Functional relationships between sympathetic nerves and pinealocytes in the mouse pineal: quantitative electron microscopic observations

Circadian disruption, melatonin rhythm perturbations and their contributions to chaotic physiology

The aim of this report is to summarize the data documenting the vital nature of well-regulated cellular and organismal circadian rhythms, which are also reflected in a stable melatonin cycle, in supporting optimal health. Cellular fluctuations in physiology exist in most cells of multicellular organisms with their stability relying on the prevailing light:dark cycle, since it regulates, via specialized intrinsically-photoreceptive retinal ganglion cells (ipRGC) and the retinohypothalamic tract, the master circadian oscillator, i.e., the suprachiasmatic nuclei (SCN). The output message of the SCN, as determined by the light:dark cycle, is transferred to peripheral oscillators, so-called slave cellular oscillators, directly via the autonomic nervous system with its limited distribution. and indirectly via the pineal-derived circulating melatonin rhythm, which contacts every cell. Via its regulatory effects on the neuroendocrine system, particularly the hypothalamo-pituitary-adrenal axis, the SCN also has a major influence on the adrenal glucocorticoid rhythm which impacts neurological diseases and psychological behaviors. Moreover, the SCN regulates the circadian production and secretion of melatonin. When the central circadian oscillator is disturbed, such as by light at night, it passes misinformation to all organs in the body. When this occurs the physiology of cells becomes altered and normal cellular functions are compromised. This physiological upheaval is a precursor to pathologies. The deterioration of the SCN/pineal network is often a normal consequence of aging and its related diseases, but in today's societies where manufactured light is becoming progressively more common worldwide, the associated pathologies may also be occurring at an earlier age.

The ultrastructure of mammalian pinealocytes: a systematic investigation

Pinealocytes are not only the principal cellular components of the pineal gland, but they are also the principal synthetic machinery of this enigmatical gland with highly diverse and often questionable empyreal roles assigned to it. Ultrastructural descriptions of pinealocytes belonging to some 70 species of mammals (a mere 2% or less of the over 4,200 mammalian species) have been summarized from the available literature with new observations on 12 species of chiropterans. Space limitation precluded any treatment of the supporting glia, neural elements, and the perivascular spaces. A detailed table lists nearly all mammalian species whose pineal ultrastructure has been investigated. Blanks in this table point to the necessity of studies on those particular groups. A tabular listing of unusual structures reported within the pinealocyte cytoplasm points out the impending experimental work on these species. Such studies using the latest techniques might provide clearer insights into the functional role of the pineal gland as an important and integral component of the neuroendocrine axis. Whereas sufficient structural information now exists on cytoplasmic organelles such as synaptic ribbons and spherules, annulate lamellae, subsurface cisterns, and the several types of synaptic arrangements seen in relation to the pinealocyte soma and its processes, the functional role of these structures in pineal synthetic processes remains to be elucidated.

Effect of continuous darkness on diurnal rhythms in small vesicles in sympathetic nerve endings of the mouse pineal-quantitative electron microscopic observations

Quantitative electron microscopic studies on the effect of continuous darkness on the diurnal rhythm of small vesicles in sympathetic nerve endings of the mouse pineal demonstrate that the numerical change of type 1 granulated vesicles, predominant small granulated vesicles, and non-granulated elliptical vesicles seen during the first half of the dark period under diurnal lighting conditions may persist for at least 14 days under continuous darkness. Furthermore, it is found that the alteration in the number of type 1 granulated vesicles and the total vesicle density observed during the light period under diurnal lighting conditions may be lost in mice kept in continuous darkness for 7 days. This result indicates that the type 1 granulated vesicles may be composed of two different populations of vesicles, i.e., granulated vesicles of population 1 and 2, and that the diurnal rhythm in the number of the granulated vesicles of population 1 may be abolished, while that of the granulated vesicles of population 2 may be maintained, under continuous darkness. The diurnal variation in the number of the type 2 granulated vesicles, which constitute a small population of small granulated vesicles, may persist in darkness. Thus, the diurnal rhythm in the number of small granulated vesicles in sympathetic nerve endings of the mouse pineal may be controlled by two different mechanisms, exogenous and endogenous.

Effects of continuous lighting or continuous darkness on large granulated vesicles in sympathetic nerve fibers of the mouse pineal--quantitative electron microscopic observations

The influence of continuous light or darkness on the large granulated vesicles in sympathetic nerve fibers of the mouse pineal was investigated by means of quantitative electron microscopic techniques. Continuous illumination at about 20 lux caused the disappearance of the diurnal rhythm in the number of the large granulated vesicles, followed by an accumulation of these vesicles. The diurnal rhythm of the large granulated vesicles was abolished in mice kept in continuous darkness for 7 days. These results suggest that the diurnal variation of the large granulated vesicles may be controlled directly by environmental light. Based on these findings, the relationships between small and large granulated vesicles were discussed.

Ultrastructure of pinealocytes of the cotton rat, Sigmodon hispidus

Fine structural features of pinealocytes of cotton rats (Sigmodon hispidus) were examined. Golgi complexes, mitochondria, endoplasmic reticulum and polysomes are usual organelles seen in the perikaryonal cytoplasm of pinealocytes. Many non-granulated vesicles (40 to 80 nm in diameter) and a few granulated vesicles (about 100 nm in diameter) are associated with the Golgi cisternae. Occasionally, the cisternae contain granular materials. The perikaryonal cytoplasm of pinealocytes is characterized by the presence of inclusion bodies. These bodies are usually round in shape, not bounded by a limiting membrane and composed of fine granular or filamentous materials of high electron-opacity, which are similar in appearance to the substance seen in the nucleolonema. Pinealocyte processes, filled with abundant non-granulated vesicles and some granulated vesicles, are mainly found within the parenchyma and occasionally in perivascular spaces.

Further studies on diurnal changes in small vesicles in sympathetic nerve endings in the mouse pineal and the effects of continuous light on the vesicles--quantitative electron microscopic observations

Diurnal variations in the number of various types of small granulated and non-granulated vesicles as well as effects of continuous light on the vesicles in sympathetic nerve endings of the mouse pineal were investigated using quantitative electron microscopic techniques. Small granulated vesicles, 40 to 80 nm in diameter, were classified into two categories, type 1 or type 2, according to the size of the granule. Small non-granulated vesicles were also divided into two categories, i.e., spherical and elliptical. Non-granulated vesicles with the long diameter more than twice the shorter one (ranging from 50 to 90 nm in long diameter) were referred to as elliptical vesicles and the other (ranging from 40 to 80 nm in diameter) as spherical vesicles. The number of small vesicles, except for the non-granulated spherical vesicles, varied diurnally in relation to the daily photoperiod. The total vesicle density also exhibited diurnal changes. On the basis of these observations, possible relationships between small vesicles and noradrenaline or serotonin were discussed. Both the diurnal variation in small vesicles and that in the total vesicle density were completely abolished by continuous lighting. Continuous light exposure for various periods until 35 days provoked no apparent changes in small vesicles, except the type 2 granulated vesicles, which were increased in number in response to continuous lighting for about 1 to 3 days.

Diurnal variation in large granulated vesicles in sympathetic nerve fibers of the mouse pineal--quantitative electron micrsocopic observations

Quantitative electron microscopic studies of the sympathetic nerve fibers of the mouse pineal demonstrated a marked diurnal rhythm in the number of the large granulated vesicles of 80 to 150 nm diameter. The number of these vesicles showed its minimum at the middle and the end of the dark period and its maximum at the end of the light period, respectively. The large non-granulated spherical and elliptical vesicles were almost constant in number throughout the day.