Dopamine receptor binding enhancement accompanies lesion-induced behavioral supersensitivity.

The binding of [3H]haloperidol to rat striatal dopamine receptors increases after lesion (made by injection of 6-hydroxydopamine) of the nigrostriatal dopamine pathway in those rats which are behaviorally supersensitive, as reflected by apomorphine-induced contralateral rotations. The enhanced binding is associated with an increased number of receptor sites with no change in their affinity.

Antischizophrenic drugs: chronic treatment elevates dopamine receptor binding in brain.

Chronic treatment of rats with the neuroleptic drugs haloperidol, fluphenazine, and reserpine elicits a 20 to 25% increase in striatal dopamine receptor binding assayed with [3H]haloperidol. This increase in receptor sites may account for behavioral supersensitivity to dopamine receptor stimulants in such animals and for tardive dyskinesia in patients treated with these drugs.

Dopamine receptor binding predicts clinical and pharmacological potencies of antischizophrenic drugs.

Tritiated haloperidol and tritiated dopamine label postsynaptic dopamine receptors in mammalian brain. Clinical potencies of butyrophenones, phenothiazines, and related drugs correlate closely with their ability to inhibit tritiated haloperidol binding. These binding methods provide a simple in vitro means for evaluating new drugs as potential antischizophrenic agents.

Ethanol sensitivity of the GABAA receptor expressed in Xenopus oocytes requires 8 amino acids contained in the gamma 2L subunit.

Expression of brain mRNA or cRNAs in Xenopus oocytes was used to determine what subunits of the GABAA receptor are required for modulation by barbiturates, benzodiazepines, and ethanol. Mouse brain mRNA was hybridized with antisense oligonucleotides complementary to sequences unique to specific subunits and injected into oocytes. Antisense oligonucleotides to the alpha 1, beta 1, gamma 1, gamma 2S + 2L, gamma 2L, or gamma 3 subunits did not alter GABA action or enhancement by pentobarbital. Action of diazepam was prevented by antisense oligonucleotides to gamma 2S + 2L and reduced by antisense sequences to gamma 2L, but was not affected by the other oligonucleotides. Ethanol enhancement of GABA action was prevented only by antisense oligonucleotides to gamma 2L (which differs from gamma 2S by the addition of 8 amino acids). Expression of either the alpha 1 beta 1 gamma 2S or the alpha 1 beta 1 gamma 2L subunit cRNA combination in oocytes resulted in GABA responses that were enhanced by diazepam or pentobarbital, but only the combination containing the gamma 2L subunit was affected by ethanol.

GABAA receptor beta 1, beta 2, and beta 3 subunits: comparisons in DBA/2J and C57BL/6J mice.

GABAA receptors link binding of GABA (gamma-aminobutyric acid) to inhibitory chloride flux in the brain. They are the site of action of several important classes of drugs, and have been implicated in animal models of epilepsy and in the actions of alcohol. We compare the sequence and expression of the beta 1, beta 2 and beta 3 subunits of GABAA receptors in two inbred strains of mice, DBA/2J and C57BL/6J, which differ markedly in seizure susceptibility and in a variety of behaviors related to alcohol. Only the beta 3 subunit had strain differences in cDNA nucleotide sequence, which did not affect amino acid sequence but which did create restriction fragment length polymorphisms (RFLPs) potentially useful in gene mapping. We have also tested mouse beta 1 and beta 2 subunits for internal alternative splicing, detecting none.

Binding sites for thyrotropin-releasing hormone in sheep nucleus accumbens resemble pituitary receptors.

TRH binds to sites in the nucleus accumbens-septal area of sheep brain. These sites appear to represent receptors for at least some of its behavioral effects in other species and are very similar to sheep pituitary receptors. All measurements were performed on ice to prevent peptide degradation. High affinity [3H]TRH binding in brain regions was distinguished from interfering low affinity binding by use of [3-Me-His2]TRH, a more potent and specific analog, in blank tubes at a 1-microM concentration. The nucleus accumbens-septal area, particularly the nucleus accumbens itself, showed the highest binding of any of a variety of brain regions surveyed. Binding sites in both nucleus accumbens and anterior pituitary had an equilibrium dissociation constant of about 20-40 nM, a rate constant for association of about 1-3 x 10(6) M-1 min-1, and a rate constant for dissociation of about 0.07 min-1. Seventeen TRH analogs showed closely similar potencies in competing for binding in the two tissues. Six weak analogs appeared to be more potent in the nucleus accumbens than in the pituitary, but this was an artifact of their relatively greater potency in competing for low affinity binding sites which are absent in pituitary. The only major difference between the high affinity binding sites in the two tissues was in their concentration, which was about 2- to 3-fold higher in the pituitary.

