Comparative analysis of neuropeptide FF-like immunoreactivity in the brain of anuran (Rana perezi, Xenopus laevis) and urodele (Pleurodeles waltl) amphibians

To hum or not to hum: Neural transcriptome signature of male courtship vocalization in a teleost fish

For many animal species, vocal communication is a critical social behavior and often a necessary component of reproductive success. Additionally, vocalizations are often demanding motor acts. Wanting to know whether a specific molecular toolkit might be required for vocalization, we used RNA-sequencing to investigate neural gene expression underlying the performance of an extreme vocal behavior, the courtship hum of the plainfin midshipman fish (Porichthys notatus). Single hums can last up to 2 h and may be repeated throughout an evening of courtship activity. We asked whether vocal behavioral states are associated with specific gene expression signatures in key brain regions that regulate vocalization by comparing transcript expression levels in humming versus non-humming males. We find that the circadian-related genes period3 and Clock are significantly upregulated in the vocal motor nucleus and preoptic area-anterior hypothalamus, respectively, in humming compared with non-humming males, indicating that internal circadian clocks may differ between these divergent behavioral states. In addition, we identify suites of differentially expressed genes related to synaptic transmission, ion channels and transport, neuropeptide and hormone signaling, and metabolism and antioxidant activity that together may support the neural and energetic demands of humming behavior. Comparisons of transcript expression across regions stress regional differences in brain gene expression, while also showing coordinated gene regulation in the vocal motor circuit in preparation for courtship behavior. These results underscore the role of differential gene expression in shifts between behavioral states, in this case neuroendocrine, motor and circadian control of courtship vocalization.

Tyrosine hydroxylase-immunoreactive neurons in the brain of tadpole of the narrow mouthed frog Microhyla ornata

Catecholamines serve as a neuromodulators of many behavioral and endocrine responses in different vertebrates including amphibians. However, the neuroanatomical studies on catecholamines, especially in the tadpole brain are limited. In this study, we report the distribution of catecholaminergic neurons in different areas of the brain in the tadpole of Microhyla ornata at metamorphic climax stage. Application of antisera against tyrosine hydroxylase (TH) revealed the presence of catecholaminergic cells and fibres in the olfactory bulb, the telencephalon, the diencephalon, the mesencephalon, the spinal cord and the pituitary gland. Whereas densest aggregations of TH-immunoreactive (TH-ir) fibres were noticed in the nucleus accumbens and the amygdala pars medialis regions of the telencephalon, highest population of TH-ir cells with dorsolaterally and rostrocaudally oriented fibres was observed in the preoptic area. Larger and distinct TH-ir cell bodies along with few dorsolaterally oriented TH-ir fibres were scattered throughout the suprachiasmatic nucleus. While moderate to intensely stained clusters of TH-ir cells were observed in dorsal and ventral hypothalamic regions, conspicuous TH-ir cells and fibres were seen in the pars distalis of the pituitary gland. In the nucleus tuberculi posterioris, numerous moderate sized TH-ir cells were found along the margin of the third ventricle and the fibres from this region were oriented dorsolaterally towards the torus semicircularis and tectal regions, whereas well organized largest TH-ir cells and fibres were seen in the tegmentum. In the spinal cord, medium sized TH-ir cells along with numerous laterally running fibres were encountered. Overall, widespread distribution of the TH-ir cells and fibres in the brain and the pituitary gland of the tadpole suggest diverse roles for the catecholamines in regulation of locomotion, olfaction, skin pigmentation and endocrine responses during final stages of metamorphosis in M. ornata.

Neuroanatomical Organization of the Brain Gonadotropin-Inhibitory Hormone and Gonadotropin-Releasing Hormone Systems in the Frog Pelophylax esculentus

