Light deprivation improves melatonin related suppression of hippocampal plasticity

GENDER-SPECIFIC DIFFERENCES OF CARDIAC VEGETATIVE CONTROL IN ADRENALINE-INDUCED NECROSIS AND LIGHT DEPRIVATION

Background. Cardiovascular disease is the main cause of morbidity predominantly in males. Stress is one of the crucial factors, especially with light desynchronosis. Objective of the study was to assess gender-specific characteristics of cardiac vegetative control in myocardial necrosis in cases of light deprivation. Methods. Cardiac vegetative control in adrenaline-induced myocardial necrosis (AIMN) in a setting of light deprivation (LD) was assessed in 72 mature white rats of both sexes. The animals were divided into 2 groups: G1 – the animals kept under day/night cyclic balance (12 hours/12 hours); G2 – the animals kept at LD (illumination 0.5-1 LX) for 10 days. On Day 11, AIMN caused by adrenaline (0.5 mg/kg) and heart rate variability (HRV) was assessed in 1 hour and 24 hours. Results. The development of AIMN at LD in the ♂G2 led to HRV increase that was caused by augmentation of parasympathetic and reduction of sympathetic cardiac effects. In cases of AIMN, changes of CVC in the ♀G2 were similar to the ♀G1. However, in 1 hour of AIMN, parasympathetic cardiac effects were more significant than in the ♀G1. While the ♀G2 AIMN animals experienced balanced sympathetic and parasympathetic actions, the predominance of the sympathetic component was evidenced in the ♀G1 AIMN animals. Conclusions. Light deprivation has different effects on baseline sympathetic/parasympathetic balance in males and females, i.e. increased parasympathetic control of heart rhythm in males and maintenance of sympathetic/ parasympathetic balance in females.

Exogenous melatonin reproduces the effects of short day lengths on hippocampal function in male white-footed mice, Peromyscus leucopus

Photoperiodism is a biological phenomenon, common among organisms living outside of the tropics, by which environmental day length is used to ascertain the time of year to engage in seasonally-appropriate adaptations. White-footed mice (Peromyscus leucopus) are small photoperiodic rodents which display a suite of adaptive winter responses to short day lengths mediated by the extended duration of nightly melatonin secretion. Exposure to short days alters hippocampal dendritic morphology, impairs spatial learning and memory, and impairs hippocampal long-term potentiation (LTP). To determine the role of melatonin in these photoperiod-induced alterations of behavioral, neuroanatomical, and neurophysiological processes in this species, we implanted male mice subcutaneously with melatonin or empty Silastic capsules and exposed them to long or short day lengths. After 10 weeks, mice were assessed for hippocampal LTP, tested for spatial learning and memory in the Barnes maze, and morphometric analysis of neurons in the hippocampus using Golgi staining. Extending the duration of melatonin exposure, by short-day exposure or via melatonin implants, impaired both Schaffer collateral LTP in the CA1 region of the hippocampus and spatial learning and memory, and altered neuronal morphology in all hippocampal regions. The current results demonstrate that chronic melatonin implants reproduce the effects of short days on the hippocampus and implicate melatonin signaling as a critical factor in day-length-induced changes in the structure and function of the hippocampus in a photoperiodic rodent.

Neuroprotection by melatonin after germinal matrix hemorrhage in neonatal rats

BACKGROUND

Germinal matrix hemorrhage (GMH) is a devastating neurological disorder of very low birth weight premature infants that leads to post-hemorrhagic hydrocephalus, cerebral palsy, and mental retardation. Melatonin is a potent antioxidant known to reverse free-radical mediated injury in the brain. This study investigated the effect of melatonin treatment after GMH injury.

METHODS

Clostridial collagenase was infused into the right germinal matrix region of neonatal rats with stereotaxic technique. Cognitive function, sensorimotor ability, cerebral, cardiac and splenic growths were measured in juvenile animals.

RESULTS

Systemic melatonin treatment ameliorated cognitive and sensorimotor dysfunction at the juvenile developmental stage. This hormone also normalized brain atrophy, splenomegaly, and cardiac hypertrophy consequences at 1 month after injury.

CONCLUSION

This study supports the role of free radicals in acute neonatal hemorrhagic brain injury. Melatonin is an effective antioxidant that can protect the infant's brain from the post-hemorrhagic consequences of mental retardation and cerebral palsy. Further mechanistic studies are warranted to determine the mechanisms behind these neuroprotective effects.

Photoperiod-mediated impairment of long-term potention and learning and memory in male white-footed mice

Adult mammalian brains are capable of some structural plasticity. Although the basic cellular mechanisms underlying learning and memory are being revealed, extrinsic factors contributing to this plasticity remain unspecified. White-footed mice (Peromyscus leucopus) are particularly well suited to investigate brain plasticity because they show marked seasonal changes in structure and function of the hippocampus induced by a distinct environmental signal, viz., photoperiod (i.e. the number of hours of light/day). Compared to animals maintained in 16 h of light/day, exposure to 8 h of light/day for 10 weeks induces several phenotypic changes in P. leucopus, including reduction in brain mass and hippocampal volume. To investigate the functional consequences of reduced hippocampal size, we examined the effects of photoperiod on spatial learning and memory in the Barnes maze, and on long-term potentiation (LTP) in the hippocampus, a leading candidate for a synaptic mechanism underlying spatial learning and memory in rodents. Exposure to short days for 10 weeks decreased LTP in the Schaffer collateral-CA1 pathway of the hippocampus and impaired spatial learning and memory ability in the Barnes maze. Taken together, these results demonstrate a functional change in the hippocampus in male white-footed mice induced by day length.

Protective effect of melatonin upon neuropathology, striatal function, and memory ability after intracerebral hemorrhage in rats

Since free radicals play a role in the mechanisms of brain injury after hemorrhagic stroke, the effect of melatonin (a potent antioxidant and free-radical scavenger) on outcomes was investigated after intracerebral hemorrhage (ICH) in rats. ICH was induced by clostridial collagenase infusion into the right caudate putamen, and several time points and doses of melatonin were studied. Brain edema and neurological function at 24 h were unchanged in comparison with vehicle-treated groups, in spite of oxidative stress reductions. Repeated treatment with the lower dose of melatonin (5 mg/kg) given at 1 h and every 24 h thereafter for 3 days after ICH, led to normalization of striatal function and memory ability over the course of 8 weeks, and less brain atrophy 2 weeks later. These results suggest that melatonin is safe for use after ICH, reduces oxidative stress, provides brain protection, and could be used for future investigations of free radical mechanisms after cerebral hemorrhage.