Ethanol in low doses augments calcium-mediated mechanisms measured intracellularly in hippocampal neurons.

The electrophysiological effects of ethanol in low doses (5 to 20 millimoles per liter or 23 to 92 milligrams per 100 milliliters) were examined intracellularly in CA1 cells of rat hippocampus in vitro. Inhibitory and excitatory postsynaptic potentials were increased when ethanol was applied to the respective synaptic terminal regions. Postsynaptically, ethanol caused a moderate hyperpolarization with increased membrane conductance, even when synaptic transmission was blocked. Ethanol augmented the hyperpolarization that followed repetitive firing or that followed the eliciting of calcium spikes in the presence of tetrodotoxin, but not the rapid afterhyperpolarization in calcium-free medium. Ethanol appears to augment calcium-mediated mechanisms both pre- and postsynaptically.

Formation and electrophysiological actions of the arachidonic acid metabolites, hepoxilins, at nanomolar concentrations in rat hippocampal slices.

Metabolites of arachidonic acid are known to be formed in the mammalian central nervous system. When intact hippocampal slices were incubated in artificial cerebrospinal fluid, 12-hydroxyeicosatetraenoic acid and two isomers of hepoxilin A3 (8R and 8S) were released as measured by gas chromatography-mass spectrometry. These compounds were released in greater amounts in the presence of noradrenaline or when arachidonic acid was added to the slices. The neuronal actions of chemically derived preparations of 8R and 8S hepoxilins and the glutathione conjugate, hepoxilin A3-C, were examined using intracellular and whole-cell electrophysiological recordings in hippocampal CA1 neurons in vitro. All compounds had the excitatory effects of lowering spike threshold and decreasing spike frequency adaptation, and the inhibitory actions of membrane hyperpolarization, enhanced postspike train afterhyperpolarizations and increased inhibitory postsynaptic potentials or currents. A synthetic analog of hepoxilin A3-C, in which the glutathione moiety is placed at carbon position 9 instead of carbon position 11 as in hepoxilin A3-C, was inactive. The actions of the hepoxilins showed a sharp dose-response relationship, with minimal threshold or no effect at 3 nM (n = 21) and maximal effects at 10 nM (n = 33). There were no significant differences between the responses to either the 8R or 8S isomers, or between hepoxilin A3 and hepoxilin A3-C. These data suggest that hepoxilins formed by the brain have significant neuromodulatory actions.

Low-dose benzodiazepine neuronal inhibition: enhanced Ca2+-mediated K+-conductance.

The water-soluble inhibitory benzodiazepine, midazolam, was applied in low nanomolar concentrations to CA1 hippocampal neurons in vitro, recorded intracellularly. The drug caused a long-lasting hyperpolarization and moderate conductance increase, which persisted with TTX-induced synaptic blockade or with intracellular injection of Cl- ions, but not in zero Ca2+ perfusate. Calcium spikes elicited in the presence of TTX were enhanced by midazolam. It was concluded that these low nanomolar concentrations, which did not enhance GABA actions, inhibited by augmenting Ca2+ mediated K+-conductance.

The excitatory effects of the specific benzodiazepine antagonist Ro14-7437, measured intracellularly in hippocampal CA1 cells.

The specific benzodiazepine antagonist, Ro14-7437, in nanomolar concentrations, caused depolarization, increased spontaneous spiking, and conductance decrease when applied to CA1 cells in vitro. These effects were resistant to intracellularly injected Cl- ions or synaptic blockade by TTX, were prevented in Ca2+-free medium, and occurred with or without prior application of midazolam, an inhibitory benzodiazepine. Ca2+-mediated AHPs and Ca2+ spikes in TTX medium were diminished by the blocker, suggesting that Ro14-7437 acted by inhibiting Ca2+-mediated K+ conductance.

Ethanol-induced dendritic alterations in hippocampal granule cells.

The effects of chronic ethanol intake were studied on the morphology of rat hippocampal granule cells. Sprague-Dawley rats were exposed to ethanol in a liquid diet for 5 months followed by a 3 week withdrawal period. A control group was fed similar amounts of the same diet but with ethanol replaced by maltose-dextrins. Intracellular recordings were performed using the hippocampal slice preparation and the granule cells from animals of both groups were injected with HRP. The ethanol treatment produced a significant increase in the average length of the dendrites of granule cells compared to the control group. Chronic ethanol intake produced a decrease in the number of dendrites in the proximal region of the tree (80-180 microns) but also a significant increase in the number of dendrites in the distal portion (260-340 microns). The decrease in the number of proximal dendrites suggests that ethanol could be affecting a population of neurons with afferent inputs in the proximal region of the tree or that ethanol could interfere with the normal maturation processes of the granule cells. The increase in the number of dendrites in the distal region of the tree suggests, however, an accelerated growth or sprouting of dendrites in the molecular layer.

