A candidate of organum vasculosum of the lamina terminalis with neuronal connections to neurosecretory preoptic nucleus in eels

Cladistians are a group of basal nonteleost actinopterygian fishes that represent an interesting group for the study of primitive brain features, most likely present in the ancestral Osteichthyes. We have investigated the catecholaminergic (CA) systems in the brain of two representative cladistian species, the bichir Polypterus senegalus and the reedfish Erpetoichthys calabaricus, by means of antibodies against tyrosine hydroxylase (TH; the first enzyme in the synthesis of catecholamines) and dopamine (DA). Double immunohistofluorescence was performed for simultaneous detection of TH with nitric oxide synthase, choline acetyltransferase, calbindin, calretinin, and serotonin, aiming to accurately establish the localization of the CA neurons and to assess possible interactions between these neuroactive substances. All forebrain CA groups of cladistians are dopaminergic, whereas noradrenergic cells are located within the rhombencephalon. Distinct groups of DA immunoreactive (DA‐ir) cells were observed in the olfactory bulb, subpallium, and preoptic area of the telencephalon. Hypothalamic groups were detected in the suprachiasmatic nucleus, retrotuberal and retromamillary areas and, in particular, the paraventricular organ showed immunoreactivity to dopamine but not to TH. Diencephalic DA‐ir groups were detected in the prethalamus, posterior tubercle, and pretectum. A small DA‐ir cell population was observed in the midbrain tegmentum only in Polypterus. CA cell groups were also located in the locus coeruleus, solitary tract nucleus, and area postrema within the rhombencephalon, the spinal cord, and the retina. The comparison of these results with other vertebrates, using a neuromeric analysis, shows highly conserved traits in all vertebrates studied but also evidences particular characteristics of actinopterygian fishes.

Section: Discussionmentioning

confidence: 99%

Organization of the catecholaminergic systems in two basal actinopterygian fishes, Polypterus senegalus and Erpetoichthys calabaricus (Actinopterygii: Cladistia)

López

Lozano

Morona

et al. 2018

“…Within the alar part of the hypothalamus, the paraventricular region of lungfishes virtually lacks dopaminergic cells and houses the magnocellular nucleus that provides vasotocin and mesotocin to the hypophysis (Goossens, Dierickx, & Vandesande, ; González & Northcutt, ). The only cells were located in the organo vasculosum, as defined for some teleosts (Mukuda et al, ) and urodeles (Corio, Thibault, & Peute, ; Morona & González, ). In contrast, the preoptic magnocellular nucleus of teleosts also typically contains some dopaminergic cells (Yamamoto et al, ; Karoubi et al, ).…”

Section: Discussionmentioning

confidence: 99%

Organization of the catecholaminergic systems in the brain of lungfishes, the closest living relatives of terrestrial vertebrates

López

González

2017

Lungfishes are a group of sarcopterygian fishes currently considered the closest living relatives of tetrapods, and represent an interesting group for the study of evolutionary traits in the transition from fishes to tetrapods. Catecholaminergic systems in the brain are among the most carefully analyzed neurotransmitter systems in the brain of most vertebrate groups. Their organization shows major shared characteristics, although traits particular to each vertebrate class have also been found, primarily between anamniotes and amniotes. Given the relevance of lungfishes in evolutionary terms, the present study provides the first comprehensive and detailed map of the catecholaminergic structures in the brain of two representative species of lungfishes, an African lungfish (Protopterus dolloi) and the Australian lungfish (Neoceratodus forsteri), as revealed by immunohistochemistry. Distinct groups of catecholaminergic cells were observed in the olfactory bulb, pallium, and preoptic area of the telencephalon, and the subpallium is devoid of these cells. Hypothalamic and diencephalic groups were detected and, in particular, the dopaminergic nucleus of the periventricular organ was evidenced with dopamine antibodies but not with anti-tyrosine hydroxylase. A well developed mesostriatal system was revealed formed by conspicuous groups of dopamine cells in the midbrain tegmentum and profuse innervation of the subpallium. Comparison of these results with those from other classes of vertebrates shows numerous common traits shared by most groups and also highlights particular features in lungfishes different from actinopterygian fishes that resemble those of amphibians and amniotes.

“…Distinct TRH‐immunoreactive neurons were seen in the OVLT, consistent with observations in the juvenile but not in the adult S. trutta fario (Díaz et al, ) and in the chick OVLT during embryonic development (Thommes, Caliendo, & Woods, ). OVLT neurons in Anguilla japonica project to vasotocin neurons in the NPO (Mukuda et al, ), raising the possibility for a role of TRH in osmotic regulation. The EN of C. batrachus and other teleosts contain NPY‐ and CART‐expressing neurons (Mazumdar et al, ; Sakharkar, Singru, Sarkar, & Subhedar, ; Singru et al, ).…”

Section: Discussionmentioning

confidence: 99%

Thyrotropin‐releasing hormone (TRH) in the brain and pituitary of the teleost, Clarias batrachus and its role in regulation of hypophysiotropic dopamine neurons

Singh

Pradhan

Nagalakashmi

et al. 2018

Thyrotropin‐releasing hormone (TRH) regulates the hypothalamic–pituitary–thyroid axis in mammals and also regulates prolactin secretion, directly or indirectly via tuberoinfundibular dopamine neurons. Although TRH is abundantly expressed in teleost brain and believed to mediate neuronal communication, empirical evidence is lacking. We analyzed pro‐TRH‐mRNA expression, mapped TRH‐immunoreactive elements in the brain and pituitary, and explored its role in regulation of hypophysiotropic dopamine (DA) neurons in the catfish, Clarias batrachus. Partial pro‐TRH transcript from C. batrachus transcriptome showed six TRH progenitors repeats. Quantitative real‐time polymerase chain reaction (qRT‐PCR) identified pro‐TRH transcript in a number of different brain regions and immunofluorescence showed TRH‐immunoreactive cells/fibers in the olfactory bulb, telencephalon, preoptic area (POA), hypothalamus, midbrain, hindbrain, and spinal cord. In the pituitary, TRH‐immunoreactive fibers were seen in the neurohypophysis, proximal pars distalis, and pars intermedia but not rostral pars distalis. In POA, distinct TRH‐immunoreactive cells/fibers were seen in nucleus preopticus periventricularis anterior (NPPa) that demonstrated a significant increase in TRH‐immunoreactivity when collected during preparatory and prespawning phases, reaching a peak in the spawning phase. Although tyrosine hydroxylase (TH)‐immunoreactive neurons in NPPa are hypophysiotropic, none of the TRH‐immunoreactive neurons in NPPa accumulated neuronal tracer DiI following implants into the pituitary. However, 87 ± 1.6% NPPa TH‐immunoreactive neurons were surrounded by TRH‐immunoreactive axons that were seen in close proximity to the somata. Superfused POA slices treated with TRH (0.5–2 μM) significantly reduced TH concentration in tissue homogenates and the percent TH‐immunoreactive area in the NPPa. We suggest that TRH in the brain of C. batrachus regulates a range of physiological functions but in particular, serves as a potential regulator of hypophysiotropic DA neurons and reproduction.