Pineal atrophy and other neuroendocrine and circumventricular features of the naked mole-rat, Heterocephalus glaber (Rüppell), a fossorial, equatorial rodent

Quantitative aspects of the microanatomy of the pineal gland and other neuroendocrine and circumventricular structures were studied in a small, reproductively suppressed, female Naked Mole-rat from central Kenya, Africa. The atrophic pineal is the smallest in absolute size (0.002135 mm3) of any so far described in a species of rodent, and in size relative to body weight is second only to that of another tropical species. The subcommissural organ and posterior collicular recess are also relatively small and less well differentiated than those in most other examined rodent species. In contrast, the subfornical organ, OVLT and median eminence are large and well vascularized. It is concluded that the pineal in this species follows the previously described trend among rodents of relatively smaller size in species whose centers of distribution are in lower latitudes. Although the pineal is atrophic, the Naked Mole-rat still exhibits 24-hour and seasonally timed patterns of behavior and seasonal reproduction. However, in this species these events are probably cued by moisture, temperature and social factors rather than by photic information.

The invagination complex in nerve endings on adrenomedullary adrenaline cells: quantitative ultrastructural description, and analysis of changes with time-of-day and their modification by sham-surgery and pinealectomy

This work describes a special ultrastructural feature, the invagination complex (IC), involving the plasma membrane of nerve endings on adrenomedullary adrenaline cells. Quantitative characteristics of the IC and their changes were studied in 122 male albino (Holtzman strain) rats in 3 surgical groups: normal (non-operated, NO) sham-operated (SO) and pinealectomized (PX), all maintained in a standardized daily photoperiod (light : dark 12 : 12 h). Animals were decapitated 14 days postsurgery and at 8 specific times during the light : dark cycle. Left adrenal glands were removed, dn strain) rats in 3 surgical groups: normal (non-operated, NO) sham-operated (SO) and pinealectomized (PX), all maintained in a standardized daily photoperiod (light : dark 12 : 12 h). Animals were decapitated 14 days postsurgery and at 8 specific times during the light : dark cycle. Left adrenal glands were removed, dn strain) rats in 3 surgical groups: normal (non-operated, NO) sham-operated (SO) and pinealectomized (PX), all maintained in a standardized daily photoperiod (light : dark 12 : 12 h). Animals were decapitated 14 days postsurgery and at 8 specific times during the light : dark cycle. Left adrenal glands were removed, dissected and prepared for electron microscopy. In section profiles the diameter of each IC was usually 0.12-0.40 micrometers, and the depth 0.2-1.0 micrometers. They were frequently seen to be located near the synaptic complex (or the active zone). Coated pits, about 50 nm wide and 60 nm deep, often opened near the bottom of the invaginations of the IC. In NO animals, relative number and depth of the ICs showed daily rhythmic changes with minimal values about 1 h after onset and maximal (acrophase) values 3--5 h later (P less than 0.02 to less than 0.005, depending on index or measure). These changes occurred 3--5 h earlier, but less apparently, in SO animals, and appeared to be more greatly modified and dampened in PX animals. Two-way analysis of variance (ANOVA) and t-tests applied to 11 kinds of indices derived from counts and measurements of the ICs, support the differences between surgical groups, at least in many instances (P less than 0.05 to less than 0.001). It is concluded that the IC is a characteristic and dynamic feature of the nerve terminals and that it may possibly have a role in such phenomena as recycling of synaptic vesicles or related membrane constituents. It is also concluded that significant time-of-day and neuroendocrine effects are demonstrable in these structures, and that the time-of-day effects shown in these chronic studies have importance in the design of acute experiments designed to further test the functional relations and importance of ICs.

Pineal effects on metabolism and glucose homeostasis: evidence for lines of humoral mediation of pineal influences on tumor growth

Results from animal experiments support the hypothesis that pineal gland function can influence some aspects of tissue metabolism and glucose homeostasis. Evidence of pineal effects on particular endocrine and sympatheto-adrenal targets contributes to an understanding of indirect routes by which pineal activity can possibly affect the growth and activity of some kinds of tumors, in part through nutrient and metabolic effects in the tissue environment of the tumor cells.

