Role of arachidonic acid in the regulation of the NMDA-evoked release of acetylcholine in striatal compartments

Characterization of ST14A Cells for Studying Modulation of Voltage-Gated Calcium Channels

In medium spiny neurons (MSNs) of the striatum, dopamine D₂ receptors (D₂Rs) specifically inhibit the Ca_v1.3 subtype of L-type Ca²⁺ channels (LTCs). MSNs are heterogeneous in their expression of dopamine receptors making the study of D₂R pathways difficult in primary neurons. Here, we employed the ST14A cell line, derived from embryonic striatum and characterized to have properties of MSNs, to study Ca_v1.3 current and its modulation by neurotransmitters. Round, undifferentiated ST14A cells exhibited little to no endogenous Ca²⁺ current while differentiated ST14A cells expressed endogenous Ca²⁺ current. Transfection with LTC subunits produced functional Ca_v1.3 current from round cells, providing a homogeneous model system compared to native MSNs for studying D₂R pathways. However, neither endogenous nor recombinant Ca_v1.3 current was modulated by the D₂R agonist quinpirole. We confirmed D₂R expression in ST14A cells and also detected D₁Rs, D₄Rs, D₅Rs, G_q, calcineurin and phospholipase A₂ using RT-PCR and/or Western blot analysis. Phospholipase C β-1 (PLCβ-1) expression was not detected by Western blot analysis which may account for the lack of LTC modulation by D₂Rs. These findings raise caution about the assumption that the presence of G-protein coupled receptors in cell lines indicates the presence of complete signaling cascades. However, exogenous arachidonic acid inhibited recombinant Ca_v1.3 current indicating that channels expressed in ST14A cells are capable of modulation since they respond to a known signaling molecule downstream of D₂Rs. Thus, ST14A cells provide a MSN-like cell line for studying channel modulation and signaling pathways that do not involve activation of PLCβ-1.

Autism as a disorder of deficiency of brain-derived neurotrophic factor and altered metabolism of polyunsaturated fatty acids

Autism has a strong genetic and environmental basis in which inflammatory markers and factors concerned with synapse formation, nerve transmission, and information processing such as brain-derived neurotrophic factor (BDNF), polyunsaturated fatty acids (PUFAs): arachidonic (AA), eicosapentaenoic (EPA), and docosahexaenoic acids (DHA) and their products and neurotransmitters: dopamine, serotonin, acetylcholine, γ-aminobutyric acid, and catecholamines and cytokines are altered. Antioxidants, vitamins, minerals, and trace elements are needed for the normal metabolism of neurotrophic factors, eicosanoids, and neurotransmitters, supporting reports of their alterations in autism. But, the exact relationship among these factors and their interaction with genes and proteins concerned with brain development and growth is not clear. It is suggested that maternal infections and inflammation and adverse events during intrauterine growth of the fetus could lead to alterations in the gene expression profile and proteomics that results in dysfunction of the neuronal function and neurotransmitters, alteration(s) in the metabolism of PUFAs and their metabolites resulting in excess production of proinflammatory eicosanoids and cytokines and a deficiency of anti-inflammatory cytokines and bioactive lipids that ultimately results in the development of autism. Based on these evidences, it is proposed that selective delivery of BDNF and methods designed to augment the production of anti-inflammatory cytokines and eicosanoids and PUFAs may prevent, arrest, or reverse the autism disease process.

Neuronal electrical high frequency stimulation enhances GABA outflow from human neocortical slices

Electrical high frequency stimulation of the globus pallidus internus or the subthalamic nucleus has beneficial motor effects in advanced Parkinson's disease. The mechanisms underlying these clinical results remain, however, unclear. From previous studies it is proposed that the gamma-aminobutyric acid (GABA) system is involved in the effectiveness of electrical high frequency stimulation. In these experiments, human neocortical slices were stimulated electrically (130 Hz) in vitro, and GABA outflow was measured after o-phthaldialdehyde sulphite derivatization using HPLC with electrochemical detection. Our results could demonstrate that high frequency stimulation (HFS) significantly increased basal GABA outflow in the presence of submaximal concentrations of the voltage-gated sodium channel opener veratridine. This effect could be abolished by the GABA antagonists bicuculline or picrotoxin. These results suggest that HFS has an activating effect on GABAergic neuronal terminals in human neocortical slices, depending on sodium and chloride influx. Since GABA plays a role in CNS disorders of basal ganglia, anxiety and epilepsy, its neocortical modulation by HFS may be (patho)physiologically relevant.

