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Biomedical subjects

F E Dudek

Publications and source records attributed to F E Dudek.

At least 127 records · Page 7Linked to original sources
PubMed1982

Synchronous neural afterdischarges in rat hippocampal slices without active chemical synapses.

Extracellular field potential and intracellular recordings from neurons in rat hippocampus show that, even with synaptic transmission blocked, antidromic electrical stimuli can trigger afterdischarges of up to 9 seconds duration; during these discharges action potentials of a single neuron were synchronized with extracellularly recorded population spikes. Apparently mechanisms other than recurrent chemical synapses can synchronize and recruit epileptiform events. Measurements of transmembrane potential indicate that transient extracellular electrical fields (ephaptic interactions) contribute to the observed synchrony; electrotonic coupling and changes in the concentration of extracellular ions may also contribute.

Action Potentials↗
PubMed1982

A physiological test for electrotonic coupling between CA1 pyramidal cells in rat hippocampal slices.

Antidromic stimulation in slices of rat hippocampal cortex was used to test for electrotonic coupling between CA1 pyramidal neurons. The slices were incubated in low Ca2+ medium containing Mn2+, in order to block chemical synapses. In a small percentage of intracellular recordings, short-latency depolarizations could be observed after chemical transmission had been blocked. Preceding somatic action potentials did not block the depolarizations. This indirect test provides electrophysiological evidence for coupling between some CA1 pyramidal cells.

Animals↗
PubMed1982

Conduction velocity and spike duration during afterdischarge in neuroendocrine bag cells of Aplysia.

Changes in conduction velocity and spike duration during electrically triggered afterdischarges were determined with extracellular recordings from bag-cell neurites of Aplysia. Spikes with high conduction velocity and short duration occurred at the onset of the afterdischarge during the period of high-frequency firing and regular interspike intervals. Later in the afterdischarge, spike frequency and conduction velocity decreased, while spike duration increased. During the short bursts within the later part of the afterdischarge, conduction velocity was highest for the first spike and decreased for successive spikes in the burst. That conduction velocity and spike frequency were both maximal during the first minute of the afterdischarge and lower during the later periods of the spike train supports the hypothesis that changes in the excitability of the bag-cell neurites occur during this firing pattern. Furthermore, the slower conduction velocity and longer duration of spikes from the bag-cell neurites late in the afterdischarge, and late in the individual bursts within the afterdischarge, suggest the hypothesis of enhanced hormone release per action potential during these periods.

Animals↗
PubMed1982

Synaptic inputs and action potentials of magnocellular neuropeptidergic cells: intracellular recording and staining in slices of rat hypothalamus.

Excitatory postsynaptic potentials (EPSPs) and action potentials of magnocellular neuropeptidergic cells (MNCs) in the paraventricular (PVN) and supraoptic nuclei (SON) were studied with intracellular recording in coronal slices of rat hypothalamus. The fluorescent dye Lucifer Yellow (LY) was injected intracellularly and the cells were subsequently identified as magnocellular (somata greater than 15 x 15 micrometer). These cells generally had a large cytoplasm-to-nucleus ratio. In PVN it was frequently possible to trace filled dendrites to the ependyma of the third ventricle, and occasionally dendritic spines could be seen. Electrical stimuli in areas dorsolateral and ventrolateral to the fornix column evoked EPSPs in some anatomically identified MNCs of PVN, which indicates that presynaptic fibers innervating MNCs approach PVN from this region. Short-latency (less than 1 msec) spikes could be evoked in many MNCs of PVN by stimulation near SON, which is consistent with the known projection to the neurohypophysis of many MNCs. Action potentials in MNCs of PVN and SON had significantly longer durations at one-third spike height (mean +/- S.D. = 2.06 +/- 0.6 msec) than hippocampal CA1 pyramidal cells (1.17 +/- 0.29 msec). This suggests that neuroendocrine cells in mammals and some lower vertebrates and invertebrates are similar in this regard.

Action Potentials↗
PubMed1982

Coupling in rat hippocampal slices: dye transfer between CA1 pyramidal cells.

Intracellular injections of Lucifer Yellow-CH (LY) into CA1 pyramidal cells were made in rat hippocampal slices to study dye transfer between neurons as evidence that these cells are electrotonically coupled. Extensive control procedures were performed which substantially reduced inadvertent staining. Over half of the neurons were dye-coupled after injections in stratus pyramidale. Dye coupling occurred even when spike amplitudes were greater than or equal to 70 mV throughout the impalement and was still present after chemical synapses were blocked with a low Ca2+ solution containing Mn2+. Somata of dye-coupled cells were usually located within 35 micrometers (post-fixation) of the injected cell and showed no preferred orientation. Fast prepotentials and dye coupling occurred independently. Neurons in superior cervical ganglia, which were sliced and injected using similar procedures, showed no dye coupling. Intradendritic injections of LY in stratum radiatum also yielded dye coupling between CA 1 pyramidal cells, although the dye coupling was less frequent. Within stratum radiatum, neither extracellular ejections nor intracellular injections of interneurons were associated with multiple staining. Thus, injection of LY into the soma or dendrite of a single CA1 pyramidal cell often resulted in multiple staining, and in many ensembles the somata were well spaced. Control experiments suggested that such dye transfer is not by an extracellular route. This implied that some CA1 cells are electrotonically coupled. Further electrophysiological and morphological studies are required to resolve the discrepancies among various techniques used to evaluate the amount of coupling in the hippocampus.

Animals↗
PubMed1982

Intracellular electrophysiology of mammalian peptidergic neurons in rat hypothalamic slices.

