Androgens and isolation from adult tutors differentially affect the development of songbird neurons critical to vocal plasticity.

Song learning in oscine birds occurs during a juvenile sensitive period. One idea is that this sensitive period is regulated by changes in the electrophysiological properties of neurons in the telencephalic song nucleus lateral magnocellular nucleus of the anterior neostriatum (LMAN), a structure critical for song development but not adult singing. A corollary of this idea is that manipulations affecting the pace and quality of song learning will concomitantly affect the development of LMAN's electrophysiological properties. Manipulations known to affect song development include treating juvenile male zebra finches with exogenous androgens, which results in abnormally truncated adult songs, and isolation of the juvenile from adult tutors and their songs, which extends the sensitive period for song learning. Previously, we showed that synaptic transmission in LMAN changes over normal song development and that these changes are accelerated or retarded, respectively, by androgen treatment and isolation from an adult tutor. The intrinsic properties of LMAN neurons afford another potential target for regulation by steroid hormones and experience of adult tutors. Indeed previous studies showed that the capacity for LMAN neurons to fire action potentials in bursts, due to a low-threshold calcium spike, and the width of single action potentials in LMAN, wane over development. Here we analyzed these and other intrinsic electrophysiological features of LMAN neurons over normal development, then tested whether either early androgen treatment or isolating juveniles from adult tutors affected the timing of these changes. The present study shows that androgen but not isolation treatment alters the developmental time at which LMAN neurons progress from the bursting to nonbursting phenotype. In addition, other intrinsic properties, including the half-height spike width and the magnitude of the spike afterhyperpolarization (AHP), were found to change markedly over development but only changes to the AHP were androgen sensitive. Interestingly of all of the synaptic and intrinsic electrophysiological properties in LMAN studied to date, only the half-height spike width continues to change in the late juvenile stages of song learning. Furthermore raising juveniles in isolation from an adult tutor transiently delays the maturation of this property. The present results underscore that beyond their effects on LMAN's synaptic properties, both androgens and adult tutor experience are potent and selective regulators of the intrinsic properties of LMAN neurons.

Slow NMDA-EPSCs at synapses critical for song development are not required for song learning in zebra finches.

Birdsong, like human speech, is learned via auditory experience during a developmentally restricted sensitive period. Within projection neurons of two avian forebrain nuclei, NMDA receptor-mediated EPSCs (NMDA-EPSCs) become fast during song development, a transition posited to limit learning. To discover whether slow NMDA-EPSCs at these synapses are required for learning, we delayed song learning beyond its normal endpoint, post-hatch day (PHD) 65, by raising zebra finches in isolation from song tutors. At PHD45, before learning, isolation delayed NMDA-EPSC maturation, but only transiently. By PHD65, NMDA-EPSCs in isolates were fast and adult-like, yet isolates presented with tutors readily learned song. Thus song learning did not require slow NMDA-EPSCs at synapses critical for song development.

Depth-profiling and diffusion measurements in ice films using infrared laser resonant desorption.

A new infrared laser resonant desorption (LRD) technique has been developed that permits depth-profiling and diffusion measurements in ice. This LRD technique utilizes an Er:YAG rotary Q-switched laser with an output wavelength of lambda = 2.94 microm and a pulse duration of approximately 100 ns. The Er:YAG laser light resonantly excites O-H stretching vibrations in the H2O molecules that form the ice. This laser resonant heating induces H2O desorption at the ice surface. Control experiments were conducted on pure and isotopically mixed laminated ice films to determine the optimum experimental parameters for the LRD depth-profiling and diffusion measurements. Depending on laser energy, the measured desorption depth was either less than, comparable to, or larger than the optical penetration depth of approximately 0.8 microm at lambda = 2.94 microm. LRD studies were used to analyze H2 18O/H2 16O stacked multilayers and laminate sandwich structures. These measurements revealed that the LRD technique can depth-profile into ice films with submicrometer spatial resolution and high sensitivity. Two types of experiments employing LRD depth-profiling were demonstrated to monitor diffusion in ice. HCl hydrate diffusion in ice was measured versus time after depositing ice/HCl/ice sandwich structures. Na diffusion into ice was studied after adsorbing Na using a continuous Na source for a given exposure time at the diffusion temperature.

Androgens modulate NMDA receptor-mediated EPSCs in the zebra finch song system.

