Two types of cholinergic innervation in cortex, one co-localized with vasoactive intestinal polypeptide

The existence of cholinergic neuronal cell bodies in mammalian cerebral cortex was long the subject of much controversy (see ref. 1 for review). Recently, however, a specific cholinergic marker, the acetylcholine synthesizing enzyme, choline acetyltransferase (ChAT, E.C.2.3.1.6), was demonstrated by immunohistochemical methods to be present in bipolar neurones in rat cortex. Here we show that at least 80% of these intrinsic cholinergic neurones also contain immunoreactivity for vasoactive intestinal polypeptide (VIP), a neuroactive peptide found to be present in a subpopulation of cortical neurones. On the other hand, we find that the ChAT-positive cells in the basal forebrain, which are another major source of cholinergic innervation of the cortex, contain no detectable VIP-immunoreactivity. In addition, we have observed by both light and electron microscopy that some VIP- and some ChAT-positive structures in cortex are closely associated with blood vessels.     

Aspartate and glutamate as possible neurotransmitters of cells in layer 6 of the visual cortex

Earlier work has suggested that aspartate, glutamate and gamma-aminobutyric acid (GABA) act as transmitters in the cerebral cortex. There is reasonable evidence for the identity of the cell population responsible for GABA release but until now there has been little evidence concerning the sources for release of aspartate and glutamate. Here we have used two approaches to identify possible neurotransmitters used by cells in the visual cortex: measurement of the efflux of endogenous compounds in conditions of synaptic release and localization of these compounds to particular cell classes using neurotransmitter-specific histochemical techniques. Our results suggest that the acidic amino acids aspartate and glutamate may be cortical neurotransmitters, as shown by calcium-dependent release from endogenous stores and by uptake specific to pyramidal cells in layer 6 of the cortex. These substances may therefore have a role in the function of layer 6 cells, which are responsible for the recurrent projection from the cortex to the lateral geniculate nucleus and for the projection within the cortex from layer 6 to layer 4.     

Integrative genomics identifies MCU as an essential component of the mitochondrial calcium uniporter

Mitochondria from diverse organisms are capable of transporting large amounts of Ca(2+) via a ruthenium-red-sensitive, membrane-potential-dependent mechanism called the uniporter. Although the uniporter's biophysical properties have been studied extensively, its molecular composition remains elusive. We recently used comparative proteomics to identify MICU1 (also known as CBARA1), an EF-hand-containing protein that serves as a putative regulator of the uniporter. Here, we use whole-genome phylogenetic profiling, genome-wide RNA co-expression analysis and organelle-wide protein coexpression analysis to predict proteins functionally related to MICU1. All three methods converge on a novel predicted transmembrane protein, CCDC109A, that we now call 'mitochondrial calcium uniporter' (MCU). MCU forms oligomers in the mitochondrial inner membrane, physically interacts with MICU1, and resides within a large molecular weight complex. Silencing MCU in cultured cells or in vivo in mouse liver severely abrogates mitochondrial Ca(2+) uptake, whereas mitochondrial respiration and membrane potential remain fully intact. MCU has two predicted transmembrane helices, which are separated by a highly conserved linker facing the intermembrane space. Acidic residues in this linker are required for its full activity. However, an S259A point mutation retains function but confers resistance to Ru360, the most potent inhibitor of the uniporter. Our genomic, physiological, biochemical and pharmacological data firmly establish MCU as an essential component of the mitochondrial Ca(2+) uniporter.     

Cholinergic neuropil of the striatum observes striosomal boundaries

Acetylcholine and dopamine are key neurotransmitters in the extrapyramidal motor system, where they are thought to lie in a 'functional balance' brought about by interactions between the terminals of the dopamine-containing nigrostriatal tract and the cholinergic interneurones of the striatum. The precise nature of these interactions is not understood, however, nor is it clear how they influence the functioning of striatal systems containing other neurotransmitters. A new clue to understanding such interplay among transmitter-coded systems in the striatum has come from the finding that many of them, including nigrostriatal afferents, follow a macroscopic ordering in which neural elements are concentrated either in or out of the striatal tissue compartments called striosomes. We here report that the cholinergic neuropil of the striatum is also compartmentalized: fibres expressing immunoreactivity to antibodies raised against choline acetyltransferase (ChAT) are sparse in striosomes and are dense in the extrastriosomal matrix. These findings suggest that the interactions between acetylcholine and other neurotransmitters in the striatum are spatially constrained, that cholinergic modulation of striatal function predomintes in the extrastriosomal matrix, and that extrapyramidal pathways originating in the matrix, including transthalamic pathways to the frontal lobes, may in particular reflect this cholinergic influence. Such a differential organization of striatal cholinergic circuitry could help to account for the selective therapeutic efficacy of anticholinergic drugs in the treatment of extrapyramidal disorders.