Growing evidence suggests that gonadotropin-inhibitory hormone (GnIH) may play a key role in mediating vertebrate reproduction. GnIH inhibits gonadotropin synthesis and release by decreasing the activity of gonadotropin-releasing hormone (GnRH) neurons as well as by directly regulating gonadotropin secretion from the pituitary. Whereas the presence of GnIH has been widely investigated in various classes of vertebrates, there are very few immunohistochemical reports focusing on GnIH in amphibians. The aim of this study was to assess the presence and neuroanatomical distribution of GnIH-like immunoreactivity in the brain of the anuran amphibian Pelophylax (Rana) esculentus (esculenta) and to explore any potential anatomical relationship with mammalian GnRH-immunoreactive (mGnRH-ir) elements. The GnIH-like immunoreactive (GnIH-ir) system constitutes two distinct subpopulations in the telencephalon and diencephalon, with the highest number of immunoreactive cells located in the preoptic and suprachiasmatic areas. GnIH-ir neurons were also observed in the medial septum, the anterior commissure, the dorsal hypothalamus, the periventricular nucleus of the hypothalamus, and the posterior tuberculum. Scattered GnIH-ir fibers were present in all major subdivisions of the brain but only occasionally in the median eminence. mGnRH-ir neurons were distributed in the mediobasal telencephalon, the medial septal area, and the anterior preoptic area. Double-label immunohistochemistry revealed that the GnRH and GnIH systems coexist and have overlapping distributions at the level of the anterior preoptic area. Some GnIH-ir fibers were in close proximity to mGnRH-ir cell bodies. Our results suggest that both the neuroanatomy and the functional regulation of GnRH release are conserved properties of the hypothalamic GnIH-ir system among vertebrate species.

RFamide Peptides in Early Vertebrate Development

RFamides (RFa) are neuropeptides involved in many different physiological processes in vertebrates, such as reproductive behavior, pubertal activation of the reproductive endocrine axis, control of feeding behavior, and pain modulation. As research has focused mostly on their role in adult vertebrates, the possible roles of these peptides during development are poorly understood. However, the few studies that exist show that RFa are expressed early in development in different vertebrate classes, perhaps mostly associated with the central nervous system. Interestingly, the related peptide family of FMRFa has been shown to be important for brain development in invertebrates. In a teleost, the Japanese medaka, knockdown of genes in the Kiss system indicates that Kiss ligands and receptors are vital for brain development, but few other functional studies exist. Here, we review the literature of RFa in early vertebrate development, including the possible functional roles these peptides may play.

Sonic hedgehog expression during Xenopus laevis forebrain development

We have analyzed the developing expression pattern of x-Shh in the Xenopus forebrain, interpreting the results within the framework of the neuromeric model to assess evolutionary trends and clues. To achieve this goal, we have characterized phenotypically the developing x-Shh expressing forebrain subdivisions and neurons by means of the combination of in situ hybridization for x-Shh and immunohistochemistry for the detection of forebrain essential regulators and markers, such as the homeodomain transcription factors Islet 1, Orthopedia, NKX2.1 and NKX2.2 and tyrosine hydroxylase. Substantial evidence was found for x-Shh expression in the telencephalic commissural preoptic area and this is strongly correlated with the presence of a pallidum and/or a basal telencephalic cholinergic system. In the diencephalon, x-Shh was demonstrated in the zona limitans intrathalamica and the x-Shh expressing cells were extended into the prethalamus. Throughout development and in the adult hypothalamic x-Shh expression was strong in basal regions but, in addition, in the alar suprachiasmatic region. The findings obtained in the forebrain of Xenopus revealed a largely conserved pattern of Shh expression among tetrapods. However, interesting differences were also noted that could be related to evolutive changes in forebrain organization.

Comparative immunohistochemical analysis of the distribution of orexins (hypocretins) in the brain of amphibians

The orexins (hypocretins) are peptides found primarily in neurons of the hypothalamus of all vertebrates. Many differences were reported about the precise location of orexin containing cells and their projections throughout the brain in different species. However, there are few direct cross-species comparisons. Previous studies in anuran amphibians have also reported notable species differences. We examined and directly compared the distribution of orexinergic neurons and fibers within the brains of representatives of the three amphibian orders, anurans, urodeles and gymnophionans. Simultaneous detection of orexins and tyrosine hydroxylase was used to assess the precise location of the orexins in the brain and to evaluate the possible influence of the orexin system on the catecholaminergic cell groups. Although some differences were noted, a common pattern for the distribution of orexins in amphibians was observed. In all species, most immunoreactive neurons were observed in the suprachiasmatic nucleus, whereas the cells in the preoptic area and the tuberal region were more variable. Orexin immunoreactive fibers in the brain of all species included abundant fibers throughout the preoptic area and hypothalamus, whereas moderate amounts of fibers were present in the pallium, striatum, septum, thalamus, optic tectum, torus semicircularis, rhombencephalon and spinal cord. The use of double immunohistochemistry in amphibians revealed orexinergic innervation in dopaminergic and noradrenergic cell groups, such as the midbrain tegmentum, locus coeruleus and nucleus of the solitary tract, as was previously reported in mammals.