Ovarian steroids modulate the release of dopamine into hypophysial portal blood and the density of anterior pituitary [3H]spiperone-binding sites in ovariectomized rats.

The concentrations of dopamine (DA) in pituitary stalk plasma and the number of DA D-2 receptor sites in the anterior pituitary gland were evaluated in ovariectomized (OVX) rats treated for 48-78 h with estradiol (E2) or vehicle and for 2-30 h with progesterone (P) or vehicle. Only the combined administration of E2 for 72-78 h and P for 24-30 h altered the release of DA into pituitary stalk blood and the number of dopaminergic binding sites in the anterior pituitary gland. The DA concentrations in pituitary stalk plasma 72 h after initiation of treatment were 1.9 +/- 0.3 (mean +/- SEM), 2.6 +/- 0.2, and 2.4 +/- 0.3 ng/ml in OVX rats treated with vehicle, E2, and P alone, respectively, and were increased significantly to 4.3 +/- 0.4 ng/ml in E2- and P-treated rats. The binding of [3H] spiperone to DA D-2 receptors was measured by a single point assay in homogenates of the individual anterior pituitary glands obtained from the same rats. Anterior pituitary tissue was incubated with 0.4 nM [3H]spiperone in the presence or absence of 10(-6) M (+)butaclamol. Binding was similar in all animals except those treated with E2 and P, in which a significant increase occurred. Three days after initiation of treatment, binding was equivalent to 49.8 +/- 5.8, 51.3 +/- 5.1, and 55.4 +/- 4.9 fmol/mg protein in OVX rats treated with vehicle, E2, and P, respectively. In contrast, a significant increase in binding to 83.7 +/- 4.6 fmol/mg protein was observed in rats given E2 and P. No differences in either parameter were apparent 48 h after starting the steroid/vehicle treatment, nor were there any differences between morning and afternoon values in any single group. Scatchard analyses were made on the binding kinetics of DA receptors in anterior pituitary glands obtained from additional rats, and 1.5- to 2-fold increases in the density of sites were observed in animals that had received both E2 and P, while the apparent affinity of the receptors was unchanged. We conclude that treatment with the combination of E2 and P is required to increase the release of DA into hypophysial portal blood and that it also increases the density of DA receptors within the anterior pituitary gland.

Ovariectomy permits progesterone to increase the binding of [3H]spiperone to the anterior pituitary gland in estrogen-primed rats.

The binding of the dopamine (DA) D2 antagonist spiperone to DA receptors in the anterior pituitary gland was evaluated in intact and ovariectomized (OVX) estrogen-primed rats in which circulating levels of progesterone (P) were varied. Nembutal (PB; 35 mg/kg, ip) was administered at 1130 h to intact proestrous animals to prevent the LH-stimulated release of ovarian P. Two hours later some of these intact rats were QVX to remove the endogenous ovarian steroids. Both intact and OVX rats were given exogenous P. All rats were killed on the following morning, and adenohypophysial binding of [3H]spiperone was evaluated at a saturating concentration. The binding in intact PB-blocked rats that received P was only 52% of that in PB-blocked rats that were OVX and received P. The binding of [3H]spiperone in PB-treated rats that were OVX and given P did not differ statistically from that in normal estrous rats. A parallel experiment was conducted on other rats that had been OVX 7 days before the sc implantation (on day 0) of Silastic capsules containing estradiol (E2). Two days later (day 2), some of these rats were injected with Nembutal at 1130 h. Two hours later, the E2 capsules of some rats were removed to simulate ovariectomy; Silastic capsules containing P were implanted into both E2-bearing and non-E2-bearing rats. All rats were killed the following morning (day 3), and the density of adenohypophysial DA receptors was assessed. Binding densities were greatest in rats bearing both E2 and P capsules and in rats from which E2 capsules were removed and replaced with P capsules. We conclude that treatment of OVX rats with the sequential combination of E2 and P increases the density of DA receptors in the anterior pituitary gland. However, in intact rats an additional ovarian product prevents the P-induced increase in the density of adenohypophysial DA receptors.

