DISTINCT PAIN RELIEVERS INDUCE ASTROGLIOSIS IN THE BRAIN OF RATS E. Bondan * , L. Viebig * , P. Brigo * , M. Augusto y , C. Silva y , P. Dossa * , C. Cardoso * and M. Martins y * Graduate Program in Environmental and Experimental Pathology, University Paulista and y Department of Veterinary Medicine, University Cruzeiro do Sul, S~ ao Paulo, Brazil Introduction: Although pain is traditionally considered to be medi- ated by neurons, recent research has shown the important roles of glial cells in pain sensation. Microglial cells have been implicated in such processes, but less is known about the role of astrocytes. Astro- gliosis is recognized as a defence reaction, conceivably aimed at limiting tissue damage and restoring homeostasis. This study aimed to assess the expression of glial fibrillary acidic protein (GFAP) in as- trocytes from the frontal cortex, hypothalamus and periaqueductal grey matter (PAG) after administration of short-term doses of distinct drugs used for pain management, but without painful stimuli. Materials and Methods: Male Wistar rats received amitriptyline (Amt, 10 mg/kg/day) or gabapentin (Gb, 60 mg/kg/day) for 10 days, by gavage or via the intraperitoneal route, methadone (Me, 4.5 mg/kg/day), morphine (Mo, 10 mg/kg/day), carbamazepine (Cbz, 40 mg/kg/day), fluoxetine (Flx, 10 mg/kg/day), amantadine (Ama, 10 mg/kg/day), S-ketamine (Ke, 50 mg/kg/day), dipyrone (Dip, 16 mg/kg/day) or 0.9% saline solution (daily). Brain samples were collected for GFAP immunohistochemical investigation in the frontal cortex, hypothalamus and PAG. Results: Morphometric analysis showed that all drugs increased GFAP expression and astrocyte size in the frontal cortex and hypo- thalamus in relation to the saline group. In the PAG this expression was increased in the groups treated with Amt, Me, Mo, Ama, Flx and Ke, but not with Gb, Cbz and Dip. Discussion: Although the precise meaning of such changes remains unclear, astrocytes appeared to react phenotypically to distinct classes of pain modulators in almost all investigated areas, probably influ- encing neurons and the entire neural microenvironment. EXTENSIVE ASTROGLIOSIS INDUCED BY SHORT-TERM METHOTREXATE ADMINISTRATION E. Vazi * , F. Holanda y , N. Santos * , C. Cardoso * , A. Bachi z , M. Martins y and E. Bondan * * Graduate Program in Environmental and Experimental Pathology, University Paulista, S~ ao Paulo, y Department of Veterinary Medicine, University Cruzeiro do Sul, S~ ao Paulo and z Brazilian Institute of Teaching and Research in Pulmonary and Exercise Immunology (IBEPIPE) S~ ao Jos  e dos Campos, Brazil Introduction: Methotrexate (Mtx), an antifolate drug, is used widely in chemotherapeutic protocols for metastatic and primary brain tumours and some autoimmune diseases. Its efficacy for brain tumours is limited by the high incidence of central nervous system (CNS) complications. This investigation aimed to assess the astrocytic response to systemic short-term Mtx administration in adult rats. Materials and Methods: Male Wistar rats received 5 or 10 mg/kg/ day of Mtx by the intraperitoneal route for 4 consecutive days (Mtx5 and Mtx10 groups) or the same volume of 0.9% saline solu- tion (control group). On the 5 th day, brain samples were collected, processed and stained with haematoxylin and eosin and luxol fast blue and subjected to immunohistochemistry for glial fibrillary acidic protein (GFAP) and vimentin expression and morphometric analysis of the frontal cortex, hippocampus, hypothalamus and mo- lecular/granular layers of the cerebellum. Brain levels of the pro-in- flammatory cytokines TNF-a and IL-1b were determined by ELISA. Results: There was no evidence of neuronal loss or demyelination in any group. Increased GFAP expression was found in all areas in the Mtx groups, although it was slightly higher in the Mtx10 group compared with the Mtx5. Reactive astrocytes labelled for vimentin were seen in the Mtx groups, but not in controls. Both TNF-a and IL-1b concentrations were decreased in the Mtx5 group compared with controls. In the Mtx10 group, TNF-a was decreased, although IL-1b was increased relative to controls. Discussion: Mtx administration induced astrogliosis in several CNS areas. In the Mtx5 group, it apparently occurred in the presence of decreased concentrations of pro-inflammatory cytokines. MYSTERIOUS SYNDROME CAUSING HIGH MORTALITY IN WILD BROWN TROUT IN EASTERN