Androgens potently regulate the development of learned vocalizations of songbirds. We sought to determine whether one action of androgens is to functionally modulate the development of synaptic transmission in two brain nuclei, the lateral part of the magnocellular nucleus of the anterior neostriatum (LMAN) and the robust nucleus of the archistriatum (RA), that are critical for song learning and production. We focused on N-methyl-D-aspartate-excitatory postsynaptic currents (NMDA-EPSCs), because NMDA receptor activity in LMAN is crucial to song learning, and because the LMAN synapses onto RA neurons are almost entirely mediated by NMDA receptors. Whole cell recordings from in vitro brain slice preparations revealed that the time course of NMDA-EPSCs was developmentally regulated in RA, as had been shown previously for LMAN. Specifically, in both nuclei, NMDA-EPSCs become faster over development. We found that this developmental transition can be modulated by androgens, because testosterone treatment of young animals caused NMDA-EPSCs in LMAN and RA to become prematurely fast. These androgen-induced effects were limited to fledgling and juvenile periods and were spatially restricted, in that androgens did not accelerate developmental changes in NMDA-EPSCs recorded in a nonsong area, the Wulst. To determine whether androgens had additional effects on LMAN or RA neurons, we examined several other physiological and morphological parameters. In LMAN, testosterone affected alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprianate-EPSC (AMPA-EPSC) decay times and the ratio of peak synaptic glutamate to AMPA currents, as well as dendritic length and spine density but did not alter soma size or dendritic complexity. In contrast, testosterone did not affect any of these parameters in RA, which demonstrates that exogenous androgens can have selective actions on different song system neurons. These data are the first evidence for any effect of sex steroids on synaptic transmission within the song system. Our results support the idea that endogenous androgens limit sensitive periods for song learning by functionally altering synaptic transmission in song nuclei.

Development of intrinsic and synaptic properties in a forebrain nucleus essential to avian song learning.

In male zebra finches, the lateral magnocellular nucleus of the anterior neostriatum (LMAN) is necessary for the development of learned song but is not required for the production of acoustically stereotyped (crystallized) adult song. One hypothesis is that the physiological properties of LMAN neurons change over development and thus limit the ability of LMAN to affect song. To test this idea, we used in vitro intracellular recordings to characterize the intrinsic and synaptic properties of LMAN neurons in fledgling [posthatch days (PHD) 22-32] and juvenile zebra finches (PHD 40-51) when LMAN lesions disrupt normal song development, and in adults (>PHD 90) when LMAN lesions are without effect. In fledglings, depolarizing currents caused LMAN projection neurons to fire bursts of action potentials because of a putative low-threshold calcium spike (LTS). In contrast, juvenile and adult LMAN projection neurons fired accommodating trains of action potentials when depolarized but did not exhibit the burst mode of firing. Electrical stimulation of thalamic afferents elicited both monosynaptic EPSPs mediated by AMPA and NMDA receptors and polysynaptic IPSPs mediated by GABAA receptors from LMAN neurons at all ages studied here. In whole-cell voltage-clamp recordings, the EPSCs (NMDA-EPSCs) consisted of fast and slow components. Unlike juvenile and adult NMDA-EPSCs, those in fledglings were dominated by the slower component. Thus, both the intrinsic and synaptic properties of LMAN neurons change markedly during early song development (PHD 22-40) and achieve several adult-like properties during early sensorimotor learning and well before the time when LMAN lesions no longer disrupt song development.

Hypercapnic arousal responses in Prader-Willi syndrome.

STUDY OBJECTIVE: Prader-Willi syndrome (PWS) is characterized by a number of abnormalities of hypothalamic function, such as hyperphagia, short stature, temperature instability, hypogonadotropic hypogonadism, and neurosecretory growth hormone deficiency. Patients with PWS are reported to have sleep-disordered breathing and have blunted hypercapnic ventilatory responses secondary to abnormal peripheral chemoreceptor function. Thus, we hypothesized that hypercapnic arousal responses would be abnormal in PWS. DESIGN: Hypercapnic arousal responses were tested in ten nonobese children and adults with PWS, aged 17.7 +/- 2.5 (SEM) years, 70% female, and nine control subjects, aged 14.2 +/- 2.6 years, 67% female. Hypercapnic challenges were performed during stage 3/4 non-rapid eye movement sleep. RESULTS: The PWS subjects had a significantly higher arousal threshold to hypercapnia compared with the controls (53 +/- 1.0 vs 46 +/- 1.7 mm Hg; p < 0.01). The PWS subjects had significantly higher baseline end-tidal CO2 levels (42 +/- 0.8 vs 38 +/- 1.1 mm Hg; p < 0.01) and more central apneas greater than 15 s/h of sleep (1.5 +/- 0.3 vs 0.1 +/- 0.1; p < 0.01). CONCLUSIONS: Elevated hypercapnic arousal thresholds during sleep are found in PWS subjects; these may be a manifestation of abnormal peripheral chemoreceptor function and may further contribute to sleep-disordered breathing in PWS patients.

