Voltage-clamp analysis and computer simulation of a novel cesium-resistant A-current in guinea pig laterodorsal tegmental neurons

Increased firing of cholinergic neurons of the laterodorsal tegmental nucleus (LDT) plays a critical role in generating the behavioral states of arousal and rapid eye movement sleep. The majority of these neurons exhibit a prominent transient potassium current (IA) that shapes firing but the properties of which have not been examined in detail. Although IA has been reported to be blocked by intracellular cesium, the IA in LDT neurons appeared resistant to intracellular cesium. The present study compared the properties of this cesium-resistant current to those typically ascribed to IA. Whole cell recordings were obtained from LDT neurons (n = 67) in brain slices with potassium- or cesium-containing pipette solutions. A transient current was observed in cells dialyzed with each solution (KGluc-85%; CsGluc-79%). However, in cesium-dialyzed neurons, the transient current was inward at test potentials negative to about -35 mV. Extracellular 4-aminopyridine (4-AP; 2-5 mM) blocked both inward and outward current, suggesting the inward current was reversed IA rather than an unmasked transient calcium current as previously suggested. This conclusion was supported by increasing [K]o from 5 to 15 mM, which shifted the reversal potential positively for both inward and outward current (+17.89 +/- 0.41 mV; mean +/- SE). Moreover, recovery from inactivation was rapid (tau = 15.5 +/- 4 ms; n = 4), as reported for IA, and both inward and outward transient current persisted in calcium-free solution [0 calcium/4 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N', N'-tetraacetic acid; n = 4] and during cadmium-blockade of calcium currents (n = 3). Finally, the transient current was blocked by intracellular 4-AP indicating that adequate dialysis occurred during the recordings. Thus the Cs-resistant current is a subthreshold IA. We also estimated the voltage-dependence of activation (V1/2 = -45.8 +/- 2 mV, k = 5.21 +/- 0.62 mV, n = 6) and inactivation (V1/2 = -59. 0 +/- 2.38 mV, k = -5.4 +/- 0.49 mV, n = 3) of this current. Computer simulations using a morphologically accurate model cell indicated that except for the extreme case of only distal A-channels and a high intracellular resistivity, our parameter estimates were good approximations. In conclusion, guinea pig LDT neurons express subthreshold A-channels that are resistant to intracellular cesium ions. This suggests that these channels differ fundamentally in their ion permeation mechanism from those previously studied. It remains to be determined if Cs+ resistance is common among brain A-channels or if this property is conferred by known A-channel subunits.     

Aging and the dendritic morphology of the rat laterodorsal and pedunculopontine tegmental nuclei

This study is based on interviews with 37 persons fulfilling the DSM-IV criteria for kleptomania recruited through newspaper advertisements, and on 50 shoplifters interviewed directly after apprehension. Our hypothesis was that there are no absolute borders between 'pure' kleptomania according to DSM-IV and other forms of shoplifting. When asked about the latest case of shoplifting, one fifth of the shoplifters reported not having stolen the item for personal use and had later discarded it. A quarter of the kleptomaniacs reported ambivalence when asked if they needed the item in question. The degree of reported impulsivity and a feeling of not being oneself at the time of the theft was the same in the two groups. The two groups also estimated their degree of impulsivity, planning, thrill, relief, vengeance, need, pleasure on a Visual Analogue Scale (VAS) as well as the degree of psychiatric imbalance on the latest theft occasion. These estimates showed that there were no differences between the groups concerning the degree of planning, psychological imbalance and the need for the stolen item in question. The kleptomaniacs rated a feeling of inner tension before the theft higher than the shoplifters. The same was true concerning a feeling of relief during the theft and impulsivity. However, the shoplifters also rated high on all these items. Altogether, these findings support our hypothesis that many shoplifters, even if they do not fulfill all DSM criteria for kleptomania, may constitute a significant medical problem and should be offered support and treatment. Anti-depressants as well as the educational programmes developed by the Shoplifters Alternatives may be effective not only in cases of kleptomania but also for more unselected groups of non-professional shoplifters.     

Synaptic signaling in an active central network only moderately changes passive membrane properties

The membrane resistance of mammalian central neurons may be dramatically reduced by synaptic events during network activity, thereby changing their integration properties. We have used the isolated neonatal rat spinal cord to provide measurements of the effect of synaptic signaling on passive membrane properties during network activity. Synaptic signaling could take place during fictive locomotor activity with only modest (on average 35%) reduction of the input resistance (Rin) and of the cell's charging time constant (tauin). Individual synaptic signals, however, often introduced a peak conductance that was greater than the input conductance (Gin = 1/Rin) without synaptic activity. The combination of moderate average synaptic conductance and large conductance of individual synaptic signals suggests that individual presynaptic neurons have large but short-lasting influence on the integration properties of postsynaptic neurons.     

