A lens-like specialization for photic input in the pineal window of an Indian catfish,Heteropneustes fossilis

Summary An unusual lens-like structure is reported in the pineal window of the Indian nocturnal catfishHeteropneustes fossilis. This is the first report of its kind for the pineal window of fishes. This structure, coupled with a pineal fossa and a pineal window, forms a specialization that apparently serves to concentrate the photic input to the intracranially situated pineal organ. This structure may play a significant role in the photoneuroendocrine function of the photosensitive pineal under conditions of low light intensity, controlling the fish's circadian rhythmic activities.The work was financially supported by CSIR, New Delhi (sanction No. 38(693)/88/EMR-II dated May, 1988) which is thankfully acknowledged.     

Estimation of the methylating capacity of the pineal gland. With special reference to indole metabolism

In order to obtain more information on the methylating capacity of the pineal gland, a method determining the formation of different 5-methoxyindoles in the pineal gland was developed. The method depends on measuring the incorporation of labelled methyl groups into the various hydroxyindoles present in the pineal gland, after incorporation of pineal tissue with labelled S-adenosyl methionine. Hydroxyindoles were not added to the incubation medium. After incubation thin-layer chromatography was performed with pineal tissue together with the incubation medium; the spots were scraped and counted.     

Pineal function cannot prevent the occurrence of castration cells in male rats

The relationship between the pineal gland and the pituitary gland was investigated in male rats. The results indicate that the hypothalamo-adenohypophysial-gonadal axis is affected by the pineal gland, but the appearance of castration cells following gonad ablation may be only slightly modified by alterations in pineal gland function.     

Pineal function cannot prevent the occurrence of castration cells in male rats

Summary The relationship between the pineal gland and the pituitary gland was investigated in male rats. The results indicate that the hypothalamo-adenohypophysial-gonadal axis is affected by the pineal gland, but the appearance of castration cells following gonal ablation may be only slightly modified by alterations in pineal gland function.     

Peripheral sympathetic innervation of the deep pineal gland of the golden hamster

Summary Both the superficial and deep pineal components of the intact hamster contain a rich network of green to yellow-green fluorescent nerve fibres. After either superior cervical ganglionectomy or after transection of the nervi conarii the majority of the fluorescing fibres disappeared from both the superficial and deep pineal mases. Although the deep pineal remained intact after surgical removal of the superficial pineal, it was devoid of any green or yellowgreen fluorescent fibres.Supported by NSF Grant No. BMS74-06275A01     

Estimation of the methylating capacity of the pineal gland. With special reference to indole metabolism

Summary In order to obtain more information on the methylating capacity of the pineal gland, a method determining the formation of different 5-methoxyindoles in the pineal gland was developed. The method depends on measuring the incorporation of labelled methyl groups into the various hydroxyindoles present in the pineal gland, after incorporation of pineal tissue with labelled S-adenosyl methionine. Hydroxyindoles were not added to the incubation medium. After incubation thin-layer chromatography was performed with pineal tissue together with the incubation medium; the spots were scraped and counted.The authors wish to express their gratitude to Prof. Dr. J.C. van de Kamer and Dr F.C.G. van de Veerdonk for their stimulating interest in these studies.     

Ultrastructure and biochemistry of the pineal organ in deep-sea lanternfishes (Myctophidae)

Summary Pineal structural and biochemical adaptations in lanternfishes included: 1) few photoreceptor outer segment discs; 2) conventional synapses between photoreceptors and pineal neurons; and 3) low levels (0–60 pg/pineal) of serotonin compared to those (>1.0 ng/pineal) in the goldfish pineal organ. These findings suggest reduced photosensory and/or neuroendocrine functions in these deep-sea fishes.     

Scanning electron microscope observations of the canaliculi in the rat pineal gland.

