Excitatory/inhibitory response types in the cochlear nucleus: relationships to discharge patterns and responses to electrical stimulation of the auditory nerve

We have studied the response properties of single units in the cochlear nucleus of unanesthetized decerebrate cats. The purpose of the study was to compare the properties of cochlear nucleus units as described in two commonly used classification schemes. Units were first classified according to their receptive-field properties based on the relative prominence of excitatory and inhibitory responses to tones and noise. Units were then classified on the basis of their discharge patterns to short tone bursts at their best frequencies (BFs). Our results show that systematic relationships exist between the receptive-field properties and discharge patterns of cochlear nucleus units. Type I units give only excitatory responses to tones and noise. They are characterized by primary-like and chopper discharge patterns. Some units in the anteroventral cochlear nucleus have prepotentials in their spike waveforms. Prepotential units most often show primary-like discharge patterns, but prepotential units characterized by nonprimary-like discharge patterns are also found. Most prepotential units lack detectable inhibitory sidebands (type I), but two of the nonprimary-like prepotential units encountered in this study had inhibitory sidebands (type III). Type III units also give excitatory responses to BF tones, but they have inhibitory sidebands. Most type III units give chopper discharge patterns, and these units can be recorded throughout the cochlear nucleus. Some type III units in the dorsal cochlear nucleus give complex discharge patterns that can be described as a composite of the pauser pattern and other patterns. The complexity of these responses seems to increase as the amount of inhibition at BF increases. Type I/III units give excitatory responses to tones and noise, but have little or no spontaneous activity so they cannot be tested directly for inhibitory responses. Type I/III units typically show chopper discharge patterns. One group of type I/III units have rate-level functions with sloping saturation, suggesting that these may receive a predominance of input from low spontaneous rate auditory nerve fibers. Type II units are nonspontaneous and give excitatory responses to tones, but give weak or no responses to noise. While type II units are homogeneous as a group in terms of their response maps. BF rate-level functions, and responses to noise, they show a variety of discharge patterns in response to short tone bursts at BF.(ABSTRACT TRUNCATED AT 400 WORDS)     

How to organize continuing education workshops and seminars

Although required in only four states at present, continuing education for lab professionals is necessary for job survival. With this growing need for CE events, here's how one lab uses these seminars to establish a leadership position in the lab community and reaps numerous professional benefits for its employees.     

Rice bran oil, not fiber, lowers cholesterol in humans

BACKGROUND: The cholesterol-lowering abilities of rice bran's fiber and oil apart from its fatty acid composition remain unclear. OBJECTIVE: The objective of the study was to assess the effects of defatted rice bran and rice bran oil in an average American diet on blood lipids in moderately hypercholesterolemic persons. DESIGN: Study 1 used a parallel-arm design. Twenty-six healthy volunteers consumed a diet with 13-22 g dietary fiber/d for 3 wk, and then 13 of the volunteers were switched to a diet with defatted rice bran to double the fiber intake for 5 wk. Study 2 was a randomized, crossover, 10-wk feeding study performed in 14 volunteers who consumed a diet with rice bran oil (1/3 of the total dietary fat) substituted for an oil blend that had a fatty acid composition similar to that of the rice bran oil. Serum lipids and factor VII were measured in both studies. RESULTS: Defatted rice bran did not lower lipid concentrations. In study 2, total cholesterol was significantly lower with consumption of the diet containing rice bran oil than with consumption of the control diet. Moreover, with consumption of the rice bran oil diet, LDL cholesterol decreased by 7% (P < 0.0004), whereas HDL cholesterol was unchanged. CONCLUSIONS: Rice bran oil, not fiber, lowers cholesterol in healthy, moderately hypercholesterolemic adults. There were no substantial differences in the fatty acid composition of the diets; therefore, the reduction of cholesterol was due to other components present in the rice bran oil, such as unsaponifiable compounds.     

Perception of the periodicity strength of complex sounds by the chinchilla

The perception of periodicity strength was studied in chinchillas using a stimulus generalization paradigm in an operant-conditioning, positive reinforcement behavioral task. Stimuli consisted of cosine-phase and random-phase harmonic complex tones, infinitely iterated rippled noises, and wideband noise. These stimuli vary in periodicity strength as measured by autocorrelation functions and are known to generate a continuum in the perception of pitch strength in human listeners. Chinchillas were trained to discriminate a cosine-phase harmonic tone complex from wideband noise and tested in the generalization paradigm using random-phase tone complexes and iterated rippled noises as probe stimuli. Chinchillas were tested in three different conditions in which the periods of the fundamental frequencies of the tone complexes were fixed at 2 ms, 4 ms, or 8 ms. Behavioral responses obtained from chinchillas were related to stimulus periodicity strength. For most animals, the behavioral responses to random-phase tone complexes were smaller than those to cosine-phase tone complexes. The behavioral responses were analyzed in terms of the Auditory Image Model of Patterson et al. [Patterson, R.D., Allerhand, M.H., Giguère, C., J. Acoust. Soc. Am. 98 (1995) 1890-1894], and the results suggest that the periodicity information in the stimulus envelope has a large influence in controlling the behavioral response of the chinchilla. Comparison of the generalization data obtained in the present study to magnitude estimation data obtained previously in human subjects suggests a greater influence of stimulus envelope for the perception of periodicity strength in chinchillas than for the perception of pitch strength in human listeners.     

