Wheel-running activity rhythms and masking responses in the diurnal palm squirrel, Funambulus pennantii.

Several studies have reported activity patterns of various diurnal species from the order Rodentia, in which most of the species are nocturnal. Most of these studies have been performed under controlled laboratory conditions. These studies found that most of these species change their activity patterns when held under laboratory conditions, have a diverse masking response to light, and their activity pattern is influenced by the presence of a running wheel. Squirrels are reported to be strictly diurnal both in the field as well as in laboratory settings, and, therefore, form an interesting species to study to better understand the switch to diurnality. The aim of the current study is to characterize the masking response and temporal organization of wheel-running activity rhythms in the palm squirrel, Funambulus pennantii, under semi-natural (NLD) and controlled laboratory conditions using different lighting schedules. Squirrels were housed individually in a resting cage with running wheel under NLD (n = 10) and squared 12:12 h of light-dark cycle (LD) (n = 20). After stable entrainment under the LD condition, squirrels were divided into two groups. One group was housed under constant darkness (DD) (n = 10) and another group under constant light (LL) (n = 10). Following the stable free-running rhythm under DD and LL, the LD condition was reinforced. The kinetics of the endogenous pacemaker was studied following a 6 h phase advance or delay of LD cycle. Further, palm squirrels were subjected to a 3.5: 3.5 h LD cycle to evaluate the masking response to light and dark. Squirrels demonstrated stable, clear, robust, and strict diurnal activity rhythm during NLD and LD. In DD and LL, F. pennantii free-ran from the phase of the previous LD cycle, and the free-running period was longer in LL than in DD. The percentage of activity during the light phase was significantly higher in NLD and LD (above 96%) compared to activity during the subjective day in the DD and LL conditions (above 91%). The alpha/rho ratio was significantly higher in the LL compared to other lighting schedules. Further, all ten squirrels re-entrained to both 6 h advance and delay shifts within 11 days. In the ultradian cycle, significant positive masking of light was evident in nine of ten squirrels. These results suggest that the: (i) circadian system of F. pennantii is stable and functional under various lighting conditions; (ii) basic temporal organization in activity pattern remained unaltered even in the presence of a running wheel; (iii) diurnality is the inherent trait of F. pennantii, and (iv) behavioral activity rhythms are governed by both the circadian clock and external masking. Thus, palm squirrels can be used as a suitable diurnal model in circadian biology to study the underlying mechanisms of diurnality and effects of different light schedules, wavelengths, and non-photic cues on physiological and behavioral parameters.

The liver micromorphology of the african palm squirrel epixerus ebii / Micromorfología del hígado de la ardilla de palma africana epixerus ebii

The normal liver histology of the African palm squirrel Epixerus ebii was investigated to fill the information gap on its micromorphology from available literature. The liver was covered by a capsule of dense connective tissue- the perivascular fibrous capsule. Beneath this capsule is the liver parenchyma were the hepatocyte were supported by reticular fibres. The hepatocytes in the lobules were hexagonal to polygonal in shape. Some hepatocytes were bi-nucleated. Clear spaces in the parenchyma must be storage sites for lipids in the liver. The classic hepatic lobules presented central vein surrounded by several liver cells. At the portal triad, hepatic vein, hepatic arteries and bile ducts were seen. While the hepatic arteries and veins were lined by endothelium, the bile ducts were lined by simple cuboidal cells. Nerve fibres were also seen in the region of the portal triad. Hepatic sinusoids lined by endothelium were seen in the liver parenchyma between liver lobules. The sinusoids contained macrophages. This report will aid wild life biologists in further investigative research and Veterinarians in diagnosing the hepatic diseases of the African palm squirrel.

Describimos la histología hepática normal de la ardilla de palma africana Epixerus ebii para llenar el vacío sobre su micromorfología en la literatura disponible. El hígado está cubierto por una cápsula de tejido conectivo denso, la cápsula fibrosa perivascular. Debajo de esta cápsula se encuentra el parénquima hepático en el cual fibras reticulares apoyan los hepatocitos. Los hepatocitos en los lóbulos son hexagonales de forma poligonal. Observamos algunos hepatocitos bi-nucleados. Evidentes espacios en el parénquima deben ser emplazamientos de almacenamiento de los lípidos en el hígado. Los lóbulos hepáticos clásicos presentan una vena central rodeada de varias células hepáticas. En la tríada portal, se observó la vena hepática, las arterias hepáticas y los conductos biliares, mientras que las arterias y venas hepáticas estaban revestidas por endotelio, los conductos biliares estaban alineados por células cuboides simples. También se observaron fibras nerviosas en la región de la tríada portal. Sinusoides hepáticos revestidos por endotelio fueron observados entre los lobulillos hepáticos en el parénquima hepático. Los sinusoides contenían macrófagos. El presente estudio ayudará a los biólogos de la fauna silvestre en una investigación más precisa, y a los médicos veterinarios en el diagnóstico de las enfermedades hepáticas en la ardilla de palma africana.