Providing Environmental Enrichment without Altering Behavior in Male and Female Wistar Rats (Rattus norvegicus).

In research using animal models, subjects are commonly maintained under standard housing conditions, mainly because of the idea that enhancing welfare conditions could alter experimental data. Another common practice in many laboratories relates to the preponderant use of males. Several reasons justifying this practice include the rapid hormonal and endocrine change in females, which may require a higher number of female animals to achieve more homogenous groups, thereby creating a dilemma with the reduction principle in animal research. In past decades, a relationship between enriched environments and enhanced cognitive functions has been reported in rats, but many of those enriched environmental protocols were not systematically or rigorously studied, leading to unexpected effects on behavior. Here we report the effects of 4 types of housing conditions (standard, structural changes, exercise, and foraging) in Wistar rats on anxiety (elevated plus maze), exploratory (open field), and stress vulnerability (forced swim test) responses. Sex was used as a blocking factor. Data show no effect of housing conditions on anxiety and exploratory behaviors, but do show an effect on stress responses. These results suggest the possibility of using a protocol for environmental enrichment without concern about altering experimental data. From this stand, new ways to enhance animal welfare in research laboratories could be designed and implemented.

PATRONES DE ALIMENTACIÓN, SUEÑO Y ACTIVIDAD REPRODUCTIVA EN JERBOS DE MONGOLIA (Meriones unguiculatus) / PATTERNS OF FEEDING, SLEEP AND REPRODUCTIVE BEHAVIOR IN MONGOLIAN GERBILS (Meriones unguiculatus)

Los jerbos de Mongolia son roedores utilizados como excelente modelo biológico. A pesar de esto, su clasificación como especie diurna, nocturna o crepuscular no ha sido clara. Los experimentos que se presentan en este artículo evaluaron patrones de alimentación, sueño-actividad y actividad reproductiva y copulativa en condiciones de luz/oscuridad 12:12 en Jerbos de Mongolia. Los resultados de los experimentos sugieren un patrón nocturno de comportamiento en estos roedores.

Mongolian Gerbils are often used as a biological model, but it remains unclear whether these rodents display nocturnal, diurnal, or crepuscular patterns of behavior. The experiments presented below studied patterns of sleep-activity, feeding, and reproductive behavior under 12:12 light dark cycles. All data from these experiments suggest a nocturnal pattern of behavior in these rodents.

Regulación circadiana del comportamiento: diferencias entre especies diurnas y nocturnas / Circadian regulation of behavior: differences between diurnal and nocturnal species

La mayoría de los organismos, incluyendo los humanos, exhiben ritmos diarios de aproximadamente 24 horas en fisiología, funciones hormonales y conducta. En mamíferos, estos ritmos son controlados por un marcapasos circadiano endógeno ubicado en el núcleo supraquiasmático (NSQ) del hipotálamo que determina la organización temporal de varias conductas y procesos fisiológicos. El control circadiano de ritmos diarios difiere en especies diurnas y nocturnas pero los mecanismos que pueden explicar dichas diferencias se desconocen aún. El objetivo de esta revisión es resumir el estado actual del conocimiento sobre los relojes circadianos y de las diferencias entre especies diurnas y nocturnas.

Most organisms, including humans, show daily rhythms of about 24 hours in physiology, hormonal function, and behavior. In mammals, these rhythmsare controlled by an endogenous circadian pacemaker localized in the suprachiasmatic nucleus (SCN) of the hypothalamus that determines thetemporal organization of several behaviors and physiological processes.Circadian control of daily rhythms differs in diurnal and nocturnal speciesbut many of the mechanisms that may explain these differences remain stillunknown. The aim of this review is to summarize our current knowledge of the circadian clocks and the differences between diurnal and nocturnal species.

Mecanismos neurobiológicos de la conducta paterna / Neurobiological mechanisms of paternal behavior

En muchas especies de mamíferos (incluyendo a los humanos) las tareas del cuidado de las crías,excepto la lactancia, son compartidas por el padre y la madre. Aunque se sabe bastante sobre losefectos de la conducta materna en el desarrollo de las crías, poco se sabe acerca de la contribucióndel padre en el desarrollo neural y de comportamiento de las mismas, ni sobre los cambios hormonaleso mecanismos neurobiológicos que hacen posible el despliegue de la conducta paterna. Elpresente artículo presenta una revisión del estado actual de la investigación en esta área.

In many mammal species (including humans) both male and female engage in similar behaviors toprotect and care for the offspring, with the exception of lactation. Although much is known aboutthe effects of maternal behavior on pup development, very little is known about the contribution ofthe male on neural development and behavior of the offspirng or about hormonal changes andneurobiological mechanisms that allow the male to display paternal behavior. This article reviewsthe status of research in these topics.