Development of a customizable universal digital hearing aid.

This paper presents the development of a digital binaural hearing aid using Texas Instruments' floating point TMS320C3X digital signal-processing chip. The device is referred to as the Customized Universal Digital Listening System (CUDLS). CUDLS uses a wide bandwidth (up to 16 kHz) and incorporates speech enhancement (noise reduction) as an integral part of the device. It is capable of sampling up to two input speech channels at a variable sampling rate. We are currently using a sampling rate of 20 kHz for each channel. We have developed our own customized hardware and software to implement CUDLS in real time with zero processing delay. The system has been designed to make it easy for the therapist to modify its features.

Modulation of the alveolar macrophage respiratory burst by hydroperoxides.

Exposure of alveolar macrophages to hydroperoxides (ROOH) inhibits subsequent stimulation of O2.- production (the respiratory burst). Previous studies (under nonoxidant stress conditions) have shown that elevation of intracellular free calcium ([Ca2+]i) participates in both initiation and termination of O2.- production. In this investigation, the effects of sublethal ROOH exposure on [Ca2+]i and the respiratory burst of rat alveolar macrophages were compared. Exposure to a sublethal range of H2O2 or tert-butylhydroperoxide (10-100 pmol/10(6) cells; initially 10-100 microM under the experimental conditions) for 15 min resulted in dose-dependent effects on the respiratory burst stimulated by various agents, ADP, ATP, zymosan-activated serum, and phorbol myristate acetate. Low concentrations of the ROOH (10 or 25 pmol/10(6) cells) were found to enhance stimulation, whereas exposure to 75 or 100 pmol/10(6) cells resulted in significant inhibition for all of the stimuli. All concentrations of ROOH caused a rapid elevation in [Ca2+]i. For those concentrations of ROOH that produced enhancement of subsequent stimulation of the respiratory burst, [Ca2+]i returned to near baseline before the end of the 15-min preincubation. The temporal- and concentration-dependent effects of ROOH on [Ca2+]i correlate with subsequent enhancement or inhibition of stimulated O2.- production. Similarities between the ROOH-induced changes in [Ca2+]i and the effect of [Ca2+]i changes in physiological regulation of the respiratory burst suggest a potential relationship.

Hypoxic and hypercapnic ventilatory responses in Prader-Willi syndrome.

Abnormalities of ventilatory control may play a significant role in the pathophysiology of sleep-disordered breathing in patients with the Prader-Willi syndrome (PWS). We measured rebreathing hypercapnic and hypoxic ventilatory responses (HCVR and HPVR, respectively) during wakefulness in 8 nonobese PWS (NOB-PWS) and 9 obese PWS (OB-PWS) patients and compared their results with those from 24 healthy nonobese control (NOB-CON) and 10 obese control (OB-CON) subjects. The slope of HCVR was similar in NOB-PWS patients and NOB-CON subjects (NS). However, HCVR was significantly lower in OB-PWS patients than in OB-CON subjects (P < 0.02). In PWS patients, the mean point of origin of the positive slope of HCVR occurred at a significantly higher end-tidal PCO2 than in either control group. During isocapnic hypoxic challenges, six PWS patients had no significant HPVR. In the remainder, mean slopes of HPVR were -0.80 +/- 0.06 l.min-1.%arterial O2 saturation-1 in five NOB-PWS patients and -0.68 +/- 0.15 l.min-1.%arterial O2 saturation-1 in six OB-PWS patients. These responses were significantly decreased compared with those in the control groups (P < 0.006). We conclude that NOB-PWS patients have normal HCVR, which is blunted in OB-PWS patients. Furthermore, isocapnic HPVR is either absent or markedly reduced in PWS patients. The severity of abnormality of the HPVR is independent of the degree of obesity. We postulate that the primary abnormality of ventilatory control in PWS affects peripheral chemoreceptor pathways.

Stimulation of the rat alveolar macrophage respiratory burst by extracellular adenine nucleotides.

Exogenous nucleotides can serve as extracellular factors that cause significant functional changes in numerous cells, including phagocytes. In the current study, addition of ATP, ADP, and ATP gamma S directly stimulated the respiratory burst (superoxide production) by rat alveolar macrophages, whereas adenosine and AMP did not. The relative potency of these nucleotides at saturating concentration was ADP > or = ATP gamma S >> ATP; however, simultaneous addition of maximally stimulatory concentrations of ADP and ATP (100 microM of each) produced an additive effect suggesting involvement of two P2 receptors. Following addition of the nucleotides, an elevation of intracellular Ca2+ ([Ca2+]i) occurred within seconds, followed by a decline within 1 min but with a prolonged elevation above baseline for at least 5 min. Removal of extracellular Ca2+ only slightly attenuated the initial elevation, indicating that adenine nucleotides stimulate the rapid release of intracellular Ca2+ stores. Removal of extracellular Ca2+ also eliminated the sustained elevation in [Ca2+]i and markedly suppressed the respiratory burst. Incubation with verapamil, a Ca2+ channel blocker, also significantly inhibited the respiratory burst stimulated by ATP. These studies demonstrate that adenine nucleotides stimulate a Ca(2+)-dependent respiratory burst by rat alveolar macrophages, probably through purinergic receptors.

