Neuronal coding by cortical cells of the frequency of oscillating peripheral stimuli.

One class of neurons in the somatic sensory cortex of unanesthetized monkeys is rhythmically entrained by sinusoidal mechanical stimulation of the skin of the hand at low frequencies. A second class, which is linked to Pacinian afferents, increases its rate of discharge in response to high-frequency peripheral stimuli but is not entrained. The vibratory sense is served by two distinct classes of cortical cells. The code for the group sensitive to low-frequency stimuli is the temporal order of impulses; for the high-frequency group the code is the labeled line.

Effect of prostaglandin E1 on neuromuscular transmission in the rat.

1 The effect of prostaglandin E1 on neuromuscular transmission in the phrenic nerve-diaphragm muscle preparation of the rat was studied with intra- and extracellular recording techniques. 2 Prostaglandin E1, in concentrations from 10 nM, induced intermittent failures in the generation of the end-plate potential in response to repeated indirect stimulation. 3 Failures appeared abruptly, the end-plate potential behaving in an all-or-nothing fashion. The effect occurred only at 36-38 degrees C when the nerve was stimulated at 30-80 Hz and was reversible upon washing with drug-free solution. 4 Since miniature end-plate potentials were not affected, such failures must be attributed to a presynaptic action of prostaglandin E1. 5 Extracellular recording suggested that prostaglandin E1 prevented the action potential from reaching the nerve terminal.

Multiresistance in Staphylococcus spp. blood isolates in Finland with special reference to the distribution of the mecA gene among the Staphylococcus epidermidis isolates. The Finnish Study Group for Antimicrobial Resistance.

A total of 570 Staphylococcus spp. blood isolates collected in Finland in 1991 were tested for susceptiblity to oxacillin and 19 additional antimicrobial agents. The Staphylococcus epidermidis isolates were also analyzed for the presence of the mecA gene by the polymerase chain reaction (PCR). Of the 238 S. epidermidis, 137 (58%) were in vitro identified as methicillin-resistant and 5 (2%) exhibited oxacillin MICs between 1 and 3 micrograms/ml. All these isolates were positive for the mecA gene in PCR as an indication of genetic resistance to methicillin, while none of the remaining 96 S. epidermidis isolates (oxacillin MICs < or = 0.25 microgram/ml) was positive. Multiresistance was observed in 123 (87%) of the 142 mecA-positive S. epidermidis. Of the 332 Staphylococcus aureus isolates, only one (0.3%) was phenotypically resistant to methicillin; the strain was also resistant to three other unrelated classes of antimicrobials. True methicillin resistance of this strain was manifested by the presence of the mecA gene in PCR. Based on these results, multiresistance was still extremely rate among the S. aureus in our country, whereas among the S. epidermidis as many as half of the blood isolates in central hospitals were multiresistant.

Regional distribution of functions in parietal association area 7 of the monkey.

The functions of cells in different parts of area 7 were studied in 5 hemispheres of three stumptail macaques (Macaca speciosa). Activity of groups of cells was recorded in non-anesthetized animals using course microelectrodes. Functional maps covering the exposed part of area 7 showed that purely visual and oculomotor responses occurred in area 7a (PG) whereas the skin was dominantly represented in area 7b (PF). Vision was also represented in 7b but here together with somatic mechanisms. Oculomotor discharges were concentrated in the medial part of area 7a, whereas motor action of the arm and hand extended across the medial part of area 7. Motor actions of the mouth were represented most laterally. A statistically significant somatotopic arrangement of the body surface was also observed: the face was represented most laterally and the body and legs most medially with large overlapping regions. In the posterior part of 7a a kinesthetic region was found with representation of joints and muscles. The combination of visual and cutaneous activation was common more laterally than the combination of visual and somatomotor activation. Laterally the visual representation ended at the border between area 7 and area 2 of S I at a locus in front of which the S I receptive fields were located inside the mouth. These results indicate that different functions are represented in different degrees in different parts of area 7. Therefore, one important determinant of the results obtained by various research groups is the area of recording within area 7.

Early visual deprivation alters modality of neuronal responses in area 19 of monkey cortex.

Monkeys deprived on vision during the first year of life by lid suture appear functionally blind after the opening of the eyes, but move actively in familiar surroundings using somesthetic cues. Microelectrode recordings of multiple unit activity in the associative visual cortical area 19 of deprived monkeys indicated that 20% of the neuron groups studies responded only during active somatic exploration. In normal animals all neuron groups studied responses exclusively to visual stimuli, but in the deprived animals only 40% of them did. Visual deprivation alters the synaptic pathways to visual associative cortex enhancing the efficiency of those inputs that can mediate somatic information to this region.

Transmission of vibration in the hand-arm system with special reference to changes in compression force and acceleration.

The transmission of longitudinal vibration in the hand-arm system of five subjects was investigated. Altogether 405 individual tests were made. Vibration was measured with an accelerometer (weight 0.4 g) fixed in turn to the wrist, the elbow, and the upper arm by means of a supporting device (weight 34 g). A handle with strain gauges attached was used to study the effect of compression force (10, 20 and 40 N) and constant acceleration (1, 3 and 10 g) on the transmission of vibration at frequencies from 20 to 630 Hz. In the curves recorded, sharp dips appeared which were evidently caused by resonances from the soft tissues of the hand. However in the hand-arm system no common resonance frequency was observed that would harmfully affect the health of workers. Vibration in the hand-arm system was attenuated at an average of 3 dB per octave at the frequencies between 20 and 100 Hz. Between 100 and 630 Hz the attenuation was about 6 dB per octave in the wrist and 10 dB per octave in the elbow and upper arm. At the frequency of 630 Hz the attenuation was hence about 35 dB in the wrist and about 45 DB in the elbow. The attenuation of vibration in the elbow joint was 2 to 4 dB at all frequencies. The hand-arm system appears to be linear at the acceleration range considered; the increase in handle vibration by, e.g., 10 dB also increased vibration in the hand by 10 dB. When the grip strength was increased fourfold, i.e., 12 dB, vibration increased only 3 to 5 dB in the hand-arm system. Thus changing the weight of a vibrating tool does not reduce vibration enough. Therefore attempts to reduce vibration should concentrate on the mechanical parts of the engines.