The kindling model of alcohol dependence: similar persistent reduction in seizure threshold to pentylenetetrazol in animals receiving chronic ethanol or chronic pentylenetetrazol.

Rats on a chronic intermittent ethanol (CIE) regimen showed a persistent reduction in seizure threshold to the convulsant drug pentylenetetrazol (PTZ). CIE rats were given ethanol by intubation on an alternate day schedule and tested at selected intervals for seizure threshold with PTZ. A significant reduction in seizure threshold, a sign of withdrawal, was observed 20 hr after the first dose. The severity of withdrawal intensified on repetition of the ethanol administration and depression-hyperexcitability cycle, with the seizure threshold reaching a maximum decrease after 12 doses and remaining reduced up to 60 doses. The reduction in seizure threshold persisted for at least 40 days of no alcohol following the 60th dose. The long-lasting decrease in seizure threshold following CIE treatment resembled the "kindling" phenomenon produced by chronic administration of PTZ (25 mg/kg, 3 times/week). The CIE rats developed, in addition, a tolerance to the anticonvulsant action of ethanol, which occurred well after the decrease in PTZ seizure threshold, and a tolerance to the hypothermic effect of ethanol, which developed rapidly. PTZ kindled rats that had never been exposed to ethanol also exhibited tolerance to the hypothermic effect of ethanol. We propose that kindling contributes to the mechanism of the development of dependence on central nervous system depressants like benzodiazepines, barbiturates, and alcohol, drugs that act on the gamma-aminobutyric acid-A receptor chloride ion channel complex. Repeated episodes of depression and withdrawal hyperexcitability are postulated to produce kindling during the repeated withdrawal episodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex differences in sensitivity to pentylenetetrazol but not in GABAA receptor binding.

Female rats have a higher threshold than males for seizures induced by the convulsant pentylenetetrazol, a GABAA receptor-chloride channel complex blocker. No sex difference was observed for the anticonvulsant activities of ethanol or diazepam to protect against pentylenetetrazol seizures. Ovariectomy reduces the pentylenetetrazol seizure threshold of females to that of males. In contrast, females have a lower threshold than males to electroshock seizures. Pentylenetetrazol receptors were compared in males and females and gonadectomized animals by binding of several radioligands to the GABAA receptor complex. No differences were found for these four groups of animals in the binding of [3H]flunitrazepam to the benzodiazepine sites and [35S]t-butyl bicyclophosphorothionate ([35S]TBPS) to the chloride channel/convulsant sites in membrane homogenates, nor for allosteric modulation of binding by GABA, the steroid anesthetic alphaxalone, or the benzodiazepine Ro 5-4864. In tissue section autoradiography, no difference was observed for these same assays nor for the binding of [3H]muscimol in the presence and absence of alphaxalone in several major regions. We conclude that circulating female sex hormones, possibly neurosteroid metabolites of progesterone, known to interact directly with the GABAA receptor complex, are involved in the sex differences in pentylenetetrazol seizure susceptibility.

Regional variation in steroid anesthetic modulation of [35S]TBPS binding to gamma-aminobutyric acidA receptors in rat brain.

Steroids that enhance gamma-aminobutyric acid (GABA)A receptor function in the central nervous system allosterically modulate the binding of the convulsant chloride channel ligand [35S]-t-butyl bicyclophosphorothionate. When assayed in membrane homogenates and in tissue sections by autoradiography, concentration-dependence curves vary with respect to both brain region and the nature of the steroid. Alphaxalone and endogenous steroid hormone metabolites inhibit the binding of [35S]-t-butyl bicyclophosphorothionate in some regions, enhance it in others and give biphasic concentration-dependence in others, apparently the result of algebraic summation of two effects involving regional-dependent enhancement or inhibition. The alphaxalone effect is additive with that produced by adding GABA to the binding assays in some regions, but synergistic in other areas. Likewise, the effect of GABA is inhibited completely by saturating concentrations of the antagonist bicuculline methochloride in some areas but only partially in others, and completely or partially reversed by the convulsant benzodiazepine Ro5-4864, depending on region. The granule cell and molecular layers of cerebellum are particularly different in these allosteric interactions. The heterogeneity of binding behavior is consistent with the presence of multiple GABAA receptor subtypes in the brain. Regional variation in subunit gene expression apparently produces a family of hetero-oligomeric GABAA receptors with different biological and pharmacological properties, including qualitative and quantitative differences in modulation by neuroactive steroids.

