Photic and nonphotic seasonal cues differentially engage hypothalamic kisspeptin and RFamide-related peptide mRNA expression in Siberian hamsters

Seasonally breeding animals use a combination of photic (i.e. day length) and nonphotic (e.g. food availability, temperature) cues to regulate their reproduction. How these environmental cues are integrated is not understood. To assess the potential role of two candidate neuropeptides, kisspeptin and RFamide-related peptide-3 (RFRP), we monitored regional changes in their gene expression in a seasonally breeding mammal exposed to moderate changes in photoperiod and food availability. Adult male Siberian hamsters (Phodopus sungorus) were housed under a long (16 h light/day; 16 L) or intermediate (13.5 L) photoperiod and fed ad lib. or a progressive food restriction schedule (FR; reduced to 80% of ad lib.) for 11 weeks. Gonadal regression occurred only in FR hamsters housed under 13.5 L. Immunohistochemistry was used to identify diencephalic populations of kisspeptin- and RFRP-immunoreactive cells, and quantitative PCR was used to measure gene expression in adjacent coronal brain sections. Photoperiod, but not food availability, altered RFRP mRNA expression in the dorsomedial sections, whereas food availability but not photoperiod altered Kiss1 expression in the arcuate sections; intermediate photoperiods elevated RFRP expression, and food restriction suppressed Kiss1 expression. Regional- and neuropeptide-specific activity of RFamides may provide a mechanism for integration of multi-modal environmental information in the seasonal control of reproduction.

Imaging mass spectrometry of neuropeptides in decapod crustacean neuronal tissues

Imaging mass spectrometry (IMS) of neuropeptides in crustacean neuronal tissues was performed on a MALDI-TOF/TOF instrument. Sample preparation protocols were developed for the sensitive detection of these highly complex endogenous signaling molecules. The neuromodulatory complements of the pericardial organ (PO) and brain of the Jonah crab, Cancer borealis, were mapped. Distributions of peptide isoforms belonging to 10 neuropeptide families were investigated using the IMS technique. Often, neuropeptides of high sequence homology were similarly located. However, two RFamide-family peptides and a truncated orcokinin peptide were mapped to locations distinct from other members of their respective families. Over 30 previously sequenced neuropeptides were identified based on mass measurement. For increased confidence of identification, select peptides were fragmented by post-source decay (PSD) and collisional-induced dissociation (CID). Collectively, this organ-level IMS study elucidates the spatial relationships between multiple neuropeptide isoforms of the same family as well as the relative distributions of neuropeptide families.

The neuromuscular junctions of the slow and the fast excitatory axon in the closer of the crab Eriphia spinifrons are endowed with different Ca2+ channel types and allow neuron-specific modulation of transmitter release by two neuropeptides

Most crustacean muscle fibers receive double excitatory innervation by functionally different motor neurons termed slow and fast. By using specific omega-toxins we show that the terminals of the slow closer excitor (SCE) and the fast closer excitor (FCE) at a crab muscle are endowed with different sets of presynaptic Ca(2+) channel types. omega-Agatoxin, a blocker of vertebrate P/Q-type channels, reduced the amplitude of EPSCs by decreasing the mean quantal content of transmitter release in both neurons by 70-85%, depending on the concentration. We provide the first evidence that omega-conotoxin-sensitive channels also participate in transmission at crustacean neuromuscular terminals and are colocalized with omega-agatoxin-sensitive channels in an axon-type-specific distribution. omega-Conotoxin, a blocker of vertebrate N-type channels, inhibited release by 20-25% only at FCE, not at SCE endings. Low concentrations of Ni(2+), which block vertebrate R-type channels, inhibited release in endings of the SCE by up to 35%, but had little effects in FCE endings. We found that two neuropeptides, the FMRFamide-like DF(2) and proctolin, which occur in many crustaceans, potentiated evoked transmitter release differentially. Proctolin increased release at SCE and FCE endings, and DF(2) increased release only at FCE endings. Selective blocking of Ca(2+) channels by different omega-toxins in the presence of peptides revealed that the target of proctolin-mediated modulation is the omega-agatoxin-sensitive channel (P/Q-like), that of DF(2) the omega-conotoxin-sensitive channel (N-like). The differential effects of these two peptides allows fine tuning of transmitter release at two functionally different motor neurons innervating the same muscle.

The lymnaea cardioexcitatory peptide (LyCEP) receptor: a G-protein-coupled receptor for a novel member of the RFamide neuropeptide family

A novel G-protein-coupled receptor (GRL106) resembling neuropeptide Y and tachykinin receptors was cloned from the mollusc Lymnaea stagnalis. Application of a peptide extract from the Lymnaea brain to Xenopus oocytes expressing GRL106 activated a calcium-dependent chloride channel. Using this response as a bioassay, we purified the ligand for GRL106, Lymnaea cardioexcitatory peptide (LyCEP), an RFamide-type decapeptide (TPHWRPQGRF-NH2) displaying significant similarity to the Achatina cardioexcitatory peptide (ACEP-1) as well as to the recently identified family of mammalian prolactin-releasing peptides. In the Lymnaea brain, the cells that produce egg-laying hormone are the predominant site of GRL106 gene expression and appear to be innervated by LyCEP-containing fibers. Indeed, LyCEP application transiently hyperpolarizes isolated egg-laying hormone cells. In the Lymnaea pericardium, LyCEP-containing fibers end blindly at the pericardial lumen, and the heart is stimulated by LyCEP in vitro. These data confirm that LyCEP is an RFamide ligand for GRL106.