Sensory responsiveness of "broad-spike" neurons in the laterodorsal tegmental nucleus, locus coeruleus and dorsal raphe of awake rats: implications for cholinergic and monoaminergic neuron-specific responses

Although cholinergic neurons in the laterodorsal and pedunculopontine tegmental nuclei have been shown to have a pivotal role in neural mechanisms of paradoxical sleep, their function during wakefulness is less understood. To examine the latter, we have recorded from "broad-spike neurons", which were distinguished by their long spike duration, in the laterodorsal tegmental nucleus of undrugged, head-restrained rats, and examined their response properties to sensory stimuli such as light touch to the tail, air puff to the face, 2 kHz pure tone and flashes of light. Broad-spike neurons from the locus coeruleus and dorsal raphe nucleus were studied for comparison; these neurons have been demonstrated to be noradrenergic and serotonergic, respectively. The broad-spike neurons in the laterodorsal tegmental nucleus have also been suggested to be cholinergic. There were two kinds of responses: (1) a simple increase or decrease in firing, reflecting an elevated level of vigilance; and (2) a phasic response composed of a single spike or brief, high frequency burst, usually diminishing or disappearing upon repetition of the stimulus. When two or more types of stimuli were effective in a neuron, they evoked responses of the same quality. Most of the dorsal raphe neurons displayed only the simple increase of firing, whereas the locus coeruleus neurons gave a phasic response with rather weak attenuation upon repetition. Compared with these, the laterodorsal tegmental neurons were heterogeneous: about one-quarter showing only a simple change of firing (half increasing, half decreasing); and two-thirds displaying phasic responses. The latter response of many neurons attenuated strongly upon repetition. The laterodorsal tegmental neurons were classified into several groups according to their spontaneous firing behavior during sleep and wakefulness, but every neuron in a group did not show the same type of response. For example, some of the neurons which were most active during paradoxical sleep and essentially silent during wakefulness decreased or stopped firing upon sensory stimulation, while others in this group had strong phasic responses. These results suggest that putative cholinergic neurons in the laterodorsal tegmental nucleus have heterogenous properties not only with respect to their spontaneous activity during sleep and wakefulness but also with respect to their response to sensory stimulation. Some of these neurons may function to induce a global attentive state in response to a novel stimulus.     

Passive and active membrane properties contribute to the temporal filtering properties of midbrain neurons in vivo

This study examined the contributions of passive and active membrane properties to the temporal selectivities of electrosensory neurons in vivo. The intracellular responses to time-varying (2-30 Hz) electrosensory stimulation and current injection of 27 neurons in the midbrain of the weakly electric fish Eigenmannia were recorded. Each neuron was filled with biocytin to reveal its anatomy. Neurons were divided into two biophysically distinct groups based on their frequency-dependent responses to sinusoidal current injection over the range 2-30 Hz. Fourteen neurons showed low-pass filtering, with a maximum decline in the amplitude of voltage responses of >2.6 dB (X = 4.30 dB, s = 1.10 dB) to sinusoidal current injection. These neurons also showed low-pass filtering of electrosensory information but with larger maximum declines in postsynaptic potential amplitude (X = 9.53 dB, s = 3.34 dB; n = 10). These neurons had broad dendritic arbors and relatively spiny dendrites. Five neurons showed all-pass filtering, having maximum decline in the amplitude of voltage responses of <2.0 dB (X = 1.16 dB, s = 0.61 dB). For electrosensory stimuli, however, these neurons showed low-, band-, or high-pass filtering. These neurons had small dendritic arbors and few or no spines. Voltage-dependent "active" conductances were revealed in eight neurons by using several levels of current clamp. In four of these neurons, the duration of the voltage-dependent conductances decreased in concert with the period of the electrosensory stimulus, whereas in the other four neurons the duration of the voltage-dependent conductances was relatively short (<30 msec) and nearly constant across sensory stimulation frequencies. These conductances enhanced the temporal filtering properties of neurons.     