SWITZERLAND, SIMILAR TO PROLIFERATIVE DARKENING SYNDROME e PATHOLOGY AND POSSIBLE CAUSES H. Schmidt-Posthaus * , C. Birrer y , C. Mehr y , V. Leib z and M. Kugler y * Department of Infectious Diseases and Pathobiology, Centre for Fish and Wildlife Health, Bern, y Department of Economic Affairs, Office for Nature, Hunting and Fisheries and z Department of Construction, Office for Water and Energy, St. Gallen, Switzerland Introduction: In the Thur, a river situated in the Eastern part of Switzerland, massive mortalities have occurred regularly in brown trout since 2016. Dead fish were recorded in a period of a few weeks in July/August and with a sharp demarcation between affected and un- affected river stretches. The majority of affected animals were 1-year old. Materials and Methods: From June to November 2018, brown and rainbow trout were sampled from the Thur. For each species, five fish were sampled every 2 weeks. Parasitology, bacteriology, virology and histology were performed. The water temperature was measured regularly. Water samples were taken every 10 minutes and pooled for daily samples for a period of 6 months. Non-target screening, target screening and suspect screening were performed. Results: Macroscopically, clinically ill fish showed dark colouration and apathy. No consistent pathogenic agent was isolated. By histology, exten- sive liver necrosis, haemorrhage and severe lymphohistiocytic myocarditis were diagnosed exclusively in brown trout. The first lesions were found in mid-August, while the highest degree of alterations occurred from the end of August to October. Full recovery did not occur until final sampling at the end of November. As alterations were in agreement with those recently described for brown trout proliferative darkening syndrome (PDS) in Germany, severely affected specimens were analysed for piscine reovirus 1 and 3, agents proposed to be involved in PDS. None of the examined samples were found to be positive. Discussion: Up to now, the cause of the described syndrome re- mains unclear. Results from water analyses are still outstanding. EVALUATION OF KOJIC ACID ACUTE TOXICITY IN ADULT ZEBRAFISH (DANIO RERIO) T. Mandalian * , D. Coprean * , O. Hritcu y , L. Hritcu x , S. Morosan z , M. Mares { and A.S. Pasca ± * Biology, University Ovidius of Constanta, Constanta y Pathology, University of Agricultural Sciences and Veterinary Medicine of Iasi, Iasi, z Laboratory Animal Science, University of Agricultural Sciences and Veterinary Medicine of Iasi, Iasi, x Biology, Alexandru Ioan Cuza University of Iasi, Iasi, { Mycology, University of Agricultural Sciences and Veterinary Medicine of Iasi, Iasi and  Pathology, University of Agricultural Sciences and Veterinary Medicine of Iasi, Iasi, Romania Introduction: Kojic acid (KA) (5-hydroxy-2-(hydroxymethyl)-4H- pyran-4-one) is a secondary metabolite product of many species of fungi (especially Aspergillus oryzae) used in the food and cosmetic in- dustry as a preserving or skin whitening agent. It can also contami- nate food and feed, inducing acute or chronic toxic effects. The aim of this study was to evaluate the toxic effects of KA in the digestive organs (i.e. liver, pancreas and gut) of adult zebrafish. Materials and Methods: The study was conducted over a 7-day period on 60 adult zebrafish divided into four groups depending on the KA concentration in water: A, control (0 mg/l); B, 100 mg/l; C, 204 mg/l; D, 284 mg/l. The liver, pancreas and intestine of the ze- brafish from each group were examined by light microscopy, using trichrome Masson and PAS staining. Results: In the liver, dose-dependent toxic degeneration of the hepato- cytes due to oxidative stress was observed. Vacuolar degeneration in group B, ballooning degeneration in group C and loss of cell integrity and necrosis in group D were diagnosed. In the pancreas, there was marked fatty stromal infiltration and severe secondary atrophy. In the first part of the gut, a significant shortening of the villi was documented: from 270  5 mm length in group B to 170  5 mm in group D. Discussion: In zebrafish, KA is responsible for acute cytotoxicity in the liver, severe fatty infiltration and secondary atrophy in the pancreas and severe impairment of intestinal digestion and absorp- tion processes, indicated by significant shortening of villi. 158 ECVP, ESVP,ECVCP and ESVCP Proceedings 2019 J. Comp. Path. 2020, Vol. 174, 157e198