were measured by enzymatic-colorimetric methods. The lipid peroxidation byproducts (malondialdehyde [MDA] and MDA-like metabolites) were measured by the thiobarbituric acid test.

RESULTS

Total antioxidant levels were lower in the MA group at PND 21 in both males and females. The activity of SOD was higher in PND 7 females from the MA group. MDA levels were higher in the MA group at PND 21 in both genders.

CONCLUSIONS

These findings suggest that prenatal-induced MA toxicity in the retina may be related to lipid peroxidation processes and oxidative stress.

Sensitized Fos expression in subterritories of the rat medial prefrontal cortex and nucleus accumbens following amphetamine sensitization as revealed by stereology

Behavioral sensitization to the locomotor activating effects of amphetamine refers to the progressive, long lasting increase in locomotor activity that occurs with repeated injections. This phenomenon is thought to result from neuroadaptations occurring in the projection fields of mesocorticolimbic dopaminergic neurons. In the present study, we investigated the effects of amphetamine sensitization on Fos immunoreactivity (Fos-IR) in subterritories of the nucleus accumbens (core and shell) and medial prefrontal cortex (mPFC; dorsal and ventral) using stereology. Rats received five daily injections of amphetamine (1.5 mg/kg, i.p.) or saline. Behavioral sensitization was measured 48 h following the last injection, in response to a challenge injection of 1.5 mg/kg amphetamine. Sensitized rats showed a greater enhancement of locomotor activity upon drug challenge compared with their saline counterparts. Densities of Fos-positive nuclei were enhanced more in the dorsal than the ventral mPFC subterritory, whereas in the nucleus accumbens, densities of Fos-positive nuclei were increased more in the core than the shell of amphetamine-sensitized rats compared to controls. These results represent, to our knowledge, the first published report using stereological methods to quantify Fos-IR in the brain and suggest functional specialization of cortical and limbic regions in the expression of behavioral sensitization to amphetamine.

Effects of methamphetamine-induced neurotoxicity on the development of neural circuitry: a hypothesis

Exposure of the developing brain to methamphetamine has well-studied biochemical and behavioral consequences. We review: (1) the effects of methamphetamine on mature serotonergic and dopaminergic pathways; (2) the mechanisms of methamphetamine neurotoxicity and (3) the role of serotonergic and dopaminergic signaling in sculpting developing neural circuitry. Consideration of these data suggest the types of neural circuit alterations that may result from exposure of the developing brain to methamphetamine and that may underlie functional defects.

Effects of neonatal exposure to cocaine in the development of the neurotransmitters retinal systems: an immunocytochemical and neurochemical study

The visual system of rodents is affected if exposure to drugs, e.g., cocaine, occurs during prenatal or early postnatal development. This study aims to evaluate, in an experimental model of neonatal exposure to cocaine in the rat, the immunocytochemical expression of tyrosine hydroxylase in the retina and the levels of different neurotransmitters and its metabolites. Male Wistar rats were given 15 mg cocaine hydrochloride/kg body weight/day, subcutaneously, in two daily doses, from the day after birth (PND1) to PND6, 13, and 29. Controls were given 0.9% saline. Groups of rats were perfused at PND7, 14, and 30 with fixative, and the retinas were processed as wholemounts, and immunostained with the antibody anti-TH. Other groups were decapitated, and the retinas were dissected and processed by high performance liquid chromatography with electrochemical detection (HPLC-EC) for determination of dopamine and metabolites (DOPAC and HVA). A reduction in the retinal surface area was detected in the PND30 cocaine group, and a decrease in the density of the small TH-IR cells was found in the PND14 cocaine group although not reaching significant levels. The other quantitative parameters did not differ between the control and cocaine groups. The levels of neurotransmitters did not significantly differ between the groups at any age. These results show a differential vulnerability of the dopaminergic system of rats exposed neonatally to cocaine when compared with the effects found after prenatal exposure to the same drug.

Toluene abuse embryopathy: longitudinal neurodevelopmental effects of prenatal exposure to toluene in rats

To determine the longitudinal effects of prenatal exposure to toluene in rats, dams received daily gavage doses of toluene diluted in corn oil on Days 6 through 19 of gestation, whereas control dams received corn oil. Litters were evaluated either on Gestational Day 19, Postnatal Day 10, or Postnatal Day 21; morphometric analysis of brain and measurements of brain DNA, cholesterol, and protein were made. Prenatal toluene exposure produced growth retarded fetuses with smaller brain and caudate-putamen volumes, fewer forebrain cell nuclei (DNA), and a reduction in both hindbrain cell size (protein/DNA) and myelination per cell (cholesterol/DNA). Postnatal catch-up growth occurred in the prenatally toluene-exposed pups, and by Postnatal Day 21 these differences had resolved. However, on Postnatal Day 21, a significant reduction in forebrain myelination/cell was present in the prenatally toluene-exposed pups. Therefore, whereas the effects of toluene administered prior to the time of the brain growth spurt were, for the most part, reversible, these exposures resulted in reduced forebrain myelination that may be permanent.

Differential effects of prenatal exposure to cocaine and amphetamine on growth parameters and morphometry of the prefrontal cortex in the rat

The purpose of this study was to investigate the differential effects of prenatal exposure to psychostimulants, e.g., cocaine or amphetamine, on basic growth parameters and morphometry of the medial prefrontal cortex of the rat. A group of pregnant Wistar rats was given 60 mg/kg body weight/day of cocaine hydrochloride and another group 10 mg/kg body weight/day of d-amphetamine sulfate, subcutaneously, from gestational days 8 to 22. Control groups of pregnant rats were pair-fed; litters were culled to eight pups (4 males and 4 females) weighed every other day until postnatal day 30 and every week until day 90. The body weight growth patterns modelled by a Gompertz curve were different in rats prenatally exposed to the two psychostimulants. Rats exposed to amphetamine had on average a slower growth than those exposed to cocaine, reaching an identical estimated adult weight. Allometric relationships between forebrain and body weight and cerebellum and body weight were described by two distinct postnatal growth phases that are different among the experimental groups. In the comparison of the two psychostimulants the relative cerebellum/body growth is lower in the offspring of the cocaine group than in the amphetamine group between PND14-PND30; between PND30-PND90 the relative growth rate is considerably higher in the offspring of the cocaine dams compared to that of the amphetamine dams. Groups of perfused animals were selected at postnatal days 14 and 30 to analyze the morphometric organization of the medial prefrontal cortex. In serial celloidin sections the volumes of the prefrontal cortex were determined; the number of neurons per unit volume of reference area was calculated using the stereological technique of the disector. The changes found in the morphometric parameters show a catch-up at postnatal day 30 of the "increased" density of neurons of the medial prefrontal cortex found at postnatal day 14. These data show differential growth patterns of offspring from cocaine- and amphetamine-exposed rats; a delayed development in the achievement of normal morphometric parameters of neurons in the prelimbic subarea of the medial prefrontal cortex occurs in the prenatally amphetamine-exposed offspring at early ages, and a catch-up is found after the first month of life. Complementary studies are needed to assess whether these changes have functional implications in the rats exposed prenatally to psychostimulants.