Rodlet cells in intestinal epithelia of infected and uninfected European eelsAnguilla anguilla from brackish and fresh water were studied by light and electron microscopy. Deropristis inflata (Trematoda) was found in eels from brackish water, whereas eels from fresh water were infected with Acanthocephalus clavula (Acanthocephala). In a comparison between uninfected and infected eels from brackish water, a higher number of rodlet cells was recorded in the intestinal epithelia of infected fish. Evidence is presented that rodlet cells secrete their contents in a holocrine manner into the lumen of the eel intestine. The occurrence of organelles within the mature rodlet cell was rare.1998 The Fisheries Society of the British Isles

Activation of serotonin-1A receptors (5-HT(1A)R) in the medulla oblongata lowers sympathetic nerve discharge and blood pressure. Binding sites for 5-HT(1A)R ligands are present in ventral medullary nuclei [e.g., rostral ventrolateral medulla (RVLM), raphe pallidus (RPa), and parapyramidal region (PPR)] that project to sympathetic preganglionic neurons in the intermediolateral cell column (IML). However, the projections and the neurochemical contents of the ventral medullary neurons that are likely to be involved in the hypotensive actions of 5-HT(1A) agonists are unclear. Using a sheep antibody to a fragment of the third intracellular loop of the 5-HT(1A)R, we localized 5-HT(1A)R immunoreactivity (ir) to IML-projecting neurons that were retrogradely labeled with rhodamine beads injected into the IML of adult male rats. The percentages of IML-projecting neurons containing 5-HT(1A)R-ir were 49% in RPa, 34% in PPR, and 44% in RVLM. Using multiple-immunofluorescence labeling, we also demonstrated 5-HT(1A)R-ir in serotonergic (5-HT) and in catecholaminergic (tyrosine hydroxylase; TH-ir) neurons of the ventral medulla. The percentages of 5-HT-ir neurons containing 5-HT(1A)R-ir were 28% in RPa, 18% in PPR, and 31% in raphe obscurus. In addition, 5-HT(1A)R-ir was present in 14% of TH-ir neurons of the RVLM. Moreover, some IML-projecting neurons in the PPR and RPa were doubly immunolabeled for 5-HT(1A)R-ir and 5-HT, and some IML-projecting neurons in the RVLM were doubly immunolabeled for 5-HT(1A)R-ir and TH-ir. These data provide anatomical evidence for the presence of 5-HT(1A)R on serotonergic and catecholaminergic bulbospinal neurons and for their potential role in directly modifying the activity of these ventral medullary neurons.

This preliminary work was designed to study, using routine procedures for light and transmission electron microscopy, the presence of rodlet cells (RCs) in or near the sensory systems of 12 adult specimens (4.0 6 1.2 cm, LT 6 SD) of zebrafish, Danio rerio Hamilton, 1822. Rodlet cells, characterized by a distinctive cell cortex (range, 0.4-1.5 mm in thickness) and conspicuous inclusions named ''rodlets,'' have a round to ovoid nucleus with irregular outline. Mature RCs are 11.5 6 1.2 mm (mean 6 SD) long and 7.8 6 1.1 mm (mean 6 SD) wide. These cells are more numerous near neuromasts enclosed by an epithelial roof and/or ossified canal wall. In contrast, very few RCs were noticed near superficial neuromasts. Based on the presence of RCs around the two cranial neuromasts of each fish, a variable number from 1 to 15 rodlet cells was found (10.4 6 3.6, mean 6 SD). The RCs were located 1.5 mm (minimal) to 73.3 mm (maximal) from the neuromast (27.9 6 17.2, mean 6 SD). Moreover, RCs were found in olfactory epithelium and in proximity to some taste buds. Interestingly, RCs were absent in the inner ear, eye, and brain. Anat Rec, 290:367-374, 2007. 2007 Wiley-Liss, Inc.

