RETROGRADE TRACING AND ELECTROPHYSIOLOGICAL FINDINGS OF COLLATERAL SPROUTING AFTER END-TO-SIDE NEURORRHAPHY

The aim of this study was to seek more potent evidences of collateral sprouting for both motor and sensory nerve fibres after end-to-side neurorrhaphy using a modified double-labelling retrograde tracing method and to investigate the function of regenerated motor axons with electrophysiological evaluation. Four groups (n=4 for each group) were used: end-to-end coaptation (six months postoperatively), end-to-side coaptation (four months and six months postoperatively) and normal control. Two fluorescent tracers (true blue and diamidino yellow) were applied to the proximal ends of tibial and common peroneal nerves, respectively after four or six months of nerve coaptation. Five days later, we only found single-labelled motor and sensory neurons in the normal and end-to-end coaptation groups, while some dual-labelled neurons can be identified in end-to-side coaptation groups. Four months after surgery, the motor nerve conduction velocity in end-to-side coaptation was significantly slower than in the normal control. But no difference was found in the sixth month. These results suggest that end-to-side neurorrhaphy can induce the functional collateral sprouting of both motor and sensory axons in the peripheral nerve.

Respiratory nuclei share synaptic connectivity with pontine reticular regions regulating REM sleep

Injection of cholinomimetics into the medial pontine reticular formation (mPRF) of intact, unanesthetized cat causes a rapid eye movement (REM) sleep-like state and respiratory depression. The mPRF contains no concentrations of respiratory neurons, and this study examined the hypothesis that respiratory depression evoked from the mPRF is synaptically mediated. The mPRF of conscious cats was injected with bethanechol to define an mPRF zone causing state-dependent respiratory depression. Bethanechol caused a 361% increase in the REM sleep-like state and a 37% decrease in minute ventilation. Additional cats were injected with the retrograde fluorescent tracers True Blue and either Fluoro-Gold or Diamidino Yellow aimed for the cholinoceptive mPRF or for the pontine respiratory group (PRG). After mPRF dye injection, 1) labeling was observed in the PRG, dorsal respiratory group (DRG), and ventral respiratory group (VRG); and 2) double-labeled cells were observed in the VRG and PRG. Dye injections into the PRG produced contralateral and ipsilateral fluorescent labeling of the mPRF, DRG, and VRG. Thus cholinoceptive regions of the mPRF involved in REM sleep generation have reciprocal monosynaptic connections with the PRG and receive monosynaptic projections from the DRG and VRG.

Selective accumulation of diamidino yellow and chromomycin A3 by retinal glial cells.

We applied the fluorescent DNA stains diamidino yellow (DY) and chromomycin A3 to rat and rabbit retinas in vivo and in vitro. They accumulated in the nuclei of a subpopulation of cells of the inner nuclear layer. The number and distribution of the fluorochrome-accumulating cells were similar to those of the Müller glia, and double-labeling experiments showed that the cells accumulating DY or chromomycin A3 contained oriented filaments of vimentin. The fluorochromes also accumulated in the sparse astrocytes and oligodendrocytes located among the myelinated fibers of the rabbit central retina. Specific accumulation in retinal glia occurred only when the fluorochromes were applied to living retinas. If the plasma membranes were disrupted by fixation or exposure to detergent, most retinal cells were stained. This indicates that the locus of specificity is the entry of the molecules into the cells. When applied to living retinas, other DNA stains selectively accumulate in subclasses of retinal neurons. Why DNA-binding molecules should selectively cross the membranes of either retinal neurons or retinal glia remains an unsolved problem.

Survival of ganglion cells which form the retino-retinal projection during optic nerve regeneration in the frog

During optic nerve regeneration in the frog, axons transiently grow along the opposite optic nerve forming a retino-retinal projection. In the present study, we crushed the left optic nerve in the frog Litoria (Hyla) moorei and later applied horseradish peroxidase (HRP) or diamidino yellow (DY) to the right optic nerve. In one series, retinae were examined 3 days after application of the tracer. The retino-retinal projection was found to be maximal at 5 weeks, fell significantly by 7 weeks, and returned to close-to-normal levels by 24 weeks. In a second series, we applied DY at 5 weeks as before but did not sacrifice the frogs until 7 weeks. Numbers of labeled ganglion cells were not significantly different from those frogs in the first series labeled and examined at 5 weeks. We conclude that ganglion cells giving rise to the retino-retinal projection had not died in appreciable numbers, presumably being sustained by collateral axons in the brain.

Colocalization of substance P and GABA in retinal ganglion cells: A computer-assisted visualization

Ganglion cells in the albino rat retina were retrogradely labeled with the fluorescent dye, diamidino-yellow, from the superior colliculus. Preembedding and postembedding immunocytochemical techniques were employed in conjunction with computer-assisted image processing to visualize SP- and GABA-immunoreactivity. Examination of flatmount and sectioned retinas revealed that approximately 3% of the ganglion cells projecting to the contralateral superior colliculus exhibit SP-immunoreactivity. Moreover, these cells were found to comprise a subpopulation of the GABA-immunoreactive cells projecting to the rat tectum.