Spinal cord neuron classes in embryos of the smooth newtTriturus vulgaris: a horseradish peroxidase and immunocytochemical study

Abstract

Spinal cord neurons were investigated in embryos of Triturus vulgaris, the smooth newt, just prior to hatching. These embryos can swim if freed from their egg membranes. Horseradish peroxidase (HRP) labelling, together with GABA and glycine immunocytochemistry (ICC), revealed nine distinct anatomical classes of neuron. 1. Ventrolateral motoneurons with mainly dorsal dendrites, sometimes a descending central axon and peripheral axon innervating the trunk muscles. 2. Dorsal primary sensory Rohon-Beard neurons innervating skin and with dorsal ascending and descending axons in spinal cord. 3. Commissural interneurons with mid-cord unipolar soma, glycine-like immunoreactivity, dendrites on initial segment of ventral axon which crosses cord to ascend or branch. 4. Dorsolateral commissural interneurons with multipolar soma in dorsolateral position with dorsal dendrites and ventral axon which crosses and ascends or branches. 5. Giant dorsolateral commissural interneurons with large dorsolateral somata widely spaced (130-250 microns spacing) with process projecting dorsally to other side, dorsolateral dendrites and ventral axon which crosses to ascend and branch. 6. Dorsolateral ascending interneurons in dorsolateral position with multipolar soma and ascending axon on same side. 7. Ascending interneurons with unipolar soma, GABA-like immunoreactivity and ascending axon on same side. 8. Descending interneurons with bi- or multi-polar soma, extensive dorsal and ventral dendrites, and descending axon on same side. They may also have ascending axons. 9. Kolmer-Agduhr cerebrospinal fluid contacting neurons with cilia and microvilli in lateral corners of neural canal. GABA-like immunoreactivity, no dendrites and ascending axon. Eight of the nine cells classes were found to bear a marked resemblance to neurons previously described in zebrafish and Xenopus embryos in terms of their anatomy, distribution and immunoreactivity to GABA and glycine. Homologies and possible functions are discussed. Giant dorsolateral commissural neurons, were not found in Xenopus or teleosts but were present in Ambystoma mexicanum and Neoceratodus. The regular, possibly segmental longitudinal distribution pattern of these cells within the cord is unusual among amphibian spinal neurons.

Activity of descending propriospinal axons in the turtle hindlimb enlargement during two forms of fictive scratching: phase analyses

“…This finding is somewhat surprising, because studies of scratching have generally focused on ipsilateral neural circuitry. On the other hand, there are many propriospinal neurons with descending crossed axons in turtles (Kusuma and ten Donkelaar, 1980;Berkowitz and Stein, 1994a), as well as in lampreys (Buchanan, 1982;Ohta et al, 1991), embryonic tadpoles (see Roberts, 1989) embryonic newts (Harper and Roberts, 1993) goldfish (Fetcho, I99 1), lizards (ten Donkelaar and de Boer van Huizen, 1978;Kusuma and ten Donkelaar, 1980) chicks (Oppenheim et al, 1988) and mammals (Burton and Loewy, 1976;Molenaar, 1978;Molenaar and Kuypers, 1978;Matsushita et al, 1979;Menetrey et al, 1985;Hongo et al, 1989;Cassidy and Cabana, 1993). In addition, during turtle fictive scratching evoked by unilateral tactile stimulation, some hindlimb muscle nerves on the opposite side of the body are often activated with a clear rhythm ( Fig.…”

Organization of Projection-Specific Interneurons in the Spinal Cord of the Red-Eared Turtle

“…These include all IN projection classes except adIINs, with further distinctions drawn according to cell or axon position, cell morphology, and the presence or absence of minor axon branches (many of the INs in zebrafish have a major longitudinal axon branch as well as a minor branch in the opposite direction). In the smooth newt all IN projection classes except dCINs have been described [Harper and Roberts, 1993]. In the Xenopus larva, 8-9 different IN types have been described [Roberts and Clarke, 1982;reviewed in Roberts, 2000], but virtually all are reported as bifurcating and most appear to be CINs with barely any IINs [Soffe et al, 1984;Dale, 1985;Roberts et al, 1988;Yoshida et al, 1998].…”

“…Although the morphology of spinal interneurons and projection neurons has been studied in all vertebrate classes [agnathans: Ohta et al, 1991;Buchanan, 2001;fish: Fetcho and Faber, 1988;Fetcho, 1990;Hale et al, 2001; amphibians: Roberts and Clarke, 1982;Roberts et al, 1987Roberts et al, , 1988Harper and Roberts, 1993;Heathcote and Chen, 1994;Binor and Heathcote, 2001;Li et al, 2001;avians: Yaginuma et al, 1994;Eide and Glover, 1996;reptiles: Berkowitz, 2004reptiles: Berkowitz, , 2005reptiles: Berkowitz, , 2007Berkowitz et al, 2006;mammals: Jankowska, 1992;Snider, 1992, 1994;Puskar and Antal, 1997;Eide et al, 1999;Antal et al, 2000;Stokke et al, 2002;Angel et al, 2004;Dai et al, 2005;Nissen et al, 2005], it is not yet clear whether a common pattern underlies the spatial organization of different morphological classes. We have previously characterized the anatomical organization of lumbar spinal neurons in embryonic and neonatal rodents using differential retrograde labeling in lumbar segments known to contain IN networks that control locomotion [Stokke et al, 2002;Nissen et al, 2005].…”

A Possible Pathway Connecting the Photosensitive Pineal Eye to the Swimming Central Pattern Generator in Young Xenopus laevis Tadpoles

“…Tadpoles were left for 90 min for HRP to fill the cells and were then fixed in 2% glutaraldehyde. After washing overnight, HRP was visualized by reaction with diaminobenzidine [DAB, see Harper and Roberts, 1993 for more details]. The only alteration to these techniques was the use of ethyl alcohol treatment to reduce background staining [Metz et al, 1989].…”