Temporal Response Profiles Research Articles

Temporal profile of ischemic tissue damage, neutrophil response, and vascular plugging following permanent and transient (2H) middle cerebral artery occlusion in the rat

We investigated the temporal profile of ischemic tissue damage, neutrophil response, and vascular occlusion after permanent and transient middle cerebral artery occlusion in the rat. Focal cerebral ischemia was induced by advancing a nylon monofilament to occlude middle cerebral artery (MCA). Two groups of rats were investigated: (1) those with permanent MCA occlusion ( n = 29), and (2) and those having the arterial occlusion released after 2 h ( n = 34). Experiments were terminated at 6, 12, 24, 48, 72, 96 and 168 h after the onset of ischemia, and brain sections were stained with hematoxylin and eosin for histological evaluation. Initially, the cortical lesion was smaller in rats subjected to transient MCA occlusion than in rats subjected to permanent MCA occlusion ( p < 0.02). The surface area of the lesion was identical in both groups at 48 h after the onset of ischemia. Neutrophil infiltration into tissue and the time of peak neutrophil infiltration occurred earlier after transient MCA occlusion than after permanent MCA occlusion (6 h, 48 h in transient; 12 h, 72 h in permanent). Within the lesions, the number of occluded vessels was significantly lower in the transient ischemia group than in the permanent ischemia group during the time interval between 12–48 h ( p < 0.01). Our data suggest that the temporal evolution of the lesion, the pattern of neutrophil infiltration and the chronology of microvascular occlusion differs depending on whether the MCA occlusion is transient (2 h) or permanent; however, significant differences in the size of the brain lesion disappeared 48 h after onset of ischemia.

Photothermal deflection measurements for monitoring heat transfer during modulated laser heating of solids

Photothermal deflection (PTD) techniques have been used to monitor various laser-heating processes, including melt, vaporization, and ablation of solids. To interpret the complex signal response resulting from transient phase changes at a surface, the temporal profile of the PTD signal response must be considered. In doing so, the case of the linear heating of a target without phase change is first studied here. Numerical and experimental work is presented to show the effect on the shape, magnitude, and phase of a PTD signal due to changes in (1) the thermophysical properties of the target material and deflecting medium, (2) the dimensions and boundary conditions of the target, (3) the distance of the probe beam from the surface of the target, and (4) the modulation frequency of the heating source. Copper and lead target materials heated in air are used in the experimental work. The PTD signals show qualitative agreement with the temperature gradient normal to the surface calculated using a numerical finite-difference two-dimensional thermal-diffusion model. The results also show that an unusual phenomenon occurs when heating with a laser or other finite-sized heating source. When the thermal diffusivity of the target and deflecting medium are different and the probe beam is close to the surface, a local maximum is observed in the time-response profile of the PTD signal during the heating cycle. The maximum occurs as a result of asymmetric changes in the temperature field over time. The shape of the PTD signal, therefore, can provide information about the laser-heating process at a surface in real time.

Directed attention and perception of temporal order.

The present research examined the effects of directed attention on speed of information transmission in the visual system. Ss judged the temporal order of 2 stimuli while directing attention toward 1 of the stimuli or away from both stimuli. Perception of temporal order was influenced by directed attention: Given equal onset times, the attended stimulus appeared to occur before the unattended stimulus. Direction of attention also influenced the perception of simultaneity. The findings support the notion that attention affects the speed of transmission of information in the visual system. To account for the pattern of temporal order and simultaneity judgments, a model is proposed in which the temporal profile of visual responses is affected by directed attention.

Delayed ventilatory response to CO2 after carbonic anhydrase inhibition with acetazolamide administration in the anesthetized rat.

In order to estimate to what extent the stimulatory action of CO2 on ventilation is mediated by the formation of H+, we studied effects on the temporal profile of ventilatory response to CO2 of carbonic anhydrase (CA) inhibition with acetazolamide in the halothane anesthetized spontaneously breathing rat. Since hydration reaction of CO2 yielding H+ is delayed by CA inhibition, the time courses of changes in tidal volume (VT), respiratory frequency (f), and minute ventilation (VE) in response to a stepwise increase in end-tidal PCO2 (delta PETCO2 15 mmHg) were compared before (control state) and after i.v. injection of acetazolamide (50 mg/kg) in the hyperoxic condition. In the control state, an increase in VT was significantly slower than that in f, and the mean response half-times (T1/2) for the increase in VT, f, and VE were 50.6, 18.1, and 31.0 s, respectively. After acetazolamide administration, responses to CO2, especially f-response and consequently VE-response became much slower, and the T1/2 for VT, f, and VE were 67.9, 55.0, and 63.0 s, respectively. The delay in VT-response was not statistically significant. The magnitude of increase in VE in the steady state hypercapnic stimulation was almost the same before and after acetazolamide administration. The results suggest that a rapid increase in f during CO2 inhalation occurs predominantly through an increase in H+ produced by hydration of CO2 with CA, whereas VT-response may occur without involvement of this process. The different time courses of VT- and f-responses and possible effects of molecular CO2 and/or H+ on the regulatory mechanisms for ventilatory pattern were discussed.