Cholecystokinin in the central nervous system of the sea lamprey Petromyzon marinus: precursor identification and neuroanatomical relationships with other neuronal signalling systems

Abstract

Cholecystokinin (CCK) is a neuropeptide that modulates processes such as digestion, satiety and anxiety. CCK-type peptides have been characterized in jawed vertebrates and invertebrates, but little is known about CCK-type signalling in the most ancient group of vertebrates, the agnathans. Here we have cloned and sequenced a cDNA encoding a sea lamprey (Petromyzon marinus L.) CCK-type precursor (PmCCK), which contains a CCK-type octapeptide sequence (PmCCK-8) that is highly similar to gnathostome CCKs. Using mRNA in situ hybridization, the distribution of PmCCK-expressing neurons was mapped in the CNS of P. marinus. This revealed PmCCK-expressing neurons in the hypothalamus, posterior tubercle, prethalamus, nucleus of the medial longitudinal fasciculus, midbrain tegmentum, isthmus, rhombencephalic reticular formation and the putative nucleus of the solitary tract. Some PmCCK-expressing neuronal populations were only observed in adults, revealing 3 important differences with larvae. We generated an antiserum to PmCCK-8 to enable immunohistochemical analysis of CCK expression, which revealed that GABA or glutamate, but not serotonin, tyrosine hydroxylase or neuropeptide Y, are co-expressed in some PmCCK-8-immunoreactive (ir) neurons. Importantly, this is the first demonstration of co-localization of GABA and CCK in neurons of a non-mammalian vertebrate. We also characterized extensive cholecystokinergic fibre systems of the CNS, including innervation of habenular subnuclei. A conspicuous PmCCK-8-ir tract ascending in the lateral rhombencephalon selectively innervates a glutamatergic population in the dorsal isthmic grey. Interestingly, this tract is reminiscent of the secondary gustatory/visceral tract of teleosts. In conclusion, this study provides important new information on the evolution of the cholecystokinergic system in vertebrates.

From gut microbiota to host appetite: gut microbiota-derived metabolites as key regulators

“…In addition, the majority of studies demonstrating the effects of GABA on host health focus on dietary GABA rather than host endogenic GABA. The rumen-protected GABA supplementation increases feed intake and inhibits CCK signaling in growing lambs and cows [155,156], which may be because GABA is co-expressed and shares the similar signal transduction pathways with CCK [150,156,157]. Thus, it does appear to be reasonable to hypothesize that GABA might be involved in the appetite control via acting on its receptors in the gastrointestinal tract and brain, which in turn influences the secretion of gut hormones and activates central neurons, respectively.…”

Ancient role of sulfakinin/cholecystokinin-type signalling in inhibitory regulation of feeding processes revealed in an echinoderm

“…It is also noteworthy that CCK is one of the most abundantly expressed neuropeptides in the cortex of the mammalian brain, where it is expressed by sub-populations of GABAergic interneurons and acts as a multi-functional molecular switch to regulate the output of cortical neuronal circuits ( Lee and Soltesz, 2011 ). Furthermore, evidence that expression of CCK in GABAergic neurons is an evolutionarily ancient association was provided by a recent study reporting co-localisation of CCK-8 and GABA in several different neuronal populations in the brain of the sea lamprey Petromyzon marinus ( Sobrido-Cameán et al, 2020 ). GABA-immunoreactive neurons have been revealed in the ectoneural region of the radial nerve cord in A. rubens ( Newman and Thorndyke, 1994 ) and sub-populations of these neurons may correspond with cells expressing SK/CCK-type neuropeptides reported in this study.…”

Expression of Urocortin 3 mRNA in the Central Nervous System of the Sea Lamprey Petromyzon marinus

“…Digoxigenin (DIG)-labeled riboprobes were synthesized using the amplified fragments as templates and following standard protocols using a T7 polymerase (Nzytech, Lisbon, Portugal). In situ hybridization (ISH) experiments with the sea lamprey Ucn3 DIG-labeled riboprobe (1 µg/mL) were performed as previously described for other neuropeptide riboprobes in the sea lamprey [32][33][34] using cryostat transverse sections of larval, juvenile and adult brains/rostral spinal cords. No staining was observed in the sections incubated with the sense probe (not shown).…”