FMRFamide in the amphibian brain: A comprehensive survey

Abstract

Mapping of FMRFamidergic neural circuitry in the amphibian brain has been done by immunohistochemical methods. Comparative evidence suggests that there are similarities and differences in the overall pattern of distribution of FMRFamide-ir elements in the brain among the three amphibian orders and within each order. FMRFamide is expressed in neurons in some circumscribed areas of the brain. A part of these neurons is concentrated in classical neurosecretory areas of the hypothalamus in a bilaterally symmetrical fashion. Similar neurons occur occasionally in the midbrain, but are virtually absent from the hindbrain. Anurans are unique among amphibians to show FMRFamide neurons in the medial septum and diagonal band of Broca. A viviparous gymnophione is known to possess a small population of such neurons in the dorsal thalamus. Together, the FMRFamide neurons contribute to an extensive fiber network throughout the amphibian brain. Descriptive developmental studies suggest that the rostral forebrain-located FMRFamide neurons originate in the olfactory placode and then migrate into the brain along the route of the vomeronasal-olfactory-terminal nerve complex. Olfactory placodal ablation in an anuran and a urodele provide experimental support to this contention. Other FMRFamide neuronal cell groups, in the hypothalamus and dorsal thalamus, are supposed to arise from non-placodal precursors. The neuroanatomical distribution (projection of immunoreactive processes to areas of the fore-, mid-, and hindbrain as well as to cerebrospinal fluid, co-localization with other neuropeptides, and presence in the median eminence) has furnished morphological correlates of possible functions of FMRFamide in the amphibian CNS. While amphibian FMRFamide-like or structurally related peptides remain to be isolated and characterized, the sum of the distribution pattern of FMRFamide-like immunoreactivity suggests that it may act as a neurotransmitter or a neuromodulator, and also may have endocrine regulatory functions.

The neuroendocrine system of invertebrates: a developmental and evolutionary perspective

“…The relationship between Drosophila insulin-like peptides and AKH (Kim & Rulifson 2004) is most likely homologous to the antagonism between glucagon and insulin in vertebrates. There exist a number of other neuropeptides, among them FMRFamides (Rastogi et al 2001, Nassel 2002, tachykinins (Nussdorfer & Malendowicz 1998) and CRF/CRF-like diuretic hormone (Schoofs et al 1997, Nassel 2002 found in vertebrate hypothalamus and insect PI.…”

Identification, localization and expression of LPXRFamide peptides, and melatonin-dependent induction of their precursor mRNA in the newt brain

“…The molluscan neuropeptide Phe-Met-Arg-Phe-NH 2 (FMRFa) was discovered in the ganglia of the venus clam (Price & Greenberg 1977), and it was suggested that the vertebrate hypothalamus possesses some unknown neuropeptides similar to FMRFa (Raffa 1988, Rastogi et al 2001). In fact, over the past decade, neuropeptides that have the ArgPhe-NH 2 (RFa) motif at their C-termini have been identified in the brains of several vertebrates.…”

Role of LPXRFamide peptide in the neuroendocrine regulation of reproduction in fish

“…The molluscan cardioexcitatory neuropeptide Phe-Met-Arg-Phe-NH2 (FMRFamide) was first found in the ganglia of the venus clam Macrocallista nimbosa [47], and RFamide peptides were subsequently characterized in various other invertebrates. Immunohistochemical studies using an antiserum against FMRFamide suggested the presence of uncharacterized RFamide peptides in vertebrate nervous systems [49,50]. Some of the FMRFamide-like immunoreactive neurons were seen to project to the hypothalamic region close to the pituitary gland, and were thus predicted to play a role in the regulation of pituitary function.…”