Long-lasting aftereffects of prism adaptation in the monkey

The errors in target-reaching that are produced by laterally displacing vision with wedge prisms decrease with trials (prism adaptation). When the prisms are removed, errors in the opposite direction are observed (aftereffect). We investigated the size of the aftereffect 24 h and 72 h after a monkey had adapted to a visual displacement (30 mm), with rapid reaching movements. The aftereffect more than half of the size of the displacement was observed when the effect was tested immediately after the monkey had been exposed to the displacement for 50 trials. In contrast, the aftereffect was not observed at 24 h even when the monkey had been exposed to the displacement for 250 trials. However, when the monkey had been exposed for 500 trials, significant aftereffects more than half of the size of the displacement were observed at 24 h and 72 h. When both arms were adapted to opposite prism displacements, the long-lasting aftereffect was further shown to be specific for the arm used during the exposure. The results indicate that the aftereffects of prism adaptation last for at least 3 days, though more than 200 trials of additional repetition are required to consolidate the short-term effects into long-lasting ones.

Detection of release of aspartate and glutamate in cat spinal dorsal horn following noxious stimulation of cutaneous and muscular afferent fibers using microdialysis

To investigate the possible mechanisms underlying the difference of NMDA and non-NMDA receptors in spinal nociception originating in skin and muscle, release of aspartate (Asp) and glutamate (Glu) in the spinal dorsal horn was detected by stimulation of cutaneous and muscular nerves in cats using microdialysis technique. Asp and Glu were increased respectively by (323 +/- 55)% and (169 +/- 16)% following stimulation of cutaneous nerve, but by (150 +/- 16)% and (218 +/- 42)% respectively following stimulation of muscular nerve. Asp increase was approximately three times higher than that of Glu following cutaneous nerve-stimulation (P < 0.01), while Glu increase was approximately twice as high as that of Asp following muscular nerve-stimulation (P < 0.05). It is likely that nociceptive cutaneous and muscular inputs preferentially elicite release of Asp and Glu respectively, resulting in a functional differentiation of NMDA and non-NMDA receptor in the mediation of different nociceptive information.

Cerebellar complex spikes encode both destinations and errors in arm movements

Purkinje cells of the cerebellum discharge complex spikes, named after the complexity of their waveforms, with a frequency of approximately 1 Hz during arm movements. Despite the low frequency of firing, complex spikes have been proposed to contribute to the initiation of arm movements or to the gradual improvement of motor skills. Here we recorded the activity of Purkinje cells from the hemisphere of cerebellar lobules IV-VI while trained monkeys made short-lasting reaching movements (of approximately 200 milliseconds in duration) to touch a visual target that appeared at a random location on a tangent screen. We examined the relationship between complex-spike discharges and the absolute touch position, and between complex-spike discharges and relative errors in touching the screen. We used information theory to show that the complex spikes occurring at the beginning of the reach movement encode the absolute destination of the reach, and the complex spikes occurring at the end of the short-lasting movements encode the relative errors. Thus, complex spikes convey multiple types of information, consistent with the idea that they contribute both to the generation of movements and to the gradual, long-term improvement of these movements.

[A microdialysis study of excitatory amino acid levels of the monkeys' caudate nucleus during the delayed go/no-go task]

Using in vivo microdialysis coupled with HPLC-fluorescent detection chemical analysis method, levels of excitatory amino acid were monitored in the caudate nucleus of rhesus monkeys (Macaca mulatta) during performance of a delayed go/no-go task in which movement or no-movement responses were executed depending on the position of a cue light. It was found that the levels of glutamate and aspartate in caudate microdialysates decreased by (31.68 +/- 3.85)% (n = 10, t9 = 6.51, P < 0.001) and (26.25 +/- 5.95)% (n = 10, t9 = 3.39, P < 0.01) respectively during the delayed go/no-go task performance as compared to their basal levels before the task performance. Glutamine and asparagine levels were also found decreased significantly (P < 0.05). In contrast, no such decreases were seen when the monkey performing a non-delayed go/no-go task or performing the task composed of delayed go-trials only. The results suggest that the excitatory amino acid transmission in the caudate nucleus may be involved in the delayed go/no-go task performance, and thereby provide a direct evidence for the modulation of motor working memory by glutamatergic transmission in caudate nucleus.

[Intracerebral microdialysis and its application in neurosciences]

As a new technique for sampling the extracellular fluid in vivo, the microdialysis is recently attractive to neuroscientists. Coupled with high sensitivity techniques for chemical microanalysis, it has been successfully used for monitoring chemical changes in extracellular environment of intact brain, and applied to some fields of neuroscience studies. In this article, its principle and some methodological aspects were described systematically, and a brief overview of its applications in neurosciences and some new advances was also given. Besides, the scope and limitations of microdialysis was discussed in the light of our own experience.