Robert M. Lebovitz

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, unanesthe‐tized animals were compared. Over the temperature range 26 to 43oC (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.

Pulse modulated and continuous wave microwave radiation yield equivalent changes in operant behavior of rodents.

Long-Evans rats were trained to the point of stable performance on a multicomponent (fixed-ratio, timeout) operant task. Different groups were exposed to continuous wave (CW) and to pulse modulated (PM) microwave radiation (MWR) during daily three-hour behavioral sessions. The rates of responding under actual and sham exposure conditions were noted. With comparable MWR dose rates, CW and PM MWR (5.8 and 6.7 mW/g, respectively) were equally effective in reducing response rates during both the fixed-ratio and the timeout components of the operant sessions. Dose rates of this order were associated with an elevation in body temperature of 0.5 to 1.0 degrees C. At 3.6 mW/g, whereas the mean rates of fixed-ratio responding were unchanged, the rates of responding during timeout were reduced significantly. Again, CW and PM MWR yielded essentially equivalent results. This MWR dose rate was not accompanied by a measurable increment in whole body temperature. It appears that (1) fixed-ratio operant responding of rats for food reward was more robust, that is, less subject to suppression by concurrent exposure to MWR than was bar-pressing during timeout, (2) PM and CW MWR, especially at the higher dose rate, effectively enhanced operant control over timeout responding and (3) the equivalent effects of CW and PM MWR support the hypothesis of a thermal basis for their effect despite the apparent inability to detect changes in whole body temperature.

Auditory unit responses to single-pulse and twin-pulse microwave stimuli

Responses of units in the cat cochlear nucleus to single microwave pulses with different durations and to twin microwave pulses with different interpulse delays are used to study microwave hearing. Inferred threshold specific absorption rate is less than 6 mW/g; inferred threshold specific absorption, less than 0.5 microJ/g. The existence of responses from units with characteristic frequencies (CFs) from 931 Hz to 25.5 kHz is not consistent with a primary role for head resonance in microwave hearing. Patterns of response amplitude have a periodicity of 1/CF and are fully explained by frequency content of the pulse stimulus and signal processing of the auditory system. For pulses shorter than about 0.24/CF, it is shown that response amplitude is predictably proportional to pulse energy.

Computer-Based Operant Behavioral System for Microwave Bioeffects Research

For the investigation of the interaction of microwave radiation (MWR) with physiologic processes, a means of exposing a large number of animals to uniform and quantifiable MWR dose rates is desired. The design and characteristics of such a system for operant behavioral studies using rats is described. Individual irradiation chambers composed of probe terminated waveguide sections operating at 1.3 GHz are used. All of the 16 active chambers are driven in parallel from a single source via a modulation insensitive hybrid power divider. An additional group of 16 nonenergized chambers provide for parallel controls. Each of the chambers includes provision for presentation of visual discriminative stimulus, detection of operant response, and delivery of food reward. These behavioral components are managed by an 8 bit microprocessor that provides the necessary speed, reliability, and flexibility at low per unit cost. The input/output interface is described briefly and a typical program flow diagram for schedule controiled conditioning sessions is given. The irradiation/behavioral system represents a novel approach to the study of microwave induced alterations in operant behavior and demonstrates the practicability of adapting inexpensive microprocessor components to the management of large operant behavioral systems.

Reactivity of penicillin-induced epileptogenic foci to selective blockade of membrane sodium-potassium ATPase via ouabain

Abstract Factors governing the onset of cell discharge at experimental seizure foci have received detailed study, but less is known about the basis for slow, spontaneous cyclic seizure activity of experimental and clinical foci. This problem was here approached by studying the reactivity of penicillin-induced interictal discharge to blockade of sodium-potassium-coupled transport. Perfusion of hippocampal foci with ouabain in artificial cerebrospinal fluid yielded a generally triphasic effect on the rate of spontaneous interictal discharge: an initial deceleration or temporary suspension; acute acceleration; then terminal slowing and cessation. The latency of onset of acute acceleration was inversely related to ouabain concentration in the perfusate. An immediate effect of the neuromuscular blocking agents gallamine and tubocurarine on interictal discharge rate was noted with high intravenous doses, as was a long-term effect of smaller doses (typical for experimental immobilization) on the subsequent response to ouabain. The relation of these interictal spike-interval data to transmembrane NaK exchange is discussed, including ion accumulation and electrogenic transport factors. The analogy with cortical spreading depression is considered.