Neuroscience Letters, 105 (1989) 1-6 1 Elsevier Scientific Publishers Ireland Ltd. NSL 06351 Absence of histochemical immunoreactivity to calcitonin gene-related peptide (CGRP) in spinal cord motoneurons from ( +)-tubocurarine-treated chick embryos Josep E. Esquerda, Dolors Ciutat and Joan X. Comella Universitat de Barcelona, Estudi General de Lleida, Facultat de Medicina, Departament de Ci~ncies M~diques Bftsiques, Lleida (Spain) (Received I January 1989; Revised version received 1 June 1989;Accepted 5 June 1989) Key words." Neuronal cell death; Calcitonin-gene related peptide; Development; Chick embryo; Spinal cord A physiological neuronal death that implicates about 50% of the motoneuron population occurs in the chick embryo between the 6th (E6) and 9th (E9) day of incubation. This natural death can be prevented by administration of neuromuscular blocking agents (e.g. (+)-tubocurarine (( + )-Tc)). In this study, calci- tonin gene-related peptide-like immunoreaetivity (CGRP-LIR) was studied in spinal cord motoneurons from normal and (+)-Tc-treated chick embryos. In normal embryos CGRP-LIR was found in a neuronal subpopulation of the spinal cord lateral motor column (LMC) that was maximal between the 14th (El4) and 16th (El6) embryonic days with a subsequent decrease. In LMC neurons from (+)-Tc-treated chick embryos examined at E14--16days no histochemically detectable CGRP-LIR could be observed. The lateral motor column (LMC) of the chick embryo spinal cord.is one of the neuronal populations in which the naturally occurring neuronal death has been extensively investigated [15]. Although poorly understood, the regulation of this phe- nomenon clearly shows a target dependence [7, 8, 18], Furthermore, the physiological death of chick LMC motoneurons can be prevented during the major period of cell death (E6--E9) by application of neuromuscular synapse-blocking agents [2, 10, 19]. Likewise, exogenous application of dibutyryl cyclic GMP produces an inhibition of motor neuron death [26]. It appears that the neurons rescued from death mature nor- mally and do not differ from the normal ones, at least under the structural and chemi- cal criteria that have been investigated to date [14, 20]. Regarding neuropeptide histochemistry, there is now evidence that LMC neurons are not a homogeneous population. Calcitonin gene-related peptide (CGRP) has Correspondence," J.E. Esquerda, Estudi General de Lleida, Departament de Cirncies Mrdiques B~isiques, Facultat de Medicina, Anselm Clav6 22, E-25007 Lleida, Catalonia, Spain. 0304-3940/89/$ 03.50 © 1989 Elsevier Scientific Publishers Ireland Ltd,