Indolamine Metabolism in the Intact and Denervated Pineal, Pineal Stalk and Habenula

Abstract

Indolamine metabolism in the rat pineal is regulated by central influences mediated through the superior cervical sympathetics. The pineal stalk and medial habenular nucleus also have serotonin-containing cells and an innervation from the superior cervical ganglion (SCG). The present study was carried out to determine if the habenula and pineal stalk are similar to the pineal in certain aspects of indolamine metabolism. No diurnal rhythm in habenular serotonin content was observed, but ganglionectomy or decentralization of SCG results in a significant increase in habenular serotonin content. Unlike the pineal, the habenula and pineal stalk exhibit no rhythm in N-acetyltransferase (N-AT) activity; the activity of the enzyme in those tissues is comparable to low values of the diurnal rhythm in the pineal. N-AT activity in the pineal stalk and habenula is unaffected by sympathectomy. Similarly, there is little, if any, hydroxyindole-O-methyltransferase (HIOMT) activity in the pineal stalk and habenula; unlike the pineal, it is unaffected by continuous environmental lighting conditions or sympathectomy. These observations indicate that neither the pineal stalk nor the habenula represents a ‘deep’ pineal in the rat but that habenular indolamine metabolism is regulated by its peripheral sympathetic innervation.

Melatonin formation in different parts of the guinea-pig pineal complex as assessed over 24 hours

“…That melatonin formation may exhibit differences in the different parts of the pineal complex is suggested by two findings in particular. Moore (1975) found in rats that the area of the deep pineal, unlike the superficial pineal, does not exhibit the typical day/night differences in NAT activity. In the gerbil, the deep pineal did not demonstrate a measurable response to light at the time of the nocturnal peak ofmelatonin formation (Rollag et al, 1984).…”

“…According to Axelrod and Weissbach (1961) the habenulae of monkey, rat and rabbit do not contain HIOMT. However, Moore (1975) described the presence of NAT and HIOMT in the rat habenular nuclei, but these enzymes did not undergo day/night differences in activity. These observations together with the findings that the commissural melatonin levels did show a rhythmic behaviour (this study) and that no pinealocytes have been described in the extrapineal portion of the habenular commissure rather suggest to us that the commissural melatonin may be taken up when these fibres pass through the proximal part of the guinea-pig pineal gland.…”

Sympathetic axons invade the brains of mice overexpressing nerve growth factor

“…tion have been described (Björklund et al, 1972;Moore, 1975;Crutcher and Davis, 1980). Sympathetic axons, however, do grow into the damaged brains of adult mammals.…”

Pineal Complex of Rats: Effects of Superficial Pinealectomy on the Deep Pineal

“…It is therefore not justified to attribute the presence of circulating melatonin after superficial pinealectomy [Ozaki and Lynch, 1976] exclusively to the persistence of the deep pineal. That the sympathetically denervated deep pineal gland is still capable of producing melatonin has been suggested by the findings of Moore [1975]. After sympathetic denervation of the pineal complex, this author found unal tered serotonin-N-acetyltransferase activity in the region of the habenulae and the pineal stalk, which in all likelihood included the deep pineal.…”