Distribution of neuropeptide FF-like immunoreactive structures in the lamprey central nervous system and its relation to catecholaminergic neuronal structures

The neuropeptide FF (NPFF) is an octapeptide of the RFamide-related peptides (FaRPs) that was primarily isolated from the bovine brain. Its distribution in the CNS has been reported in several mammalian species, as well as in some amphibians. Therefore, in order to gain insight in the evolution on the expression pattern of this neuropeptide in vertebrates, we carried out an immunohistochemical study in the sea lamprey, Petromyzon marinus. The distribution of NPFF-like-immunoreactive (NPFF-ir) structures in the lamprey brain is, in general, comparable to that previously described in other vertebrate species. In lamprey, most of the NPFF-ir cells were found in the hypothalamus, particularly in two large populations, the bed nucleus of the tract of the postoptic commissure and the tuberomammillary area. Numerous NPFF-ir cells were also observed in the rostral rhombencephalon, including a population in the dorsal isthmic gray and the reticular formation. Additional labeled neurons were found inside the preoptic region, the parapineal vesicle, the periventricular mesencephalic tegmentum, the descending trigeminal tract, the nucleus of the solitary tract, as well as in the gray matter of the spinal cord. The NPFF-ir fibers were widely distributed in the brain and the spinal cord, being, in general, more concentrated throughout the basal plate. The presence of NPFF-ir fibers in the lamprey neurohypophysis suggests that the involvement of NPFF-like substances in the hypothalamo-hypophyseal system had emerged early during evolution.

Spatiotemporal sequence of appearance of NPFF-immunoreactive structures in the developing central nervous system of Xenopus laevis

Neuropeptide FF-like immunoreactive (NPFFir) cells and fibers were analyzed through development of Xenopus laevis. The first NPFFir cells appeared in the embryonic hypothalamus, which projected to the intermediate lobe of the hypophysis, the brainstem and spinal cord. Slightly later, scattered NPFFir cells were present in the olfactory bulbs and ventral telencephalon. In the caudal medulla, NPFFir cells were observed in the nucleus of the solitary tract only at embryonic and early larval stages. Abundant NPFFir cells and fibers were demonstrated in the spinal cord. The sequence of appearance observed in Xenopus shares many developmental features with mammals although notable differences were observed in the telencephalon and hypothalamus. In general, NPFF immunoreactivity developed earlier in amphibians than in mammals.

Evolutionary origin and divergence of PQRFamide peptides and LPXRFamide peptides in the RFamide peptide family. Insights from novel lamprey RFamide peptides

Among the RFamide peptide groups, PQRFamide peptides, such as neuropeptide FF (NPFF) and neuropeptide AF (NPAF), share a common C-terminal Pro-Gln-Arg-Phe-NH(2) motif. LPXRFamide (X = L or Q) peptides, such as gonadotropin-inhibitory hormone (GnIH), frog growth hormone-releasing peptide (fGRP), goldfish LPXRFamide peptide and mammalian RFamide-related peptides (RFRPs), also share a C-terminal Leu-Pro-Leu/Gln-Arg-Phe-NH(2) motif. Such a similar C-terminal structure suggests that these two groups may have diverged from a common ancestral gene. In this study, we sought to clarify the evolutionary origin and divergence of these two groups, by identifying novel RFamide peptides from the brain of sea lamprey, one of only two extant groups of the oldest lineage of vertebrates, Agnatha. A novel lamprey RFamide peptide was identified by immunoaffinity purification using the antiserum against LPXRFamide peptide. The lamprey RFamide peptide did not contain a C-terminal LPXRFamide motif, but had the sequence SWGAPAEKFWMRAMPQRFamide (lamprey PQRFa). A cDNA of the precursor encoded one lamprey PQRFa and two related peptides. These related peptides, which also had the C-terminal PQRFamide motif, were further identified as mature endogenous ligands. Phylogenetic analysis revealed that lamprey PQRFamide peptide precursor belongs to the PQRFamide peptide group. In situ hybridization demonstrated that lamprey PQRFamide peptide mRNA is expressed in the regions predicted to be involved in neuroendocrine and behavioral functions. This is the first demonstration of the presence of RFamide peptides in the agnathan brain. Lamprey PQRFamide peptides are considered to have retained the most ancestral features of PQRFamide peptides.