Actions of arachidonic acid and hepoxilin A3 on mammalian hippocampal CA1 neurons.

The effects of arachidonic acid and its lipoxygenase metabolites, the hepoxilins, were investigated in rat hippocampal CA1 neurons in vitro by intracellular electrophysiological recordings. Both arachidonic acid and the hepoxilins cause a hyperpolarization which is sometimes followed by a later depolarization, augment the postspike train long-lasting afterhyperpolarization (AHP) and increase orthodromic inhibitory postsynaptic potentials (IPSPs). These data show that this arachidonic acid metabolic pathway has significant actions on mammalian central neurons, and may represent an important mechanism of neuromodulation.

Effects of enkephalin analogue and naloxone on cat spinal cord dorsal root potentials.

A systemically active enkephalin analogue, FK33824, given intravenously depressed dorsal root potentials in cat spinal cord. The negative DR V and positive DR VI, measured by computer, were both decreased; this effect was reversed by small doses of intravenous naloxone. Naloxone, given alone, with no previous analogue produced no changes in dorsal root potentials suggesting the absence of a basal enkephalin tone. A second injection of FK33824 was much less effective that the first dose. The results were discussed in relation to presynaptic mechanisms for analgesia: we proposed that FK33824 causes presynaptic inhibition by modulation rather than by depolarization of primary afferent fibers.

Serotonin-1A receptor activation in hippocampal CA1 neurons by 8-hydroxy-2-(di-n-propylamino)tetralin, 5-methoxytryptamine and 5-hydroxytryptamine.

Serotonin (5-HT) usually induced a slow hyperpolarization lasting several minutes on first drop-application onto CA1 neurons. Subsequent applications always caused a briefer (less than 2 min) hyperpolarization, usually followed by a depolarization. 8-Hydroxy-2(di-n-propylamino)tetralin, a 5-HT1A receptor agonist, and 5-methoxytryptamine, a 5-HT1 receptor agonist, produced only the long-lasting hyperpolarization. The application of 5-HT agonists caused a persistent prolongation of the post-spike train afterhyperpolarization. These observations suggest that the long-lasting hyperpolarization produced by 5-HT may be mediated by the activation of the 5-HT1A receptor subtype.

Comparison of the clearance of radiolabelled nose drops and nasal spray as mucosally delivered vaccine.

The distribution and nasal clearance of 99Tcm-labelled albumin (18.5 MBq), used as a mucosal vaccine surrogate for FluMist, was determined in three volunteers. The subjects were randomized in a cross-over clinical study design to receive either large-particle aerosal (nasal spray) followed by nose drops, or nose drops followed by the nasal spray, 1 week apart. Gamma scintigraphy was used to measure the distribution and clearance. The 'vaccine' delivered as drops was cleared from the nose into the oesophagus and upper stomach at very variable rates. In contrast, the nasal spray was uniformly distributed and cleared from the nasopharynx with a 50% mean clearance time of 50 min (range 40-60 min) and was not detected in the lungs.

Adherence of radiopharmaceuticals and labeled cells to intravenous tubing.

A survey of 67 nuclear medicine departments revealed no agreement on which radiolabeled agents could be injected through intravenous lines (IVs) and which required direct venipuncture. Labeled cells and several common radiopharmaceuticals were tested for adherence to intravenous tubing. Residual activity remaining in the tubing after an adequate flush was less than 1% of the injected dose in each case. Administration of radiolabeled agents through existing IVs is an acceptable alternative to direct venipuncture in many cases.

[Cytochemical method for detecting dehydrogenase activity in the leukocytes of native blood smears]. / Tsitokhimicheskaia metodika vyiavleniia aktivnosti degidrogenaz v leikotsitakh nativnykh mazkov krovi.

A cytochemical method of detection of dehydrogenases in blood leucocytes is proposed. Native smears are dried up in the air to be incubated at 37 degrees C in gel-containing medium composed of polyvinyl alcohol, sucrose, a corresponding substrate, cofactors and inhibitors of cytochrome oxidases activity. Using corresponding media, activities of succinate, malate, glutamate, lactate-, alpha-glycerophosphate, alcohol, beta-oxybutyrate and glucoso-5-phosphate dehydrogenases were revealed. Half-reduced diformazan providing diffuse rosy staining of cells was removed after the incubation, and the incubation medium was washed out by rinsing the smears in 60% acetone solution. As a result monochromatic micropreparations may be received. Finally, smears are fixed in formalin. The above method provides a reduced loss of enzymes, preserves a good cell morphology and eliminates non-dehydrogenase effects of tetrazolium reduction into formazan.

