ABSTRACT
GABA(A) receptor function was studied in cerebral cortical vesicles prepared from rats after intracerebroventricular microinjections of antisense oligodeoxynucleotides (aODNs) for alpha1, gamma2, beta1, beta2 subunits. GABA(A) receptor alpha1 subunit aODNs decreased alpha1 subunit mRNA by 59+/-10%. Specific [3H]GABA binding was decreased by alpha1 or beta2 subunit aODNs (to 63+/-3% and 64+/-9%, respectively) but not changed by gamma2 subunit aODNs (94+/-5%). Specific [3H]flunitrazepam binding was increased by alpha1 or beta2 subunit aODNs (122+/-8% and 126+/-11%, respectively) and decreased by gamma2 subunit aODNs (50+/-13%). The "knockdown" of specific subunits of the GABA(A )receptor significantly influenced GABA-stimulated 36Cl- influx. Injection of alpha1 subunit aODNs decreased basal 36Cl- influx and the GABA Emax; enhanced GABA modulation by diazepam; and decreased antagonism of GABA activity by bicuculline. Injection of gamma2 subunit aODNs increased the GABA Emax; reversed the modulatory efficacy of diazepam from enhancement to inhibition of GABA-stimulation; and reduced the antagonist effect of bicuculline. Injection of beta2 subunit aODNs reduced the effect of diazepam whereas treatment with beta1 subunit aODNs had no effect on the drugs studied. Conclusions from our studies are: (1) alpha1 subunits promote, beta2 subunits maintain, and gamma2 subunits suppress GABA stimulation of 36Cl- influx; (2) alpha1 subunits suppress, whereas beta2, and gamma2 subunits promote allosteric modulation by benzodiazepines; (3) diazepam can act as an agonist or inverse agonist depending on the relative composition of the receptor subunits: and (4) the mixed competitive/non-competitive effects of bicuculline result from activity at alpha1 and gamma2 subunits and the lack of activity at beta1 and beta2 subunits.
Subject(s)
Cerebral Cortex/metabolism , Chlorides/metabolism , Oligodeoxyribonucleotides, Antisense/pharmacology , Receptors, GABA-A/genetics , gamma-Aminobutyric Acid/pharmacology , Animals , Base Sequence , Bicuculline/pharmacology , Cerebral Cortex/drug effects , Flunitrazepam/pharmacokinetics , Male , Open Reading Frames , Rats , Rats, Sprague-Dawley , Receptors, GABA-A/physiology , Reverse Transcriptase Polymerase Chain Reaction , gamma-Aminobutyric Acid/metabolismABSTRACT
1. The effects of ipsapirone, nefazodone, tiaspirone, BMS-20661, buspirone and gepirone on the hypothalamic-pituitary-adrenal (HPA) axis were studied. These drugs were selected because they have serontonin 1A (5-HT1A) receptor-binding capability and have the potential for therapeutic activity in the treatment of major affective or anxiety disorders or both. 2. Plasma corticosterone level was used as the end point for determining the effect of each drug on the HPA axis. Each drug increased the plasma corticosterone levels in a dose-dependent manner. The ED50 values were 0.8 mg/kg for BMS-20661, 3.5 mg/kg for gepirone, 3.9 mg/kg for buspirone, 5.3 mg/ kg for tiaspirone, 10.5 mg/kg for ipsapirone and 73.5 mg/kg for nefazodone. Ipsapirone and buspirone were more efficacious than the other four drugs. 3. The effect of a 10-mg/kg (35 mg/kg for nefazodone) test dose of each drug reached a peak between 30 min and 1 hr, and plasma corticosterone levels generally returned to control levels after 2 hr. 4. When the drugs were given 30 min before decapitation, in conjunction with a rotatory stress, BMS-20661 significantly inhibited the stress-induced rise, whereas ipsapirone and gepirone caused a significant increase in plasma corticosterone levels. However, when the drugs were given 2 hr before decapitation, nefazodone caused a significant decrease, whereas ipsapirone, BMS-20661 and gepirone produced significant increases in HPA axis activity. An 0800 hr dose of 0.1 mg/kg of dexamethasone suppressed the 1500 hr HPA activity by 73.1%. The 0.1-mg/kg dose of dexamethasone significantly reduced the drug-activated HPA axis activity of all of the drugs from their saline-control levels. The rank order, from least to greatest inhibitory effect, produced by this dexamethasone treatment on the drug-control levels was gepirone (-42.6%), tiaspirone (-48.9%), buspirone (-56.1%), nefazodone (-68.5%), insapirone (-70.0%), and BMS-20661 (-74.3%).
Subject(s)
Hypothalamo-Hypophyseal System/drug effects , Pituitary-Adrenal System/drug effects , Serotonin Agents/pharmacology , Animals , Circadian Rhythm/drug effects , Circadian Rhythm/physiology , Corticosterone/blood , Dexamethasone/pharmacology , Dose-Response Relationship, Drug , Glucocorticoids/pharmacology , Male , Rats , Stress, Psychological/metabolismABSTRACT
The effects of tandospirone, enciprazine, gepirone, buspirone (5-HT1A agents) and carvotroline (5-HT2) on hypothalamic-pituitary-adrenocortical activity (HPA) activity were studied. These drugs increased the plasma corticosterone levels in a dose-dependent manner. Their ED50 values were 3.8, 31.8, 3.1, 3.4 and 7.0 mg/kg, respectively. Drug effects peaked between 30 min and 1 h, and plasma corticosterone levels returned to control levels after 2 h. When the drugs were given in conjunction with a rotatory stress, gepirone and enciprazine increased and carvotroline decreased plasma corticosterone levels. Dexamethasone (0.1 mg/kg) pretreatment reduced drug-activated HPA axis activity.