Experimental and spontaneous pineal tumors: findings relating to endocrine and oncogenic factors and mechanisms

Pineocytomas have been induced in a high percentage of hamsters inoculated intracerebrally within 24 hours after birth with particular strains of a human papovavirus. Studies on biochemical and ultrastructural charactertistics and transformation of such experimentally induced pineal tumors have led to important conclusions and implications: (1) Many of the differentiated pineocytoma cells contained organelles and related structures that are characteristic of hamster pineocytes, and others that are reminiscent of possible phylogenetic precursors, including pineal photoreceptor cells. (2) An inverse relationship was noted between degree of cytological differentiation and level of hydroxyindole-O-methyltransferase (HIOMT) activity in the pineocytomas. (3) It is therefore apparent that even when pineal tumor formation leads to great increase in pinealocyte-like cells, their enzymatic capacity for synthesis fo melatonin, and possibly of other humoral products, may be only 4 to 7% of that of normal pinealocytes if they are of a relatively less differentiated type. A number of important and basic questions are accessible and remain to be investigated via experimental pineocytomas, such as: (1) nature and significance of cytological interactions within the pineal; (2) probable occurrences, correlations and transformations of other pineal biosynthetic and hormonal processes; (3) degree and nature of environmental (photic, circadian and circannual factors) and physiologic controls; and (4) kinds of modifications of pineal-related functions.

Effect of methionine, glycine and serine on serine hydroxymethyltransferase activity in rat glioma and human neuroblastoma cells

Human neuroblastoma SK-N-SH-SY5Y (5Y) and rat glioma (C6) cells were cultured with supplemental methionine, glycine, or serine for three to six days. Serine hydroxmethyltransferase (SHMT: L-serine: tetrahydrofolate 5, 10-hydroxymethyltransferase, EC 2.12.1) was assayed radiometrically in whole cell homogenates, crude supernatant fractions and crude particulate fractions. No significant changes in specific activity or cellular morphology were noted at methionine, glycine, or serine concentrations up to 16 mM. Serine concentrations of 20 and 40 mM led to significantly lower gliomal enzyme specific activities. This activity was unevenly distributed between soluble and particulate fractions, with 190 and 398 nmoles of HCHO formed per mg of protein per hour, respectively. Growth stage and time of incubation were major determinants of enzyme specific activity. C6 cells' specific activity rose slowly with increasing time in culture until cellular confluence. At this time there was a pronounced elevation in specific activity, occurring more rapidly in cells grown in 1.2 mM methionine. Intracellular amino acid analysis of C6 cells demonstrated a significant rise in methionine after four days in media containing 0.2 mM methionine. No appreciable diminution in the intracellular levels of glycine or serine occurred following incubation in excess methionine. It is concluded that SHMT-specific activity in C6 and 5Y cells is not regulated by glycine, serine, or methionine levels and that high concentrations of these amino acids (> 30 mM) are not detrimental to these cells derived from the CNS.

Adrenal and hypothalamic dopamine-beta-hydroxylase activity in the hamster: evidence for species-distinctive day-night and post-pinealectomy differences in activity

Dopamine-beta-hydroxylase (DBH) activities were measured in the adrenal gland and hypothalamus of the golden hamster (Mesocricetus auratus) by means of a sensitive radioenzymatic method. Groups of unoperated control (C), sham pinealectomized (SPX), and pinealectomized (PX) adult males were sacrificed shortly before (09:00 h) and after (11:00 h) the onset of darkness of the daily photoperiod of LD 12:12 (lights on 22:00 h to 10:00 h). In neither adrenal gland nor the hypothalamus were there any day-night changes in the C groups. Pinealectomy led to no significant differences in hypothalamic DBH activity either in light or in dark. However, intracranial surgery resulted in increased DBH activity in the adrenal gland, evident in both light and dark. Although this increase was greatest in the PX groups, intracranial surgery in SPX groups also showed a trend of increase in adrenal DBH, evident even one month after surgery. Such an increase, however, was not found in hypothalamic DBH in the same SPX groups. In both the adrenal gland and the hypothalamus, copper-sensitive endogenous inhibitors of DBH did not show any notable change in concentration, either in relation to the daily light-to-dark change or as a consequence of intracranial surgery. These and related results suggest that important interspecies variations exist in DBH activities in relation to diurnal changes, and also in control or modulation by pineal and other factors.