Distribution of Neuropeptide FF-Like Immunoreactivity in the Brain of Dermophis mexicanus (Amphibia; Gymnophiona): Comparison with FMRFamide Immunoreactivity

Neuropeptide FF (NPFF) is an FMRFamide-related peptide widely distributed in the mammalian brain. NPFF immunohistochemistry labeled cell bodies in a few locations and dense fiber networks throughout the brain. Recently, the distribution of NPFF immunoreactive (NPFF-ir) cells and fibers in the brain of anuran and urodele amphibians was studied and, as in mammals, significant species differences were noted. To further assess general and derived features of the NPFF-containing neuron system in amphibians, we have investigated the distribution of NPFF-ir cell bodies and fibers in the brain of the gymnophionan Dermophis mexicanus by means of an antiserum against bovine NPFF. This distribution was compared to that of FMRFamide immunoreactivity. Major traits shared with anurans and urodeles were the abundant fiber labeling in the ventral telencephalon, hypothalamus, isthmus, ventrolateral medulla and dorsal spinal cord. In addition, in the three amphibian orders the majority of the NPFF-ir cells were located in the preoptic-hypothalamic region. However, distinct particular features were present in the gymnophionan such as the lack of NPFF-ir cells in the telencephalon, brainstem and spinal cord and the absence of NPFF-ir fibers in the hypophysis and the olfactory bulbs. This pattern was distinct from that observed for FMRFamide distribution. Striking differences were noted in the pallium, caudal hypothalamus and midbrain tegmentum where FMRFamide-containing cells were localized. The present results in Dermophis support the idea that data from gymnophionans must be included when stating the amphibian condition of a given system because important variations are obvious when gymnophionans are compared with anurans and urodeles.

The common organization of the amygdaloid complex in tetrapods: new concepts based on developmental, hodological and neurochemical data in anuran amphibians

Research over the last few years has demonstrated that the amygdaloid complex in amniotes shares basic developmental, hodological and neurochemical features. Furthermore, homolog territories of all main amygdaloid subdivisions have been recognized among amniotes, primarily highlighted by the common expression patterns for numerous developmental genes. With the achievement of new technical approaches, the study of the precise neuroanatomy of the telencephalon of the anuran amphibians has been possible, revealing that most of the structures present in amniotes are recognizable in these anamniotes. Thus, recent investigations have yielded enough results to support the notion that the organization of the anuran amygdaloid complex includes subdivisions with origin in ventral pallial and subpallial territories, a strong relationship with the vomeronasal and olfactory systems, abundant intra-amygdaloid connections, a main output center involved in the autonomic system, profuse amygdaloid fiber systems, and distinct chemoarchitecture. When all these new data about the development, connectivity and neurochemistry of the amygdaloid complex in anurans are taken into account, it becomes patent that a basic organization pattern is shared by both amniotic and anamniotic tetrapods.

Distribution of neuropeptide FF-like immunoreactivity in the brain of the lizardGekko gecko and its relation to catecholaminergic structures

The present study provides a detailed description of the distribution of neuropeptide FF (NPFF)-like immunoreactivity in the brain of the lizard Gekko gecko. NPFF is found to be involved in nociception, cardiovascular regulation, and endocrine function. Because of its known relationship with catecholamines in mammals, double staining with tyrosine hydroxylase (TH) antibodies was used to corroborate this for reptiles. The present study revealed that NPFF-like-immunoreactive (NPFF-ir) cells and fibers were widely distributed throughout the brain. Major NPFF-ir cell groups were observed in the diagonal band nucleus of Broca, hypothalamus, and dorsal horn of the spinal cord. Additional cells were found in the anterior olfactory nucleus, lateral and dorsal cortices, dorsolateral septum, and diencephalic intergeniculate leaflet formation. Dense plexuses of NPFF-ir fibers were identified in the diagonal band nucleus of Broca, septum, preoptic and hypothalamic areas, isthmic region, ventrolateral tegmentum, solitary tract nucleus, and dorsolateral funiculus of the spinal cord. Extensive fiber staining also occurred in the nucleus accumbens and the midbrain tectum. Although an intimate relationship between NPFF-ir and TH-ir structures was obvious at many places in the brain, colocalization of these two substances was not observed. In conclusion, the distribution of NPFF in the brain of Gekko shares more features with anamniotes in terms of number of cell groups, more elaborate networks of fibers, and lack of colocalization with catecholamines than with mammals, suggesting a decrease in the distribution of this peptide in the latter vertebrate group.