Prenatal ethanol exposure affects temperature responses of adult rats to pentobarbital and diazepam alone and in combination with ethanol.

Long-term effects of prenatal alcohol exposure on body temperature responses to pentobarbital and diazepam and to either drug in combination with ethanol were studied in adult rats who were the offspring of dams fed a 5.0% w/v ethanol-containing liquid diet during the last 2 weeks of gestation. Adult offspring of pair-fed and chow-fed dams served as nutritional and normal controls, respectively. Pentobarbital (6.25-25.0 mg/kg) and diazepam (2.5-10.0 mg/kg) produced significantly greater dose-related hypothermic responses in females than males. Following either pentobarbital or diazepam administration female prenatally ethanol-exposed (E) rats responded with a greater fall in body temperature than the controls. Significantly greater hypothermia occurred in both male and female E rats than in controls when ethanol (1.5 g/kg) was administered together with pentobarbital or diazepam. However, the drug combinations did not produce additive effects on body temperature in any prenatal treatment group. Pentobarbital produced acute cross-tolerance to ethanol while diazepam potentiated ethanol's effect. These studies confirm and extend our previous findings of enhanced hypothermic responses to ethanol in adult rats exposed to ethanol in utero and indicate that maternal alcohol consumption produces long-term effects on the central thermoregulatory systems of offspring.

Relationship between the temperature and endocrine changes induced by cholinesterase inhibitors.

Cholinesterase inhibitors induce changes in plasma hormones in the rat. Since these compounds induce hypothermia the question has been raised as to whether the endocrine responses are secondary to the fall in core temperature. The time course of the changes in temperature and plasma levels of corticosterone, growth hormone and prolactin have been examined following injection of diisopropylphosphofluoridate (DFP), soman or physostigmine. All three cholinesterase inhibitors caused an initial rise in corticosterone; DFP decreased growth hormone; physostigmine reduced prolactin. The time course of the hypothermia after DFP and soman did not correlate with that of the rise in corticosterone. The data do not suggest that the hormone changes are secondary to the temperature change.

Prenatal exposure to ethanol potentiates morphine-induced hypothermia in adult rats.

We have shown that adult rats, exposed to ethanol in utero, are hypersensitive to the analgesic and pituitary-adrenal activating effects of morphine. In the present experiment, two other responses to morphine, hyperthermia and hypothermia, were examined. Compared to controls, adult rats prenatally exposed to ethanol showed a potentiated hypothermic response to 10 and 30 mg/kg morphine. Hyperthermia elicited by low doses of morphine (1.25-5.0 mg/kg) was not affected by prenatal exposure to ethanol. These results extend our observations suggesting that exposure to ethanol in utero produces long-lasting perturbations in opioid systems. That hyperthermia is not affected, however, indicates that these changes are apparently not ubiquitous.

Altered stress responsiveness in adult rats exposed to ethanol in utero: neuroendocrine mechanisms.

In our first studies the activity of the hypothalamo-pituitary-adrenal (HPA) axis was found to be significantly greater in response to certain stressors, including ethanol, in adult rats exposed to ethanol as fetuses (fetal ethanol-exposed [FEE] rats) than in pair-fed-derived or normal controls. Stress responsiveness in FEE rats was examined further by measuring stress-induced analgesia after inescapable footshock. Analgesia was enhanced in adult FEE rats by a prolonged/intermittent naloxone-reversible form of footshock, but not by a brief/continuous naloxone-insensitive form, suggesting that the effect was opioid-mediated. Adult FEE rats showed greater analgesic and plasma corticosterone responses to morphine challenges than control rats. Preliminary results also indicated that when adult FEE rats were exposed daily to the intermittent footshock stress (10 min/day) they consumed significantly more ethanol than controls. Whether the altered stress responsiveness reflects fetal ethanol-induced effects on the development of the HPA axis was determined by measuring brain and plasma content of corticosterone in FEE and control neonates. At birth, in FEE pups, whole brain and plasma corticosterone levels are significantly raised. On postnatal day 7, when basal plasma corticosterone concentrations have attained normal values, FEE rats display blunted corticosterone responses to ethanol administration, indicating persistent effects of the fetal ethanol exposure despite its termination one week previously. The precise contribution of these neonatal hormonal alterations to the long-term effects of fetal ethanol exposure on stress responsiveness remains to be determined.