The scanning electron microscope has shown rich ramifications of the parenchymal canaliculi forming a three-dimensional network of anastomosing intercellular spaces in the rat pineal gland. Every pineal cell seems to be in contact with this channel system. An abundance of cellular processes can be found within the canaliculi which may play an important role in the histophysiology of the pineal body.     

Ultrastructure and biochemistry of the pineal organ in deep-sea lanternfishes (Myctophidae)

Pineal structural and biochemical adaptations in lanternfishes included: 1) few photoreceptor outer segment discs; 2) conventional synapses between photoreceptors and pineal neurons; and 3) low levels (0-60 pg/pineal) of serotonin compared to those (greater than 1.0 ng/pineal) in the goldfish pineal organ. These findings suggest reduced photosensory and/or neuroendocrine functions in these deep-sea fishes.     

Histochemical localization of cholinesterases in the neural tissue of the pineal in the rhesus monkey.

The neural tissue of the monkey pineal contains both acetyl and butyryl cholinesterases. Acetylcholinesterase was localized in the cisternae of the nuclear membrane, rough endoplasmic reticulum, on the plasma membrane of the neurones, and on the axolemma of both non-myelinated and myelinated fibres. The enzyme was not found in the axosomatic or axo-dendritic synapses. It is therefore suggested that the pineal neurones have a cholinergic function rather than a cholinoceptive one.     

Scanning electron microscope observations of the canaliculi in the rat pineal gland

Summary The scanning electron microscope has shown rich ramifications of the parenchymal canaliculi forming a three-dimensional network of anastomosing intercellular spaces in the rat pineal gland. Every pineal cell seems to be in contact with this channel system. An abundance of cellular processes can be found within the canaliculi which may play an important role in the histophysiology of the pineal body. Dedicated to Prof. Dr. med.W. Bargmann on the occasion of his 70th birthday.     

The pineal and melatonin: regulators of circadian function in lower vertebrates

The pineal has been identified as a major circadian pacemaker within the circadian system of a number of lower vertebrates although other pacemaking sites have been implicated as well. The rhythmic synthesis and secretion of the pineal hormone, melatonin, is suggested as the mechanism by which the pineal controls circadian oscillators located elsewhere. Both light and temperature cycles can entrain the pineal melatonin rhythm. The pineal, therefore, acts as a photo and thermoendocrine transducer which functions to synchronize internal cycle with cycles in the environment. A model is presented which portrays the pineal as a major component of a 'multioscillator' circadian system and which suggests how these multiple circadian clocks are coupled to each other and to cycles of light and temperature in the external world.     

Development of rhythmic melatonin synthesis in cultured pineal glands and pineal cells isolated from chick embryo

The chick pineal gland exhibits circadian rhythms in melatonin synthesis under in vivo and in vitro conditions. A daily rhythm of melatonin production was first detectable in pineal glands isolated from chick embryos at embryonic day 16 and incubated under a LD cycle. All pineal glands isolated from 17-day-old and older embryos were rhythmic while no gland isolated at embryonic day 14 and 15 exhibited a daily rhythm in melatonin synthesis. Melatonin production in static cultures of embryonic pineal cells was rhythmic over 48 h if the cells were kept under a LD cycle. When embryonic pineal cells were incubated in constant darkness the rhythm in melatonin production was damped within 48 h. These results suggest that chick pineal cells from embryonic day 16 onwards are photosensitive but that the endogenous component of the melatonin rhythm is not completely developed at that age. A soluble analogue of cAMP stimulated and norepinephrine inhibited melatonin synthesis in cultured embryonic pineal cells. These findings indicate that the stimulatory and inhibitory pathways controlling melatonin synthesis in the mature pineal gland are effective in pineal cells isolated from chick embryos at least 2 days before hatching.     

Effect of testosterone on the hypothalamic-pituitary-gonadal axis of pinealectomized and pineal-intact male rats.

