Allopregnanolone In Rats Research Articles

Hemisphere-dependent Changes in mRNA Expression of GABAA Receptor Subunits and BDNF after Intra-prefrontal Cortex Allopregnanolone Infusion in Rats

Allopregnanolone is a neurosteroid implicated in mood disorders such as depression and anxiety. It acts as a GABAA receptor (GABAAR)-positive allosteric modulator and changes the expression of GABAAR subunits and of brain-derived neurotrophic factor (BDNF) in different brain regions. It has been demonstrated that such neurochemical changes may have an asymmetrical pattern regarding brain hemispheres. The aim of this study was to verify the behavioral and hemisphere-specific neurochemical effects of the bilateral intra-prefrontal cortex (intra-PFC) infusion of allopregnanolone in rats. Rats were exposed to the forced swim test and to the grooming microstructure test, followed by the right and left hemisphere-specific quantification of mRNA expression by Real-Time PCR of δ and γ2 GABAAR subunits and BDNF in the PFC and in the hippocampus. Though we did not observe any significant effects in the behavioral tests, intra-PFC allopregnanolone infusion bilaterally increased the mRNA expression of the δ subunit in the same area and of BDNF in the hippocampus. Both mRNA expressions of the γ2 subunit and BDNF were higher in the right than in the left PFC of control animals, and the hemisphere differences were not seen after allopregnanolone infusion. Overall hippocampal BDNF expression was also higher in the right hemisphere, but this asymmetry was not normalized by allopregnanolone. No asymmetries or changes were observed in the hippocampal mRNA expression of GABAAR subunits. These results point to a hemisphere-dependent regulation of GABAAR subunits and BDNF that can be modulated by intra-PFC allopregnanolone infusion, even in the absence of associated behavioral effects.

Involvement of cocaine- and amphetamine-regulated transcript peptide in the hyperphagic and body weight promoting effects of allopregnanolone in rats

Allopregnanolone (ALLO), a gamma-aminobutyric acid (GABA) type A receptor active neurosteroid, elicits hyperphagic response in rodents. Since GABA-A receptors are present on the peptidergic neurons in the hypothalamus, we were interested in finding out if ALLO and neuropeptide cocaine- and amphetamine-regulated transcript (CART) interact and influence feeding behavior. While subcutaneous ALLO treatment, for a period of 7 days, produced a significant increase in food intake and body weight, pretreatment with subthreshold dose of CART (intracerebroventricular) attenuated both the effects. On the other hand, subcutaneous administration of dehydroepiandrosterone sulfate (DHEAS; GABA-A inhibitor neurosteroid) for a period of 7 days resulted in a significant reduction in food intake and body weight. These effects of DHEAS were potentiated by intracerebroventricular pretreatment with subeffective dose of CART. The brains of ALLO-treated rats were processed for the immunohistochemical analysis of CART immunoreactive elements. ALLO treatment resulted in a significant reduction in CART immunoreactivity in the hypothalamic arcuate, paraventricular and lateral nuclei, and nucleus accumbens shell. The results of the present study suggest that ALLO and CART might interact in the brain, and influence food intake and body weight. However, further investigations are needed to clarify the precise mechanisms by which ALLO modulate feeding behavior.

Neonatal neurosteroid levels are determinant in shaping adult prepulse inhibition response to hippocampal allopregnanolone in rats

Diverse studies indicate that the alteration of the physiological levels of neurosteroids in early neonatal phases provokes alterations in the maturation of certain cerebral structures. Allopregnanolone (ALLO) has important modulatory effects in the hippocampus during the postnatal period where the adult pattern of inhibitory transmission is being established. In order to study whether endogenous neonatal ALLO levels would be a determinant parameter involved in mediating adult hippocampal GABAA system maturation, we investigated the effects of neonatal finasteride (50mg/kg, SC) treatment and ALLO (ALLO; 20mg/kg, SC) supplementation on an animal behavioural model with relevance to neurodevelopmental disorder, such as schizophrenia. Two sets of experiments were conducted. Neonatal treatment (from postnatal day (pnd) 5 to pnd9) was performed in 23 male Wistar rats and steroid quantification was performed in hippocampal homogenates at pnd9. A second group (n=127) underwent neonatal treatment (pnd5-pnd9) and were submitted to hippocampal surgery at 80d. The behavioural response to bilateral intrahippocampal neurosteroid administration (ALLO, 0.2μg/0.5μl per side or pregnenolone sulphate 5ng/0.5μl per side) on novelty-induced exploration activity and prepulse inhibition (PPI) was assessed at 95d. Results showed that neonatal ALLO and finasteride administration decreased novelty directed exploratory behaviour and impaired the prepulse inhibition of the acoustic startle response at 95 days of age. Moreover, intrahippocampal ALLO increased head-dipping behaviour independently of the neonatal treatment, while intrahippocampal ALLO decreased PPI only in finasteride and ALLO groups. The results obtained in the present study indicate the importance of neonatal neurosteroid levels in the development of hippocampal function and their relevance in a behavioural phenotype that some have likened to that present in schizophrenia.

