Rubidium chloride fuses split circadian activity rhythms in hamsters housed in bright constant light.

Chronotypic effects of rubidium (Rb) were examined in hamsters whose circadian activity rhythms had split into two components while they were housed in bright constant light. Seven of 12 hamsters receiving RbCl in drinking water for 10 weeks showed fusing of the components into an intact rhythm compared with none of 7 control hamsters (p = 0.016).

Lateral hypothalamic lesions in ground squirrels: rapid recovery and residual deficits.

The effects of lateral hypothalamic (LH) lesions were studied in golden-mantled ground squirrels, Spermophilus lateralis, a species of mammalian hibernator that displays endogenous circannual body weight cycles when kept in constant conditions. The lesions were made during the weight-gain phase. Evidence that the lesions were well placed included interruption of weight gain, transient aphagia, disrupted nest building, increased spillage of food crumbs and in some cases abnormal postures or movement.

Colliding of activity onset and offset: evidence for multiple circadian oscillators.

When hamsters, Mesocricetus auratus, are kept in dim light, wheel running at the onset and the offset of their active phase have different circadian periods. As a result, the active phase expands and eventually the two activity components collide. There is then a temporary explosion of activity at a time that was previously in the rest period.

Affective disorders and circadian rhythms.

Abnormal circadian rhythms have been associated with affective disorders. A review of this rapidly expanding area of investigation shows that while a clear causal relationship has not yet been proven, a knowledge of the circadian system and its dysfunction can help in understanding unipolar and bipolar depression. Evidence suggests that existing therapies such as lithium and antidepressants act upon the circadian system.

Electrically induced behavior and neural specificity in ground squirrels and dormice.

Electrical stimulation of the lateral hypothalamus in 2 species of hibernator, dormice (Glis glis) and ground squirrels (Spermophilus lateralis), suggests that induced behaviors may reflect activation of specific neural systems, rather than merely activation of a single central mechanism interacting with internal and external cues and past experience (prepotency hypothesis). In dormice, the stimulation induced feeding on powdered food; in squirrels it induced either feeding or picking up of food pellets. Consistent with neural specificity in both species were high probabilities of emergence (78-81%) of a behavior during stimulation at an electrode site, with no greater ease of emergence at a second site tested.

Neurohumoral stimulation of lipogenesis during altered states of energy balance.

Acid extracts of bovine hypothalamus stimulate lipogenic activity in adipose tissue. We employed a rat fat cell bioassay system to determine whether tissue concentrations of the active material vary as a function of spontaneous alterations in energy balance in hibernators and/or the obesity resulting from bilateral electrolytic lesions of the ventromedial area of the hypothalamus in rats. When hypothalamic extracts and partially purified plasma were fractionated using reverse-phase high-pressure liquid chromatography, both the void volume and material eluting 17 min after the start of a 25-min linear methanol gradient enhanced glucose incorporation into total lipid.

Ventromedial hypothalamic lesions in rats: gradual elevation of body weight set-point.

Bilateral electrolytic (DC) or radiofrequency (RF) lesions of the ventromedial hypothalamic (VMH) area produced two abnormal stages of fattening in adult female rats. Following a negatively-accelerated, curvilinear phase of weight gain which lasted 10 weeks, a linear phase of fattening continued for an additional 30 weeks at a rate approximately double that of operated control rats of the same age. During this second phase of fattening, lesioned rats were food-restricted between the 20th and 26th weeks postlesion.