RESUMEN
Scanning and transmission electron microscopic observations were made on the anterior and posterior lateral line system of larvae of the blind cavefish, Phreatichthys andruzzii. The investigations were conducted on 36 specimens belonging to three different ages of juvenile: 7, 14, and 28 days posthatching. The basic sensory unit of the mechanoreceptive system is a superficial "neuromast," which is composed of sensory hair cells (HCs) embedded in nonsensory support cells (SCs) frequently covered with a cupula. Head neuromasts had the longest cupulae. These organs presented the same structure and ultrastructure in the head and along the body of all specimens of P. andruzzii of different ages. Hair cells of neuromasts of P. andruzzii larvae were pear-shaped cells approximately 10-20 microm high and 3-5 microm in diameter. The nucleus of each hair cell was large and basally placed, the cytoplasm contained numerous mitochondria and each HC had a single long kinocilium and several short stereocilia. The majority of SCs were elongated in shape and their nuclei occupied a significant portion of the cytoplasm. The support cells at the margin of the neuromast were particularly thin. Both types of support cells possessed well-developed rough endoplasmic reticulum and Golgi apparatus. The size and number of neuromasts and their component cells increased with the age of larvae (ANOVA, P < 0.05). The dimensions of the neuromasts of the anterior lateral line (head) did not differ significantly from those of the posterior lateral line (trunk) (ANOVA, P > 0.05).
Asunto(s)
Cyprinidae/anatomía & histología , Sistema de la Línea Lateral/anatomía & histología , Mecanorreceptores/citología , Animales , Citoplasma/metabolismo , Retículo Endoplásmico Rugoso/metabolismo , Aparato de Golgi/metabolismo , Células Ciliadas Auditivas/fisiología , Larva/anatomía & histología , Sistema de la Línea Lateral/fisiología , Mecanorreceptores/fisiología , Mitocondrias/metabolismoRESUMEN
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. Post-mortem 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.
Asunto(s)
Encefalopatías/veterinaria , Cyprinidae/parasitología , Enfermedades de los Peces/patología , Trematodos/patogenicidad , Infecciones por Trematodos/veterinaria , Animales , Encéfalo/parasitología , Encéfalo/ultraestructura , Encefalopatías/parasitología , Encefalopatías/patología , Enfermedades de los Peces/parasitología , Estadios del Ciclo de Vida , Microscopía Electrónica de Transmisión/veterinaria , Trematodos/ultraestructura , Infecciones por Trematodos/patologíaRESUMEN
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 +/- 1.2 cm, LT +/- SD) of zebrafish, Danio rerio Hamilton, 1822. Rodlet cells, characterized by a distinctive cell cortex (range, 0.4-1.5 microm in thickness) and conspicuous inclusions named "rodlets," have a round to ovoid nucleus with irregular outline. Mature RCs are 11.5 +/- 1.2 microm (mean +/- SD) long and 7.8 +/- 1.1 microm (mean +/- 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 +/- 3.6, mean +/- SD). The RCs were located 1.5 microm (minimal) to 73.3 microm (maximal) from the neuromast (27.9 +/- 17.2, mean +/- 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.
Asunto(s)
Mecanorreceptores/ultraestructura , Pez Cebra/anatomía & histología , Animales , Mecanorreceptores/fisiología , Pez Cebra/fisiologíaRESUMEN
Morphological identification of tapeworm species at larval stages (procercoids and cysticercoids) is often difficult because few diagnostic characters are available. In the present study, a molecular approach (sequencing of partial 18S rDNA gene) was used to evaluate the genetic similarity between adult specimens of Cyathocephalus truncatus (Pallas, 1871) (Cestoda: Spathebothriidea) found in fish, its definitive host, and procercoids of the same species recovered from amphipod, Echinogammarus stammeri (Karaman, 1931). Furthermore, cestode cysticercoids of uncertain species were found in the amphipod's hemocoel. The sequences obtained from adults and procercoids were identical, and even very similar to those of C. truncatus available in GenBank, whereas the sequences obtained from cysticercoids differed significantly from those of adults and procercoids, indicating that these larvae belong to another species; later it was demonstrated that they were cysticercoids of Microsomacanthus pachycephala (Linstow, 1972), a cestode of the Hymenolepididae (Cyclophyllidea). The results of this investigation show that the comparison of nucleotide sequence data may avoid misclassification of developmental stages of parasites, which use the same intermediate host.