Comparison of auditory P300 habituation from active and passive conditions

The P3(00) event-related brain potential (ERP) was elicited using auditory stimuli and tasks in which the subject discriminated between standard and target tones or with passive task conditions in which the subject did not respond to either the standard or target stimuli. All stimulus presentations consisted of a series of ten-tone sequences in which the first six tones were always the standard and one of the last four tones was the target. The passive tasks were presented twice to assess for habituation effects. P3 amplitude was largest for the oddball task compared to the passive tasks, and repetition of the passive paradigm demonstrated a decrease in amplitude between conditions. P3 amplitude did not decrease across trials within any of the separate response conditions. P3 latency was shorter for the active discrimination relative to the passive tasks. The results suggest that the P3 component can be obtained reliably with passive procedures and does not habituate within a trial block. However, repeated blocks of passive stimulus presentations will cause the P3 ERP to diminish in size.     

Nicotine modifies the activity of ventral tegmental area dopaminergic neurons and hippocampal GABAergic neurons

While trying to mimic the dose and time course of nicotine as it is obtained by a smoker, we found the following results. The initial arrival of even a low concentration of nicotine increased the firing rate of dopaminergic neurons from the ventral tegmental area (VTA) and increased the spontaneous vesicular release of GABA from hippocampal neurons. Longer exposure to nicotine caused variable, but dramatic, desensitization of nicotinic receptors and diminished the effects of nicotine. The addictive properties of nicotine as well as its diverse effects on cognitive function could be mediated through differences in activation and desensitization of nicotinic receptors in various areas of the brain.     

Glycine-activated chloride currents of neurons freshly isolated from the ventral tegmental area of rats

This paper describes the preparation and characterisation of poly(lactide-co-glycolide) (PLG) nanoparticles containing the enzyme L-asparaginase. L-Asparaginase was encapsulated in PLG nanospheres using a water-in-oil-in-water solvent evaporation technique. The effect of the copolymer molecular weight and the presence of carboxyl-end groups in the copolymer chain on the physicochemical and in vitro release properties of the nanoparticles was investigated. Results indicated that size, encapsulation efficiency and in vitro release properties (enzymatic activity retention and protein quantification) of the nanoparticles were affected by the PLG molecular weight. As expected, nanoparticles made of high-molecular-weight PLG had a larger size, a higher loading and la slower release rate than those made od a low-molecular-weight PLG. Nevertheless, the most relevant factor affecting the entrapment and release of L-asparaginase from PLG nanoparticles was the presence of free carboxyl-end groups in the PLG chain. The nanoparticles made of PLG with free carboxyl-end groups had a high protein loading (4.86%, w/w) and provided a continuous delivery of the active enzyme for 20 days. However, the enzyme loading was lower (2.65%, w/v) and no active enzyme was detected in the release medium after a 14-day incubation period when nanoparticles were made of PLG with carboxyl-end groups esterified. These results give evidence of the potential of PLG nanospheres for the continuous delivery of L-asparaginase for extended periods of time and show the effect of the PLG chain end-groups in the amount and activity of the enzyme loaded into the nanospheres.     

Relationship between perceptual style and responses to visual motion under active and passive viewing conditions.

Selected 20 extreme field-dependent and 20 extreme field-independent male college students based on rod-and-frame test scores. Ss viewed an 8-min segment of film showing high-speed automobile travel. Half watched the film passively, and half watched while actively initiating leg movements in response to the car's expected turning direction. Skin conductance level was monitored from 2 nonpalmar sites, and the Ss reported the extent to which specific sensations were experienced. It was found that in the passive viewing condition field-independent Ss showed greater increases in skin conductance levels than field-dependent Ss, but in the active viewing condition both types of individuals showed similar increases. Electrodermal activity change was associated with reported sensations of general discomfort and illusory motion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of predictive information on responses of tonically active neurons in the monkey striatum

Influence of predictive information on responses of tonically active neurons in the monkey striatum. J. Neurophysiol. 80: 3341-3344, 1998. We investigated how the expectation of a signal of behavioral significance influences the activity of tonically active neurons in the striatum of two monkeys performing a simple reaction time task under two conditions, an uncued condition in which the trigger stimulus occurred randomly in time and a cued condition in which the same trigger was preceded by an instruction stimulus serving as a predictive signal for the forthcoming signal eliciting an immediate behavioral reaction. Both monkeys benefited from the presence of the instruction stimulus to reduce their reaction time, suggesting an increased ability to predict the trigger onset during cued trials compared with uncued trials. A majority of neurons (199/272, 73%) showed a phasic reduction in activity after the onset of the trigger stimulus in the uncued condition, whereas only 38% responded to the same stimulus when it was preceded by the instruction. Furthermore, magnitudes of trigger responses in the uncued condition were significantly higher than in the cued condition. Fifty-seven percent of the neurons responded to the instruction stimulus, and one-half of the neurons losing their response to the trigger in the cued condition responded to the instruction stimulus. These findings suggest that responses of tonic striatal neurons to a trigger stimulus for movement were influenced by predictive information.     