Effects of pinealectomy and pineal incubation medium and sonicates on insulin release by isolated pancreatic islets in vitro

The present studies were designed to investigate the mechanism of previously-reported nocturnal hyperinsulinemia in the pinealectomized rat. Isolated islets were obtained from anesthetized control, sham-pinealectomized and pinealectomized rats, with 5 rats per surgical groups, during the early dark phase of the daily lightdark cycle. Batches of 3 islets each were incubated in various combinations of 2, 10 or 30 mM glucose with control buffer, medium in which cerebral cortex or pineal glands had previously been incubated for 2 hours, or sonicates of these same tissues. Insulin released into the culture medium was measured by radioimmunoassay. A significant hypersecretion of insulin was demonstrable in the islets from the pinealectomized animals. A stimulatory effect of both pineal medium and sonicates upon insulin release was similarly observed. Neither of these effects displayed an interaction with the concentration of glucose in the islet incubation medium and they, therefore, appear to be mediated by a mechanism which operates independently of stimulation by glucose. These results indicate that the rat pineal gland can exert direct effects upon insulin release from the islets, possibly through a humoral route. Further studies are in progress to characterize the nature and mode of action of the insulinotropic agent present in and released from the pineal gland.

Circadian changes in adrenal dopamine-beta-hydroxylase activity: dependency of change at darkness onset, and the effect of pinealectomy, on animal strain and age

In a previous study we found a daily darkness- and pineal-dependent rise in adrenal dopamine-beta-hydroxylase (DBH) activity in 4-month-old S1 rats. The present investigation shows that aged (12 to 14-month-old) S1 rats do not have such a change in DBH activity. Similarly in the relatively younger (100-day-old) rats of a different (Holtzman) strain such a change was not found. Also pinealectomy did not seem to have any effect on adrenal DBH in either of these two strains of rats, young or old at times just before and after the onset of darkness. In both S1 and Holtzman rats, the concentration of copper-sensitive endogenous inhibitors of DBH remained unaltered following the surgical extirpation of pineal. Photoperiodic change from light to dark also had no significant effect on the inhibitor content in these two strains of rats. It is concluded that there are age and strain dependencies in the behavior of adrenal DBH activity at the daily onset of darkness.

Androgens and brain differentiation. Effects of testosterone on protein synthesis in neonatal rat hypothalamic and cerebral slices

Protein synthetic activity of anterior hypothalamic and neocortical brain slices from androgenized neonatal female rats was studied in vitro in an attempt to clarify the mechanism of action of testosterone on the developing hypothalamus. The short-term effects of testosterone propionate injections of the animals on the protein synthetic activity of the slices were assayed by means of incorporation of 14C-leucine into acid-insoluble protein. Although a high dose (1 mg/animal) of testosterone propionate stimulated increased incorporation in neocortical and anterior hypothalamic slices, a lower dose and other approaches failed to demonstrate a stimulation regionally specific to the anterior hypothalamus. It is concluded that if testosterone has specific stimulatory effects on protein synthesis in the anterior hypothalamus of neonatally androgenized rats, these are not readily demonstrable by methods used with other steroid target tissues.

Daily rhythmic changes in synaptic vesicle contents of nerve endings on adrenomedullary adrenaline cells, and their modification by pinealectomy and sham operations

Nerve endings on adrenaline cells in male rat adrenal medullas were investigated by quantitative electron microscopy, with sampling at 8 times during a standard light: dark (12:12) photoperiod. Number (N) per unit area of 2 vesicle types (small clear vesicle, SCV; large granular vesicle, LGV) and % of LGV per total vesicle N were determined. Normal (non-operated) animals showed a circadian rhythm (p less than 0.005) in mean SCVN and one with nearly opposite phase relations in % LGVN. Doubly sham-operated animals had a similar rhythm in %LGVN but diminished circadian change in SCVN. Pinealectomized animals had a circadian pattern in SCVN, but this differed from that of normals in having a 2nd peak, a delay or phase shift of the primary peak, and an increased amplitude of the rhythmic changes.