Long-term effects of fetal ethanol exposure on pituitary-adrenal response to stress.

Pregnant female rats were fed either a 5.0-5.5% w/v ethanol-containing liquid diet ad lib or pair-fed the isocaloric control diet during gestation weeks 2 and 3. At 75-105 days of age, female offspring of the ethanol-treated dams showed significantly greater corticosterone responses than pair-fed- or normally-derived offspring to the stress of cardiac puncture or of noise and shaking, while pituitary-adrenal responses to exposure to a novel environment, cold or 2-3 days of fasting were normal. Adrenal sensitivity to ACTH in dexamethasone-suppressed adult offspring was unaffected by the prenatal treatment. The results demonstrate that fetal ethanol exposure enhances adult pituitary-adrenal responses to certain stressors, including alcohol as demonstrated previously, and suggest that the long-term effects may be mediated by developmental actions of alcohol on central neural mechanisms involved in the regulation of this neuroendocrine system.

Neuroendocrine effects of fetal alcohol exposure.

While the actions of alcohol on endocrine function in adults are well-documented, the effects of fetal exposure to alcohol on neuroendocrine function in neonates and adults are only beginning to be investigated. Recent reports are reviewed which demonstrate effects of fetal alcohol exposure on pituitary-adrenal function, GH secretion, thyroxine levels and sexual differentiation in newborn rodents. Our studies of the long-term effects of fetal and early postnatal exposure to alcohol on pituitary-adrenal and body temperature responses to a challenge dose of ethanol in adult rats are described. Both responses are enhanced in prenatally, but not in postnatally exposed rats, indicating that the effects of fetal alcohol exposure on physiological systems, such as the endocrine and thermoregulatory systems, persist to adulthood. Based on apparent similarities in the somatic and cerebral deficits which occur following fetal alcohol exposure and neonatal corticosteroid treatment, a hypothesis is developed for the role of alcohol-induced activation of the HPA axis during gestation in the adverse effects of fetal alcohol exposure.

Fetal exposure to ethanol enhances pituitary-adrenal and temperature responses to ethanol in adult rats.

Long lasting effects of perinatal ethanol exposure were studied in adult rats who were the offspring of dams fed a 5.0% w/v ethanol-containing liquid diet ad libitum or pair-fed the isocaloric control diet during gestation weeks 2 and 3 or during postnatal week 1. Fetal exposure to ethanol reduced body weight of pups at birth unless the ethanol diet was supplemented with casein; neonatal exposure to the ethanol or pair-fed diets, casein supplemented or not, reduced pup weights until day 21 postnatally when weights of all fetally or neonatally exposed pups were normal. Between 52 and 120 days of age females were tested for pituitary-adrenal and temperature responses to a challenge dose of ethanol. Prenatally ethanol-exposed rats showed significantly higher plasma corticosterone titers and developed a greater hypothermia in response to an intraperitoneal injection of ethanol (0.75--1.5 g/kg) than did pair-fed controls. Similar responses enhancement did not occur in the postnatally ethanol-exposed rats. Temporal patterns of blood ethanol levels after an intraperitoneal injection of ethanol (1.5 g/kg) were similar in prenatally ethanol-exposed females and their pair-fed controls. The data indicate that exposure to ethanol in utero exerts persistent effects on the offspring, rendering them more responsive to the hypothermic and pituitary-adrenal activating effects of alcohol as adults.