Morphological and membrane properties of rat magnocellular basal forebrain neurons maintained in culture

Morphological and electrophysiological characteristics of magnocellular neurons from basal forebrain nuclei of postnatal rats (11-14 days old) were examined in dissociated cell culture. Neurons were maintained in culture for periods of 5-27 days, and 95% of magnocellular (>23 micron diam) neurons stained positive with acetylcholinesterase histochemistry. With the use of phase contrast microscopy, four morphological subtypes of magnocellular neurons could be distinguished according to the shape of their soma and pattern of dendritic branching. Corresponding passive and active membrane properties were investigated with the use of whole cell configuration of the patch-clamp technique. Neurons of all cell types displayed a prominent (6-39 mV; 6.7-50 ms duration) spike afterdepolarization (ADP), which in some cells reached firing threshold. The ADP was voltage dependent, increasing in amplitude and decreasing in duration with membrane hyperpolarization with an apparent reversal potential of -59 +/- 2.3 (SE) mV. Elevating [Ca2+]o (2.5-5.0 mM) or prolonging spike repolarization with 10 mM tetraethylammonium (TEA) or 1 mM 4-aminopyridine (4-AP), potentiated the ADP while it was inhibited by reducing [Ca2+]o (2.5-1 mM) or superfusion with Cd2+ (100 microM). The ADP was selectively inhibited by amiloride (0.1-0.3 mM or Ni2+ 10 microM) but unaffected by nifedipine (3 microM), omega-conotoxin GVIA (100 nM) or omega-agatoxin IVA (200 nM), indicating that Ca2+ entry was through T-type Ca2+ channels. After inhibition of the ADP with amiloride (300 microM), depolarization to less than -65 mV revealed a spike afterhyperpolarization (AHP) with both fast and slow components that could be inhibited by 4-AP (1 mM) and Cd2+ (100 microM), respectively. In all cell types, current-voltage relationships exhibited inward rectification at hyperpolarized potentials >/=EK (approximately -90 mV). Application of Cs+ (0.1-1 mM) or Ba2+ (1-10 microM) selectively inhibited inward rectification but had no effect on resting potential or cell excitability. At higher concentrations, Ba2+ (>10 microM) also inhibited an outward current tonically active at resting potential (VH -70 mV), which under current-clamp conditions resulted in small membrane depolarization (3-10 mV) and an increase in cell excitability. Depolarizing voltage commands from prepulse potential of -90 mV (VH -70 mV) in the presence of tetrodotoxin (0.5 microM) and Cd2+ (100 microM) to potentials between -40 and +40 mV cause voltage activation of both transient A-type and sustained delayed rectifier-type outward currents, which could be selectively inhibited by 4-AP (0.3-3 mM) and TEA (1-3 mM), respectively. These results show that, although acetylcholinesterase-positive magnocellular basal forebrain neurons exhibit considerable morphological heterogeneity, they have very similar and characteristic electrophysiological properties.     

Chronic interleukin-6 alters NMDA receptor-mediated membrane responses and enhances neurotoxicity in developing CNS neurons

Recent studies show that the cytokine interleukin-6 (IL-6) is expressed at elevated levels in the CNS in several disease states and contributes to the neuropathological process. The mechanisms through which IL-6 exerts its CNS effects are primarily unknown. We have investigated the pathophysiological effects of IL-6 on developing CNS neurons using a culture model system and a chronic treatment paradigm. Here, we show, using current- and voltage-clamp recordings, that chronic IL-6 treatment of developing cerebellar granule neurons increases the membrane and current response to NMDA and that these effects are the primary mechanism through which IL-6 produces an enhanced calcium signal to NMDA. We also show that calcium influx through voltage-sensitive calcium channels contributes to the enhanced calcium signal to NMDA in the IL-6-treated neurons in a developmentally regulated manner and that the membrane depolarization to NMDA is more sensitive to the NMDA receptor antagonist ifenprodil in the IL-6-treated neurons compared with control neurons at a late developmental stage, consistent with a larger proportion of NMDA receptors containing the NMDAR2B subunit in the IL-6-treated neurons. Additional studies show that IL-6 treatment reduces the number of granule neurons in culture and enhances neurotoxicity involving NMDA receptors. These results support a pathological role for IL-6 in the CNS and indicate that NMDA receptor-mediated functions are likely to play a critical role in neuropathological changes observed in CNS diseases associated with elevated CNS levels of IL-6.     