Experimental spinal cord injury: effects of trauma or ischemia on TRH and muscarinic receptors.

Traumatic spinal cord injury in rats and ischemic spinal cord injury in rabbits were associated with time-dependent, localized decreases in thyrotropin-releasing hormone (TRH) and muscarinic receptor binding. Changes were not evident in the first 24 to 48 hours, consistent with the hypothesis that secondary alterations in spinal cord may occur relatively late after injury. TRH receptor binding, but not muscarinic receptor binding, recovered by 3 weeks following trauma. Since TRH and acetylcholine may serve as excitatory neurotransmitters within the spinal cord, such changes could contribute to the functional neurologic impairment that follows injury.

A PCR shortcut to oocyte expression.

We describe a new method, RNA amplification with oocyte expression, for efficient expression of proteins in the Xenopus oocyte after PCR amplification of cDNA coding regions, using as examples mouse GABAA receptor alpha 1 and beta 2 subunits. RNA is reverse-transcribed and the cDNAs are amplified using 5' primers containing a T7 RNA polymerase promoter and a consensus ribosome binding site and 3' primers giving a short poly(A) tail. This is followed by direct in vitro transcription of the PCR products and injection of the resulting mRNAs into Xenopus oocytes. The method gave abundant GABA-gated chloride channels in the oocyte membrane, as measured by recording agonist-induced currents. It promises to be a rapid route to expression of cloned proteins in oocytes, without requiring actual clones, and is free of possible variations in efficiency from untranslated regions.

Guanine nucleotides modulate TRH-receptor binding in sheep anterior pituitary.

Binding of thyrotropin-releasing hormone (TRH, thyroliberin) to receptors in chilled membrane resuspensions from sheep anterior pituitary glands is reduced in affinity almost 2-fold by micromolar concentrations of guanosine 5'-triphosphate (GTP) and the hydrolysis-resistant analog guanyl-5'-yl imidodiphosphate (GppNHp) added to tissue during a 10-min preincubation at 37 degree C. Guanosine 5'-diphosphate (GDP) produced a similar effect at 1 mM, while GMP, ATP, ADP and AMP appeared relatively inactive. The number of TRH-binding sites was not affected by the nucleotide treatments. These results are consistent with reports of guanine nucleotide effects on other receptor types and with evidence suggesting an adenylate cyclase mechanism for some of TRH's effects in the anterior pituitary.

The alpha 1, alpha 2, and alpha 3 subunits of GABAA receptors: comparison in seizure-prone and -resistant mice and during development.

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in brain, opens chloride channels through actions on GABAA receptors. We now report base and amino acid sequences of the alpha 1, alpha 2, and alpha 3 subunits from GABAA receptors of audiogenic seizure-prone (DBA/2J) and -resistant (C57BL/6J) inbred strains of mice. Inbreeding had fixed different alleles of the alpha 1 subunit in the two strains, giving five base differences in the cDNAs. None of these affected amino acid sequence, but one did create a NsiI restriction site potentially useful in mapping genomic DNA. No base or amino acid sequence differences between the strains were detected for the other two subunits. Northern blots revealed no apparent strain differences in message levels for these three subunits in whole brains of the mice at 3 weeks of age, the peak of seizure susceptibility in DBA/2J, but did reveal distinct regional and developmental patterns of expression among the subunits in mouse brain.

The mouse GABA(A) receptor alpha3 subunit gene and promoter.