Sublethal oxidant stress induces a reversible increase in intracellular calcium dependent on NAD(P)H oxidation in rat alveolar macrophages.

A concentration-dependent elevation of intracellular calcium ([Ca2+]i) and oxidation of NAD(P)H occurred in alveolar macrophages during exposure to sublethal tert-butylhydroperoxide concentrations (tBOOH) (< or = 100 microM in 1 ml with 1 x 10(6) cells). Oxidation of NAD(P)H preceded a rise in [Ca2+]i. The elevation of [Ca2+]i was reversible at < 50 microM tBOOH exposure and the return to the steady state [Ca2+]i correlated temporally with repletion of NAD(P)H. At > 50 microM tBOOH, the changes in NAD(P)H and [Ca2+]i were sustained. The relative contributions of NADPH and NADH oxidation were examined by varying the substrates supplying reducing equivalents and by inhibiting glutathione reductase activity. The results suggested that at < 50 microM tBOOH, oxidation of NADPH predominated, while at > 50 microM tBOOH, NADH oxidation predominated. A complex relationship between the relative roles of NADPH and NADH oxidation and the elevation of [Ca2+]i was revealed: (i) reversible oxidation of NADPH is associated with the initial and reversible elevation of [Ca2+]i at < 50 microM tBOOH; (ii) the sustained elevation of [Ca2+]i at > 50 microM tBOOH correlates with the sustained oxidation of NADH; and (iii) the changes in [Ca2+]i did not depend on influx of extracellular Ca2+. We speculate that at low tBOOH, Ca2+ was released from the NADPH/NADP(+)-sensitive mitochondrial Ca2+ pool while higher tBOOH caused additional Ca2+ release from GSH/GSSG-sensitive nonmitochondrial Ca2+ pools with sustained elevation of [Ca2+]i due to decreased mitochondrial Ca2+ reuptake.

Hypercapnic and hypoxic ventilatory responses in parents and siblings of children with congenital central hypoventilation syndrome.

Children with congenital central hypoventilation syndrome (CCHS) have abnormal ventilatory responses to metabolic stimuli. As there is a genetically determined component of chemoreceptor sensitivity, parents and siblings of children with CCHS may also have blunted ventilatory responses to hypercapnea and hypoxia. To test this, we studied hypercapnic ventilatory responses and hypoxic ventilatory responses in six mothers, four fathers, and five siblings (6 to 49 yr of age) of seven children with CCHS and compared them with 15 age- and sex-matched control subjects (5 to 47 yr of age). Pulmonary function tests were not different between relatives of children with CCHS and control subjects. To measure hypercapnic ventilatory responses, subjects rebreathed 5% CO2/95% O2 until PACO2 reached 60 to 70 mm Hg. To measure hypoxic ventilatory responses (L/min/% SaO2), subjects rebreathed 14% O2/7% CO2/balance N2 at mixed venous PCO2 until SaO2 fell to 75%. All tests were completed in less than 4 min. Instantaneous minute ventilation, mean inspiratory flow (tidal volume/inspiratory time), and respiratory timing (inspiratory timing/total respiratory cycle timing) were calculated on a breath-by-breath basis. Hypercapnic ventilatory responses were 1.97 +/- 0.32 L/min/mm Hg PACO2 in children with CCHS relatives and 2.23 +/- 0.23 L/min/mm Hg PACO2 in control subjects. Hypoxic ventilatory responses were -1.99 +/- 0.37 L/min/% SaO2 in the relatives and -1.54 +/- 0.25 L/min/% SaO2 in the control subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

A semiautomated journal check-in and binding system; or variations on a common theme.

The journal check-in project described here, though based on a computerized system, uses only unit-record equipment and is designed for the medium-sized library. The frequency codes used are based on the date printed on the journal rather than on the expected date of receipt, which allows for more stability in the coding scheme. The journal's volume number and issue number, which in other systems are usually predetermined by a computer, are inserted at the time of check-in. Routine claiming of overdue issues and a systematic binding schedule have also been developed as by-products.