Role of conserved threonine and tyrosine residues in acetylcholine binding and muscarinic receptor activation. A study with m3 muscarinic receptor point mutants.

Structure-function relationship studies of the m3 muscarinic acetylcholine receptor have recently identified a series of threonine and tyrosine residues (all located within the hydrophobic receptor core) that are critically involved in acetylcholine binding (Wess, J., Gdula, D., and Brann, M.

Lack of proconvulsant action of GABA depletion in substantia nigra in several seizure models.

The effect of intranigral application of a gamma-aminobutyric acid (GABA) synthesis inhibitor, was examined in 3 different rat seizure models. Bilateral intranigral infusion of isoniazid (150 micrograms) did not potentiate the effect of subcutaneous administration of a threshold dose (1.5 mg/kg) of the GABA antagonist bicuculline.

Selective stimulation of kainate but not quisqualate or NMDA receptors in substantia nigra evokes limbic motor seizures.

Bilateral microinjection of kainic acid (30-117 pmol) into the substantia nigra induced convulsive seizures resembling those elicited from limbic system structures. The convulsive seizures, which consisted of facial and forelimb clonus with rearing and falling, developed after a latency of more than 30 min and were preceded by wet dog shakes and non-convulsive seizure activity registered electroencephalographically. The convulsant effect of intranigral kainic acid was strictly dose-dependent (ED50 = 60 pmol) and anatomically site-specific.

[3H]1-methyl-4-phenyl-2,3-dihydropyridinium ion binding sites in mouse brain: pharmacological and biological characterization.

Because 1-methyl-4-phenyl-2,3-dihydropyridinium ion (MPP+) appears to damage the dopaminergic neuron and cause neuronal death, we characterized [3H]MPP+ binding sites in mouse brain membranes. Among several compounds tested, debrisoquin [3,4-dihydro-2(1H)-isoquinolinecarboxamidine] and some analogues were able to antagonize [3H]MPP+ binding. Debrisoquin is able to block adrenergic transmission and inhibit the activity of monoamine oxidase A (MAO-A).

Seizures evoked from area tempestas are subject to control by GABA and glutamate receptors in substantia nigra.

The functional relationship between the substantia nigra (SN) and the area tempestas (AT), an epileptogenic site in the deep prepiriform cortex, was investigated. Stimulation of GABA receptors in SN with muscimol, or blockade of nigral excitatory amino acid receptors with 2-aminophosphonoheptanoic acid (AP7), protected against convulsions evoked by the unilateral focal injection of bicuculline in the AT. The protective effects were obtained only with bilateral nigral injections; unilateral manipulations were without anticonvulsant effect.

Properties of 3H-MPTP binding sites in human blood platelets.

Our study demonstrates that 3H-1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (3H-MPTP) specifically binds to platelet membrane sites in humans. This specific, high affinity and saturable binding has properties similar to those of 3H-MPTP binding to rat and monkey brain, with a higher affinity. Deprenyl, a specific inhibitor of MAO type B enzyme, was the most potent drug in displacing 3H-MPTP from platelet binding sites.

High affinity binding sites for 1-methyl-4-phenyl-pyridinium ion (MPP+) are present in mouse brain.

The possible involvement of 1-methyl-4-phenyl-pyridinium ion (MPP+) in the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) prompted us to search for and characterize [3H]MPP+ binding sites in the mouse. Our data show that [3H]MPP+ binds saturably and with high affinity to mouse brain membranes. Scatchard analysis resulted in one straight line.

STUDIES ON ISOLATED NUCLEI. II. ISOLATION AND CHEMICAL CHARACTERIZATION OF NUCLEOLAR AND NUCLEOPLASMIC SUBFRACTIONS.

This paper describes the subfractionation of nuclei isolated from guinea pig liver by the procedure presented in the first article of the series (8). Centrifugation in a density gradient system of nuclear fractions disrupted by sonication permits the isolation of the following subfractions: (a) a nucleolar subfraction which consists mainly of nucleoli surrounded by a variable amount of nucleolus-associated chromatin and contaminated by chromatin blocks derived primarily from von Kupffer cell nuclei; (b) and (c), two nucleoplasmic subfractions (I and II) which consist mainly of chromatin threads in a coarser (I) or finer (II) degree of fragmentation. The protein, RNA, and DNA content of these subfractions was determined, and their RNA's characterized in terms of NaCl-solubility, nucleotide composition, and in vivo nucleotide turnover, using inorganic (32)P as a marker.

STUDIES ON ISOLATED NUCLEI. I. ISOLATION AND CHEMICAL CHARACTERIZATION OF A NUCLEAR FRACTION FROM GUINEA PIG LIVER.

This article describes a method for the isolation of nuclei from guinea pig liver. It involves the homogenization of the tissue in 0.88 M sucrose-1.