Neuropeptide Y localization in telencephalic and diencephalic structures of the ground squirrel brain.

The distribution of neuropeptide Y-immunoreactive (NPY-IR) perikarya, fibers, and terminals was investigated in the brain of two species of hibernatory ground squirrels, Spermophilus tridecemlineatus and S. richardsonii, by means of immunohistochemistry. In the telencephalic and diencephalic structures studied, distinct patterns of NPY-IR were observed which were essentially identical in male and female animals of both species.

Immunohistochemical evidence for the presence of neuropeptides in the hypothalamic suprachiasmatic nucleus of ground squirrels.

The cytoarchitecture and immunocytochemical distribution of neuropeptides (corticotropin-releasing factor, CRF; neuropeptide Y, NPY; oxytocin, OXY; vasopressin, VP; and vasoactive intestinal polypeptide, VIP) were studied in the hypothalamic suprachiasmatic nuclei (SCN) in male and female ground squirrels of two species (Spermophilus tridecemlineatus and S. richardsonii). Immunoreactive (IR) perikarya were found in sections incubated with VP or VIP antisera.

Comparative studies on the retinal dopamine response to altered magnetic fields in rodents.

Previously it was demonstrated that experimental alteration of the ambient magnetic field at night significantly reduced catecholamine levels in the retinae of Sprague-Dawley rats. As this effect appeared to depend on intact photoreceptors, it seemed of interest to examine whether the dopamine response to altered magnetic fields (MFs) differed between rod-dominant retinae and cone-dominant retinae. Furthermore, the effect of MFs on daytime dopamine content was explored.

Pineal sensitivity to nighttime swimming stress changes during the active season in Richardson's ground squirrels (Spermophilus richardsonii).

Melatonin synthesis in the pineal gland, which is primarily regulated by the environmental lighting regime, can also be influenced by other factors that elicit modifications in sympathetic tone. The objectives of this study were to determine if forced swimming alters the normal pattern of melatonin production in the pineal gland of the Richardson's ground squirrel (Spermophilus richardsonii). In early June, the squirrels were forced to swim for 10 min during the photophase or during the scotophase.

Melatonin synthesis in the pineal gland of the Richardson's ground squirrel (Spermophilus richardsonii): influence of age and insulin-induced hypoglycemia.

The nocturnal rises in pineal N-acetyltransferase (NAT) activity and melatonin levels were compared in young (25-35 days old) and adult (at least 1 year old) Richardson's ground squirrels. When expressed as NAT activity per pineal gland, the nighttime rise in the activity of this enzyme was less in young than in the adult animals; conversely, the melatonin content of the pineal glands of young animals was higher at one point (4 a.m.

Changes in serotonin levels, N-acetyltransferase activity, hydroxyindole-O-methyltransferase activity, and melatonin levels in the pineal gland of the Richardson's ground squirrel in relation to the light-dark cycle.

Pineal serotonin and melatonin levels and the activities of hydroxyindole-O-methyltransferase (HIOMT) and N-acetyltransferase (NAT) were studied over a 24-hour period in the pineal gland of the diurnally active Richardson's ground squirrel (Spermophilus richardsonii). Under alternating light-dark conditions (light:dark hours 14:10), pineal serotonin and melatonin levels exhibited a rhythm with high values occurring either during the day (serotonin) or during the night (melatonin). NAT activity was also markedly increased during darkness.

The influence of various irradiances of artificial light, twilight, and moonlight on the suppression of pineal melatonin content in the Syrian hamster.

The purpose of the present studies using artificial light was to determine how the timing and duration of exposure influence the light-induced suppression of pineal melatonin levels in hamsters. An 8-min exposure to 0.186 microW/cm2 of cool white fluorescent light caused a continued depression of pineal melatonin even when animals were returned to darkness.

Influence of light irradiance on hydroxyindole-O-methyltransferase activity, serotonin-N-acetyltransferase activity, and radioimmunoassayable melatonin levels in the pineal gland of the diurnally active Richardson's ground squirrel.

When Richardson's ground squirrels were kept under light:dark cycles of 14:10 h there was no nocturnal rise in pineal hydroxyindole-O-methyltransferase (HIOMT) activity. Conversely, the 10 h dark period was associated with large nocturnal rises in both pineal serotonin-N-acetyltransferase (NAT) activity and radioimmunoassayable melatonin levels. The nighttime rises in pineal NAT and melatonin were not suppressed by the exposure of the animals to a light irradiance of 925 mu W/cm2 during the normal dark period.

Studies on the regulation of pineal melatonin production in the Richardson's ground squirrel (Spermophilus richardsonii).

The acute exposure of wild-captured Richardson's ground squirrels to fluorescent light (intensity = 370-400 ftc) at 2400h, 4 hours after the onset of darkness, was followed by a slight depression in the activity of pineal N-acetyltransferase (NAT); during the same 60 min period, pineal melatonin levels were not inhibited. Conversely, when laboratory-raised squirrels were either exposed to light at night or kept in their normal period of darkness, pineal NAT activity and melatonin levels differed greatly between the two groups. In darkness both NAT and melatonin rose sharply and remained elevated during most of the night.

The effects of the light:dark cycle and sympathetically-active drugs on pineal N-acetyltransferase activity and melatonin content in the Richardson's ground squirrel, Spermophilus richardsonii.

When adult Richardson's ground squirrels, born in the wild, are kept in the laboratory under light:dark cycles of 14:10 (lights out at 2000 h), pineal N-acetyltransferase (NAT) activity and melatonin levels begin to rise shortly after lights out; both reach peak levels by 4 h into the dark phase. The rise in pineal NAT activity is partially blocked by phentolamine, an alpha-receptor blocker, and totally blocked by propranolol, a beta-receptor blocker. Phentolamine had no inhibitory influence on the nocturnal rise in pineal melatonin while propranolol partially prevented the increase in melatonin.

Ultrastructure of pinealocytes of the kangaroo rat (Dipodomys ordi).

The ultrastructure of the pinealocytes of the wild-captured ord kangaroo rat (Dipodomys ordi) was examined. A homogeneous population of pinealocytes was present in the pineal gland of the kangaroo rat. The Golgi apparatus, granular endoplasmic reticulum, mitochondria, lysosomes, dense-core vesicles, vacuoles containing a flocculent material and lipid droplets were consistent components of the pinealocyte cytoplasm, whereas infrequently-observed organelles included centrioles, multivesicular bodies, subsurface cisternae, "synaptic" ribbons and cilia.

Studies on pineal melatonin levels in a diurnal species, the eastern chipmunk (Tamias striatus): effects of light at night, propranolol administration or superior cervical ganglionectomy.

Five experiments were carried out on the control of melatonin levels in the pineal gland of a diurnal species, the Eastern chipmunk (Tamias striatus). We confirmed that the exposure of chipmunks of fluorescent white light of 3,981-4,304 lux during the normal dark period does not prevent the rise in pineal melatonin levels normally associated with darkness. Also, the administration of propranolol (20 mg/kg) at 8 p.

Day-night differences in the number of pineal "synaptic" ribbons in two diurnal rodents, the chipmunk (Tamias striatus) and the ground squirrel (Spermophilus richardsonii).

Daytime numbers of pineal "synaptic" ribbons higher than reported in the pineal gland of any other mammalian species were observed in two diurnal rodents, the eastern chipmunk and Richardson's ground squirrel. The number of "synaptic" ribbons was lower during the daytime and higher at night in both of these species.