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Biomedical subjects

S Greenberg

Publications and source records attributed to S Greenberg.

At least 145 records · Page 8Linked to original sources
PubMed1987

Neural temporal coding of low pitch. I. Human frequency-following responses to complex tones.

The neural basis of low pitch was investigated in the present study by recording a brainstem potential from the scalp of human subjects during presentation of complex tones which evoke a variable sensation of pitch. The potential recorded, the frequency-following response (FFR), reflects the temporal discharge activity of auditory neurons in the upper brainstem pathway. It was used as an index of neural periodicity in order to determine the extent to which the low pitch of complex tones is encoded in the temporal discharge activity of auditory brainstem neurons. A tone composed of harmonics of a common fundamental produces a sensation of pitch equal to that of the 'missing' fundamental. Such signals generate brainstem potentials which are spectrally similar to FFR recorded in response to sinusoidal signals equal in frequency to the missing fundamental. Both types of signals generate FFR which are periodic, with a frequency similar to the perceived pitch of the stimuli. It is shown that the FFR to the missing fundamental is not the result of a distortion product by recording FFR to a complex signal in the presence of low-frequency bandpass noise. Neither is the FFR the result of neural synchronization to the waveform envelope modulation pattern. This was determined by recording FFR to inharmonic and quasi-frequency-modulated signals. It was also determined that the 'existence region' for FFR to the missing fundamental lies below 2 kHz and that the most favorable spectral region for FFR to complex tones is between 0.5 and 1.0 kHz. These results are consistent with the hypothesis that far-field-recorded FFR does reflect neural activity germane to the processing of low pitch and that such pitch-relevant activity is based on the temporal discharge patterns of neurons in the upper auditory brainstem pathway.

Acoustic Stimulation↗
PubMed1987

Acetaminophen prophylaxis of adverse reactions following vaccination of infants with diphtheria-pertussis-tetanus toxoids-polio vaccine.

The effect of acetaminophen on reducing the frequency and severity of adverse reactions following diphtheria-pertussis-tetanus toxoids-polio vaccine was studied in a randomized clinical trial involving 519 vaccinations in 383 infants 2 to 6 months of age and 70 infants 18 months of age. Significantly fewer local and systemic reactions were reported in acetaminophen-treated infants at 2 to 6 months of age. Acetaminophen also reduced the incidence of fever greater than 38.0 degrees C from 44% to 27%. Only 0.9% of acetaminophen-treated infants had overall behavioral changes rated as severe by parents compared to 13% of the placebo group. Infants vaccinated at 18 months of age had higher rates of systemic and local reactions than younger infants. Acetaminophen did not result in significant reductions in reaction rates after the booster at 18 months. We conclude that acetaminophen administered at the time of primary vaccination with diphtheria-pertussis-tetanus toxoids-polio can significantly reduce the frequency and severity of common adverse reactions.

Acetaminophen↗
PubMed1987

Responses of auditory-nerve fibers to multiple-tone complexes.

To relate level-dependent properties of auditory-nerve-fiber responses to nasal consonant-vowels to the basic frequency selective and suppressive properties of the fibers, multitone complexes, with the amplitude of a single (probe) component incremented, were used as stimuli. Quantitative relations were obtained between the systematic increase of fiber synchrony to the probe tone and the decrease of synchrony to CF, as the amplitude of the probe tone was increased. When such relations are interpreted as a measure of fiber frequency selectivity based on a relative synchrony criterion, a breadth of frequency tuning is obtained, at a 70-dB SPL multitone sound-pressure level, which is generally broader than that of the fiber's threshold tuning curve. Quantitative comparisons with the same fiber's responses to the nasal speech sounds indicate that the fiber's speech responses share some common features with its probe-tone responses.

Animals↗
PubMed1987

The safety and efficacy of once-daily dilevalol in patients with mild hypertension: a placebo-controlled study.

Dilevalol is a stereoisomer of labetalol, with a unique combination of beta-adrenergic blocking effects and selective beta 2-agonist activity. The safety and efficacy of dilevalol in patients with systemic hypertension were evaluated in a placebo-controlled, double-blind, randomized study. After a 4-week placebo run-in period, patients with mild hypertension (supine diastolic blood pressure of 95-105 mmHg) were randomized to receive either placebo (n = 14) or increasing doses of dilevalol (n = 15), 100-800 mg, once daily, to achieve normalization of pressure and/or a reduction of supine diastolic pressure of greater than or equal to 10 mmHg. This was followed by a 4-week maintenance phase. Compared with placebo, dilevalol, 200-800 mg/day, lowered supine and standing systolic and diastolic blood pressures significantly, while causing a modest reduction in heart rate. The drug was well tolerated without evidence of orthostasis. Dilevalol, in doses of 200-800 mg/day, is a safe and effective drug for the treatment of patients with mild hypertension.