Antidepressant effect and changes of GABAA receptor γ2 subunit mRNA after hippocampal administration of allopregnanolone in rats

The present study aimed to verify the effect of bilateral intra-hippocampus administration of the neurosteroid allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one; 3alpha, 5alpha-THP) in the forced swimming test (FST) and in the alpha4 and gamma2 GABA(A) receptor subunits gene expression. Results showed that bilateral intra-hippocampal allopregnanolone administration of 2.5 microg/rat ( P<0.05) reduced immobile behavior and increased climbing behavior in the FST. Overall, for all doses of allopregnanolone tested (1.25, 2.5, 5.0 microg/rat), an increase of gamma2 (P<0.05) GABA(A) subunit mRNA was observed. There was a higher increase in the gamma2 gene expression in the right hemisphere than in the left hemisphere (P<0.01) after allopregnanolone treatment. Intra-hippocampal allopregnanolone did not change the expression of the alpha4 subunits. In conclusion, intra-hippocampal administration of allopregnanolone produces an antidepressant-like effect in the FST at an intermediate dose, confirming the potential of neurosteroids as a new class of antidepressant drugs. Our findings suggest that the gamma2, but not the alpha4 GABA(A) subunit, needs further evaluation to be involved in the antidepressant effect of allopregnanolone in the hippocampus and that there is a hemispheric diversity in the biochemical effect of the drug.

Electrophysiological Effects of Allopregnanolone in Rats With a History of Ethanol Exposure

Sensitivity to the anticonvulsant effects of allopregnanolone (ALLO) is enhanced during the early phase of ethanol (EtOH) withdrawal. However, it is unclear whether this enhanced sensitivity generalizes to ALLO's neurobehavioral effects during protracted abstinence. The purpose of this study was to examine the neurophysiological effects of ALLO in rats with a history of chronic EtOH exposure after a protracted period of abstinence. Male Wistar rats were exposed to EtOH vapor for 14 hr/day for 5 weeks. Blood EtOH levels were maintained between 200 and 250 mg/dl. The effects of ALLO (0.0-10 mg/kg, intraperitoneally) on motor activity, the electroencephalogram (EEG), and auditory event-related potentials then were assessed after 6 to 8 weeks of abstinence from EtOH. ALLO's effects on the EEG were consistent with previous studies and were unaffected by EtOH exposure. ALLO increased high-frequency EEG power and shifted peak EEG frequencies in a benzodiazepine- and barbiturate-like manner in both the cortex and the hippocampus. The effects of ALLO on event-related potentials were attenuated in rats with a history of EtOH exposure. Low doses of ALLO (1 and 5 mg/kg) reduced cortical P1 amplitude in response to the standard tone but only in the control group. ALLO also increased N1 amplitude in the hippocampus of the control group while having no significant effect in EtOH-exposed rats. Low doses of ALLO (1 and 5 mg/kg) were found to increase motor activity. These data indicate that a history of EtOH exposure attenuates some of the neurophysiological effects of ALLO in a manner consistent with cross-tolerance. Taken together, these data suggest that increased sensitivity to ALLO's neurobehavioral effects is limited to the early phases of EtOH withdrawal and may not extend to more protracted periods of abstinence.

Reinforcing effects of the neurosteroid allopregnanolone in rats

The GABA A receptor positive modulator allopregnanolone (3α-hydroxy-5α-pregnan-20-one) is a potent neurosteroid with behavioral and biochemical characteristics similar to ethanol, barbiturates, and benzodiazepines. This suggests that neurosteroids may provide an alternative class of sedative/hypnotic, anticonvulsant, and anxiolytic pharmacotherapies. However, there is evidence from animal models that neurosteroids may be susceptible to abuse by humans. Thus, the present study evaluated the reinforcing effects of orally administered allopregnanolone in rats. In the first experiment, male Long–Evans rats ( n=9) were allowed to voluntarily consume a 50-μg/ml allopregnanolone (50A) solution or water in an unlimited-access two-bottle choice procedure for 10 days. Subsequently, the same animals were trained to lever-press to receive a 50A solution in daily 30-min operant sessions using a sucrose substitution procedure. In the two-bottle choice procedure, rats consumed significantly more allopregnanolone than water, suggesting that allopregnanolone was serving as a reinforcer. In the operant self-administration procedure, allopregnanolone did not maintain levels of responding that were different from water, suggesting that allopregnanolone did not function as a reinforcer in this procedure. These results suggest that orally administered allopregnanolone possesses reinforcing properties; however, additional studies are necessary to determine whether operant oral self-administration will be a viable index of allopregnanolone's reinforcing effects.

Neurosteroids and reward: allopregnanolone produces a conditioned place aversion in rats

The neurosteroid 3α-hydroxy-5α-pregnan-20-one (allopregnanolone) has been reported to have rewarding properties in mice tested for place conditioning. Another study found that allopregnanolone reduced dopamine (DA) output in the nucleus accumbens (NAc) of rats. As many rewarding stimuli increase accumbens DA, these results may appear contradictory. Thus, the present study examined the rewarding properties of allopregnanolone in rats tested for place conditioning using an unbiased conditioning procedure. In control studies, a place preference was observed following conditioning with intraperitoneal (2.0 mg/kg) or intracerebroventricular (i.c.v.) (100 μg/0.5 μl) amphetamine. Conditioning with i.c.v. allopregnanolone produced a significant aversion at a dose of 5.0 μg (in 5.0 μl) and a near aversion at 25.0 μg (in 8.3 μl); doses of 0 μg (i.e., vehicle alone, in 10 μl) or 30.0 μg (in 10 μl) produced little effect on place preference. During conditioning, locomotor activity was stimulated by amphetamine using either route of administration, but allopregnanolone had no significant main effect on locomotor activity. Thus, there was a dissociation between the effects of drugs on locomotor activity vs. place conditioning. Results show that i.c.v. amphetamine produces a place preference, whereas allopregnanolone produces either no effect or an aversion, depending on the dose.