LIM-homeodomain genes as territory markers in the brainstem of adult and developing Xenopus laevis

We investigated expression patterns of the LIM-homeodomain (LIM-hd) genes x-Lhx1, x-Lhx2, x-Lhx5, and x-Lhx9 in the brainstem of Xenopus laevis during larval development and in the adult. The two groups of paralogous genes, x-Lhx1/x-Lhx5 and x-Lhx2/x-Lhx9, showed fundamentally different expression patterns, being expressed in ventral versus dorsal territories of the midbrain and hindbrain, respectively. Indeed, prominent expression of x-Lhx1/5 was found in the mesencephalic tegmentum and the hindbrain reticular formation, whereas conspicuous x-Lhx2/9 expression was observed in the torus semicircularis and isthmic nucleus. A few shared expression domains for the two pairs of paralogs included the optic tectum and the anterodorsal and pedunculopontine nuclei. In each structure, expression of the two paralogs was almost identical, indicating that the regulation of their expression in this part of the brain has evolved slightly since gene duplication occurred. Notable exceptions included the expression of x-Lhx1 but not x-Lhx5 in the Purkinje cells and the expression of x-Lhx9 but not x-Lhx2 in the lateral line nucleus. The analysis of LIM-hd expression patterns throughout development allowed the origin of given structures in early embryos to be traced back. x-Lhx1 and x-Lhx5 were relevant to locate the cerebellar anlage and to follow morphogenesis of the cerebellar plate and cerebellar nuclei. They also highlighted the rhombomeric organization of the hindbrain. On the other hand, x-Lhx2 and x-Lhx9 showed a dynamic spatiotemporal pattern relative to tectal development and layering, and x-Lhx9 was useful to trace back the origin of the isthmus in early development.

Comparative Immunohistochemical Study of Carassius RFamide Localization in Teleost Guts in Different Salinity Habitats

Carassius RFamide (C-RFa) is a peptide, isolated originally from the brain of Japanese crucian carp and sharing homologies with mammalian prolactin-releasing peptides. From the physiological aspect, it is known that C-RFa has contraction-promoting action on fish intestines, but its localization in peripheral tissues is unknown. We observed the localization of C-RFa in teleost guts using an immunohistochemical technique. C-RFa-like immunoreactive (irC-RFa) sites were observed in not only the smooth muscle cells in the longitudinal muscle layer, but also in both Auerbach's and Meissner's nerve plexus in the stomach, pyloric ceca and intestine. In epithelial mucous cells, irC-RFa sites were observed in the surface mucous cells in the stomach in freshwater fish (FW), and in the goblet cells of the apical sites in the villi of the pyloric ceca and intestine in all fish. In the stomach, irC-RFa sites were found in the fundic glands of the body regions in seawater (SW) and brackish water (BW) fish, but not in FW fish. This study confirmed that one of the functions of C-RFa is the smooth muscle contraction of the longitudinal muscle layer in digestive organs. We suggest that C-RFa may have functional roles in both central and peripheral neurotransmission. In addition, it appears that the difference in C-RFa localization of SW, BW, and FW fish reflects the adaptation of the stomach function to different salinity habitats.

Hodological characterization of the medial amygdala in anuran amphibians

Early studies in anuran amphibians defined the amygdala as a single unit that only later could be subdivided into medial and lateral parts with the achievement of sensitive immunohistochemical and tracing techniques. However, the terminology used was often misleading when comparing with "homologous" amygdaloid nuclei in amniotes. Recently, the basal telencephalon of anurans has been demonstrated to be more complex than previously thought, and distinct amygdaloid nuclei were proposed on the basis of immunohistochemistry. Moreover, developmental data are increasing that support this notion. In the present study, we analyzed the patterns of afferent and efferent connections of the medial amygdala (MeA; formerly amygdala pars lateralis), considered as the main target of the vomeronasal information from the accessory olfactory bulb, as in other vertebrates. By means of axonal transport of dextran amines, the afferent and efferent connections of the MeA were traced in Rana perezi and Xenopus laevis under in vivo and in vitro conditions. Largely similar results were found in both species. The results showed abundant intratelencephalic and extratelencephalic connections that were readily comparable to those of other tetrapods. Most of these connections were reciprocal and, in particular, the strong relation of the MeA with the hypothalamus, via the stria terminalis, was demonstrated. Immunohistochemical techniques showed staining patterns that revealed abundant peptidergic afferents to the MeA, as well as minor inputs containing other neurotransmitters such as catecholamines. Double-labeling experiments demonstrated that the peptidergic fibers that reach the MeA originate in the ventral hypothalamus, whereas the catecholaminergic innervation of the MeA arises in the caudal extent of the posterior tubercle. Taken together, the results about connectivity in our study support the comparison of the MeA in anurans with its counterparts (and similarly named) amygdaloid nuclei in amniotes. Most of the hodological features of the medial amygdala seem to be shared by those tetrapods with well-developed vomeronasal systems.