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R M Lebovitz

Publications and source records attributed to R M Lebovitz.

82 records · Page 5Linked to original sources
PubMed1975

Monoaminergic mechanisms in aversive brain stimulation.

In these experiments we have examined the role of brain monoamines in the fearlike aversive responses produced by the electrical stimulation of the dorsal midbrain tegmentum (DMT). Chronic bipolar stimulating electrodes were bilaterally implanted into the DMT of 77 rats. Electrical stimulation via 34 of these electrodes produced fearlike, escape seeking responses. These animals were then trained for stable stimulus escape using a decremental bar pressing paradigm. In this paradigm, each bar press reduced the stimulation current by a predetermined fraction (5 percent) of the initial current level. Perceived aversive strength of the initial stimulus current was thereby represented by an increasing function of the number of bar presses to escape. Administration of the catecholamine depleting drug alpha-methyl-para-tyrosine yielded no change in bar pressing relative to saline-injected controls. However, the serotonin depleting drub para-chlorophenylalanine produced a marked increase in decremental bar pressing compared to saline-injected controls. These results suggest that fearlike responses to DMT stimulation may be dependent upon brain serotonin levels and relatively insensitive to levels of brain catecholamines.

Animals↗
PubMed1975

Effects of temperature on interictal discharge at penicillin epileptogenic foci.

The effects of local brain temperature on acute focal penicillin epilepsy in the exposed hippocampus of cat were studied. Results from anesthetized and from immobilized, unanesthetized animals were compared. Over the temperature range 26 to 43 degrees C (at the alveus), the interictal spike interval and duration of the spike discharge varied inversely with temperature. The former showed a Q10 of 2.4 and the latter a Q10 of 1.5, with no difference due to type of preparation. A significant trans-hippocampal thermal gradient may imply that these values are underestimates by 20% or more. The low Q10 of duration of the paroxysmal discharge was consistent with the known temperature dependence of impulse conduction velocity of intracortical neural networks. The high Q10 of the interictal interval, on the other hand, was consistent with the view that some slow endogenous, perhaps metabolic factor such as a NA,K-ATPase modulated excitability at the focus of penicillin spikes.

Action Potentials↗
PubMed1970

A theoretical examination of ionic interactions between neural and non-neural membranes.

Evidence from electron microscopy indicates that the separation between adjacent membranes of the central nervous system (CNS) is less than 500 A and perhaps as small as 100-250 A. The rapid K(+) efflux associated with the neural action potential may therefore be sufficient to affect the local extracellular potassium concentration and, via their partial dependence upon the potassium equilibrium potential, alter the electrical states of nearby neural and glial membranes. This new concept of a transient and local depolarizing "ionic interaction" between active and inactive membranes of the CNS is here examined theoretically and its magnitude calculated as a function of (a) the intermembrane separation, (b) the membranes' electrochemical characteristics, and (c) the rate at which K(+) can diffuse away from the vicinity of the active (neural) membrane. My results indicate that the interaction is in the millivolt range and therefore significant in the modulation of postsynaptic and presynaptic information processing; in particular configurations the postulated interaction alone may be suprathreshold. Membrane noise and local synchrony in groups of neurons may reflect these local, K(+)-mediated interactions. The transient ionic interaction between active neural and nearby glial membrane is also in the millivolt range; however, the relevance of neuroglia to neuronal function is obscure. Certain pathological states, such as seizure and spreading depression, have an obvious phenomenological correspondence to the results presented here and are briefly discussed.

Action Potentials↗