Clinical Trials as Topic↗
PubMed1987

Effects of glucocorticoids on the rabbit carotid body.

Weekly intramuscular injections of slow-release, depot methyl prednisolone to 15 adult Dutch rabbits did not bring about an increase in the volume of their carotid bodies. However, they caused swelling of chief cells with discrete areas of pallor in the cytoplasm. Factors responsible for these changes appear to be increased storage of catecholamines and an increased number of swollen mitochondria.

Adrenal Glands↗
PubMed1986

Frequency selectivity of single cochlear-nerve fibers based on the temporal response pattern to two-tone signals.

The physiological basis of auditory frequency selectivity was investigated by recording the temporal response patterns of single cochlear-nerve fibers in the cat. The characteristic frequency and sharpness of tuning was determined for low-frequency cochlear-nerve fibers with two-tone signals whose frequency components were of equal amplitude and starting phase. The measures were compared with those obtained with sinusoidal signals. The two-tone characteristic frequency (2TCF) is defined as the arithmetic-center frequency at which the fiber is synchronized to both signal frequencies in equal measure. The 2TCF closely corresponds to the characteristic frequency as determined by the frequency threshold curve. Moreover, the 2TCF changes relatively little (2%-12%) over a 60-dB intensity range. The 2TCF generally shifts upward with increasing intensity for cochlear-nerve fibers tuned to frequencies below 1 kHz and shifts downward as a function of intensity for units with characteristic frequencies (CF's) above 1 kHz. The shifts in the 2TCF are considerably smaller than those observed with sinusoidal signals. Filter functions were derived from the synchronization pattern to the two-tone signal by varying the frequency of one of the components over the fiber's response area while maintaining the other component at the 2TCF. The frequency selectivity of the two-tone filter function was determined by dividing the vector strength to the variable frequency signal by the vector strength to the CF tone. The filter function was measured 10 dB down from the peak (2T Q 10 dB) and compared with the Q 10 dB of the frequency threshold curve. The correlation between the two measures of frequency selectivity was 0.72. The 2T Q 10 dB does change as a function of intensity. The magnitude and direction of the change is dependent on the sharpness of tuning at low and moderate sound-pressure levels (SPL's). The selectivity of the more sharply tuned fibers (2T Q 10 dB greater than 3) diminishes at intensities above 60 dB SPL. However, the broadening of selectivity is relatively small in comparison to discharge rate-based measures of selectivity. The selectivity of the more broadly tuned units remains unchanged or improves slightly at similar intensity levels. The present data indicate that the frequency selectivity and tuning of low-frequency cochlear-nerve fibers are relatively stable over a 60-dB range of SPL's when measured in terms of their temporal discharge properties.

Animals↗
PubMed1986

A two-stage nonlinear cochlear model possesses automatic gain control.

A model of the cochlea is explored using as stimuli two simultaneously presented sinusoids of equal amplitude. The model consists of two stages: a linear bandpass filter, followed by a reservoir-type representation of the hair-cell/nerve-fiber complex. Fast Fourier transforms of the model's output were computed. While the amplitudes of the individual response components were strongly nonlinear functions of intensity, the ratio of the magnitudes of the response components at the frequencies of the two stimulating sinusoids was found to be nearly equal, over a wide intensity range, to the ratio of the amplitudes which those stimulating sinusoids possessed at the output of the filter. Thus the reservoir stage exerts "automatic gain control".

Adaptation, Physiological↗
PubMed1986

A direct growth effect of growth hormone in rat hindlimb shown by arterial infusion.