The association of homocysteine and related factors to brachial artery diameter and flow-mediated dilation

Brachial artery flow-mediated dilation (BAFMD) has been proposed as a measurement of the degree and severity of cardiovascular disease. The purpose of this study was to (1) evaluate the associations between BAFMD and homocysteine, folate, vitamin B(12), vitamin B(6); (2) examine the influence of 5,10-methylenetetrahydrofolate reductase (MTHFR) genotypes on homocysteine levels and BAFMD; and (3) evaluate the effect of homocysteine on the baseline diameter of the vessel vs BAFMD. A total of 174 healthy research subjects were examined for BAFMD, homocysteine, folate, vitamin B(12), vitamin B(6), and MTHFR genotype, nucleotide 677 C-->T. The data indicated a significant inverse correlation between homocysteine and BAFMD (r = -0.1763, P = .02). There was a significant difference in BAFMD between MTHFR genotype groups (P = .01) (T/T vs C/C, P = .042; C/C vs C/T, P = .13; T/T vs C/T, P = .003). Homocysteine was significantly associated with the baseline brachial artery diameter (r = 0.1878, P = .013). The data confirmed a significant inverse correlation between baseline diameter and BAFMD (r = -0.3321, P = .0001). Regression analysis indicated that the MTHFR genotype, homocysteine, and age were significant predictors of BAFMD (P = .0001, r(2) = 0.118). When the baseline brachial diameter was incorporated into the model, the effect of homocysteine on BAFMD disappeared. The present data indicate an association between homocysteine and BAFMD and reduced BAFMD in individuals with the MTHFR nucleotide 677 T/T genotype, despite similar blood values for folate and homocysteine. Finally, the data suggest that the effect of homocysteine on vascular reactivity is in part a consequence of its influence on baseline brachial artery diameter.     

Responses of cochlear nucleus units in the chinchilla to iterated rippled noises: analysis of neural autocorrelograms.

Temporal encoding of stimulus features related to the pitch of iterated rippled noises was studied for single units in the chinchilla cochlear nucleus. Unlike other periodic complex sounds that produce pitch, iterated rippled noises have neither periodic waveforms nor highly modulated envelopes. Infinitely iterated rippled noise (IIRN) is generated when wideband noise (WBN) is delayed (tau), attenuated, and then added to (+) or subtracted from (-) the undelayed WBN through positive feedback. The pitch of IIRN[+, tau, -1 dB] is at 1/tau, whereas the pitch of IIRN[-, tau, -1 dB] is at 1/2tau. Temporal responses of cochlear nucleus units were measured using neural autocorrelograms. Synchronous responses as shown by peaks in neural autocorrelograms that occur at time lags corresponding to the IIRN tau can be observed for both primarylike and chopper unit types. Comparison of the neural autocorrelograms in response to IIRN[+, tau, -1 dB] and IIRN[-, tau, -1 dB] indicates that the temporal discharge of primarylike units reflects the stimulus waveform fine structure, whereas the temporal discharge patterns of chopper units reflect the stimulus envelope. The pitch of IIRN[+/-, tau, -1 dB] can be accounted for by the temporal discharge patterns of primarylike units but not by the temporal discharge of chopper units. To quantify the temporal responses, the height of the peak in the neural autocorrelogram at a given time lag was measured as normalized rate. Although it is well documented that chopper units give larger synchronous responses than primarylike units to the fundamental frequency of periodic complex stimuli, the largest normalized rates in response to IIRN[+, tau, -1 dB] were obtained for primarylike units, not chopper units. The results suggest that if temporal encoding is important in pitch processing, then primarylike units are likely to be an important cochlear nucleus subsystem that carries the pitch-related information to higher auditory centers.     

An evaluation of the flammability of five dental gloves.

OBJECTIVE: To assess the flammability of five brands of dental procedure glove. DESIGN: A total of ten gloves of each brand (Biogel-D, Premier Protectors, Roeko-D, Safeskin Satin Plus and Schottlander Low Allergy) underwent flammability testing. Five of these were tested as supplied (unwashed) and five following the application of the hand disinfectant Hydrex (washed). Each glove was stretched over a metal frame and the time to ignition, when exposed to a standardised butane flame, recorded. In addition, the thickness of each glove was also assessed by micrometer measurement. RESULTS: All the gloves tested ignited in less than 2.5 seconds. Two way analysis of variance revealed significant effects of glove type (P< 0.001) and treatment (P< 0.05), together with a significant interaction of these factors (P < 0.05), upon the ignition time. Washing Roeko-D gloves with Hydrex significantly (P< 0.01) retarded the ignition time compared with those in the unwashed state. Both the glove thickness and material type appeared to be related to ignition time. CONCLUSION: The work presented here demonstrates the acute and varying flammability of a range of dental procedure gloves. It should serve as a reminder to those who routinely use open flames whilst gloved of the dangers of this practice.