Quantitative age-related changes in NADPH-diaphorase-positive neurons in the ventral lateral geniculate nucleus

Glutamatergic and GABAergic neurons in the vLGN mediate the nociceptive effects of green and red light on neuropathic pain

Phototherapy is an emerging non-pharmacological treatment for depression, circadian rhythm disruptions, and neurodegeneration, as well as pain conditions including migraine and fibromyalgia. However, the mechanism of phototherapy-induced antinociception is not well understood. Here, using fiber photometry recordings of population-level neural activity combined with chemogenetics, we found that phototherapy elicits antinociception via regulation of the ventral lateral geniculate body (vLGN) located in the visual system. Specifically, both green and red lights caused an increase of c-fos in vLGN, with red light increased more. In vLGN, green light causes a large increase in glutamatergic neurons, whereas red light causes a large increase in GABAergic neurons. Green light preconditioning increases the sensitivity of glutamatergic neurons to noxious stimuli in vLGN of PSL mice. Green light produces antinociception by activating glutamatergic neurons in vLGN, and red light promotes nociception by activating GABAergic neurons in vLGN. Together, these results demonstrate that different colors of light exert different pain modulation effects by regulating glutamatergic and GABAergic subpopulations in the vLGN. This may provide potential new therapeutic strategies and new therapeutic targets for the precise clinical treatment of neuropathic pain.

Alterations in nitric oxide synthase in the aged CNS

Aging is associated with neuronal loss, gross weight reduction of the brain, and glial proliferation in the cortex, all of which lead to functional changes in the brain. It is known that oxidative stress is a critical factor in the pathogenesis of aging; additionally, growing evidence suggests that excessive nitric oxide (NO) production contributes to the aging process. However, it is still unclear how NO plays a role in the aging process. This paper describes age-related changes in the activity of NADPH-diaphorase (NADPH-d), a marker for neurons containing nitric oxide synthase (NOS), in many CNS regions. Understanding these changes may provide a novel perspective in identifying the aging mechanism.

Age-related changes in nitric oxide synthase in the lateral geniculate nucleus of rats

Age-related changes in nitric oxide production in the visual system have not been well characterized. Therefore, we used staining and image-processing approaches to describe changes in levels of neuronal nitric oxide synthase (nNOS), the NADPH-diaphorase (NADPH-d) histochemical marker, and 3-nitrotyrosine in the lateral geniculate nucleus (LGN) of young and aged rats. The LGN plays an important role in the visual system, as it acts as a visual relay nucleus. Quantitative analysis of NADPH-d-positive and nNOS-immunoreactive neurons revealed significant optical density increases in the dorsal LGN and ventral LGN of aged rats; however, no significant changes were observed in the number of neurons with age. 3-Nitrotyrosine immunoreactivity was increased in the dorsal LGN and ventral LGN of aged rats. These results indicate that increased nitric oxide production and peroxynitrite may be associated with alterations in visual function during aging.

NADPH-diaphorase activity in the superficial layers of the superior colliculus of rats during aging

Neurons in the superficial layers of the superior colliculus are key elements in the visual system of rodents since they receive extensive afferent projections from retinal ganglion cells. The NADPH-diaphorase histochemical technique was used to detect differences in neuronal nitric oxide synthase (nNOS) in the superficial layers of the superior colliculus (sSC) of young adult (3 months) and aged (24 and 26 months) rats. The orientation of the dendritic processes of NADPH-diaphorase-positive neurons, cross-sectional area, and number of neurons per mm2 were analyzed. NADPH-d histochemistry revealed a high number of NADPH-d-positive cells in the stratum zonale and stratum griseum superficiale in adult and aged animals. NADPH-d-positive neurons were classified into the following morphological types: marginal, horizontal, pyriform, narrow-field vertical, wide-field vertical, and stellate. During aging, narrow field vertical and wide field vertical neurons present somatic atrophy and an increase in dendritic processes with dorsoventral orientation, whereas wide field vertical neurons show a decrease in those with lateromedial orientation. Marginal neurons undergo somatic hypertrophy at 26 months when compared with those at 3 months. The remaining types of neurons do not undergo size changes. Finally, the number of NADPH-d-positive neurons per mm2 in the various types of morphology does not significantly change with age. It is suggested to be likely that the aging process in the nitrergic neurons of the sSC does not lead to significant changes in the synthesis of NO from the constitutive NOS isoforms.