Anatomy of the Hesse photoreceptor cell axonal system in the central nervous system of amphioxus

Abstract

The present study reports the organization of the Hesse cell axonal system in the central nervous system of the amphioxus, with the use of a polyclonal antiserum raised against lamprey gonadotropin-releasing hormone-I (GnRH-I). In the spinal cord, the rhabdomeric photoreceptor cells of the bicellular organs were well labeled with this antibody. These cells sent smooth, straight, lateral processes that bent and became beaded as they passed ventrally and crossed to the contralateral side of the cord. There, the processes of several cells aggregated to give rise to a longitudinal fiber bundle. Beaded collaterals of these processes were directed to ventral neuropil and did not appear to contact giant Rohde cell axons. The crossed projections of the Hesse photoreceptors are compared with those of vertebrate retinal ganglion cells. Other antisera raised against GnRH weakly labeled rhabdomeric photoreceptors located dorsally in the brain, the Joseph cells. The finding that GnRH antibodies label amphioxus photoreceptor cells and axons is not definitive proof that the photoreceptors contain GnRH. Regardless of whether the antibody recognizes amphioxus GnRH, which has not yet been identified by structure, the antibody has revealed the processes of the Hesse photoreceptor cells.

Vertebrate Cranial Placodes as Evolutionary Innovations—The Ancestor's Tale

“…Since this peptide activates only one out of four GnRH receptors, additional GnRH peptides are probably present in amphioxus but remain to be identified. GnRH positive cells have been localized to the neural tube but not to Hatschek's pit or preoral ectoderm (Castro, Becerra, Manso, Sherwood, & Anadon, 2006;.…”

Amphioxus photoreceptors - insights into the evolution of vertebrate opsins, vision and circadian rhythmicity

“…DO photoreceptor cells are described as having a single basal axon. The data from larvae showed that projections from the first DO are ipsilateral (Lacalli, 2002), whereas in adult amphioxus the projections from the DO are contralateral (Castro et al, 2006). Amphioxus larvae exhibit two different swimming modes -slow undulatory swimming involved mainly in vertical diurnal migration, and rapid muscular movement for escape (Guthrie, 1975;Lacalli and Kelly, 2003).…”

Characterization and Putative Role of a Type I Gonadotropin-Releasing Hormone in the Cephalochordate Amphioxus

“…Consistent with this, a similar but more accurate work has recently demonstrated the occurrence of GnRH-positive neurons in the amphioxus central nervous system by means of a large set of antisera generated against different GnRH peptides (19). However, the authors were not able to identify the nature of the target peptide owing to the kind of approach used.…”

“…It is becoming an important model for studies of development and evolution due to its simplified genome and close relationship to vertebrates. To our knowledge, the presence of GnRH/GnRHlike peptides in amphioxus has been reported only after immunohistochemical analysis (18,19) in which the authors reported GnRH presence in the amphioxus nervous system and in the Hatschek's pit. Our aim was 2-fold: first, to ascertain whether or not a peptide with GnRH activity is present in this key animal model, and second, to isolate this peptide to study its evolution at the base of the chordate clade.…”