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

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.

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.

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 somatostatin-like immunoreactivity in the brain of the caecilian Dermophis mexicanus (Amphibia: Gymnophiona): comparative aspects in amphibians

The organization of the somatostatin-like-immunoreactive (SOM-ir) structures in the brain of anuran and urodele amphibians has been well documented, and significant differences were noted between the two amphibian orders. However, comparable data are not available for the third order of amphibians, the gymnophionans (caecilians). In the present study, we analyzed the anatomical distribution of SOM-ir cells and fibers in the brain of the gymnophionan Dermophis mexicanus. In addition, because of its known relationship with catecholamines in other vertebrates, double immunostaining for SOM and tyrosine hydroxylase was used to investigate this situation in the gymnophionan. Abundant SOM-ir cell bodies and fibers were widely distributed throughout the brain. In the telencephalon, pallial and subpallial cells were labeled, being most numerous in the medial pallium and amygdaloid region. Most of the SOM-ir neurons were found in the preoptic area and hypothalamus and showed a clear projection to the median eminence. Less conspicuously, SOM-ir structures were found in the thalamus, tectum, tegmentum, and reticular formation. Both SOM-ir cells and fibers were demonstrated in the spinal cord. The double-immunohistofluorescence technique revealed that catecholaminergic neurons and SOM-ir cells are largely intermingled in many brain regions but form totally separated populations. Many differences were found between the distribution of SOM-ir structures in Dermophis and that in anurans or urodeles. Some features were shared only with anurans, such as the abundant pallial SOM-ir cells, whereas others were common only to urodeles, such as the organization of the hypothalamohypophysial SOM-ir system. In addition, some characteristics were found only in Dermophis, such as the localization of the SOM-ir spinal cells and the lack of colocalization of catecholamines and SOM throughout the brain. Therefore, any conclusions concerning the SOM system in amphibians are incomplete without considering evidence for gymnophionans.