Electrophysiological properties and cholinergic responses of rat ventral oral pontine reticular neurons in vitro

This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters.     

The membrane of giant molluscan neurons: electrophysiologic properties and the origin of the resting potential

The molluscan neuron, because of its large size and accessibility, has been an important model for studying the electrophysiology of nerve cells. This review catalogs data about specific molluscan neurons, but the greater importance of this material is in the broad picture of how a neuronal membrane maintains internal potential and is responsive to changes in the environment. Electrical properties of the membrane. The mechanisms which contribute to the resting potential in molluscan neurons can be separated into ionic and metabolic components. When the electrogenic sodium pump is eliminated experimentally, the ionic component of the potential follows the constant field equation quite closely. Many of the "constants" and "parameters" which characterize the membrane of molluscan neurons are actually variables which depend upon temperature, ionic environment, and membrane potential. The evaluation of the electrical parameters is complicated by extensive infoldings of the somatic membrane, and by large axons which drain current from the soma. Most molluscan neurons have a very high specific membrane resistance and a correspondingly low potassium permeability. Membrane capacitance is close to the 1 microF/cm2 value which characterizes biological membranes. The current-voltage relation of molluscan neurons may be complicated by inward-going rectification, but if that is inhibited the I-V curve follows the prediction of either the constant field equation or a simple electrical model. Factors which modify membrane behavior. The resting potential of molluscan neurons is very sensitive to changes in temperature and Ko, through a combination of effects upon the electrogenic sodium pump, inward-going rectification, and the membrane "parameters". Inward-going rectification depends upon a rectifying K conductance, and can be eliminated by cold or the removal of Ko. Strong or prolonged currents have time-dependent effects upon the membrane, and excessive polarization leads to a "high conductance state". The underlying (non-rectifying) K permeability of the membrane is relatively insensitive to temperature and ionic changes, whereas the Na permeability increases with warming. Membrane resistance varies with both temperature and ions (because the I-V curve is sensitive to these conditions) but membrane capacitance is relatively insensitive to external factors. Electrogenic sodium transport. Sodium transport is electrogenic in molluscan neurons. It can be stimulated by warm temperatures and an excess of substrate (e.g. high Nai); it can be inhibited by cold, by an absence of substrate (e.g. low Ko), or by pharmacologic agents such as cyanide or ouabain.(ABSTRACT TRUNCATED AT 400 WORDS)     

Temporary inactivation of ventral tegmental area neurons with either muscimol or baclofen reversibly disrupts maternal behavior in rats through different underlying mechanisms.

The purpose of this study was to examine the effects of inactivation of ventral tegmental area (VTA) projection neurons, while sparing fibers of passage, on maternal behavior in rats. Because VTA neurons contain GABA-A and GABA-B receptors, the effects of muscimol or baclofen were studied. Although bilateral injections of either drug into the VTA disrupted maternal behavior, it is likely that they did so through different underlying mechanisms. Muscimol disrupted both retrieval of pups and nursing behavior, while causing stereotyped motor activity. Baclofen disrupted retrieval behavior without affecting nursing behavior, and control injections of baclofen into the region dorsal to VTA were ineffective. The effects of VTA baclofen on maternal behavior are similar to the effects of interference with mesolimbic dopamine (DA) function. The case is made that muscimol probably caused a hyperexcitation of VTA DA neurons through a process of disinhibition. In contrast, baclofen may have depressed the activity of all VTA projection neurons, including VTA DA neurons. Baclofen is a promising tool to explore whether medial preoptic area neurons interact with VTA neurons to control active maternal responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Altered subthreshold sodium currents and disrupted firing patterns in Purkinje neurons of Scn8a mutant mice

Sodium currents and action potentials were characterized in Purkinje neurons from ataxic mice lacking expression of the sodium channel Scn8a. Peak transient sodium current was approximately 60% of that in normal mice, but subthreshold sodium current was affected much more. Steady-state current elicited by voltage ramps was reduced to approximately 30%, and resurgent sodium current, an unusual transient current elicited on repolarization following strong depolarizations, was reduced to 8%-18%. In jolting mice, with a missense mutation in Scn8a, steady-state and resurgent current were also reduced, with altered voltage dependence and kinetics. Both spontaneous firing and evoked bursts of spikes were diminished in cells from null and jolting mice. Evidently Scn8a channels carry most subthreshold sodium current and are crucial for repetitive firing.     