We have developed a method for infusing substances into one hindlimb of the rat via the arterial supply. A catheter attached to an osmotic minipump is inserted into the right superior vesical artery and advanced to the junction of the right common iliac artery. This arrangement permits either constant or pulsatile infusion for 7 days. We employed this method to study the direct action of rat growth hormone (rGH) on the proximal tibial epiphysial plate in hypophysectomized rats. Infusion of neither the solvent nor ovine prolactin (2 micrograms X rat-1 X day -1) affected epiphysial plate width compared with control (uninfused) legs. The rGH infused at 0.4 and 2.0 micrograms X rat-1 X day-1 produced dose-related local growth effects that were of similar magnitude with either constant or pulsatile (eight 1-h pulses/day) infusion. However, the higher dose of rGH also resulted in a systemic effect (i.e., epiphysial plate growth in the uninfused limb), and the pulsatile mode produced a greater systemic effect than that produced by constant infusion. Our results indicate that GH can act directly on cartilage in vivo to maintain growth and that its effectiveness is not enhanced by pulsatile delivery. In contrast, the indirect (i.e., systemic) growth effects of the hormone may be enhanced by intermittent infusion. Our infusion system is well suited for studying the direct effect of substances on hindlimb tissues in conscious, unrestrained rats over extended periods.

Animals↗
PubMed1985

A team approach to drool control in cerebral palsy.

An analysis of the surgical reduction of drooling in children with cerebral palsy is presented, describing a team approach to the problem. All children were housed in a residential facility. The criteria for selection and evaluation of these patients by speech therapists, dentists, plastic surgeons, pediatricians, and teachers are also presented. Results show this approach to be successful: there were minimal postoperative complications; the amount of drool was significantly reduced; and the overall performance of the patients was improved.

Cerebral Palsy↗
PubMed1983

Characteristics of postsynaptic alpha 1 and alpha 2 adrenergic receptors in canine vascular smooth muscle.

A previous study suggested the existence of two distinct postsynaptic alpha adrenergic receptors in canine intralobar pulmonary arteries (IPA) and veins. The present study, performed using rings of canine IPA and dorsal metatarsal vein (DMV), was designed to characterize the factors affecting the postsynaptic alpha 1 and alpha 2 receptors of these blood vessels. The responses of IPA and DMV to norepinephrine (NE), transmural nerve stimulation, phenylephrine (PE), guanabenz, and clonidine were obtained in the presence and absence of alterations in pH, extracellular calcium ion, sulfhydryl bond reduction and oxidation, and destruction of adrenergic nerves with 6-hydroxydopamine. The data demonstrate that: (i) alpha 2-receptors are inactivated by changes in pH above or below pH 7.4, contain a labile disulfide group, are susceptible to modulation by increases and decreases in calcium ion, and appear to be decreased by destruction of adrenergic nerves; (ii) the NE and PE sensitive alpha 1-receptors are insensitive to alterations in pH, refractory to disulfide reduction by dithiothreitol, slightly susceptible to modulation by calcium ion, and increased by destruction of adrenergic nerves. These data support the conclusion that the two subtypes of postsynaptic alpha adrenergic receptors differ in their properties and susceptibility to modification by alteration of the physiological environment.

Animals↗
PubMed1983

Differences in adrenergic receptor populations in canine dorsal metatarsal veins and intralobar pulmonary arteries.

The contractile responses of the canine intralobar pulmonary arteries (IPA) and dorsal metatarsal veins (DMV) to alpha adrenergic receptor agonists were evaluated in the absence and presence of alpha receptor antagonists to determine the type of post-synaptic alpha receptor predominant in the cutaneous and pulmonary canine vasculature. Rings of IPA, in vitro, contracted in response to the alpha 1 receptor agonist phenylephrine (PE), and the mixed alpha agonist norepinephrine (NE) but did not contract in response to clonidine (C), an alpha 2 receptor agonist. DMV contracted in response to each of the agonists. The contractile responses of the IPA to NE and PE were antagonized by tolazoline, phentolamine, clonidine and prazosin. The contractile responses of the DMV to clonidine were only antagonized by clonidine and phentolamine but not by tolazoline or prazosin. These data suggest that: 1) IPA are selectively endowed with post-synaptic alpha 1 adrenergic receptors; 2) DMV are endowed with both post-synaptic alpha 1 and alpha 2 adrenergic receptors; and 3) clonidine interacts with alpha 1 adrenergic receptors to elicit alpha blockade and with alpha 2 adrenergic receptors to initiate contraction of the DMV. In an attempt to verify this hypothesis, experiments were performed in solutions in which the pH was altered above or below pH 7.4. Under these conditions, the agonist properties of clonidine were selectively inhibited whereas its blocking potency was retained. These data support the conclusion that clonidine is antagonistic at alpha 1 adrenergic receptors and agonistic at alpha 2 adrenergic receptors.

