Chronic intermittent exposure to ethanol during adolescence produces tolerance to the hypnotic effects of ethanol in male rats: a dose-dependent analysis.

Adolescence is a time period when distinct behavioral and neurophysiological changes occur. Novelty seeking is common during this developmental period, and binge alcohol consumption by adolescents is prevalent. Adolescents, as compared to adults, have been shown to display decreased sensitivity to many effects of ethanol, including effects that may serve as cues to moderate consumption. Consequently, reduction of these factors could facilitate drinking behaviors in adolescents, which may disrupt normal developmental processes. Chronic intermittent ethanol exposure (CIEE) to high doses of ethanol in rats has been shown to prevent normal developmental increases in sensitivity to ethanol-induced loss of righting reflex (LORR). However, it is unknown whether the same disruptions would occur following CIEE to more moderate and low alcohol doses. The present study was designed to evaluate the effects of CIEE in rats to several different doses during adolescence on ethanol-induced LORR in adulthood. Male rats were weighed and treated intraperitoneal with 1.0, 2.0, 3.0, or 4.0 g/kg ethanol or equivolume saline (equivalent to 4.0 g/kg dosings) every 48 hours for 20 days beginning on postnatal day (PN) 30. LORR was measured following each ethanol exposure. Finally, LORR was measured in both ethanol and saline-exposed animals following 4.0 g/kg ethanol challenge on PN 50 and following a 12-day withdrawal period (PN62). Duration of LORR remained unchanged throughout the adolescent exposure period. However, when LORR was measured on PN50 and PN62, 4.0 and 3.0 g/kg treatment groups displayed significantly less LORR compared to the free feeding and 1.0 g/kg ethanol treated groups. Animals displayed no tolerance development to LORR throughout the chronic exposure period even though moderate and high doses of ethanol were used. CIEE to high (3.0 or 4.0 g/kg) doses of ethanol disrupted the expected developmental increase in sensitivity to ethanol-induced LORR. These results may have implications for human adolescent drinkers. Specifically due to adolescents' relative resistance to the hypnotic effects of alcohol and their tendency to intake alcohol in an intermittent, or binge-like, manner such tolerance might lead to increases in alcohol abuse in this population of drinkers.

Acute mild footshock alters ethanol drinking and plasma corticosterone levels in C57BL/6J male mice, but not DBA/2J or A/J male mice.

Stress is an often-reported cause for alcohol consumption in humans. Acute intermittent footshock is a frequently used paradigm to produce stress in laboratory animals including mice. The effect produced by intermittent footshock stress on ethanol self-administration has been inconsistent: both increases and decreases in ethanol consumption have been reported. The current set of studies further investigates, in three commonly studied mouse strains, the effect of footshock stress on ethanol self-administration. Furthermore, the effect of footshock on plasma corticosterone levels was determined to investigate potential biochemical correlates. Adult male C57BL/6J, DBA/2J, and A/J mice were allowed to self-administer 10% (wt/vol) ethanol for 12 days in a standard 23-h two-bottle paradigm before receiving either 15 min of mild inescapable footshock or no footshock. Shock intensity was equal to the mean intensity at which each strain vocalized as previously determined. Following footshock, animals had the opportunity to self-administer ethanol for an additional 23 h. Separate animals were subjected to either footshock or no shock prior to collection of plasma for corticosterone. Mild footshock stress altered ethanol self-administration and increased plasma corticosterone levels in C57BL/6J mice. Footshock stress did not alter ethanol self-administration or plasma corticosterone levels in DBA/2J or A/J mice. These data demonstrate that mild footshock stress is a suboptimal method of modeling the stress-induced increases in ethanol consumption often reported by humans.

Different effects of selective dopamine uptake inhibitors, GBR 12909 and WIN 35428, on HIV-1 Tat toxicity in rat fetal midbrain neurons.

Drug abuse is a risk factor for neurological complications in HIV infection. Cocaine has been shown to exacerbate HIV-associated brain pathology and enhance neurotoxicity of HIV-1 Tat and gp120 proteins. In this study, we found that the selective inhibitor of dopamine transporter (DAT) function, 1-[2-[bis(4-fluorophenyl) methoxy]ethyl]-4-(3-phenylpropyl) piperazine (GBR 12909, vanoxerine), but not the selective inhibitors of serotonin and norepinephrine (SERT and NET) transporters, sertraline and nizoxetine, emulated cocaine-mediated enhancement of Tat neurotoxicity in rat fetal midbrain primary cell cultures. Similar to cocaine, the significant increase of Tat toxicity in midbrain cell cultures was observed at micromolar dose (5microM) of GBR 12909. However, different doses of another selective dopamine uptake inhibitor, WIN 35428 did not affect Tat neurotoxicity. The study supports the hypothesis that changes in control of dopamine (DA) homeostasis are important for the cocaine-mediated enhancement of HIV-1 Tat neurotoxicity. Our results also demonstrate that inhibitors of DA uptake, which can bind to different domains of DAT, differ in their ability to mimic synergistic toxicity of cocaine and HIV-1 Tat in the midbrain cell culture.

