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Biomedical subjects

D Joshi

Publications and source records attributed to D Joshi.

31 records · Page 2Linked to original sources
PubMed1985

Light flashes of different durations (0.063-3.33 msec) phase shift the circadian flight activity of a bat.

The phase-response curve (PRC) for the circadian rhythm in the flight activity of a cave-dwelling bat, Hipposideros speoris, constructed with 0.063-msec light flashes, reported here is the first of its kind for any circadian system and is unlike any other phase-response curves constructed for other nocturnal animals. The phase responding with maximal advances (90 degrees) and the phase responding with maximal delays (0 degree) of this PRC were exposed to light flashes of systematically varying durations from 0.083 to 3.33-msec. For 0 degree phase, the flashes of 0.063-3.33 msec effected delay phase shifts of comparable magnitude. For 90 degrees phase, the flashes of 0.063-1.0 msec effected advance phase shifts, whereas 3.33-msec flashes effected unmistakable delay phase shifts with advancing transients. Phase shifts evoked with such light flashes are further compared with phase shifts evoked with pulses of longer durations (15 min to 2.8 hr) for H. speoris.

Animals↗
PubMedDate not supplied

Loss of LH-RH neurons in the rostral forebrain of old female C57BL/6J mice.

This study reports the quantitative immunohistochemical distribution of luteinizing hormone-releasing hormone (LH-RH) neurons within the rostral forebrain of young (5-6 month) and old (26-28 month) C57BL/6J mouse. Old mice demonstrated a significant (18%) loss of LH-RH-containing neurons (p less than 0.001, ANOVA). The most striking losses involved the preoptic area (24%) and more rostral regions (26%). The presence of pituitary or mesenteric tumors in older mice did not affect the density of LH-RH neurons. These observations indicate that LH-RH neurons comprise part of the neuronal population previously reported to be reduced in the preoptic area of older mice (4).

Aging↗
PubMedDate not supplied

Loss during aging of beta-endorphinergic neurons in the hypothalamus of female C57BL/6J mice.

Beta-endorphin (B-EP) content is often reduced in hypothalami of aging rodents. The objective of this study was to determine whether reduced B-EP content is associated with a reduced number of B-EP immunoreactive neurons. Serial coronal sections extending from the caudal hypothalamus through the retrochiasmatic area were examined by quantitative light microscopy in mature (5-6 month) and senescent (24-28 month) mice that had been ovariectomized 1 week earlier and injected with colchicine 24-48 h before sacrifice. Old mice were acyclic. As expected, B-EP immunoreactive cell bodies were restricted to the region of the arcuate nucleus. There was a 35% loss of B-EP immunopositive neurons in old, macroscopically disease-free animals. By contrast, some old animals with pituitary tumors had no loss of B-EP neurons. These results suggest that a subpopulation of B-EP neurons either die or stop synthesizing detectable concentrations of B-EP in aged mice. The basis for the absence of reduced B-EP neurons in some mice with pituitary tumors is unclear, but this observation underscores the importance of distinguishing age-related changes associated with diseases of aging from those that are independent of such diseases.

Aging↗
PubMedDate not supplied

Estrogen, the ovary, and neutotransmitters: factors associated with aging.

Our studies in the C57BL/6J mouse have been designed to examine the interactions of aging and the ovary, and their mutual effects on neuroendocrine function. In the pituitary, ovarian status and not age determines responsiveness to gonadotropin hormone releasing hormone (GnRH), but estrogen (E2) is an important mediator in CNS changes, and removal of the ovary (OVX) is deleterious to the neuroendocrine hypothalamus. OVX for just six days in young animals results in synaptic loss between noradrenergic terminals and gonadotropin hormone releasing hormone (GnRH) neurons. Long-term OVX, hypothesized to protect against neuroendocrine aging, fails to guard against any studied age-related changes. Some age-related changes occur as early as midlife. Although neuron number remains constant at middle age, opiatergic neurons undergo significant functional changes by producing opiate antagonist peptides. This change appears to be caused by alterations in the prohormone convertases, which cleave propeptide to peptide. Altered peptides may trigger the loss of reproductive capacity. The midlife shift in opiate peptide production is a component of natural developmental processes that begin in the neonate and continue through old age. In the cholinergic system, E2 mediates numbers of cholinergic receptors, cholinergic neurons, and cholinergic-modulated memory systems in both young and old animals. Regardless of age, ovarian steroids, if present at physiologic levels, are beneficial to the neuroendocrine CNS, and long-term deprivation from ovarian-produced factors is deleterious in the systems we have examined. Our studies have shown that deprivation from ovarian steroid hormones in the female appears to be a major factor in the health of the CNS and in events associated with aging.

Aging↗