Previous studies indicate that steroid hormones alter pineal biochemistry, and it has been suggested that at least part of the negative feedback effect of steroid hormones on pituitary gonadotropin release may be mediated by the pineal gland. In this study, pinealectomy did not alter the inhibitory effect of testosterone on neuroendocine-gonadal activity in the male rat, suggesting that the pineal gland does not mediate the response of the rat hypothalamic-pituitary axis to testosterone.     

Histochemical localization of cholinesterases in the neural tissue of the pineal in the rhesus monkey

Summary The neural tissue of the monkey pineal contains both acetyl and butyryl cholinesterases. Acetylcholinesterase was localized in the cisternae of the nuclear membrane, rough endoplasmic reticulum, on the plasma membrane of the neurones, and on the axolemma of both non-myelinated and myelinated fibres. The enzyme was not found in the axosomatic or axo-dendritic synapses. It is therefore suggested that the pineal neurones have a cholinergic function rather than a cholinoceptive one.This study was supported by the WHO.     

The pineal and melatonin: Regulators of circadian function in lower vertebrates

Summary The pineal has been identified as a major circadian pacemaker within the circadian system of a number of lower vertebrates although other pacemaking sites have been implicated as well. The rhythmic synthesis and secretion of the pineal hormone, melatonin, is suggested as the mechanism by which the pineal controls circadian oscillators located elsewhere. Both light and temperature cycles can entrain the pineal melatonin rhythm. The pineal, therefore, acts as a photo and thermoendocrine transducer which functions to synchronize internal cycle with cycles in the environment. A model is presented which portrays the pineal as a major component of a multioscillator circadian system and which suggests how these multiple circadian clocks are coupled to each other and to cycles of light and temperature in the external world.     

Electron diffraction of the metallic elements in the pineal organ of a freshwater fish,Mystus vittatus (Bloch.)

Summary By electron diffraction pattern the presence of metallic elements, particularly chromium-nickel, chromium phosphide, copper, aluminum-copper and zinc has been shown in the pineal organ of a freshwater teleost,M. vittatus. It is likely that their occurrence within the pineal is due to binding with the neurosecretory material fractions/ligands.The technical assistance of O.N. Srivastava and financial assistance of CSIR, India, are gratefully acknowledged.     

The pineal and melatonin: Regulators of circadian function in lower vertebrates

Summary The pineal has been identified as a major circadian pacemaker within the circadian system of a number of lower vertebrates although other pacemaking sites have been implicated as well. The rhythmic synthesis and secretion of the pineal hormone, melatonin, is suggested as the mechanism by which the pineal controls circadian oscillators located elsewhere. Both light and temperature cycles can entrain the pineal melatonin rhythm. The pineal, therefore, acts as a photo and thermoendocrine transducer which functions to synchronize internal cycle with cycles in the environment. A model is presented which portrays the pineal as a major component of a multioscillator circadian system and which suggests how these multiple circadian clocks are coupled to each other and to cycles of light and temperature in the external world.     

Photoreceptors in the pineal of lower vertebrates: Functional aspects

Summary The pineal of lower vertebrates characteristically contains true and modified photoreceptors with functional und structural homologies to retinal photoreceptors. Afferent nerves convey photic information from the pineal to sensory areas of the brain stem. Light also influences synthetic activity within the organ, controlling the rhythm in melatonin production which is generated endogenously. The molecular mechanisms underlying this rhythmic event are described and the hypothesis advanced that the pineal transduces several forms of environmental stimulus involved in the regulation of rhythmic function.     

Central neural control of pineal melatonin synthesis in the rat

To investigate a possible central neural influence on nocturnal pineal metabolic activity in rats, frontal transsections of the stria medullaris thalami were conducted. Enzymes involved in melatonin synthesis, i.e. N-acetyltransferase and hydroxyindole-O-methyl-transferase, exhibited reduced activities in operated animals when compared to controls. These results indicate a modulatory role of central structures on nocturnal pineal indole metabolism.