The magnocellular neuropeptidergic cells (MNCs) of the paraventricular and supraoptic nuclei have been a model for biochemical and physiological studies of peptidergic neurons in the mammalian brain, but nearly all the electrophysiological studies of these vasopressinergic and oxytocinergic neuroendocrine cells are based on extracellular recordings. This paper reviews recent literature on electrophysiological properties of neurons in the magnocellular nuclei in which the rat in vitro slice preparation and intracellular recording were used. Spontaneously occurring action potentials and synaptic potentials (excitatory and inhibitory) have been observed in hypothalamic slices. The spike patterns have included slow and irregular firing, short rapid bursts of inactivating spikes, and slow phasic discharge with prolonged active and silent periods. Some studies have shown that increased osmolality causes neuronal firing, but this area is controversial. Intracellular injections of lucifer yellow have shown that some MNCs are dye-coupled and electron microscopic observations with the freeze-fracture technique have revealed occasional gap junctions, thus suggesting that some MNCs are electrotonically coupled. Both excitatory and inhibitory postsynaptic potentials have been evoked with extracellular stimulation. Therefore, action potentials, synaptic potentials, burst discharges, and probably electrotonic coupling have been found with intracellular recording in mammalian neuroendocrine cells. Future studies with intracellular recording and staining followed by immunohistochemical identification of cells should provide significant new information on the membrane physiology and synaptic pharmacology of vasopressinergic and oxytocinergic cells.

Action Potentials↗
PubMed1981

Electrotonic coupling between pyramidal cells: a direct demonstration in rat hippocampal slices.

Intracellular recordings from pairs of neurons in slices of rat hippocampus directly demonstrated electronic coupling between CA3 pyramidal cells. When two neurons were impaled simultaneously (as verified by subsequent double staining with horseradish peroxidase), current pulses injected into one cell caused voltage changes in other cells. These interactions were bidirectional. Fast prepotentials, historically thought to represent spike activity in dendrites, resulted from action potentials in other electronically coupled pyramidal cells. These data directly demonstrate electrotonic coupling between neurons in the mammalian brain and indicate that some fast prepotentials are coupling potentials. Coupling between pyramidal cells could mediate synchronization of normal rhythmic activity and of burst discharges during seizures.

Action Potentials↗
PubMed1981

Dye transfer through gap junctions between neuroendocrine cells of rat hypothalamus.

Most magnocellular neurosecretory cells that terminate in the posterior pituitary secrete either vasopressin, oxytocin, or enkephalin. Intracellular injection of the fluorescent dye Lucifer Yellow into single magnocellular neurons in slices of rat hypothalamus resulted in dye transfer between these cells. Freeze-fracture replicas of these cells occasionally revealed gap junctions, which presumably contain channels that mediate the dye coupling. These two independent techniques strongly suggest that some mammalian neuropeptidergic cells are electrotonically coupled, providing a possible means for recruitment and synchronization of their electrical activity.

Animals↗
PubMed1981

Soma spike of neuroendocrine bag cells of Aplysia californica.

Soma action potentials of the neuroendocrine bag cells of Aplysia californica were studied with intracellular recording and current injection. Spikes in artificial sea water (ASW) were either graded with increasing depolarizing current pulses, or had a well-defined threshold. The latter spikes typically had faster rise times with larger overshoots and hyperpolarizing afterpotentials. Repetitive stimulation led to spike potentiation (SP), manifested as an increase in overshoot amplitude and duration of successive spikes in a train. SP was usually detectable at 0.5 Hz, and maximal between 0.8 and 4 Hz. Concomitant accommodation occurred rapidly at greater than or equal to 5 Hz. The increase in spike duration during SP resulted from a progressive enhancement of an inflection on the repolarizing phase. The inflection was dependent on membrane potential; small depolarizations (5-10 mV) enhanced it; hyperpolarization (less than 35 mV) reduced it. Solutions with O--Na+ (Tris-substituted) or O--Ca2+ (1 mM EGTA) revealed mixed Na+/Ca2+ spikes with variable degrees of Na+ versus Ca2+ dominance. Cd2+, Co2+, and Mn2+ reversibly abolished the inflection on the repolarizing phase, indicating that it is Ca2+ mediated; the spike was reduced irreversibly at higher concentrations. SP was generally reduced only if the spike was severely attenuated. It is proposed that SP results primarily from a voltage- and time-dependent potassium inactivation which then unmasks a calcium current. SP may play a role in augmenting the release of egg-laying hormone.

Action Potentials↗
PubMed1980

Intracellular recordings from the paraventricular nucleus in slices of rat hypothalamus.

1. The electrical activity of thirty-five neurones in the lateral area of the paraventricular nucleus (p.v.n.) was recorded intracellularly in vitro from slices of rat hypothalamus. 2. Spontaneously occurring action potentials were observed in twenty-four of the neurones. The temporal pattern of action potentials was generally slow and irregular; occasionally some cells fired bursts of action potentials. 3. Depolarizations with a fast rising phase and slow decay occurred spontaneously in most cells. These depolarizations exhibited a wide range of amplitudes in each cell (up to 33 mV), showed temporal summation, and could serve as pre-potentials for spontaneously occurring action potentials. Presumably, these depolarizations were excitatory post-synaptic potentials (e.p.s.p.s.). 4. Depolarizing current injection could evoke action potentials. Extracellular stimuli dorsolateral to the fornix column occasionally elicited action potentials which had a short and invariant latency and which could respond to stimulation rates of 100 Hz. In some cases, extracellular stimuli in the same area evoked depolarizations which had long and variable latency and were similar to those occurring spontaneously. These two types of responses probably represent antidromic and orthodromic activation respectively. 5. Intracellular injections of horseradish peroxidase suggest that these recordings were obtained primarily, but not exclusively, from magnocellular neuroendocrine cells. This is consistent with previous anatomical studies on the location of magnocellular elements in p.v.n.

Action Potentials↗