The Suprachiasmatic Nucleus of the Dromedary Camel (Camelus dromedarius): Cytoarchitecture and Neurochemical Anatomy

Abstract

In mammals, biological rhythms are driven by a master circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Recently, we have demonstrated that in the camel, the daily cycle of environmental temperature is able to entrain the master clock. This raises several questions about the structure and function of the SCN in this species. The current work is the first neuroanatomical investigation of the camel SCN. We carried out a cartography and cytoarchitectural study of the nucleus and then studied its cell types and chemical neuroanatomy. Relevant neuropeptides involved in the circadian system were investigated, including arginine-vasopressin (AVP), vasoactive intestinal polypeptide (VIP), met-enkephalin (Met-Enk), neuropeptide Y (NPY), as well as oxytocin (OT). The neurotransmitter serotonin (5-HT) and the enzymes tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) were also studied. The camel SCN is a large and elongated nucleus, extending rostrocaudally for 9.55 ± 0.10 mm. Based on histological and immunofluorescence findings, we subdivided the camel SCN into rostral/preoptic (rSCN), middle/main body (mSCN) and caudal/retrochiasmatic (cSCN) divisions. Among mammals, the rSCN is unusual and appears as an assembly of neurons that protrudes from the main mass of the hypothalamus. The mSCN exhibits the triangular shape described in rodents, while the cSCN is located in the retrochiasmatic area. As expected, VIP-immunoreactive (ir) neurons were observed in the ventral part of mSCN. AVP-ir neurons were located in the rSCN and mSCN. Results also showed the presence of OT-ir and TH-ir neurons which seem to be a peculiarity of the camel SCN. OT-ir neurons were either scattered or gathered in one isolated cluster, while TH-ir neurons constituted two defined populations, dorsal parvicellular and ventral magnocellular neurons, respectively. TH colocalized with VIP in some rSCN neurons. Moreover, a high density of Met-Enk-ir, 5-HT-ir and NPY-ir fibers were observed within the SCN. Both the cytoarchitecture and the distribution of neuropeptides are unusual in the camel SCN as compared to other mammals. The presence of OT and TH in the camel SCN suggests their role in the modulation of circadian rhythms and the adaptation to photic and non-photic cues under desert conditions.

Immunohistochemical identification of oxytocin neurons in the suprachiasmatic nucleus of the male and female albino rats:A morphometrical study

“…The OT immune-reactive neurons showed strong brown colour extending sometimes to the processes. This comes in agreement with previous report in camel, OT-ir perikarya were located within the SCN mainly in the ventrolateral part, with round or multipolar soma [4] .…”

“…In Camel, SCN was described as a bilateral aggregation of neurons extending in rostro-caudal direction. Based on histological results, the SCN showed a distinct topography allowing to subdivide it into rostral (rSCN), main body (mSCN) and caudal (cSCN) divisions [4] .…”

The bovine anterior hypothalamus: Characterization of the vasopressin–oxytocin containing nucleus and changes in relation to sexual differentiation

“…The present study found that the SCN of cattle contained sparse NPY‐ir fibers, originating from the geniculate body and transmitting nonphotic information to the SCN (Saderi et al, ), as in the sheep. Calbindin was found anteriorly to the SCN but no neuron body was found in the SCN itself, which is unlike in the camel (El Allali et al, ) and human (Mai et al, ). In humans, the SCN does contain galanin somata (Gai, Geffen, & Blessing, ) while in the rat only a few galanin immunoreactive neurons located in the SCN (Melander et al, ).…”

“…The VIP‐stained bovine SCN was much larger than what is described in Okamura () using Nissl staining and compared to the VIP‐stained human SCN (Zhou, Hofman, & Swaab, , ). The largest part of VIP cell bodies was present in the medioventral part of the bovine SCN as in the human (Swaab et al, ), ovine (Tessonneaud, Cooper, Caldani, Locatelli, & Viguier‐Martinez, ), the camel (El Allali et al, ), and rodent SCN (Abrahamson & Moore, ). This is in contrast with the SCN of the opossum, a marsupial (Cassone, Speh, Card, & Moore, ), in which VIP neurons are localized dorsally.…”

“…This is in contrast with the SCN of the opossum, a marsupial (Cassone, Speh, Card, & Moore, ), in which VIP neurons are localized dorsally. NPY has been described in neurons of the human SCN (Mai, Kedziora, Teckhaus, & Sofroniew, ), while the SCN of rodents (Moore, Gustafson, & Card, ; Moore, Speh, & Leak, ), and the camel (El Allali et al, ), contained only fibers, particularly sparse in the sheep (Tillet, Caldani, & Tramu, ). The present study found that the SCN of cattle contained sparse NPY‐ir fibers, originating from the geniculate body and transmitting nonphotic information to the SCN (Saderi et al, ), as in the sheep.…”