Sex mediates dopamine and adrenergic receptor expression in adult rats exposed prenatally to cocaine.

The extent of catecholaminergic receptor and respective behavioral alterations associated with prenatal cocaine exposure varies according to exogenous factors such as the amount, frequency, and route of maternal exposure, as well as endogenous factors such as specific brain regions under consideration and sex of the species. The goal of the current study was to use autoradiography to delineate possible moderators of dopaminergic and adrenergic receptor expression in adult rat offspring exposed to cocaine in utero. The current study demonstrated sex-dependent D1 receptor, alpha2, and noradrenergic transporter binding alterations in prelimbic, hippocampus, and anterior cingulate regions of adult rat brains exposed to cocaine during gestational days 8-21. Of further interest was the lack of alterations in the nucleus accumbens for nearly all receptors/transporters investigated, as well as the lack of alterations in D3 receptor binding in nearly all of the regions investigated (nucleus accumbens, prelimbic region, hippocampus, and cingulate gyrus). Thus, the current investigation demonstrated persistent receptor and transporter alterations that extend well into adulthood as a result of cocaine exposure in utero. Furthermore, the demonstration that sex played a mediating role in prenatal cocaine-induced, aberrant receptor/transporter expression is of primary importance for future studies that seek to control for sex in either design or analysis.

Neurotoxicity of HIV-1 Tat protein: involvement of D1 dopamine receptor.

Neurotoxic viral proteins released from HIV-infected cells are believed to play a major role in the pathogenesis of the dementia displayed in a significant number of AIDS patients. HIV-1 associated neuropathology severely affects dopaminergic regions of the brain. Growing evidence indicates that HIV-1 neurotoxic proteins, such as Tat may affect the function of the dopamine transmission system. In turn, molecular components of dopamine neurotransmission may participate in a complex network of Tat-induced cell responses which result in neurodegeneration. In this study we investigated whether D1 dopamine receptors are involved in the mechanism of Tat neurotoxicity in primary rat neuronal cell cultures. We found that in rat midbrain cell cultures, which express significant levels of D1 dopamine receptors, the specific D1 antagonist SCH 23390 attenuates the cell death caused by HIV-1 Tat. In rat hippocampal cell cultures, where the expression of D1 receptors is low, SCH 23390 did not change the toxicity of Tat. Thus, the protective effect of SCH 23390 in rat primary neuronal cell cultures is a function of the level of D1 receptor protein expression. Our results provide further evidence for the involvement of the dopaminergic transmission system in the mechanism of HIV-1 Tat neurotoxicity.

Automation of the novel object recognition task for use in adolescent rats.

The novel object recognition task is gaining popularity for its ability to test a complex behavior which relies on the integrity of memory and attention systems without placing undue stress upon the animal. While the task places few requirements upon the animal, it traditionally requires the experimenter to observe the test phase directly and record behavior. This approach can severely limit the number of subjects which can be tested in a reasonable period of time, as training and testing occur on the same day and span several hours. The current study was designed to test the feasibility of automation of this task for adolescent rats using standard activity chambers, with the goals of increased objectivity, flexibility, and throughput of subjects.

Chronic intermittent ethanol exposure during adolescence reduces the effect of ethanol challenge on hippocampal allopregnanolone levels and Morris water maze task performance.

