Masakatsu Ureshi

Stimulus frequency dependence of the linear relationship between local cerebral blood flow and field potential evoked by activation of rat somatosensory cortex

We investigated the relationship between evoked local cerebral blood flow (LCBF) and the field potential induced by somatosensory activation. The specific aim of the present study was to examine the correlation between variations of evoked LCBF and field potential when the stimulus duration was changed, and the dependency of the correlation on stimulus frequency. Evoked LCBF was measured using laser-Doppler flowmetry and the field potential was observed using a tungsten electrode inserted into the cortex alpha-chloralose-anesthetized rats. The cortex was activated by electrical stimulation of the hind paw with a 1.5 mA pulse (0.1 ms) applied at frequencies of 0.5, 1, 5 and 10 Hz for durations of 2, 5, 8, 10 or 15s. We extended our previous finding [Neurosci. Res. 40 (2001) 281-290], that both the magnitude of evoked LCBF (integrated LCBF) and the summed field potential (SigmaFP) exhibited a maximum at a stimulus frequency of 5 Hz to five different stimulus durations. Moreover, although variations of integrated LCBF and SigmaFP induced by changes in the stimulus duration were linearly correlated, the slope of the regression line depended on the stimulus frequency. This stimulus frequency dependence of the integrated LCBF-SigmaFP linear relationship may be because the vessel response is frequency dependent.

Nonlinear correlation between field potential and local cerebral blood flow in rat somatosensory cortex evoked by changing the stimulus current

The relationship between local cerebral blood flow (LCBF) and field potential (FP) evoked by hindpaw stimulation in rat somatosensory cortex has been investigated while changing stimulus current. The change in LCBF was measured using laser-Doppler flowmetry and the field potential was acquired using a tungsten electrode inserted into the cortex of alpha-chloralose-anesthetized rats. The cortex was activated by electrical stimulation of the hind paw with 5 Hz pulses (0.1 ms) applied at currents of 1.0, 1.5, 2.0 and 2.5 mA for 5 s. It was found that the summed FP is nonlinear with respect to stimulus current, whereas the integrated LCBF response is linear across the range of currents used in the experiment. This means that the relationship between the summed FP and integrated LCBF is nonlinear as a function of stimulus current.

Reproductive Behavior and Physiology in the Cricket Gryllus bimaculatus

Gryllus bimaculatus males have a reproductive cycle consisting of a mating stage and a sexually refractory stage. During the mating stage, the male exhibits distinct behavior that encompasses three main stages: calling, courtship, and copulation. The last stage, copulation, is carried out in a fixed manner by the stimulus-response chain. The final copulatory act, spermatophore extrusion, is caused by stimulation of mechano-sensilla in the epiphallus during genitalia coupling, which terminates the mating stage. The sexually refractory stage starts with spermatophore extrusion, during which the male is rather aggressive and does not exhibit any mating behavior. A male first shows spermatophore preparation when stimulated by the female, then forms the new spermatophore, and finally recommences the calling song, i.e., the start of the mating stage. Physiological investigations reveal that the male mating behavior is mainly controlled by the brain and the terminal abdominal ganglion (TAG), which exerts three types of inhibition on the pattern generators for mating behavior. The brain also facilitates sexual excitation via octopamine. One of the conspicuous features of the reproductive behavior in Gryllus bimaculatus is that the sexually refractory stage between spermatophore preparation and the start of calling song is time fixed at around 1 h. Experiments utilizing the targeted cooling of the central nervous system indicate a presence of a time-measuring mechanism (“timer”) that is located within the TAG. Long-term spike recordings of neurons also support the presence of such a timer within the TAG. Finally, the occurrence of mating-like actions in larval nymphs is discussed. All of these findings have now generated a large body of work that will help establish Gryllus as a new experimental system for studying reproductive behavior and physiology in crickets and other insect species.