The behavior, cortisol concentration and cerebral hemisphere activity of twelve marmoset monkeys were determined during standardized predatory stress-related events. Each subject was submitted to three 5-min trials, randomly held at 2-week intervals: a human intruder, a taxidermized oncilla cat and a no-stimulus control trial. Stimuli were positioned outside the home-cage and the ensuing reaction recorded. Baseline tympanic membrane temperature (TMT) was subtracted from the post-trial measure to determine changes in blood flow induced by ipsilateral brain activity. Cortisol was assayed immediately after the post-trial TMT assessments. Both genders reacted fearfully/anxiously towards the stimuli - each condition inducing a distinct pattern. Cortisol increased only when females were confronted with the wildcat, with higher levels of alarm calls predicting lower cortisol release. When either stimulus was present, changes in TMT were detected, albeit only in the right ear. The specific directional shift in temperature was gender- and stimulus-dependent, requiring further investigation. The control trial did not alter any of the parameters. Marmosets thus exhibit flexible multileveled coping strategies towards different aversive events, yet in general these seem to be asymmetrically processed by the right cerebral hemisphere.

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In this study, two circadian related centers, the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) were evaluated in respect to their cytoarchitecture, retinal afferents and chemical content of major cells and axon terminals in the rock cavy (Kerodon rupestris), a Brazilian rodent species. The rock cavy SCN is innervated in its ventral portion by terminals from the predominantly contralateral retina. It also contains vasopressin, vasoactive intestinal polypeptide and glutamic acid decarboxilase immunoreactive cell bodies and neuropeptide Y, serotonin and enkephalin immunopositive fibers and terminals and is marked by intense glial fibrillary acidic protein immunoreactivity. The IGL receives a predominantly contralateral retinal projection, contains neuropeptide Y and nitric oxide synthase-producing neurons and enkephalin immunopositive terminals and is characterized by dense GFAP immunoreactivity. This is the first report examining the neural circadian system in a crepuscular rodent species for which circadian properties have been described. The results are discussed comparing with what has been described for other species and in the context of the functional significance of these centers.

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