Cell dialysis by sharp electrodes can cause nonphysiological changes in neuron properties

We recorded from lobster and leech neurons with two sharp electrodes filled with solutions often used with these preparations (lobster: 0.6 M K2SO4 or 2.5 M KAc; leech: 4 M KAc), with solutions approximately matching neuron cytoplasm ion concentrations, and with 6.5 M KAc (lobster, leech) and 0.6 M KAc (lobster). We measured membrane potential, input resistance, and transient and sustained depolarization-activated outward current amplitudes in leech and these neuron properties and hyperpolarization-activated current time constant in lobster, every 10 min for 60 min after electrode penetration. Neuron properties varied with electrode fill. For fills with molarities ≥2.5 M, neuron properties also varied strongly with time after electrode penetration. Depending on the property being examined, these variations could be large. In leech, cell size also increased with noncytoplasmic fills. The changes in neuron properties could be due to the ions being injected from the electrodes during current injection. We tested this possibility in lobster with the 2.5 M KAc electrode fill by making measurements only 10 and 60 min after penetration. Neuron properties still changed, although the changes were less extreme. Making measurements every 2 min showed that the time-dependent variations in neuron properties occurred in concert with each other. Neuron property changes with high molarity electrode-fill solutions were great enough to decrease neuron firing strongly. An experiment with 14C-glucose electrode fill confirmed earlier work showing substantial leak from sharp electrodes. Sharp electrode work should thus be performed with cytoplasm-matched electrode fills.

A Direct Comparison of Whole Cell Patch and Sharp Electrodes by Simultaneous Recording From Single Spinal Neurons in Frog Tadpoles

High-impedance, sharp intracellular electrodes were compared with whole cell patch electrodes by recording from single spinal neurons in immobilized frog tadpoles. A range of neuron properties were examined using sharp or patch test electrodes while making simultaneous recordings with a second control patch electrode. Overall, test patch electrodes did not significantly alter the activity recorded by the control electrode, and recordings from the two electrodes were essentially identical. In contrast, sharp electrode recordings differed from initial control patch recordings. In some cases, differences were due to real changes in neuron properties: the resting membrane potential became less negative and the neuron input resistance ( Ri) fell; this fall was larger for neurons with a higher Ri. In other cases, the control patch electrode revealed that differences were due to the recording properties of the sharp electrode: tip potentials were larger and more variable; resting potentials appeared to be more negative; and spike amplitude was attenuated. However, sharp electrode penetration did not, in most cases, significantly alter the pattern of neuron firing in response to injected current or the normal pattern of activity following sensory stimulation or during fictive swimming. We conclude that sharp electrodes introduce a significant leak to the membrane of tadpole spinal neurons compared with patch electrodes but that this does not change the fundamental firing characteristics or activity of the neurons.

A cortical EEG frequency with a REM-specific increase in amplitude

1. We used period/amplitude (PA) analysis to survey electroencephalography (EEG) across vigilance states in the Sprague-Dawley rat. We found a fast cortical EEG frequency band, which we designate rho, whose wave amplitude in rapid eye movement (REM) was elevated above the levels in both waking and nonrapid eye movement (NREM). Rho wave amplitudes in NREM and waking were similar. 2. Rho occurred between 20 and 30 Hz, which appears to be a transitional range. In the 5-Hz band below rho, EEG wave amplitudes are higher in both NREM and REM than in waking; above 30 Hz, amplitudes are higher in waking and REM than in NREM. The augmented amplitude of rho in REM may result from a unique point of interaction of EEG mechanisms of sleep and waking. 3. In addition to its theoretical interest, rho is of practical value for scoring REM sleep. It could obviate the need to record hippocampal theta EEG, eliminating electrode penetration of the brain and reducing the number of leads required to classify rat vigilance states.

Effects of light and darkness on oxygen distribution and consumption in the cat retina.

These experiments were done to investigate the effects of light and darkness on the oxygenation of the retina in anesthetized cats. Measurements were made with double-barreled oxygen microelectrodes capable of recording both oxygen tension (PO2) and local voltages. Diffuse white illumination presented to a dark-adapted retina led to an increase in PO2 of up to 30 mmHg in the outer half of the retina. Changes were maximal at approximately 75% depth, corresponding to the outer nuclear layer. No change or decrease in PO2 was observed in the inner retina. Light-evoked increases in outer retinal PO2 were graded with the duration and strength of illumination, and were maximal in response to 60 s of illumination at rod saturation. For these stimuli, the increase at the onset of illumination was slower (average half-time, 12.2 s) than the recovery at the end of illumination (average half-time, 5.9 s), but for stimuli above rod saturation, PO2 recovered much more slowly. The profile of PO2 was measured during electrode penetration and withdrawal and during light and dark adaptation. Dark-adapted profiles were characterized by a minimum PO2 of nearly 0 mmHg at depths of 65-85%, and a steep gradient from the minimum to the choroid. During light adaptation at rod saturation, PO2 was elevated in the outer half of the retina and the minimum was eliminated. Fits of the profiles to a one-dimensional model of oxygen diffusion indicated that light reduced the oxygen consumption of the outer retina to approximately 50% of its dark-adapted value.

