Search

Serotonin (5-HT) binding sites from bovine and rat cerebral cortex membranes share pharmacological properties that allow both to be subclassified by the same criteria. We show here that [3H]5-HT binding sites from human cortex also possess pharmacological properties that follow the same subclassification scheme as for bovine and rat cortex. In addition, we show that solubilized 5-HT1 and 5-HT3 sites from all three species have an s20,w value of 3.4. Despite these similar pharmacological and physical characteristics, we can demonstrate antigenic differences between receptor types and species. Human 5-HT1A sites can be distinguished from human 5-HT1B, 5-HT2, and 5-HT3 sites and from equivalent sites in rat and bovine cortex. The anti-human 5-HT1A antibodies were discovered in the blood of an autistic child and may have clinical or etiologic significance for this disorder.

Dopamine receptors were examined by Scatchard analysis in the striatal and olfactory tubercle regions of 11 inbred mouse strains. Simultaneous determinations of the binding characteristics of 3H-labeled 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (ADTN), a dopaminergic agonist, and [3H]spiroperidol, a dopaminergic antagonist, were examined. Among the 11 strains, the equilibrium dissociation constant (Kd) for agonist binding did not vary in either the striatum or the olfactory tubercle. Similarly, no strain differences were observed in the Kd for spiroperidol in either region, although the Kd for spiroperidol in the olfactory tubercle was uniformly higher than that in the striatum. Measurement of receptor concentrations revealed strain differences of up to 2-fold for both [3H]ADTN and [3H]spiroperidol binding sites. Within each brain region, the densities of agonist and antagonist binding sites correlated significantly. However, between brain regions there was no correlation in the density of agonist or antagonist binding sites, which suggests that mesolimbic and nigrostriatal dopamine neurons may be under independent genetic control. Analysis of [3H]spiroperidol displacement by clofluperol, aceperone, cinanserin, and mianserin in four inbred mouse strains revealed that 88-90% of the striatal spiroperidol sites are dopaminergic, with the remainder being serotonergic. In contrast, 53-66% of the olfactory tubercle [3H]spiroperidol binding sites are dopaminergic and 34-47% are serotonergic. These data suggest that genetic differences in serotonin receptors and dopamine receptors may exist among inbred mouse strains.

High-affinity [3H]serotonin binding activity has been solubilized from bovine cerebral cortical membranes by using Triton X-100, Tween-80, and octyl-beta-D-glucopyranoside. This mixture of detergents solubilizes the high-affinity [3H]serotonin binding activity present in crude membrane preparations with retention of 75-90% specific binding. The detergent mixture was chosen because it can easily be removed from the solubilized fraction by dialysis and polystyrene bead adsorption, thus permitting further purification and isolation of the binding sites. Saturation analysis reveals multiple components of high-affinity [3H]serotonin binding. In crude bovine cortical membranes, at least two binding components are present. A higher-affinity binding component, as defined from curvilinear Scatchard plots, has a Kd for [3H]serotonin of 1-3 nM, whereas a lower-affinity component has a Kd of 10-20 nM. In the solubilized preparation, only a single class of binding sites is apparent, with a Kd of 50-100 nM. Removal of detergents by dialysis and polystyrene bead adsorption results in restoration of the curvilinear Scatchard plot with apparent Kds similar to those observed in crude membrane preparations and with increased Bmax values for each component. [3H]Serotonin binding activity in the solubilized preparation is stable to Sephacryl S-300 column chromatography and to glycerol gradient sedimentation. Saturation analysis of the peak binding fractions from both these procedures once again yields curvilinear Scatchard plots, indicating that the multiple high-affinity binding components are preserved and migrate together. The molecular weight, Stokes radius, and frictional coefficient of the binding site(s) have been calculated. After detergent removal the solubilized material shows many of the characteristics usually attributed to S1 receptors, such as high affinity for [3H]serotonin and its analogs and low affinity for serotonin antagonists.

Levels of three adrenal catecholamine synthesizing enzymes and isolation-induced fighting behavior were studied in two related sublines of the Balb/c inbred mouse strain. Enzyme levels were twice as high in the adrenals of Balb/cJ mice as in those of the Balb/cN mice; heterozygous progeny were intermediate between their parents in the levels of the three enzymes. These sublines also showed marked differences in their fighting behavior after a 2-week isolation period. Balb/cJ mice fought immediately after presentation of an intruder mouse, while Balb/cN mice did not fight at any time during the test. Heterozygous progeny behaved more like the Balb/cN (non-fighters). Analysis of F(2) mice suggested that the differences in fighting behavior were determined by a single gene, with fighting being recessive.

A genetic analysis of differences in adrenal phenylethanolamine N-methyltransferase (EC 2.1.1.X) and tyrosine hydroxylase (EC 1.99.1.X.) and brain tyrosine hydroxylase was performed in three inbred mouse strains. In adrenal glands, the pattern of inheritance of both enzymes was similar; genes carried by the CBA/J strain appeared to be dominant to those of the other strains. The pattern of inheritance of tyrosine hydroxylase activity in adrenals differed from that in the brain. In both tissues, dominant genes appeared to determine intermediate, rather than extreme, levels of enzyme activities.