Cystathionine synthase in rat brain: regional and time-of-day differences and their metabolic implications

In relation to concern for probable interrelations of cystathionine synthase (CS, EC 4.2.1.21) and methionine, one-carbon, and 5-hydroxytryptamine metabolism, we have investigated tissue and time-of-day differences in CS activity in the laboratory rat under standardized conditions. Liver, kidney, and pancreas had highest CS activities; nine regions of the CNS had mean activities ranging from 4.5% (lumbosacral cord) to 24.5% (hypothalamus) of mean hepatic activity; pituitary and adrenal glands lacked detectable CS activity. Although significantly lower CS activity occurred in liver (9%, P less than 0.050) and kidney (13%, P less than 0.025) during the interval two hours before to two hours after the daily onset of darkness, no significant changes were found in hypothalamus, cerebellum, or medulla oblongata. Regional CNS differences in CS activity appeared to be without correlation in relation to published data on relative contents of 5-hydroxytryptamine, tryptophan 5-hydroxylase (EC 1.14.16.4), 5,10-Methylene reductase (N5-methyltetrahydrofolate-NAD-oxidoreductase, (EC 1.1.1.78), or 5-methyltetrahydrofolate. Therefore, among CNS regions examined, a critical deficiency in ability to metabolize a homocysteine load is considered to be unlikely under normal conditions.

Quantitative morphology and environmental responses of the pineal gland in the collared lemming (Dicrostonyx groenlandicus)

Collared lemmings from Churchill, Manitoba, and their descendants were studied in captivity to define neuroendocrine and related histophsiological characteristics and responses, particularly in relation to photic and temperature conditions. Relatively great pineal size (0.1755 +/- 0.0167 mm3, or 3.08 +/- 0.30 = pineal volume in mm3 X 10(3)/body weight in gm; N = 16) shown in this arctic rodent is consistent with the suggestion that pineal size and significance may tend to be greater in more northern (higher latitude) species. Total number of nucleated cells per pineal averaged 137,000 +/- 10,500. Pinealocytes (105,000 +/- 8,700/pineal) and other cell types were present in relative numbers typical of mammalian pineal glands, and were not numerically correlated with age, sex, or location or circumstances of birth and early postnatal life. Chronic exposure to warmer (21-27 degrees C) in comparison with colder (-9 to -6 degrees C) environments, whatever the illumination, led to greater pinealocyte activity, as shown especially by nucleolar diameter, throughout most of the nine regions of the organ analyzed cytologically (all regions combined: P less than 0.001). Increased pinealocyte activity in chronic darkness was suggested by similar evidence (P less than 0.01), but in comparison with the thermal effects, was less marked and more variable in different regions of the organ. These and other findings of this study indicate that the Dicrostonyx pineal organ is morphologically unique, relatively large in size, and cytologically responsive to environmental conditions.

Modification of plasma dopamine-beta-hydroxylase activity by adrenal and pineal extirpations, and time of day dependency of changes

Plasma level of dopamine-beta-hydroxylase (DBH; EC 1.14.2.1) activity has been considered important both as a diagnostic aid and as an indicator of temporal changes in sympathetic activity. The present study sought to evaluate the possible dependency of some phases of the circadian rhythm in plasma DBH on adrenal and pineal glands. Male Holtzman (albino) rats were shamoperated, adrenalectomized (AX), pinealectomized (PX) or both adrenalectomized and pinealectomized (AXPX) at 32-35 days of age and after acclimation to controlled conditions with a fixed, 12-h, daily photoperiod (LD 12:12). Animals were killed at selected times 15 days postoperatively, and plasma DBH was measured using a sensitive radioenzymatic method. Results from two successive experiments showed that there was significant reduction in plasma DBH in the AXPX animals, but that this was evident only during the middle of the dark phase. PX and AX alone did not bring about any change in the DBH activity at any of the two times tested. These results show that combined endocrine manipulations can alter the circulatory DBH activity level and that such changes can be evaluated only within the definition of a circadian pattern.