Chronic intermittent ethanol exposure (CIEE) in adolescent rats has been shown to produce long-lasting hypnotic, metabolic, and functional tolerance. Recently, it has been hypothesized that allopregnanolone mediates some effects of ethanol, including ethanol-induced impairments in the performance of the Morris Water Maze Task (MWMT). The current studies explore the relationship between cortical and hippocampal allopregnanolone levels and ethanol-induced impairments in the MWMT following CIEE treatment in adolescent rats. Adolescent rats were administered 5.0 g/kg ethanol or saline every 48 h for a 20-day period beginning on postnatal day (P) 30. Training in the spatial version of the MWMT occurred on nontreatment days. Following completion of CIEE treatment and training, MWMT performance was tested 30 min after ethanol (2.0 g/kg) or saline challenge on P 50 and P 62. A separate group of rats were CIEE treated and received an ethanol (2.0 g/kg) or saline challenge on P 50 or 62, and were used for hippocampal and cortical allopregnanolone determination. CIEE during adolescence produced tolerance to both ethanol-induced impairments in the MWMT and ethanol-induced allopregnanolone levels in the hippocampus on P 50. However, when animals were tested at P 62, the reduction in ethanol-induced MWMT impairments found in CIEE rats was reversed and allopregnanolone levels from both saline or ethanol challenge were increased above levels found in control animals. Taken together, these results suggest that CIEE during adolescence produces tolerance to ethanol-induced impairments in MWMT and corresponding changes in ethanol-induced allopregnanolone levels in the hippocampus. Furthermore, cognitive tolerance is reversible and time dependent, but the reversal of cognitive tolerance is not correlated with normalization of hippocampal allopregnanolone levels.

Dopaminergic marker proteins in the substantia nigra of human immunodeficiency virus type 1-infected brains.

With the advent of highly active antiretroviral therapy, human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) is becoming a more chronic, manageable disease; nevertheless, the prevalence of neurological complications of AIDS is increasing. In this study, protein levels of tyrosine hydroxylase (TH) and dopamine transporter (DAT) in the substantia nigra of HIV-infected brains and -seronegative controls were determined by immunoblotting. The immunoreactivity of neuronal specific enolase (NSE) was used to assess cell loss. Although there were no changes in levels of immunoreactive DAT or NSE proteins in HIV brains, levels of immunoreactive TH were significantly reduced, relative to controls. These results suggest that decreases in TH, the rate-limiting enzyme of dopamine synthesis, may be a factor in the neurological manifestations of HIV infection.

Prenatal cocaine exposure alters alpha2 receptor expression in adolescent rats.

BACKGROUND: Prenatal cocaine exposure produces attentional deficits which to persist through early childhood. Given the role of norepinephrine (NE) in attentional processes, we examined the forebrain NE systems from prenatal cocaine exposed rats. Cocaine was administered during pregnancy via the clinically relevant intravenous route of administration. Specifically, we measured alpha2-adrenergic receptor (alpha2-AR) density in adolescent (35-days-old) rats, using [3H]RX821002 (5 nM). RESULTS: Sex-specific alterations of alpha2-AR were found in the hippocampus and amygdala of the cocaine-exposed animals, as well as an upregulation of alpha2-AR in parietal cortex. CONCLUSION: These data suggest that prenatal cocaine exposure results in a persistent alteration in forebrain NE systems as indicated by alterations in receptor density. These neurochemical changes may underlie behavioral abnormalities observed in offspring attentional processes following prenatal exposure to cocaine.

Chronic intermittent ethanol exposure during adolescence blocks ethanol-induced inhibition of spontaneously active hippocampal pyramidal neurons.

BACKGROUND: Binge alcohol drinking among adolescents has been a serious public health problem. A model of binge alcohol, chronic intermittent ethanol exposure (CIEE), during adolescence significantly attenuates ethanol-induced spatial memory deficits in rats. However, the attenuation was absent following a 12-day ethanol-free period. Since spatial memory is hippocampal dependent, a reduction in ethanol-induced spatial memory impairments may be due to a reduction in the ability of ethanol to inhibit the firing rate of single hippocampal pyramidal neurons following CIEE. METHODS: Beginning on postnatal day 30 (P30), male adolescent Sprague-Dawley rats (Harlan) were administered 5.0 g/kg ethanol (n = 10, CIEE-treated group) or an equivolume saline (n = 10, CISE-treated group) every 48 hours for 20 days. Single hippocampal pyramidal neurons from 5 CIEE-treated rats and 5 CISE-treated rats were recorded on the day following completion of the chronic intermittent exposure procedure (animals now P50). Additionally, neurons from 5 CIEE-treated rats and 5 CISE-treated rats were recorded 12 days after the completion of the chronic intermittent exposure procedure (animals now P62). RESULTS: Ethanol exposure during adolescence completely blocked ethanol-induced inhibition of hippocampal pyramidal neurons in rats that were CIEE exposed. However, the effect of CIEE on hippocampal neurophysiology was time dependent. Specifically, neurons recorded from CIEE-treated rats after a 12-day ethanol-free period had similar maximal inhibition as neurons from CISE-treated animals, although the time to reach inhibition was significantly greater in neurons from CIEE-treated rats. CONCLUSION: Chronic ethanol exposure during adolescence produces a reduction, or tolerance, to ethanol-induced inhibition of hippocampal pyramidal neural activity. Although the tolerance was greatly reversed after a 12-day ethanol-free period, neurons from CIEE animals inhibited slower than neurons from CISE animals. Since the hippocampus is known to be involved not only in spatial memory, but also in many other types of memory formation, the altered hippocampal functions because of CIEE during adolescence should be taken as a serious warning for society.