Adrenergic alpha-Agonists↗
PubMed1983

Association of genital mycoplasmas with exudative vaginitis in a 10 year old: a case of misdiagnosis.

A 10-year-old girl with a 1-year history of lower genitourinary tract symptoms suggestive of bacterial infection but with numerous negative urine cultures was referred to the University of Alabama urology clinic after empirical treatment with multiple antibiotics failed to resolve her symptoms. An extensive urologic evaluation revealed no structural or physiologic abnormalities, but an exudative vaginitis was noted and large numbers of Ureaplasma urealyticum and Mycoplasma hominis were isolated from the lower genital tract. Cultures for Chlamydia, viruses, and routine bacterial pathogens were negative. After initiation of tetracycline therapy, symptoms resolved and subsequent cultures for mycoplasmas were negative. In addition, a seroconversion was noted for M hominis but not for U urealyticum. Chlamydia serology was negative. It was later learned that the patient had been sexually molested just prior to the onset of symptoms. This case illustrates the necessity of early consideration of a mycoplasmal etiology in the patient with persistent genitourinary symptoms and no obvious bacterial pathogen, or in the patient whose condition is refractory to routine antibiotic therapy.

Child↗
PubMed1983

Differential inhibition of 5-hydroxytryptamine (5-HT) mediated contraction of rat thoracic aortae by phentolamine and tolazoline: correlation with inhibition of 5-HT binding and calcium ion.

The contribution of alpha receptor stimulation to the contractile responses of vascular smooth muscle to 5-HT was evaluated, in vitro utilizing helical strips of rat thoracic aortae (RTA). The contractile responses of RTA to 5-HT and norepinephrine (NE) were inhibited by the alpha receptor blocking agent phentolamine. The inhibition persisted in RTA obtained from rats treated with reserpine (1.5 mg/kg/day for 6 days). Analysis of the interaction of phentolamine with 5-HT and NE demonstrated that: 1) phentolamine is a competitive inhibitor of the responses to 5-HT; and 2) the pA2 values for the interaction of phentolamine with 5-HT and NE differed. When the concentration of calcium ion in the physiologic saline solution (PSS) was increased from 1.6 mM to 2.5 mM, phentolamine was approximately 100 times more potent an inhibitor of the response to NE than 5-HT. Phentolamine decreased the binding of 14C-5-HT to rat thoracic aortae in control PSS, but not when the calcium concentration was increased to 2.5 mM. Tolazoline inhibited the contractile responses of RTA to NE but not 5-HT. The data support the conclusion that the contractile responses of RTA to 5-HT are mediated by receptors similar to the alpha receptor. The ability of phentolamine to inhibit 5-HT induced contraction may be dependent on the ability of phentolamine to bind to anionic sites of the 5-HT receptor. The inhibitory effect of calcium ion may result from its ability to combine with, and neutralize, these negatively charged moieties on the smooth muscle membrane. The lack of effect of tolazoline may result from the absence of the third ring structure present in the phentolamine molecule, and therefore an inability to bind to these postulated anionic sites. Alternatively, the absence of an imino-nitrogen in the chain separating the phenyl and imidazole groups of tolazoline may prevent tolazoline from interacting with the 5-HT receptor. The different pA2 values for phentolamine mediated inhibition of the responses to 5-HT and NE, and the ability of NE to poorly displace 5-HT from the RTA, despite blockade of alpha receptors with tolazoline, support the possibility that the 5-HT receptor of RTA differs from the alpha receptor and that phentolamine has affinity for both 5-HT and adrenergic receptors.

Animals↗
PubMed1982

Asymptomatic pulmonary embolism. A common event in high risk patients.

Ventilation and perfusion lung scans were obtained before and at weekly intervals following hip surgery or major amputation in 158 patients. Pulmonary arteriograms were obtained in 21 of 33 patients developing perfusion patterns strongly suggesting embolism; 19 of the 21 arteriograms demonstrated pulmonary embolism. From autopsy and clinical data, 36 patients were diagnosed as having an embolus while under study, and 12 patients were suspected of having had an embolus during their illness but prior to entry into the study. Only four of these 48 patients experienced symptoms suggestive of pulmonary embolism. We conclude that asymptomatic pulmonary embolism is a common event in the populations studied.

Amputation, Surgical↗