The distribution of vasotocin and mesotocin immunoreactivity in the hypothalamic magnocellular neurosecretory nuclei of the Saharan herbivorous lizard, Uromastix acanthinurus Bell, 1825 (Sauria-Agamidae)

Abstract

An immunohistochemical study of the magnocellular neurosecretory nuclei was performed in the hypothalamus of the desert lizard Uromastix acanthinurus using polyclonal antibodies against arginine vasotocin (AVT), mesotocin (MST) and neurophysins I and II (NpI, NpII). AVT- and MST-immunoreactivities were localized in individual neurons of the supraoptic, periventricular, and paraventricular nuclei and in scattered neurosecretory cells. The supraoptic nuclei (SONs) can be subdivided into rostral, medial and caudal portions. The rostral portion of the SONs was called the SON-ventral aggregation (V SON) because the neurosecretory neurons are present in the ventral part of the hypothalamus along the optic chiasma (OC). Their perikarya and fibres were only AVT-ir. The medial part of the SONs was constituted of two clusters of neurosecretory neurons located in the two lateral ends of the OC to form the SON-lateral aggregations (L SON). In the caudal end of the last one, some MST-ir perikarya appeared. The caudal part of the SONs was constituted of a dorso-lateral aggregation (D SON) of ir-neurons spreading over the lateral forebrain bundle (LFB). AVT- and MST- perikarya were observed in this caudal portion of the SONs, AVT-ir neurons being more numerous. AVTergic and MSTergic magnocellular neurons were present in the periventricular nuclei (PeVNs). Parvocellular and magnocellular AVT- and MST-ir were observed in the paraventricular nuclei (PVNs). The fibres emerging from the magnocellular neurons which belong to these nuclei and the scattered cells ran along the hypothalamic floor and entered the median eminence (ME) to end in the neural lobe of hypophysis. As a rule, immunoreactivity was also observed in all the regions of the forebrain with vasotocinergic and mesotocinergic perikarya and fibres. The immunoreactive distribution was similar to that described in other reptiles.