Journal of neurophysiology
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1. The effects of culturing hypothalamic neurons in glutamate receptor antagonists were studied with fura-2 Ca2+ digital imaging of groups of synaptically coupled neurons. Removal of D-2-amino-5-phosphonovalerate (AP5) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) from cultures chronically blocked for periods of 14-188 days caused a dramatic increase in neuronal Ca2+ to abnormally high levels 5- to- 10 fold greater than the normal intracellular levels of 50-100 nM. ⋯ Relative to control cultures of the same period in vitro, chronically blocked neurons showed an enhanced Ca2+ influx when stimulated with the glutamate receptor agonists kainate (+70%), NMDA (+62%), or glutamate (+34%) in the presence of tetrodoxin. When the data from control and chronically blocked cultures stimulated with glutamate receptor agonists were pooled, without exception all the smallest responses were found in the control neurons. Compared with controls, chronically blocked neurons showed an exaggerated response to glutamate in the presence of nimodipine, indicating that Ca2+ hyperexcitability was not due to changes in voltage activated L-type Ca2+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)
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Comparative Study
Temporal resolution of neurons in cat inferior colliculus to intracochlear electrical stimulation: effects of neonatal deafening and chronic stimulation.
1. Cochlear implants have been available for > 20 yr to profoundly deaf adults who have lost their hearing after acquiring language. The success of these cochlear prostheses has encouraged the application of implants in prelingually deaf children as young as 2 yr old. ⋯ This variation in pulse response was partially correlated with the unit's response to sinusoids. Most onset neurons responded only to pulse frequencies below 20 pulses per second (pps). Most sustained units responded best to pulse frequencies < 100 pps, and most ceased to respond to pulse frequencies > 300 pps.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. An experimental approach was developed that allowed recording of neurophysiological activity from single putative cochlear efferents in the auditory brain stem of anesthetized chickens with the use of glass micropipettes. The aim of this study was to study spontaneous and tone-evoked activity from single efferent neurons in the chick and to compare their properties with those of other vertebrate hair cell organs. ⋯ The others either showed regular spontaneous activity, or their time-interval histograms showed longer modes than ascending fibers. In general, mean spontaneous activity was lower than in ascending fibers, being < 30 spikes/s. 7. In contrast to reports from mammalian studies, in which efferents only showed on peristimulus time (PST) response pattern to tonal stimuli (chopper), two different response types were found in this study: two excitation types (chopper and primary-like) and one suppression type.(ABSTRACT TRUNCATED AT 400 WORDS)
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1. Two complimentary techniques were used to study cortical function in six human upper limb amputees: positron emission tomographic (PET) measurements of regional cerebral blood flow (rCBF) were made in subjects during limb movements to study activation of the primary motor (M1), primary somatosensory (S1), and association cortices; and electromyographic responses to transcranial magnetic stimulation (TMS) were measured in proximal upper limb muscles to assess the excitability of corticospinal neurons in subjects at rest. 2. To explore possible cortical mechanisms governing the phantom limb phenomenon, PET and TMS findings were compared between subjects with acquired, traumatic upper limb amputations (n = 3), in whom phantom limb symptoms were prominent, and congenital upper limb amputees (n = 3) without phantom limbs. 3. ⋯ Abnormal blood flow increases also were present in the partially deafferented M1/S1 cortex of traumatic amputees during movement of the ipsilateral, intact arm. Abnormal ipsilateral M1/S1 responses were not present during movement of the intact arm in the congenital group. 5. TMS studies showed that the abnormal blood flow increases in the partially deafferented M1 cortex of traumatic amputees were associated with increased corticospinal excitability.(ABSTRACT TRUNCATED AT 250 WORDS)
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1. Responses of neurons in primary auditory cortex (AI) of the barbiturate anesthetized adult cat were studied using cochlear stimulation with electrical and acoustic stimuli. Acoustic stimulation of the ear ipsilateral to the studied cortical hemisphere with brief biphasic clicks was compared with electrical stimulation of the contralateral cochlea with brief biphasic electrical pulses delivered via a feline cochlear prosthesis. ⋯ The characteristic latency behavior for each neuronal response was found to be very similar for acoustic and electrical stimulation. Correlation analysis revealed a close relationship between latency parameters of the two electrical stimulation conditions, a weaker relationship between the longitudinal electrical and the acoustic conditions, and the weakest relationship between the radial electrical and acoustic conditions. 6. Correlation analysis for rate and latency parameters revealed several relationships between these response aspects.(ABSTRACT TRUNCATED AT 400 WORDS)