HIV-1 Tat neurotoxicity in primary cultures of rat midbrain fetal neurons: changes in dopamine transporter binding and immunoreactivity.

HIV-1 neurotoxic proteins (Tat, gp120) are believed to play a major role in pathogenesis of dementia in a significant portion of the AIDS patient population. Dopaminergic systems appear to be particularly important in HIV-associated dementia. In the current studies, we determined that primary cell cultures prepared from the midbrain of 18-day-old rat fetuses are sensitive to Tat neurotoxicity and investigated the possible effects of Tat on DAT-specific ligand binding and DAT immunoreactivity in rat fetal midbrain cultures. We found that Tat neurotoxicity was associated with a significant decrease in [3H]WIN 35428 binding. Immunostaining of cell cultures with antibodies recognizing the C-end epitope of DAT did not reveal significant changes in DAT immunoreactivity. The results of this study implicate involvement of monoamine transmission systems in HIV-associated dementia.

Impairments in spatial learning and memory: ethanol, allopregnanolone, and the hippocampus.

Acute ethanol administration impairs performance in many cognitive tasks that are dependent on hippocampal function. For example, acute ethanol administration produces dose-dependent impairments in spatial learning. Ethanol also decreases the spatial specificity of hippocampal place cells. Such findings raise the possibility that ethanol affects learning and memory by altering, either directly or indirectly, neuronal activity in the hippocampus and related structures. Acute ethanol administration induces a dose- and time-dependent increase in brain concentration of the neuroactive steroid allopregnanolone. Allopregnanolone is a potent GABAA receptor agonist and produces effects similar to the effects produced by ethanol. Blockade of de novo biosynthesis of allopregnanolone alters many of ethanol's effects including ethanol-induced suppression of spontaneous activity in medial septum/diagonal band of Broca neurons and hippocampal pyramidal neurons. These findings suggest that ethanol-induced increases in allopregnanolone levels might play a central role in the effects of acute ethanol on cognitive processing and hippocampal function. The impact of ethanol on spatial cognitive processing and hippocampal function will be reviewed. In addition, the possibility that ethanol-induced changes in neuroactive steroid levels contribute to the impact of ethanol on spatial learning and hippocampal function will be explored.

Chronic intermittent injections of high-dose ethanol during adolescence produce metabolic, hypnotic, and cognitive tolerance in rats.

BACKGROUND: Many humans are first exposed to ethanol during adolescence, the time at which they are most likely to binge drink ethanol. Chronic intermittent ethanol (CIE) exposure produces ethanol tolerance in adolescent rodents. Recent studies suggested that adolescent animals administered CIE experienced increased cognitive impairment following an ethanol challenge. These studies further explore development of ethanol tolerance caused by CIE in adolescence, and whether CIE during adolescence leads to altered ethanol response in adulthood. METHODS: Beginning postnatal day (P) 30, adolescent rats were administered 5.0 g/kg ethanol or saline every 48 hours for 20 days. In experiment I, animals were tested for differential weight gain. In experiment II, loss of righting reflex (LORR) was observed after each injection, then at completion of pretreatment all animals were tested with 5.0 g/kg ethanol and LORR was observed. In experiment III, blood ethanol levels were observed and elimination rates calculated after the first and fifth pretreatments. All animals were tested with 5.0 g/kg at completion of pretreatment and elimination rates were recalculated. In experiment IV, animals were trained on the spatial version of the Morris Water Maze Task (MWMT) on non-treatment days. Following completion of pretreatment and training, animals were tested after receiving an ethanol (1.0, 1.5, or 2.0 g/kg), or saline. Tests for experiments II, III, and IV were repeated in the same animals following 12 ethanol-free days. RESULTS: Chronic intermittent ethanol exposure during adolescence caused differential weight gain (experiment I). Adolescent rats developed tolerance to ethanol-induced LORR (experiment II) and metabolic tolerance to ethanol (experiment III). This tolerance was seen after 12 ethanol-free days. CIE also attenuated ethanol-induced spatial memory deficits in the MWMT (experiment IV). This effect was not long-lasting. CONCLUSIONS: Following CIE pretreatment during adolescence, tolerance developed to the hypnotic and cognitive impairing effects of ethanol, along with increased metabolic rate and decreased weight gain. These results further emphasize the ability of CIE to produce a variety of effects during adolescence, some having long-lasting consequences.