Effects of pinealectomy and of sham-pinealectomy on blood glucose levels in the alloxan-diabetic rat

Alloxan-diabetic male rats were used to test effects of pinealectomy (PX) and of sham-pinealectomy (SPX) on blood glucose levels at mid-dark in the daily light-dark (LD 12:12) cycle. Animals received a diabetogenic dose of alloxan 10 days postoperatively. Blood glucose was measured on days -1,1,2,3,4,5,7,10 and 15 after 8-hour fasts. Pinealectomized (PX) and non-operated (C) animals were equivalent in their hyperglycemia following alloxan. SPX animals contrastingly showed significantly less response to alloxan than did animals of the other two groups. This difference of the SPX animals was in terms of lower hyperglycemia, better maintenance of body weight and of survival. It is concluded that intracranial surgery alone (SPX) and without visible brain damage can affect mechanisms of glucose homeostasis, and that at least in some circumstances such a surgical effect is not only different from effects of surgical pinealectomy (PX), but is also probably not pineal-dependent.

Hypothalamic dopamine-beta-hydroxylase activity: fluctuations with time of day and their modifications by intracranial surgery, adrenalectomy, and pinealectomy

Hypothalamic and plasma dopamine-beta-hydroxylase [DBH, EC 1.14.2.1] activites were measured by a coupled radioenzymatic method. Animals representing five experimental groups [intact controls, adrenalectomized, pinealectomized, adrenalectomized pinealectomized, doubly sham-operated] were killed and sampled at 8 times through the 24-hr daily cycle, 15 days postoperation, and at 50-52 days of age. Hypothalamic DBH in intact control animals had statistically significant fluctuations in relation to time of day. These changes were lost or dampened in groups that had had intracranial surgery and were characteristically shifted by adrenalectomy, either alone or with pinealectomy. Plasma DBH fluctuations in the same animals resembled those in hypothalamus in some features (e.g., peak near mid-dark; shift in daily maxima and minima after adrenalectomy) and differed in others [e.g., no effect of intracranial surgery or of sham operation; adrenalectomized pinealectomized animals resembled the solely pinealectomized]. Although temporal patterns in hypothalamic DBH activity thus differed in the experimental animal groups, the daily means of hypothalamic DBH activity were similar.

Quantitative characteristics of the Feyrter cells and neuroepithelial bodies of the fetal rabbit lung in normoxia and short term chronic hypoxia

We report here quantitative data on the Feyrter (single) cells (APUD cells) and neuroepithelial bodies (grouped Feyrter cells), in the lungs of rabbit fetuses at 26, 27.5 and 29 days gestational age, during normoxia and short term chronic hypoxia. The apparent number of these cells declines during this period; we suggest that this might be due to increased hypoxemia. Moreover, the number of cells in the lungs of fetuses from short term chronically hypoxic mothers is lower than in the normoxic animals. These findings are in agreement with our previous studies in short term chronically hypoxic neonatal rabbits, and suggest that the increased hypoxemia in the fetus, caused by the induction of hypoxia in the mother, constitutes a stimulus for secretory activity of the Feyrter cells and neuroepithelial bodies (NEBs). This in turn could be part of the mechanism responsible for maintaining the pulmonary vasoconstriction due to hypoxemia. Our results from fetuses of normoxic does provide base line data on the chronological importance of the Feyrter cells and NEBs.

A radioautographic study of the neuroepithelial bodies of the lungs in fetal and neonatal rabbits

The neuroepithelial bodies (NEB's) of the lung of 29-day-old fetuses and 1-day-old rabbits, under the conditions of this study, neither take up 3H-thymidine nor undergo mitosis. Also the NEB's are not derived at these times from proliferations of other kinds of epithelial cells in the intrapulmonary airways. It is, therefore, suggested that the difference in numbers of NEB's previously observed by us, between the 29-day fetus and the 1-day-old rabbit, is due either to regranulation or acquisition of argyrophilic material by the NEB's or differentiation of other epithelial types. It is concluded that the NEB's are composed of well differentiated cells, which have a greatly reduced capacity to undergo mitosis.