Complementary expression of calcium binding proteins delineates the functional organization of the locomotor network

Abstract

Neuronal networks in the spinal cord generate and execute all locomotor-related movements by transforming descending signals from supraspinal areas into appropriate rhythmic activity patterns. In these spinal networks, neurons that arise from the same progenitor domain share similar distribution patterns, neurotransmitter phenotypes, morphological and electrophysiological features. However, subgroups of them participate in different functionally distinct microcircuits to produce locomotion at different speeds and of different modalities. To better understand the nature of this network complexity, here we characterized the distribution of parvalbumin (PV), calbindin D-28 k (CB) and calretinin (CR) which are regulators of intracellular calcium levels and can serve as anatomical markers for morphologically and potential functionally distinct neuronal subpopulations. We observed wide expression of CBPs in the adult zebrafish, in several spinal and reticulospinal neuronal populations with a diverse neurotransmitter phenotype. We also found that several spinal motoneurons express CR and PV. However, only the motoneuron pools that are responsible for generation of fast locomotion were CR-positive. CR can thus be used as a marker for fast motoneurons and might potentially label the fast locomotor module. Moreover, CB was mainly observed in the neuronal progenitor cells that are distributed around the central canal. Thus, our results suggest that during development the spinal neurons utilize CB and as the neurons mature and establish a neurotransmitter phenotype they use CR or/and PV. The detailed characterization of CBPs expression, in the spinal cord and brainstem neurons, is a crucial step toward a better understanding of the development and functionality of neuronal locomotor networks.

A Subset of Palisade Endings Only in the Medial and Inferior Rectus Muscle in Monkey Contain Calretinin

“… 52 A recent study of the expression of calcium-binding proteins in motoneurons in the spinal cord of the locomotor system in zebrafish revealed that CR was highly expressed in fast motoneurons, but not in slow motoneurons. 53 This is in contrast to our findings in the oculomotor system, where CR is present only in a subpopulation of neurons activating multiply innervated tonic muscle fibers with slow contractions, 54 whereas the motoneurons activating singly innervated twitch muscle fibers lack CR, but contain parvalbumin. 55 , 56 On the other hand, in the rostral mesencephalon a subgroup of saccadic premotor burst neurons (only those involved in upgaze) contain CR.…”

Ontogeny of Neurons Containing Calcium‐Binding Proteins in the Preoptic Area of the Guinea Pig: Sexually Dimorphic Development of Calbindin

“…The specificity of the primary antisera used in the present study has been confirmed by the manufacturers and by numerous researchers in various previous papers (Zimmermann and Schwaller, ; Drexel et al ., ; Mészár et al ., ; Berg et al ., ) including our team (Najdzion et al ., ; Zakowski et al ., ; Hermanowicz‐Sobieraj et al ., ; Równiak et al ., ). The rabbit anti‐CB (CB‐38), mouse anti‐CB (300), and mouse anti‐CR (6B3) antisera include immunoblots of the guinea pig brain homogenates, which were specifically stained by these antibodies, exhibiting bands at 28, 28, and 29 kDa, respectively (manufacturer's technical information).…”

Adult spinal motoneurons change their neurotransmitter phenotype to control locomotion

“…Retrograde labeling of axial motor neurons was performed in anesthetized zebrafish with 0.03% tricaine methane sulfonate (MS-222, E10521; Sigma-Aldrich) by using dye injections with tetramethylrhodamine-dextran (3,000 molecular weight, D3307; Thermo Fisher) or with biotinylated dextran (3,000 molecular weight, D7135; Thermo Fisher) into all muscles or into specific muscle fiber types (slow, intermediate, or fast) in myotomes 14–16 ( 21 , 42 , 43 ). All of the injected animals were allowed to recover for 5 h to overnight to help the retrograde transport of the tracer.…”