We used receptor autoradiography to determine the distribution of excitatory and inhibitory amino acid neurotransmitter binding sites in the cerebellar cortex of the pigeon (Columba livia). alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid, kainate and metabotropic binding sites had highest levels in the molecular layer. N-methyl-D-aspartate binding sites, assayed with both [3H]glutamate under selective conditions and with [3H]glycine binding to the associated strychnine-insensitive glycine site, had highest levels in the granule cell layer. There was little specific binding of the non-competitive N-methyl-D-aspartate antagonist, [3H]MK-801. The level of gamma-aminobutyric acid (GABA)-A binding sites was higher than GABA-B binding sites in both molecular and granule cell layers with the highest level of GABA-A sites in the granule cell layer. The highest level of GABA-B binding sites was in the molecular layer. [3H]Flunitrazepam binding levels were approximately the same in both molecular and granule cell layers. With the exception of kainate binding sites, the distribution of binding sites was identical to that seen in the cerebellar cortex of mammals. Our results support the concept that the chemoarchitecture of the cerebellar cortex has been conserved in the course of vertebrate evolution.

Animals↗

PubMedDate not supplied

The spinocerebellar ataxias.

The spinocerebellar ataxias (SCAs) are diseases characterized by the progressive degeneration and subsequent loss of neurons accompanied by reactive gliosis, degeneration of fibers from the deteriorating neurons, and clinical symptoms reflecting the locations of the lost neurons. The degenerative changes affect specific neuronal groups while others remain preserved, and these diseases can therefore be viewed as system degenerations. The SCAs result from either genetically transmitted diseases with dominant inheritance or unknown causes with sporadic occurrence. Most of these disorders affect the cerebellum and its pathways, resulting in progressive deterioration of cerebellar function manifested by increasing unsteadiness of gait, incoordination of limb movements with impairment of skilled movements such as handwriting, and a distinctive dysarthria. Other neuronal systems are affected in some of these disorders, notably the corticospinal pathway, basal ganglia, and autonomic nuclei of the brain stem and spinal cord.

Humans↗

PubMedDate not supplied

Effects of radiographic contrast agents on spinal cord physiology.

Segmental reflexes in the spinal cords of cats anesthetized with chloralose were used to evaluate the neurophysiologic effects of radiographic contrast agents. The exposed lumbar spinal cord was bathed with concentrations of ionic and nonionic agents including saline, sodium meglumine diatrizoate, meglumine iothalamate, meglumine iocarmate, and metrizamide. The following responses were evaluated: flexor and extensor monosynaptic reflex; polysynaptic flexion reflexes; spontaneous ventral root activity. Hypertonic solutions generally produced a transient decrease in all reflex activity for up to 1 hour. Isotonic solutions produced no significant changes in the monosynaptic responses, but an increase in amplitude of polysynaptic responses, and increased spontaneous activity. The usual facilitory effects of flexion reflex on the flexor monosynaptic reflex were unchanged, but the expected inhibitory effect of flexion reflex on the extensor monosynaptic reflex was changed to excitatory. The relative ability to produced these effects was sodium meglumine diatrizoate greater than meglumine iothalamate greater than meglumine iocarmate greater than metrizamide.

Action Potentials↗

PubMedDate not supplied

Properties of acoustic reflex adaptation.

The dynamic behavior of the acoustic reflex to continuous sinusoidal stimuli was investigated. The major purpose was to determine the temporal characteristics of reflex adaptation as frequency (0.5, 1.0, 2.0, 3.0, 4.0 kHz) and suprathreshold level (6, +12, +18 dB re reflex threshold) were systematically varied. Repeated measurements were made with an impedance bridge on six normal listeners. Both relative and absolute impedance changes were analyzed. The results revealed large intersubject variability. Four general conclusions were reached regarding the effect of stimulus frequency and suprathreshold level on adaptation: 1) as the stimulus frequency increases, the rate of adaptation increases; 2) the adaptation curves appear to form distinct groups, at the low frequencies adaptation rates are significantly slower than those at 2.0 kHz and above; 3) the onset of adaptation occurs at an earlier time for the higher frequencies; and 4) the rate of adaptation was found to be independent of suprathreshold level. The changes in adaptation with frequency of the stimulus may be expressed by an equation involving inter-related time constants for the growth and adaptation portions of the reflex curve in accordance with a descriptive model suggested by Tietze.

Acoustic Stimulation↗

PubMedDate not supplied

An Internet multicast symposium concerning the microcirculation of the islets of Langerhans.

The Internet Globally-linked Computer System was used to conduct an international scientific symposium. The symposium was held at the VAMC-Long Beach and consisted of prepared lectures that were multicast over the Internet. The basic unit of hardware used for the Internet Multicast was the Silicon Graphics Indy Unix Workstation, which was equipped with a color video camera. The multicast required four additional pieces of software from the file transfer protocol. The multicast backbone protocol allowed for simultaneous audio and video signals (the presenter, the slides, and the videotape images of islet microcirculation studies) to be transmitted over the computer network. The faculty included 12 experts in microcirculation, who gave 15-min lectures that included a question and answer period. All lectures were received at 14 computer stations in six countries. Eleven of the faculty gave their lectures at the VAMC-Long Beach, and one gave her lecture at the Massachusetts Institute of Technology in Boston, MA. The presenter from Boston was able to receive and answer questions from the faculty at the VAMC-Long Beach. An estimated $12,000 was saved in travel, hotel, and food costs and an estimated 180 travel hours were saved by viewers who did not have to travel to the symposium. We have demonstrated that a scientific symposium can be conducted using the Internet. We propose that many of our future meeting will be organized over the computer network. This format of multiimage projections allows us to effectively communicate in a personal way with a reduction in expensive and time-consuming travel.

Animals↗