Temporal and spatial integration in the rat SI vibrissa cortex

Glass micropipettes were used to record the activity of 124 single units in the somatosensory vibrissa cortex (SI) of 16 rats in response to combined deflections of contralateral vibrissae. Compact multiangular electromechanical stimulators were used to stimulate individual vibrissal hairs alone or in combinations of two or three adjacent whiskers. Each whisker was stimulated independently to produce controlled temporal and spatial patterns of mechanical stimuli. Following displacement of a vibrissa, unit discharges to subsequent deflections of adjacent whiskers are reduced in a time-dependent fashion. Response suppression is strongest at short interdeflection intervals, i.e., 10-20 ms and decreases progressively during the 50-100 ms following the first deflection. In many cases this period also corresponds with a reduction in ongoing unit discharges. Response suppression was not observed for first-order neurons recorded in the trigeminal ganglion of barbiturate-anesthetized rats. In the cortex, the presence and/or degree of response suppression depends on a number of spatial factors. These include 1) the angular direction(s) in which the individual hairs are moved, 2) the sequence in which two whiskers are deflected, that is, which one is deflected first, 3) the particular combination of whiskers stimulated, and 4) the number (2 or 3) of vibrissae comprising the multiwhisker stimulus. Within a vertical electrode penetration, one particular whisker typically elicits the strongest excitatory and inhibitory effects; other, nearby vibrissae elicit variable (or no) excitation or inhibition. Excitatory and inhibitory subregions of a receptive field could thus be distributed asymmetrically around the maximally effective whisker. In these cases, the receptive fields displayed spatial orientations. Quantitative criteria were used to classify 30 cortical units on the basis of the distribution of inhibitory subregions on either side of the maximally effective whisker. Twenty-one of these cells had receptive fields (RFs) with symmetrical inhibitory side regions. Responses of the other nine units were strongly suppressed by a preceding deflection of a vibrissa on one side but relatively unaffected, or even slightly facilitated, by preceding deflection of the whisker on the other side.(ABSTRACT TRUNCATED AT 400 WORDS)

Primate frontal eye fields. II. Physiological and anatomical correlates of electrically evoked eye movements

We studied single neurons in the frontal eye fields of awake macaque monkeys and compared their activity with the saccadic eye movements elicited by microstimulation at the sites of these neurons. Saccades could be elicited from electrical stimulation in the cortical gray matter of the frontal eye fields with currents as small as 10 microA. Low thresholds for eliciting saccades were found at the sites of cells with presaccadic activity. Presaccadic neurons classified as visuomovement or movement were most associated with low (less than 50 microA) thresholds. High thresholds (greater than 100 microA) or no elicited saccades were associated with other classes of frontal eye field neurons, including neurons responding only after saccades and presaccadic neurons, classified as purely visual. Throughout the frontal eye fields, the optimal saccade for eliciting presaccadic neural activity at a given recording site predicted both the direction and amplitude of the saccades that were evoked by microstimulation at that site. In contrast, the movement fields of postsaccadic cells were usually different from the saccades evoked by stimulation at the sites of such cells. We defined the low-threshold frontal eye fields as cortex yielding saccades with stimulation currents less than or equal to 50 microA. It lies along the posterior portion of the arcuate sulcus and is largely contained in the anterior bank of that sulcus. It is smaller than Brodmann's area 8 but corresponds with the union of Walker's cytoarchitectonic areas 8A and 45. Saccade amplitude was topographically organized across the frontal eye fields. Amplitudes of elicited saccades ranged from less than 1 degree to greater than 30 degrees. Smaller saccades were evoked from the ventrolateral portion, and larger saccades were evoked from the dorsomedial portion. Within the arcuate sulcus, evoked saccades were usually larger near the lip and smaller near the fundus. Saccade direction had no global organization across the frontal eye fields; however, saccade direction changed in systematic progressions with small advances of the microelectrode, and all contralateral saccadic directions were often represented in a single electrode penetration down the bank of the arcuate sulcus. Furthermore, the direction of change in these progressions periodically reversed, allowing particular saccade directions to be multiply represented in nearby regions of cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Theoretical Aspects of Radiofrequency Lesions in the Dorsal Root Entry Zone

The history and physical principles of radiofrequency (rf) lesion making are reviewed. The advantages of the rf lesion method are presented, with emphasis on its importance in small, critical regions such as the dorsal root entry zone (DREZ). The evolution and specifications of a satisfactory DREZ rf electrode are described. DREZ lesion sizes for this electrode at specific electrode tip temperatures were experimentally determined in animals and were used as a guide to determine acceptable clinical lesioning parameters. Emphasis is placed on lesion temperature monitoring and on the stability of electrode penetration into the spinal cord to achieve consistent and safe results.