Improvement of carrier capture efficiency of shortperiod GaAs/AlGaAs quantum wire array by a new lithography method Appl. Phys. Lett. 69, 955 (1996); 10.1063/1.117093 GaAs/AlGaAs quantum wires fabricated by SiO2 cappinginduced intermixing Random telegraph fluctuations in GaAs/Al0.4Ga0.6As resonant tunneling diodes AIP Conf.

Previous studies have shown that traumatic brain injury (TBI) significantly reduces cerebral blood flow determined in vivo and reduces vascular reactivity in the pial circulation measured with cranial window preparations. We have now tested the hypothesis that TBI induces these changes by impairing intrinsic contractile activity of cerebral arteries. Anesthetized rats underwent moderate (2.2 atm) and severe (3.0 atm) midline fluid percussion TBI or sham injury following which posterior cerebral or middle cerebral arteries were isolated and isometric force generation was measured. Moderate (n = 5) and severe (n = 3) trauma had no effect on the magnitude of serotonin- or K+-induced force generation or sensitivity to serotonin in arteries isolated within 10 min of TBI. Functional disruption of the endothelium of posterior cerebral arteries isolated 10 min after moderate trauma or sham injury caused a reduction in the active tension response to serotonin that was similar in both groups. Blockade of cyclooxygenase with 5 microM indomethacin had no effect on serotonin-induced force generated by vessels with moderate trauma or in sham-treated rats. Acetylcholine induced an endothelium-dependent relaxation of posterior and middle cerebral arteries; the magnitude of the response was unaffected by moderate TBI. To determine whether prolonged in situ exposure of vessels to the traumatized cerebral milieu could reveal an alteration in intrinsic contractility, posterior cerebral arteries were isolated 30 min after TBI; again, no differences in the tension or relaxation responses were observed. It is concluded that midline fluid percussion TBI did not affect contraction or relaxation of proximal middle or posterior cerebral arteries in rats.

ABSTRACT. We performed intracardiac electrophysioactivity, either in the surface ECG or in the His or right logic studies of the effects of vasoactive intestinal peptide ventricular electrode catheter (VIP, 0.125 pg/kg/min) on sinus and atrioventricular (AV) nodal function, intracardiac conduction, and myocardial refractoriness in two groups of neonatal dogs (aged 6-16 d). Group in autonomic physiology, f 4% (mean f SD), after exposure to 0.1-0.5 nmol of VIP ( p < 0.001). In nine other newborns (aged 4-16 days), the VIP is one o f these neuropeptides that has been identified effect of selective a,-and a2-adrenergic receptor blockade throughout the autonomic nervous system. It is a 28-amino acid on the positive c~ronotrop~c effect of VIP was evaluated. peptide that. within the heart, appears to be most highly localized ~h~ effect of VIP on sinus cycle length was not altered by in the regions o f the sinus and AV nodes and atrial myocardium. the a,-adrenergic receptor blocker prazosin or by the ,,-It is believed that VIP is most likely colocalized with acetylchoadrenergic receptor blocker yohimbine. These data indicate line within cardiac postganglionic parasympathetic nerves ( 1 ). It that, in the neonatal dog, VIP shortens sinus cycle length has been suggested that VIP may be ~hysiologically active as a and AV nodal conduction time but has no effect on infra-neurotransmitter because it has been shown to increase intrinsic nodal conduction or myocardial refractoriness. We find no cardiac pacemaker rate. enhance AV nodal conduction, and evidence that VIP's chronotropic effect is modified by a-shorten myocardial refractoriness it1 lvil8o and it1 vitro in adult adrenergic receptor blockade. V I P may play a role in the dogs (1-5). Although the effects o f VIP in the adult heart have neural modulation of heart rate and AV nodal conduction been well described. there has been little or no information in the neonate. (Pediatr Res 35: 244-249, 1994) regarding the actions o f VIP in the developing heart. At least one study reported that the effect o f VIP on heart rate may be very Abbreviations different in the early neonatal period compared with later in life VIP, vasoactive intestinal peptide (6). This study also suggested that there might be a link between AV, atrioventricular the cardiovascular effects o f VIP and tu-adrenergic receptor activ-AH interval, the time from the onset of the atrial elecwo-ity in the newborn (6). This is o f significance because developgram to the onset of the His bundle electrogram in the mentally determined differences in cardiac chronotropic reHis electrode catheter sponses and in intracellular signal transduction in response to tu-PA interval, the time from the onset of the P wave on the adrenergic stimulation have been previously well documented surface ECG to the onset of the atrial electrogram in the (7-10). Therefore. the purpose o f our study was to characterize His electrode catheter the effects o f VIP on the electrophysiologic properties o f the H V interval, the time from t...

ABSTRACT. We have previously demonstrated that vagal phase-response curves (PRC), which characterize the effects of critically timed, brief vagal stimuli on sinus node automaticity, exhibit a fundamentally different shape in the canine newborn than in the adult. In this study we analyzed the changes in sinus cycle length in response to critically timed, brief vagal stimuli, delivered to the decentralized cervical right and left vagosympathetic trunks, in two older age groups: 14 1 -mo-old puppies (ages 21-36 d), and eight 2-mosld puppies (ages 56-62 d). Vagal PRC were constructed by plotting the magnitude (percent change) of the vagal chronotropic response as a function of the phase of the cardiac cycle at which the vagus nerve was stimulated. At 1 mo of age adult-type PRC were observed, but in only six of the puppies (43%) and only in response to right vagal stimulation. By 2 mo of age adulttype PRC were observed in seven of eight puppies (88%) in response to right vagal stimulation and in three of eight (38%) in response to left vagal stimulation. Thus, clear developmental changes in the phase dependence of the vagal chronotropic response can be tracked over the first 2 mo of life in the dog. (Pediatr Res 35: 5541,1994) Abbreviations AV, atrioventricular PRC, phase-response curve(s) magnitude of the vagal response being partly dependent upon the phase of the cardiac cycle in which the burst occurs, a potential mechanism exists for fine, beat-by-beat regulation of heart rate and AV nodal conduction by the parasympathetic nervous system.We have reported previously that classical phase dependence of the vagal response is not, however, observed in newborn animals (14). Specifically, we have shown that in the canine newborn phase-response curves generated in response to brief, critically timed vagal stimuli for both sinus cycle length and AV nodal conduction exhibit a different shape or configuration than reported in the adult. In the newborn, rather than a gradual increase in the magnitude of the vagal response as the stimulus is delivered progressively later within the cardiac cycle, we observed most typically no change in the magnitude of the response or, at times, even a decrease in the response. This suggested to us that the newborn might not have the same mechanism for fine regulation of heart rate and AV nodal conduction by the parasympathetic nervous system as the adult.In this study we report the changes that occur during early postnatal development in the response of heart rate to brief, critically timed vagal stimulation. We demonstrate that in the dog there is a maturation of the response elicited to brief vagal stimulation during the first 60 d of life, with gradual emergence of the adult-type vagal phase-response curve. In addition, we provide evidence that the shape of the vagal PRC during this period of development is, in part, dependent upon the time course of acetylcholine release and hydrolysis. MATERIALS AND METHODSPrevious in vivo and in vitro studies have demonstrated clearly that the effec...