Input resistance, electrical excitability, and size of ventral horn cells in cat spinal cord

Experiments on cat lumbosacral alpha motoneurones showed that, in comparison with cells possessing rapidly conducting axons, the cells with slowly conducting axons have the higher input resistance, that they need weaker stimulating currents to reach the threshold for repetitive firing, and that they need a relatively larger increment in current strength for a given increase in firing rate. Measurements of the number and diameters of dendritic trunks gave larger values for the larger cell bodies. The discussion deals with the interrelation between cell geometry, electrical properties, and the reflex action of alpha motoneurones.     

Microelectrophoresis of biogenic amines on hypothalamic thermosensitive cells

The rat hypothalamus contains thermally insensitive, normally sensisitive, and highly thermosensitive cells. The responses of thermosensitive neurons to microelectrophoretically applied acetylcholine, norepinephrine, and 5-hydroxy-tryptamine were the same in both rats and cats. The firing rate of warm-sensitive interneurons was accelerated by acetylcholine and inhibited by norepinephrine. The firing rate of cool-sensitive interneurons was accelerated by norepinephrine and, in one case, was inhibited by 5-hydroxytryptamine. Thermodetector cells were relatively insensitive to these amines, but were sensitive to current flow. These results from the rat, but not from the cat, agree with the data for thermoregulatory responses following microinjection of these amines into the hypothalamus.     

带油管道施工动火的安全措施

在带油管道上施工动火危险生较大，易引起火灾事故。在动火管段施工过程中，对动火管段要进行隔离和清扫。常用的隔离方法有封堵器封堵，冷冻法封堵和隔离物法封堵，其中冷冻法一般用于输送易凝介质管道上；对管道内易燃物的清除可采用位差空油，用水置换油，气体扫线和吸和排油等方法。     

Contours and contrast: responses of monkey lateral geniculate nucleus cells to luminance and color figures

The responses of single units in the monkey lateral geniculate nucleus to different portions of figures which differed from their backgrounds in color and brightness were examined. Border enhancement was found in the response to luminance figures but not in the response to color figures. In addition, cells showed border enhancement only in the case of a figure which produced an increment (as opposed to a decrement) in their firing rates. In situations in which very striking brightness contrast is seen perceptually, the cells do not show the corresponding changes in firing rate across the whole pattern. The lateral inhibitory mechanisms found in the retina and geniculate can thus account for luminance border enhancement, but not entirely for simultaneous brightness or color contrast, for which other cortical processes of some sort must be responsible.     

The spatial periodicity of grid cells is not sustained during reduced theta oscillations

Grid cells in parahippocampal cortices fire at vertices of a periodic triangular grid that spans the entire recording environment. Such precise neural computations in space have been proposed to emerge from equally precise temporal oscillations within cells or within the local neural circuitry. We found that grid-like firing patterns in the entorhinal cortex vanished when theta oscillations were reduced after intraseptal lidocaine infusions in rats. Other spatially modulated cells in the same cortical region and place cells in the hippocampus retained their spatial firing patterns to a larger extent during these periods without well-organized oscillatory neuronal activity. Precisely timed neural activity within single cells or local networks is thus required for periodic spatial firing but not for single place fields.     

Neuron activity related to short-term memory

Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test. Most cells increase firing during the cue presentation period or at the beginning of the ensuing delay; spike discharge highler than that in intertrial periods is present in some cells throughout the delay. These changes are interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory     

Intracellular study of recurrent facilitation

Recurrent facilitation in the cat's spinal cord has been studied in deep peroneal and quadriceps motoneurons with the use of intracellular recording. The presence of facilitation was indicated by several criteria, among them increased firing index of the cells or decreased latency of firing. In many, but not all, facilitated cells the conditioning volley caused a small visible depolarization. Subthreshold synaptic potentials were frequently increased in magnitude by the conditioning volley, which also increased the effectiveness of a stimulus applied through the microelectrode. Facilitation was found in a large percentage of the motoneurons investigated and was clearly able to bring about pronounced changes in the excitability and firing behavior of these cells.     

Specific GABAA circuits for visual cortical plasticity

Weak inhibition within visual cortex early in life prevents experience-dependent plasticity. Loss of responsiveness to an eye deprived of vision can be initiated prematurely by enhancing gamma-aminobutyric acid (GABA)-mediated transmission with benzodiazepines. Here, we use a mouse "knockin" mutation to alpha subunits that renders individual GABA type A (GABA(A)) receptors insensitive to diazepam to show that a particular inhibitory network controls expression of the critical period. Only alpha1-containing circuits were found to drive cortical plasticity, whereas alpha2-enriched connections separately regulated neuronal firing. This dissociation carries implications for models of brain development and the safe design of benzodiazepines for use in infants.     

人工增雨过程中科学用弹量和射击方法研究

利用＂三七＂高炮炮弹爆炸后AgI在不同温度下的成冰率及前后2个温度梯度倍数关系,以及高炮83型增雨弹引信自炸时间和射角及其所达垂直高度、水平距离、斜距等资料,计算出理想浓度的理想弥散半径和发射角度,从而分析得出在人工增雨作业中适宜的用弹量和作业方法,以期利用合理的射击方法,使用最少的人雨弹,达到最佳的增雨效果。     

HCN2 ion channels play a central role in inflammatory and neuropathic pain

The rate of action potential firing in nociceptors is a major determinant of the intensity of pain. Possible modulators of action potential firing include the HCN ion channels, which generate an inward current, I(h), after hyperpolarization of the membrane. We found that genetic deletion of HCN2 removed the cyclic adenosine monophosphate (cAMP)-sensitive component of I(h) and abolished action potential firing caused by an elevation of cAMP in nociceptors. Mice in which HCN2 was specifically deleted in nociceptors expressing Na(V)1.8 had normal pain thresholds, but inflammation did not cause hyperalgesia to heat stimuli. After a nerve lesion, these mice showed no neuropathic pain in response to thermal or mechanical stimuli. Neuropathic pain is therefore initiated by HCN2-driven action potential firing in Na(V)1.8-expressing nociceptors.     