Circadian regulation of dailyrhythms in orexinergic neurons in diurnal and nocturnal rodents / Regulación circadiana de los ritmos diarios en neuronas

The work presented here focuses on the differential regulation of circadian rhythmi city by the central nervous systems of the diurnal Arvicanthis niloticus (or grass rat) and the nocturnal Rattus norvegicus (or lab rat). In grass rats, neurons expressing orexin (ORX) showed a significant daily endogenous rhythm in the expression of Fos that correlated with the rhythm in sleep and wakefulness, and was reversed when compared to that seen in lab rats. Ingrass rats ORX-positive neurons received substantial projections from vasoactive intestinal polypeptide (VIP) neurons of the suprachiasmatic nucleus (SCN). In contrast few VIP positive fibers were seen adjacent to ORX positive neurons in lab rats. This species difference suggests a direct control by the SCN on neurons expressing ORX in grass rats and a more indirect regulation in lab rats. These results are consistent with the hypothesis that differences between diurnal and nocturnal species are dueto differences in the functions of targets of the SCNsuch as the ORX neurons and the dorsomedial hypothalamus.(DMH)

El trabajo que se presenta aquí se centra en la regulación diferencial que ejerce el sistema nervioso central sobre ritmos circadianos en una especie diurna, Arvicanthis niloticus, o rata Nile grass y una especie nocturna, Rattus norvegicus, o rata de laboratorio. En Nile grass, las neuronas que expresan orexina (ORX) mostraron un ritmo endógeno diario en la expresión de Fos, ritmo que correlaciona con el ciclo de sueño y vigilia de esta especie y que es opuesto en comparación con el ritmo visto en ratas de laboratorio. En Nile grass las neuronas de ORX reciben proyecciones sustanciales desde neuronas del núcleo supraquiasmático (SCN) que expresan el péptido vasoactivo intestinal (VIP). En contraste, en ratas de laboratorio se encontraron muy pocas fibras positivas para VIP adyacentes a neuronas de ORX. Esta diferencia entre especies sugiere un control directo por parte del SCN sobre neuronas que expresan ORX en Nile grass y una regulación más indirecta en ratas de laboratorio. Estos resultados son consistentes con la hipótesis según la cual las diferencias entre especies diurnas y nocturnas se deben a diferencias en las funciones de regiones que reciben eferencias del SCN tales como las neuronas de ORX y el hipotálamos dorsomedial.(DMH)

Temporal and spatial distribution of immunoreactive PER1 and PER2 proteins in the suprachiasmatic nucleus and peri-suprachiasmatic region of the diurnal grass rat (Arvicanthis niloticus).

The suprachiasmatic nucleus (SCN) of the hypothalamus contains the primary circadian pacemaker in both diurnal and nocturnal mammals. The lower subparaventricular zone (LSPV) immediately dorsal to the SCN may also play an important role in the regulation of circadian rhythms. The SCN contains a multitude of oscillator cells that generate circadian rhythms through transcriptional/translational feedback loops involving a set of clock genes including per1 and per2. Little is known about the temporal and spatial features of the proteins encoded by these genes in day-active mammals. The first objective of this study was to characterize the expression of PER1 and PER2 in the SCN of a diurnal rodent, the unstriped Nile grass rat (Arvicanthis niloticus). The second objective was to evaluate the hypothesis that a molecular clock could exist in the LSPV, where endogenous rhythms in Fos expression are seen in grass rats but not in laboratory rats. Animals were kept on a 12:12 light/dark cycle and perfused at 4-h intervals, and their brains were processed for immunohistochemical detection of PER1 and PER2. Both proteins were seen in the SCN where they peaked early in the dark phase, providing further evidence that the differences between diurnal and nocturnal patterns of behavior emerge from mechanisms lying downstream from the pacemaker within the SCN. Rhythmic expression of PER1 and PER2 was also seen in the LSPV providing support for the hypothesis that this region might participate in circadian time keeping in the diurnal grass rat. In addition, rhythms were seen lateral to the LSPV and the SCN. Results of this study are discussed in light of similarities and differences in the circadian time-keeping systems of day- and night-active animals.

Diurnal and nocturnal rodents show rhythms in orexinergic neurons.

Orexin (ORX) A and B (hypocretins) are excitatory neuropeptides produced by neurons of the lateral hypothalamus that have been implicated in the regulation of the sleep-wake cycle. In rats, Fos (the product of the cfos gene) expression shows daily rhythms in areas involved in sleep and wakefulness and orexinergic neurons show elevated Fos expression during the night. The present study directly compared the daily pattern of Fos expression in orexinergic neurons in diurnal (A. niloticus; grass rats) and nocturnal (R. norvegicus; lab rats) rodents. Animals kept on a 12:12 light-dark cycle were perfused at six different Zeitgeber times (ZT), with lights on at ZT 0: 1, 5, 13, 17, 20 and 23. In both nocturnal and diurnal rodents orexinergic neurons showed rhythms in Fos expression, with more Fos seen during the active phase of each species. In the diurnal species, Fos expression in cells of the lateral hypothalamus that do not produce ORX was elevated at ZT 20, a time when these animals sleep, and was low at ZT 13, a time of peak of activity. These results provide further evidence for a link between activity in orexinergic neurons and wakefulness and that in grass rats, other neurons of the lateral hypothalamus may work in an antagonistic fashion with respect to orexinergic neurons to regulate wakefulness in this diurnal species.