Gamma-aminobutyric acid (GABA) type A receptors are multisubunit ligand-gated ion channels which mediate inhibition in the brain. The GABA(A) receptor alpha3 subunit gene exhibits extensive variation in its developmental and regional expression, but the detailed mechanisms governing the expression patterns of this gene remain unknown. We have cloned and begun to characterize the murine alpha3 subunit gene Gabra3. All but one of the 10 exons and the intron-exon boundaries have been sequenced; the first intron is in the 5' untranslated region (5'UTR) of the alpha3 mRNA. Rapid amplification of the cDNA 5'-end (5'-RACE) and RNase protection indicated many transcription start sites, with the major site (=+1) corresponding to a 5'UTR of 178 bases. Most sites were in or just downstream of a region of 55 (mouse) and 25 (human) GA repeats in the proximal promoter, as revealed by genome walking of Gabra3 and the human gene GABRA3. No canonical TATA or CAAT boxes or initiator (Inr) sites were found in either promoter, but both contained conserved consensus sites for several transcription factors. Progressive deletion of the mouse promoter produced positive or negative effects on expression of reporter (luciferase) constructs, with the highest observed activity in several types of transiently transfected cells for a construct containing bases -320 to +35. The GA repeats and a much shorter nearby series of four GC repeats, the first three of which are part of a consensus E2F site, appear to contribute significantly to mouse promoter activity. Upstream GA repeats enhanced activity of the SV40 promoter, and the GA repeat sequence bound nuclear proteins from several tissues.

Transcriptional regulation of GABAA receptor gamma2 subunit gene.

We have cloned the promoter regions of the genes for the mouse and human gamma2 subunits of the type A receptors for gamma-aminobutyric acid (GABA). For the mouse, the two major transcription start sites were at +1 (by definition) and +43, as established by rapid amplification of cDNA ends (RACE) and primer extension. This numbering places the start methionine at +297. There was no TATA or CCAAT box. Both mouse and human sequences have a candidate neuron-restrictive silencer element (NRSE) site in the first intron (+956 in mouse). We made assorted mouse-based promoter/reporter (luciferase) constructs starting from a core extending from -331 to +136, varying sizes at both ends, and including and excluding the putative NRSE and more proximal sequences. These were tested by transient transfection in several neuron-like and non-neuronal cell lines. Both proximal and distal downstream elements appeared to help direct expression to neuron-like cells, the NRSE in the intron, by repression in non-neurons, and a 24-bp portion of the 5' untranslated region starting at +113 (named GPE1) by preferentially promoting expression in neuron-like cells. Cotransfected human NRSF (transcription factor for NRSE) reduced reporter expression in neuron-like cells for constructs containing the NRSE in two locations. In gel mobility shift assays, the mouse gamma2 NRSE and a consensus NRSE both bound in vitro translated NRSF very similarly, and the NRSF gave the same major shifted band with the mouse gamma2 NRSE as was observed with nuclear extracts.

The alpha5 subunit of the murine type A GABA receptor.

GABA[A] receptors in the brain convert binding of GABA (gamma-aminobutyric acid) to inhibition by chloride currents. Several important classes of drugs, including benzodiazepines and alcohol, modulate these receptors, which have also been implicated in epilepsy. We describe the alpha5 subunit of GABAA receptors in mice, comparing inbred DBA/2J mice, prone to juvenile audiogenic seizures, with seizure resistant C57BL/6J mice. We find no sequence differences between the strains, although there are several interesting amino acid differences from the rat. We also compare the expression of the alpha5 subunit in whole brains of DBA/2J mice to that in C57BL/6J mice at 21 days, the peak of the former's seizure susceptibility, again finding no significant difference. We further describe the pattern of expression of alpha5 mRNA during mouse brain development, with a peak at 3 days after birth, and among five brain regions in the adult mouse, with the highest levels in the hippocampus. Finally, we present preliminary evidence for rare alternative splicing of this subunit's message, in the N-terminal extracellular domain, to give a form not translatable into a functional protein.

Visualization and identification of TRH receptors in rodent brain by autoradiography and radioreceptor assays: focus on amygdala, N. accumbens, septum and cortex.

Thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH(2)) is a tripeptide found in numerous regions of the vertebrate central nervous system (CNS). This study has provided evidence for a heterogeneous distribution of specific, nanomolar-affinity recognition sites for MeTRH in mouse and rat CNS. Membrane binding experiments revealed the following profile of these sites in mouse CNS: amygdala (AM) > olfactory tubercle > olfactory bulb (OB) > hypothalamus > striatum > pons-medulla > hippocampus > spinal cord > midbrain > cerebral cortex (CC) ? retina (RT) ? pituitary (PIT). Concurrent assays of rat brain homogenates indicated a similar order of regional enrichment in MeTRH binding sites as the mouse but the former species appeared to have an exceptionally higher density in RT and PIT compared to the latter animal. In contrast, mouse OB and AM seemed to possess a greater density of MeTRH sites than the same rat tissues. The pharmacological specificity of mouse and rat AM and PIT MeTRH binding sites was, however, almost identical and helped identify these entities as TRH receptors. Qualitative light-microscopic autoradiographic localization of TRH receptors in rat and mouse brain sections confirmed the relative distribution data obtained from membrane assays. In particular, the regions most enriched in TRH receptors determined by this technique were the various amygdaloid and hypothalamic nuclei, medial septum, n. accumbens and the inner cortical layers, areas for which numerous functional correlates have been previously demonstrated for TRH. These membrane and radiohistochemical data support a transmitter role for TRH in rodent CNS and indicate its putative sites of action.

Properties and distribution of TRH receptors in normal and spastic mutant mouse brain and spinal cord.

Specific binding sites for thyrotropin-releasing hormone (TRH) were labelled with the potent analog, [(3)H] (3-Me-His(2))TRH, in the brain and spinal cord of the mutant mouse spastic and nonafflicted littermate controls. Equilibrium binding parameters determined from competition assays indicated dissociation constant (K(d)) of 4-5 nM in selected regions of the brain in both groups of animals. Detailed examination of the TRH receptor density at 1 nM [(3)]MeTRH concentration revealed a marked heterogeneous distribution (amygdala hippocampus = n. accumbens/striatum ? midbrain > spinal cord > pons/medulla = hypothalamus ? cerebellum) . An almost identical anatomical localization profile of TRH receptors was apparent in control and spastic mice. The pharmacological specificity of [(3)H]MeTRH binding sites in the spinal cord and amygdala of these animals was again closely similar and resembled that documented previously for other mammalian species. In conclusion, TRH receptors in spastic mutant mice exhibit similar properties and brain regional distribution as their normal counterparts.

Rat brain TRH receptors: kinetics, pharmacology, distribution and ionic effects.

Optimal conditions for measuring receptor binding for thyrotropin-releasing hormone (TRH) in the rat central nervous system (CNS) have been determined using 3H-labelled [3-Me-His2]TRH [( 3H]MeTRH). Binding assays conducted at 0 degree C for 5-6 h using sodium phosphate- and/or Hepes-buffered tissue resuspensions, with subsequent filtration through Whatman GF/B filters, yielded the best results. Association and dissociation of [3H]MeTRH binding to amygdala membranes were time and temperature dependent. Dissociation kinetics appeared biphasic. Progressive reduction in receptor affinity and capacity and increased radioligand breakdown were observed at elevated temperatures. Bacitracin (25-1000 microM) prevented peptide degradation but inhibited receptor binding (8-37%). Detailed competition experiments using MeTRH and other drugs yielded a pharmacological profile similar to that observed previously in other tissues indicating TRH receptor identification. Highest density of TRH receptors was observed in the retina and numerous limbic areas. Monovalent and divalent cations modulated [3H]MeTRH binding by reducing apparent receptor number.

A synthetic standard for competitive RT-PCR quantitation of 13 GABA receptor type A subunit mRNAs in rats and mice.

We describe a synthetic 769-bp DNA internal standard, GABARQuant 1, for measuring mRNAs of 13 GABA(A) receptor subunits by reverse transcriptase-polymerase chain reaction (RT-PCR). When it is transcribed into cRNA, added in known amounts to target mRNAs in extracts from rat or mouse tissue. competitively reverse transcribed into cDNA, and amplified by the polymerase chain reaction (PCR), the relative intensities of the amplified, stained target and standard DNA bands enable measurement of small amounts of mRNAs for GABA(A) receptor subunits alpha1-6, beta1-3, gamma1-3 and delta and the three cellular markers beta-actin, light neurofilament protein, and glutamine synthetase. For the subunits, most standard products (263-504 bp) differ in size from target products (398-564 bp) by 10-20%. Primer pairs span at least one intron, to prevent interference by genomic DNA, and at least one rat versus mouse restriction fragment length polymorphism (RFLP), to enable rat products to be distinguished from mouse products.