[Properties and organization of pyramidal neurons of the rat motor cortex]. / Svoistva i organizatsiia piramidnykh neironov motornoi kory krysy

Antidromic potential sin cortical neurons elicited by stimulation of pyramids and different segments of the spinal cord were studied with the aid of extracellular recording in rats. Axons of about 2/3 of the cells under study formed the cortico-spinal tract passing through the ventral portion of the dorsal column up to the lumbar segments of the spinal cord. Conduction velocity along the cortico-spinal axons varied from 2.3 to 17.0 m/sec.

Pentobarbital inhibits hippocampal neurons by increasing potassium conductance.

The effects of sodium pentobarbital were studied using intracellular recordings from CA1 and CA3 pyramidal cells in slices of guinea pig hippocampus. Drugs were applied either by perfusion or by pressure ejection at concentrations of 10(-6), 10(-5), and 10(-4) M. Pentobarbital at all concentrations caused neuronal hyperpolarization, decreased spontaneous activity, and sometimes decreased input resistance. Hyperpolarization also occurred in zero calcium perfusate or with tetrodotoxin in the perfusate. The postspike train long-lasting afterhyperpolarization, which is an intrinsic calcium-mediated potassium conductance, was increased at all doses. gamma-Aminobutyric acid induced depolarizing dendritic responses were augmented only at 10(-4) M pentobarbital. It is proposed that one of the important mechanisms of pentobarbital neuronal inhibition, particularly at lower doses, is an increase in potassium conductance.

Serotonin agonist and antagonist actions in hippocampal CA1 neurons.

The actions of serotonin (5-HT) and its putative agonists and antagonists were examined in vitro on hippocampal CA1 neurons using intracellular recordings, demonstrating that the cellular pharmacological effects can not necessarily be predicted from binding characteristics alone. The first response following 5-HT application was often a long-lasting (several minutes) hyperpolarization associated with decreased input resistance. Subsequent 5-HT applications caused only brief hyperpolarizations (30-120 s) and associated decreased input resistance, often followed by membrane depolarization. The post-spike train afterhyperpolarization (AHP) was prolonged for several minutes following the 5-HT induced hyperpolarization. 5-HT1 agonists (8-hydroxy-2-(di-n-propylamino)tetralin, 5-methoxytryptamine, MK-212) caused a prolonged hyperpolarization, decreased input resistance, and enhancement of the AHP. 5-HT applied following agonist application elicited only short-lasting hyperpolarizations. The 5-HT2 antagonists, cyproheptadine and mianserin, and a nonspecific 5-HT antagonist, methysergide, also caused a prolonged hyperpolarization with decreased input resistance. Spiperone, a nonspecific 5-HT antagonist, and ritanserin, a putative specific 5-HT2 receptor antagonist, depolarized CA1 neurons with little or no change in input resistance. The 5-HT-induced short-lasting hyperpolarization was not affected by drop application of 5-HT antagonists, except for methysergide, but perfusion of methysergide, ritanserin, and spiperone attenuated this response. The long-lasting 5-HT hyperpolarization might be mediated by 5-HT1A receptor activation, and the short-lasting hyperpolarization by another serotonergic receptor subtype.

Enhanced neuronal K+ conductance: a possible common mechanism for sedative-hypnotic drug action.

It is commonly thought that central nervous system depressant drugs exert their actions through enhancement of gamma-aminobutyrate (GABA)-mediated mechanisms. Recently, the cellular electrophysiological evidence from this laboratory and others suggests that both sedative hypnotics and general anaesthetics inhibit central neurons by increasing potassium conductance (GK). We have utilized the mammalian in vitro hippocampal and cerebellar slice preparations at 34-36 degrees C. Intracellular recordings from CA1, CA3, and cerebellar Purkinje cells were obtained. Low dose (sedative) concentrations of ethanol (less than or equal to 20 mM), two different benzodiazepines (midazolam and clonazepam in low nanomolar concentrations), and pentobarbital (10(-6) to 10(-4) M) were applied by pressure ejection or were bath perfused. All drugs caused a hyperpolarization with decreased spontaneous activity, and enhanced post spike afterhyperpolarizations (AHPs). These long-lasting AHPs are presumably due to enhanced calcium-mediated GK. Increased responsiveness to focally applied GABA was only seen at higher doses (ethanol, 100 mM; midazolam, 10(-7) M; pentobarbital, 10(-4) M). These data suggest that the above neurodepressant drugs, when applied at sedative doses to hippocampal pyramidal cells, enhance GK and not the actions of GABA.