Dentate gyrus NMDA receptors mediate rapid pattern separation in the hippocampal network

Forming distinct representations of multiple contexts, places, and episodes is a crucial function of the hippocampus. The dentate gyrus subregion has been suggested to fulfill this role. We have tested this hypothesis by generating and analyzing a mouse strain that lacks the gene encoding the essential subunit of the N-methyl-d-aspartate (NMDA) receptor NR1, specifically in dentate gyrus granule cells. The mutant mice performed normally in contextual fear conditioning, but were impaired in the ability to distinguish two similar contexts. A significant reduction in the context-specific modulation of firing rate was observed in the CA3 pyramidal cells when the mutant mice were transferred from one context to another. These results provide evidence that NMDA receptors in the granule cells of the dentate gyrus play a crucial role in the process of pattern separation.     

Neural representations of location composed of spatially periodic bands

The mammalian hippocampal formation provides neuronal representations of environmental location, but the underlying mechanisms are poorly understood. Here, we report a class of cells whose spatially periodic firing patterns are composed of plane waves (or bands) drawn from a discrete set of orientations and wavelengths. The majority of cells recorded in parasubicular and medial entorhinal cortices of freely moving rats belonged to this class and included grid cells, an important subset that corresponds to three bands at 60° orientations and has the most stable firing pattern. Occasional changes between hexagonal and nonhexagonal patterns imply a common underlying mechanism. Our results indicate a Fourier-like spatial analysis underlying neuronal representations of location, and suggest that path integration is performed by integrating displacement along a restricted set of directions.     

Cell size and rate of protein synthesis in ventral horn neurones

Autoradiographic studies show that small ventral horn neurones synthesize protein at a greater rate per unit area of cytoplasm than do large ones. It is suggested that this is related to the faster rate of firing of the smaller neurones.     

Both mu and delta opiate receptors exist on the same neuron

Low concentrations of the relatively selective opiate receptor agonists dihydromorphine and normorphine (mu receptor agonists) and D-Ala 2-D-Leu 5-enkephalin (a delta receptor agonist) were applied to single enteric neurons while the frequency of action potential firing was recorded. Most neurons that were inhibited by the mu agonists were also inhibited by the delta agonist, but the two receptors could be distinguished by the higher concentration of naloxone required to antagonize the delta agonist. The results indicate that enteric neurons bear both mu and delta receptors and that cell firing is inhibited if either receptor type is activated.     

Operant conditioning of single-unit response patterns in visual cortex

Unit responses to photic stimuli were studied in cat visual cortex. After the baseline response pattern of a cell was determined, conditioning trials were given during which reinforcement was contingent upon increased firing during a selected segment of the poststimulus interval. Density of reinforcement increased substantially in about half the cells studied; significant increases in firing occurred within, but not outside, the criterion segment.     

Erratum

In the article "A firing over formaldehyde" (News and Comment, 7 Aug., p. 630), the directors of two agencies were incorrectly identified. The head of the biology division at Oak Ridge National Laboratory is Richard Griesemer. The head of the National Institute of Environmental Health Sciences is David Rall.     

Electrotonic spread of dendritic potentials in feline pyramidal cells

In pyramidal cells synaptic activation of the entire apical dendritic tree distal to the branch point of the major shaft can dominate the neuronal firing pattern. Uniform synaptic activation of distant parts of the dendritic tree (~ 750 microns from the soma) would produce potential changes at the soma of 2 to 3 percent of the magnitude of the dendritic potential changes. Even these small somatic potential changes could modulate the frequency of firing of neurons depolarized close to or above firing level by more proximal synaptic inputs.     

Direction-selective units in rabbit retina: distribution of preferred directions

The preferred directions of 102 direction-selective ganglion cells in the rabbit retina have been determined. Cells of the "on-off" type form four nonoverlapping groups; cells of the "on" type fall into three groups. The on-off groups appear to correspond to the directions of apparent object displacement produced by contractions of the four rectus muscles. Each group of cells could, without further processing, provide the error signal for a visual servo-systerm minimizing retinal image motion.     

Dopamine modulation of the effects of gamma-aminobutyric acid on substantia nigra pars reticulata neurons

Studies were conducted to assess whether basal ganglia output neurons originating in the substantia nigra pars reticulata might be affected by dopamine released from dendrites of neighboring substantia nigra pars compacta neurons. Dopamine applied by iontophoresis increased the baseline firing rates of approximately half of the substantia nigra pars reticulata cells tested. The more significant finding, unrelated to the increase in firing, was the ability of dopamine to attenuate the inhibitory responses of these cells to iontophoretically applied gamma-aminobutyric acid. These findings suggest a role for dopamine as a neuromodulator and further suggest that it can act at sites beyond the striatum to modify transmission from the basal ganglia to motor nuclei.