A Search for Discrete Cholinergic Nuclei in the Human Ventral Forebrain

Abstract: Slices cut from five frozen human brains were dissected into 2-mm cubes and assayed for choline acetyltransferase (ChAT) activity and protein content. A pattern of enrichment of ChAT activity was found ventral to the anterior commissure; this finding is consistent with the location of the enzyme in the cells of the nucleus basalis of Meynert. The region beneath the anterior commissure was the only place a discrete enrichment of activity could be found, and the precise topography of the enrichment was somewhat variable from brain to brain. The results are discussed in the light of recent knowledge concerning the source of the cortical cholinergic innervation.     

Identification and characterization of two novel lymphocyte function-associated antigens, L24 and L25

We describe the function and cell distribution of two novel cell surface antigens, L24 and L25. These antigens are broadly distributed on human lymphocytes. Monoclonal antibodies specific for these molecules block lysis by Class I- and II-specific cytotoxic T lymphocytes, but do not affect any other T cell functions tested. Anti-L24 antibody immunoprecipitates a molecule composed of two disulfide-linked monomers of 140 kd each. Anti-L25 antibody immunoprecipitates three proteins of 150, 85, and 75 kd. The study of these and other function associated molecules may provide insight into mechanisms of cytotoxic T lymphocyte recognition and/or function.     

Muscarinic Agonists Evoke Neurotransmitter Release: Possible Roles for Phosphatidyl Inositol Bisphosphate Breakdown Products in Neuromodulation

Carbachol (CCh), a muscarinic agonist that elicits the formation of inositol trisphosphate (IP3) and diacylglycerol (DG), induces a calcium-dependent [3H]norepinephrine ([3H]NE) release [IC50 = (2.7 +/- 0.5) X 10(-4) M] in rat brain slices. Similarly, other muscarinic agonists evoke [3H]NE release which is specifically inhibited by muscarinic antagonists such as 3-quinuclidinyl benzilate, atropine, and N-methyl-4-piperidyl benzilate. The atropine-sensitive evoked release is effectively inhibited by neomycin (IC50 = 50 microM), a phospholipase C inhibitor that interferes with IP3-dependent cellular processes. In addition, polymyxin B, a rather selective inhibitor of protein kinase C (PK-C), abolishes the agonist-mediated release with a half-maximal effective concentration of 0.53 microM (750 ng/ml). These results have a significant implication for the mechanism by which agonists generating IP3 and DG act as inducers of neurotransmitter release in the CNS. However, since both neomycin and polymyxin B act also as N-calcium-channel blockers, other possible mechanisms are discussed. The CCh-induced release suggests that in the CNS an agonist-receptor interaction leads to a calcium-dependent neurotransmitter release, most likely via promoting the IP3/DG as second messengers followed by activation of PK-C.     

De novo and maintenance DNA methylation by a mouse plasmacytoma cell DNA methyltransferase

A DNA methyltransferase of Mr = 140,000 that is active on both unmethylated and hemimethylated DNA substrates has been purified from the murine plasma-cytoma cell line MPC 11. The maximal rate of methylation was obtained with maintenance methylation of hemimethylated Micrococcus luteus or M13 DNAs. At low enzyme concentrations, the highest rate of de novo methylation occurred with single-stranded DNA or relatively short duplex DNA containing single-stranded regions. Strong substrate inhibition was observed with hemimethylated but not unmethylated DNA substrates. Fully methylated single-stranded M13 phage DNA inhibited neither the de novo nor the maintenance reactions, but unmethylated single-stranded M13 DNA strongly inhibited the maintenance reaction. The kinetics observed with hemimethylated and single-stranded substrates could be explained if the enzyme were to bind irreversibly to a DNA molecule and to aggregate if present in molar excess. Such aggregates would be required for activity upon hemimethylated but not single-stranded DNA. For de novo methylation of duplex DNA, single-stranded regions or large amounts of methyltransferase appear to be required. The relative substrate preference for the enzyme is hemimethylated DNA greater than fully or partially single-stranded DNA greater than fully duplex DNA.     

Effects of Neuronal Activity on Inositol Phospholipid Metabolism in the Rat Autonomic Nervous System

The effect of nerve stimulation on inositol phospholipid hydrolysis in autonomic tissue was assessed by direct measurement of [3H]inositol phosphate production in ganglia that had been preincubated with [3H]inositol. Within minutes, stimulation of the preganglionic nerve increased the [3H]inositol phosphate content of the superior cervical sympathetic ganglion indicating increased hydrolysis of inositol phospholipids. This effect was blocked in a low Ca2+, high Mg2+ medium. It was also greatly reduced when nicotinic and muscarinic antagonists were present together in normal medium. However, neither the nicotinic antagonist nor the muscarinic antagonist alone appeared to be as effective as both in combination. In other experiments, stimulation of the vagus nerve caused dramatic increases in [3H]inositol phosphate in the nodose ganglion but did not increase [3H]inositol phosphate in the nerve itself. This effect was insensitive to the cholinergic antagonists. Thus, neuronal activity increased inositol phospholipid hydrolysis in a sympathetic ganglion rich in synapses, as well as in a sensory ganglion that contains few synapses. In the sympathetic ganglion, synaptic stimulation activated inositol phospholipid hydrolysis and this was primarily due to cholinergic transmission; both nicotinic and muscarinic pathways appeared to be involved.     

Notes on the food of feral mink Mustela vison in England and Wales

There is some apprehension about the possible effect of the introduced American mink Mustela vison upon the indigenous British fauna, either as a predator exerting new and excessive pressure upon native prey species, or as a carnivore competing for prey resources against native carnivores. Concern is also felt by preservers of game, and by keepers of small domestic animals (poultry and rabbits) about the mink's potential as a pest. To investigate the food habits of the mink in England and Wales the alimentary canals of 1165 trapped animals were examined, yielding 204 samples for analysis. The resulting information provides a general picture of the mink's diet, including seasonal variations. Comparisons were possible with similar work carried out in other countries, and with the diets of other British carnivores. Tentative conclusions were reached regarding the broad pattern of food relationships between the mink and other British animals, wild and domestic.