Ontogeny of pituitary adenylate cyclase-activating polypeptide (PACAP) in the frog (Rana ridibunda) tadpole brain: Immunohistochemical localization and biochemical characterization

Abstract

The anatomic distribution and biochemical characteristics of the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) were investigated in the central nervous system of the frog, Rana ridibunda, during development. Three to four days after hatching, at stages IV-VII, PACAP-immunoreactive perikarya were detected in the dorsal thalamus within the anterior ventral area, and a few fibers were found in the medial pallium. Positive cell bodies were first observed in the hypothalamus at stages VIII-IX, at the level of the dorsal and ventral infundibular nuclei. In these regions, the number of positive perikarya increased during ontogeny. In tadpoles, during the mid- and late premetamorphosis, a more complex organization of the PACAP-immunoreactive system was found in the thalamus with the appearance, at stages IX-XII, of two additional groups of positive neurons in the ventrolateral area and posterocentral nucleus. At stages XIII-XVIII of larval development and subsequent larval stages, PACAP-immunoreactive fibers were found in the median eminence. In newly metamorphosed animals, several additional groups of positive perikarya appeared in the medial pallium, the preoptic nucleus, the torus semicircularis, the tegmentum of the mesencephalon, and the cerebellum. The immunoreactive peptide contained in the tadpole brain was characterized by high performance liquid chromatography analysis combined with radioimmunoassay quantification. At all stages investigated, the predominant form of PACAP-immunoreactive material coeluted with synthetic frog PACAP38. The occurrence of PACAP soon after hatching indicates that the peptide may exert neurotrophic activities. The existence of immunoreactive elements in several thalamic regions at mid- and late premetamorphic stages suggests that PACAP may act as a neurotransmitter, neuromodulator, or both, during ontogenesis. Finally, the presence of PACAP-immunoreactive perikarya in hypothalamic nuclei and nerve fibers in the median eminence supports the view that PACAP may play a role in the control of pituitary hormone secretion during larval development.

Pituitary adenylate cyclase‐activating polypeptide and its receptors in amphibians

“…Comparison of the distribution of PACAP-immunoreactivity in tadpoles and adult frogs reveals that PACAP is transiently expressed in the caudal part of the medial pallium and in Purkinje cells (Mathieu et al, 2001;Yon et al, 1992). This observation suggests that, in these structures, PACAP may act as a neurotrophic factor, as previously demonstrated in mammals (Gonzalez et al, 1997;Vaudry et al, 1998;.…”

“…This observation suggests that PACAP may interact with the ANF neuronal system to modulate various functions such as heart rate and hydromineral homeostasis. The transient expression of PACAP in Purkinje cells of frog tadpoles (Mathieu et al, 2001), as previously shown in newborn rats (Nielsen et al, 1998;Skoglösa et al, 1999a), suggests that the peptide may be involved in the control of proliferation, differentiation, and/or migration of nerve cells during development. In support of this hypothesis, it has been shown that PACAP acts as a neurotrophic factor regulating multiplication of nerve cells, neurite outgrowth, and apoptosis in the developing rat brain (Gonzalez et al, 1997;Lu and DiCicco-Bloom, 1997;Lu et al, 1998;Vaudry et al, 1998;.…”

“…Conversely, several populations of PACAP-containing neurons, which are present in the adult frog brain, are not detected during larval development. For instance, PACAP-immunoreactive perikarya are present in the nucleus accumbens septi, the pallial commissure, the bed nucleus of the pallial commissure, the nucleus profondus, and the anteroventral nucleus of the tegmentum in adult frogs (Yon et al, 1992) but are not found in tadpoles or newly metamorphosed animals (Mathieu et al, 2001). These observations, indicate that the maturation of the PACAP neuronal system is not fully completed immediately after metamorphosis but still continues in juvenile animals.…”

“…OF AMPHIBIANS The distribution of PACAP-immunoreactive neurons has been determined in the brain of the frog R. ridibunda during development from premetamorphosis (stage IV) to postmetamorphosis (stage XXV) (Mathieu et al, 2001). Soon after hatching, at stages IV-VII, PACAP-immunoreactive perikarya are exclusively present in the anterior ventral area of the dorsal thalamus.…”

“…Confocal laser scanning microscopy analysis reveals that, in these neurons, PACAP is sequestered in neurosecretory vesicles (Fig. 4). (2) In tadpoles and adult frogs, PACAP-immunoreactive fibers originating from hypothalamic nuclei traverse the infundibulum and terminate in the vascular layer of the median eminence (Mathieu et al, 2001;Yon et al, 1993a). A dense network of PACAP-immunoreactive axons is found in close vicinity of the portal blood capillaries.…”