Substantia nigra stimulation evoked antidromic responses in rat neostriatum

Summary Electrical stimulation of the substantia nigra of rats elicits a burst of small amplitude waves with a latency of 4–6 ms that may last for 10–15 ms throughout much of the neostriatum. Frontal cortex stimulation also elicits a burst response, which can occlude the substantia nigra response. The substantia nigra evoked burst response was still present after chronic neocortical ablation or thalamic transection or both treatments combined. The response corresponds to the first sharp negative wave of the substantia nigra evoked neostriatal field potential. Single substantia nigra evoked action potentials were recorded in neostriatum with a mean latency of 9.8 ms, ranging from 4–22 ms. These action potentials were considered to be antidromic because 1) they were occluded during appropriate collision intervals by orthodromic action potentials elicited by frontal cortex stimulation. Subthreshold frontal cortex conditioning stimulation did not alter the threshold for activation from substantia nigra. The refractory period for the axon was at least as long as that for the soma and ranged between 0.8–2.0 ms. The antidromic responses failed to follow low frequency stimulation (< 40 Hz for 3000 ms). This failure occurred in the axon between substantia nigra and globus pallidus. The burst response and first sharp negative wave of the field potential probably represent the antidromic activation of the ubiquitous and densely packed medium spiny neostriatal projection neurons. These responses 1) occur at the same latency, 2) respond in the same manner to twin pulse and repetitive stimulation and 3) are occluded by frontal cortex stimulation in the same manner as antidromic action potentials.     

Noradrenergic terminal excitability: effects of opioids

The local infusion of morphine or D-Ala2, Met5-enkephalinamide into the frontal cortical terminal fields of noradrenergic neurons of the nucleus locus coeruleus resulted in a decrease in the excitability of the axon terminal regions to direct electrical stimulation. These effects were concentration dependent and could be blocked or partially reversed by the local infusion of naloxone. Some evidence was obtained for a differential antagonizing effect of naloxone upon the effects of morphine and D-Ala2, Met5-enkephalinamide. These results are discussed with respect to an effect of opioids on the polarization and/or ionic conductance of the terminal fields of locus coeruleus neurons, and to the possible regulation of neurotransmitter release by presynaptic opiate receptors.     

Chapter V. A comparison of CATI and non-CATI questionnaires

It appears likely that a greater proportion of surveys will use the telephone as a medium of sampling and data collection in the future. As software developments proceed and computer hardware costs shrink, many of these will use CATI systems. This experiment can be used as a benchmark for the transition to CATI because it provides documentation on potential problems with changing modes. For most criteria, there are only small differences between CATI and non-CATI interviewing in this project. The criteria include response rates, reactions of the interviewer and respondent, and most health statistics of interest. There are, however, some exceptions to this finding of equivalence between methods. The first exception is the result that the average number of minutes per CATI interview exceeded that for non-CATI interviews. There also is some evidence that the interviewer variability estimates tend to be lower in CATI than non-CATI. Finally, there is evidence of lower skip error problems in the CATI interviews. The first of these results affects survey costs; the second and third, survey error. The first may be a function of software or hardware choice and thus can be addressed in new CATI designs. The second and third will be of benefit to all CATI systems in the future.     

The effects of sub-anaesthetic doses of ketamine on memory, cognitive performance and subjective experience in healthy volunteers

The cognitive and subjective effects of sub-anaesthetic doses of ketamine on healthy volunteers were examined. Twelve healthy volunteers received 25 mg ketamine, 10 mg ketamine and saline placebo, i.m. in a double-blind, Latin square design. A cognitive, perceptual and self-report test battery was administered over 45 min. The order of tests was rotated to control for timing effects. Ketamine (25 mg) significantly affected verbal learning and memory, parallel visual search, some measures of psychomotor performance, measures of arousal, subjective mood ratings and visual perception. Measures of attention and frontal lobe functioning were relatively unaffected. Thus, low doses of ketamine had selective, dose-related effects on memory, perceptual and psychomotor functions. The disruption of memory and perceptual processes may help to explain the unique subjective state induced by ketamine.     

Production of 5–15 µm Diameter Alginate-Polylysine Microcapsules by an Air-Atomization Technique

A novel method of preparing small-sized microcapsules using a Turbotak air-atomizer is reported. Alginate-polylysine microcapsules containing Bacillus Calmette Guérin vaccine have been prepared by an adaptation of the method of Lim (1) which allows the manufacture of small-sized microcapsules. A Turbotak is used to spray sodium alginate solution into calcium chloride solution to form temporary calcium alginate microgel capsules. These temporary microgel droplets are subsequently cross-linked with polylysine to form permanent membranes. Microcapules in the size range of 5–15 µm have been produced which can be compared to an average diameter of 300 µm obtained by the method reported by Lim. The microcapsule size is dependent on the conditions of operation of the Turbotak and the concentration of the sodium alginate solution. Particles within the size range 5–15 µm can be reproducibly manufactured using the conditions of operation reported here. Other size ranges below the minimum of 300 µm reported by Lim are also feasible using this technique.     

Aortico-pulmonary paraganglioma: report of a case with ultrastructural study and review of the literature.

The light microscopic and ultrastructural features of an aortico-pulmonary paraganglioma (A-PP) are presented. The tumor was characterized by organoid clustering of neoplastic chief cells to form Zellballen. Argyrophilic granules were demonstrated within chief cell cytoplasm using a modified Grimelus technique. Ultrastructurally, three distinct cell types were present within the tumor: endothelial cells, pericytes and neoplastic chief cells. Membrane-bound neurosecretory granules were present and measured 100 to 2000 nm in diameter. "Light" and "dark" chief cells were less distinct than previously reported in other head and neck paragangliomas. Analysis of the 36 documented A-PP reported in the English literature reveals that the tumor has been either incompletely excised or has been considered unresectable in one-third of the cases. The reported surgical mortality is 9%, or approximately equal to the incidence of malignant behavior. The treatment of choice is surgical resection but when this is not possible, radiation may be a useful adjunct in therapy.     

Plasma dopa concentrations after different preparations of levodopa in normal subjects

1 The concurrent administration of levodopa with a decarboxylase inhibitor produced a plasma concentration/time curve comparable with 1/4 to 1/5 of the dose of levodopa given alone.

2 There was no evidence to suggest that the decarboxylase inhibitor slowed the rate of elimination of levodopa from plasma.

3 Metoclopramide (Maxolon) increased the rate of levodopa absorption. Higher plasma concentrations of levodopa during the first 2 h after dosing were followed by lower plasma concentrations during the third and fourth hours. The amount of levodopa absorbed after Larodopa as indicated by the AUC was not altered by adding metoclopramide.

4 None of the current preparations of levodopa produced sustained plasma concentrations.

5 In vitro testing confirmed that Brocadopa Temtabs tablets disintegrate and dissolve slowly. In vivo, Brocadopa Temtabs behaved as a slow release preparation but it did not produce sustained plasma concentrations of levodopa.

     

Formal retrospective case review and sudden infant death

A review of 24 consecutive sudden infant deaths was undertaken to evaluate the importance of the various stages in the postmortem assessment of such cases. Death in three cases was caused by obvious trauma. Of the remainder, 16 were attributed to sudden infant death syndrome (SIDS), 4 to accidental asphyxia (identified by death scene examination and/or formal case review) and 1 to a lingual thyroglossal duct cyst. Three (14%) of 21 deaths thought to be SIDS after postmortem examination were attributed to asphyxia following subsequent formal case review.