Neuronal electrical high frequency stimulation modulates presynaptic GABAergic physiology

Electrical high frequency deep brain stimulation (DBS) of the globus pallidus internus (GPi) or the subthalamic nucleus (STN) has dramatic beneficial motor effects in advanced Parkinson's disease (PD). However, the mechanisms underlying these clinical results remain unclear. It is proposed that the gamma-aminobutyric acid (GABA) system is involved in the effectiveness of DBS. To prove this hypothesis, rat striatal slices were stimulated electrically (130 Hz) in vitro; GABA and glutamate (GLU) outflow from striatal slices of normal or kainic acid-lesioned rats were measured after o-phthaldialdehyde sulphite derivatization using HPLC with electrochemical detection. Our results could demonstrate that high frequency stimulation (HFS) did not modulate basal GABA outflow in the perfusate. In the presence of submaximal concentrations of the voltage-gated sodium channel opener veratridine, HFS significantly enhanced GABA outflow. When the GABA transporter inhibitor, nipecotic acid, was added to the incubation medium, the HFS effects decreased to nearly control values. Destruction of striatal GABAergic neurons by kainic acid completely reversed the effects of HFS on GABA outflow. In the present study no effect of HFS on glutamate outflow was observed under any condition. These results suggest that HFS has a specific effect on GABAergic neuronal terminals resulting in an enhancement of extracellular GABA in the caudate nucleus. This effect is probably due to an inhibitory effect of HFS on the GABA uptake system rather than to stimulation of vesicular GABA release from GABAergic neurons, which are both associated with the presynaptic GABAergic physiology.

Facilitation by endogenous tachykinins of the NMDA-evoked release of acetylcholine after acute and chronic suppression of dopaminergic transmission in the matrix of the rat striatum

Using a microsuperfusion method in vitro, the effects of the NK1, NK2, and NK3 tachykinin receptor antagonists SR140333, SR48968, and SR142801, respectively, on the NMDA-evoked release of [3H]-acetylcholine were investigated after both acute and chronic suppression of dopamine transmission in striosomes and matrix of the rat striatum. NMDA (1 mm) alone or with D-serine (10 microm) in the presence of alpha-methyl-p-tyrosine (100 microm) markedly enhanced the release of [3H]-acetylcholine through a dopamine-independent inhibitory process. In both conditions, as well as after chronic 6-OHDA-induced denervation of striatal dopaminergic fibers, SR140333, SR48968, or SR142801 (0.1 microm each) reduced the NMDA-evoked release of [3H]-acetylcholine in the matrix but not in striosome-enriched areas. These responses were selectively abolished by coapplication with NMDA of the respective tachykinin agonists, septide, [Lys5,MeLeu9,Nle10]NKA(4-10), or senktide. Distinct mechanisms are involved in the effects of the tachykinin antagonists because the inhibitory response of SR140333 was additive with that of either SR48968 or SR142801. In addition, the SR140333-evoked response remained unchanged, whereas those of SR48968 and SR142801 were abolished in the presence of N(G)-monomethyl-l-arginine (nitric oxide synthase inhibitor). Therefore, in the matrix but not in striosomes, the acute or chronic suppression of dopamine transmission unmasked the facilitatory effects of endogenously released substance P, neurokinin A, and neurokinin B on the NMDA-evoked release of [3H]-acetylcholine. Whereas substance P and neurokinin A are colocalized in same efferent neurons, their responses involve distinct circuits because the substance P response seems to be mediated by NK1 receptors located on cholinergic interneurons, while those of neurokinin A and neurokinin B are nitric oxide-dependent.

Nutritional factors in the pathobiology of human essential hypertension

Endothelial cells produce vasodilator and vasoconstrictor substances. Dietary factors such as sodium, potassium, calcium, magnesium, zinc, selenium, vitamins A, C, and E, and essential fatty acids and their products such as eicosanoids can influence blood pressure, cardio- and cerebrovascular diseases, and concentrations of blood lipids and atherosclerosis. There might be a close interaction between these dietary factors, sympathetic and parasympathetic nervous systems, the metabolism of essential fatty acids, nitric oxide, prostacyclin, and endothelium in human essential hypertension. A deficiency in any one factor, dietary or endogenous, or alterations in their interactions with each other, can lead to endothelial dysfunction and development of hypertension. Therefore, alterations in the metabolism of essential fatty acids might be a predisposing factor to the development of essential hypertension and insulin resistance.