Analysis of voltage-dependent membrane currents in spatially extended neurons from point-clamp data

1. Numerical methods were used to evaluate voltage space-clamp performance in the investigation of a voltage-dependent inward current similar to the noninactivating Ca current. In addition, the cell is equipped with a repolarizing system, represented by leak and outwardly rectifying outward conductances. The electrotonically compact model cell is represented by a cable with an electrotonic length of 1 space constant under control conditions, but that becomes effectively only 0.33 space constants during a 90% reduction of the leak and outward conductance. The cable is perfectly voltage clamped at one end. 2. The apparent voltage dependence, activation, and inactivation of the clamp current depend on the distribution of the membrane slope conductance along the cable; this depends on 1) the distribution of the inward current along the cable and 2) the amplitude of the inward current relative to the amplitudes of the leak and voltage-dependent outward currents. 3. Under control conditions, the membrane voltage decays steeply with distance from the command voltage at the clamp site to almost resting potential for most of the rest of the cable. This is because the leak and outward current are dominant over the inward current. The inward current is activated primarily at the clamped part of the cable. Clamp currents are activated instantaneously. The clamp-current current-voltage (I-V) relation is less steep with depolarization because the membrane potential for locations away from the clamp site lags behind the clamp potential. 4. When the conductances for leak and outward current are reduced by 90%, these conductances lose their dominance. The membrane slope conductance now has a range with negative values.(ABSTRACT TRUNCATED AT 250 WORDS)     

A subset of ventral tegmental area neurons is inhibited by dopamine, 5-hydroxytryptamine and opioids

Neurons originating in the ventral tegmental area are thought to play a key role in the formation of addictive behaviors, particularly in response to drugs such as cocaine and opioids. In this study we identified different populations of ventral tegmental area neurons by the pharmacology of their evoked synaptic potentials and their response to dopamine, 5-hydroxytryptamine and opioids. Intracellular recordings were made from ventral tegmental area neurons in horizontal slices of guinea-pig brain and electrical stimulation was used to evoke synaptic potentials. The majority of cells (61.3%) hyperpolarized in response to dopamine, depolarized to 5-hydroxytryptamine, failed to respond to [Met]5enkephalin and exhibited a slow GABAB-mediated inhibitory postsynaptic potential. A smaller proportion of cells (11.3%) hyperpolarized in response to [Met]5enkephalin, depolarized to 5-hydroxytryptamine, failed to respond to dopamine and did not exhibit a slow inhibitory postsynaptic potential. These two groups of cells corresponded to previously described "principal" and "secondary" cells, respectively. A further group of cells (27.4%) was identified that like the principal cells, hyperpolarized to dopamine. However, these "tertiary cells" also hyperpolarized to both 5-hydroxytryptamine and [Met]5enkephalin and exhibited a slow, cocaine-sensitive 5-hydroxytryptamine(1A)-mediated inhibitory postsynaptic potential. When principal and tertiary cells were investigated immunohistochemically, 82% of the principal cells were positive for tyrosine hydroxylase compared with only 29% of the tertiary cells. The 5-hydroxytryptamine innervation of both these cell types was investigated and a similar density of putative contacts was observed near the somata and dendrites in both groups. This latter finding suggests that the existence of a 5-hydroxytryptamine-mediated inhibitory postsynaptic potential in the tertiary cells may be determined by the selective expression of 5-hydroxytryptamine receptors, rather than the distribution or density of the 5-hydroxytryptamine innervation. We conclude that tertiary cells are a distinct subset of ventral tegmental area neurons where cocaine and mu-opioids both mediate inhibition.     

液膜萃取法回收废胶体钯活化液中的钯

传统钯回收方法存在成本高、分离效率低,适合高含量钯回收等问题,试验采用液膜萃取法回收废胶体钯活化液中的钯,并考察了内相试剂用量、流动载体用量、表面活性剂用量、油内比、乳水比、外相酸碱度等因素对钯萃取率的影响.结果表明:以9％N503、4％Span80、2％液体石蜡、85％磺化煤油组成膜相,内相试剂EDTA溶液浓度为0....