The spatial distribution and histopathological changes induced by metacercariae of the digenean trematode Diplostomum phoxini (Faust, 1918) in the brains of European minnows Phoxinus phoxinus (L.) from the River Endrick, Scotland, were studied by light and electron microscopy. Postmortem examination of a sample of 34 minnows revealed that 50% (n = 17) of the population was infected with 13.7 ± 2.6 (mean ± SE; range 1 to 38) metacercariae per infected host. Serial histological sections of the infected minnow brains revealed that the metacercariae were unevenly distributed throughout the brain, with aggregations occurring in the cerebellum, the medulla oblongata and the optic lobes. In fish with highest intensities of infection, over 40% of the cerebellar area and about 30% of the medulla oblongata area were occupied by larvae. Metacercariae disrupt the integrity of brain tissue, with individuals being found in small pockets surrounded by cellular debris. Metacercariae were rarely encountered on the surface of the brain. Electron microscopic examination of infection sites revealed that the granular layer surrounding metacercariae was necrotic, exhibited nuclear degradation and was marked by vacuolation of the cytoplasm. Rodlet cells, the only inflammatory cell types recorded in this study, were found only in parasitized brains and in close proximity to the teguments of metacercariae. It is hypothesised that secretions released from the teguments of metacercariae are a counter response to protect the metacercariae from the fish brain's cellular defence mechanisms. KEY WORDS: Brain infection · Digenean trematode · Phoxinus phoxinus · Rodlet cells · Histopathology · Ultrastructure Resale or republication not permitted without written consent of the publisherDis Aquat Org 75: [51][52][53][54][55][56][57][58][59] 2007 gata and the optic lobes, centres of the brain that are responsible for host motor activity, sensory functions and vision (Barber et al. 2000, Shirakashi & Goater 2005. Until recently, metacercariae were generally regarded as immature, non-feeding and metabolically inactive stages waiting for transmission to the next/ definitive host (Bush et al. 2001, Poulin & Latham 2003. However, a recent study by Goater et al. (2005) demonstrated via experimental infection that the metacercariae of Ornithodiplostomum ptychocheilus Faust, 1917 in Pimephales promelas Rafinesque, 1820 undergo a series of complex developmental changes associated with their feeding on host brain tissue.A histological examination of Phoxinus phoxinus heads in the current study revealed the presence of rodlet cells only in infected brains, notably in the epithelium lining the ventricles of the optic lobes. It is believed that rodlet cells play a role within the piscine inflammatory response (Dezfuli et al. 2000, Manera & Dezfuli 2004, Reite 2005, Reite & Evensen 2006. We found rodlet cells only within the infected brain of a fish, and our findings are briefly compared with the information available on their presence in other f...

Serotonin (5-hydroxytryptamine, 5-HT) is well known to be involved in many aspects of bivalve biology, especially in the control of reproductive function. In this work, a neurochemical and immunohistochemical study was carried out in the visceral ganglion of Venus verrucosa (Bivalvia: Veneridae), with the aim of elucidating the features of 5-HT neurotransmission and its influence on gamete emission in this poorly investigated bivalve species. 5-HT release was characterized: tritium efflux, evoked from the isolated [3H]5-HT preincubated visceral ganglion by high potassium concentrations, was shown to possess the characteristics of neurotransmitter release (sodium and calcium dependence, auto-feedback regulation). Serotonergic cell bodies and axonal tracts were labelled by immunohistochemistry, confirming that the released 5-HT originates in a pool of neurons in the visceral ganglion. \ud The presence and distribution of serotonin was immunohistochemically checked in the gonads as well. A plexus of immunopositive fibres was observed in the gonadic tissue of both sexes, specifically located in the follicle walls, and this innervation appeared to come from branching of the cerebro-visceral connectives, whereas no peripheral serotonergic neurons were identified. The immunohistochemical data were supported by light and electron microscope observations.\ud Exogenous 5-HT was applied to Venus verrucosa specimens by intramuscular injection; it induced spawning in both sexes; the response rate was significantly higher in males than in females, as previously observed in some other species of gonochoric bivalves. These findings suggest the existence of a serotonergic neurotransmission in Venus verrucosa, possibly regulating the reproductive process