Electrical Responses of Pineal Cells to Pineal Indoles and Putative Transmitters in Intact and Blinded Pigeons

Abstract

The effects of micro-electrophoretically applied pineal indoles, melatonin (MEL), 5-methoxytryptophol (MTL) and 5-hydroxytryptophol (HTL) and of the neurotransmitters, noradrenaline (NOR), acetylcholine (ACH) and γ-aminobutyric acid (GABA) on the electrical activity of pineal cells were studied in anaesthetized pigeons. Recordings were made from both sighted and blinded birds during both the day- and night-time. Both excitatory and inhibitory responses to the application of all substances tested were observed, while in all cases unresponsive cells were also found. The pattern of responses to MEL, MTL and to NOR varied significantly depending on whether the cells in the sighted pigeons were tested during the day or at night. This day/night rhythm of responses to MEL and to MTL also occurred in the blinded pigeons, although this was not the case for the effects of NOR. Units which were orthodromically excited by electrical stimulation of the habenular complex were also excited by application of GABA. The activity of these units was also likely to be enhanced by application of ACH. The results suggest that the pigeon pineal organ exhibits intrinsic circadian rhythmicity which does not require entrainment signals from the retina. They also indicate that the activity of pineal cells could be influenced by neurotransmitter input provided from within the gland or via its innervation.

Single-cell recordings from chick pineal glands in vitro reveal ultradian and circadian oscillations

“…It may be argued that the firing observed in our study was not endogenous but was caused by degenerating intrapineal sympathetic fibres and the resulting leakage of noradrenaline. That the firing may be principally affected by noradrenaline was shown in pigeon pineal glands in which the microiontophoretically administered substance stimulated, inhibited or did not affect the firing [24]. However, since the electrical activity we observed was uniform and followed distinct rhythmic patterns (see below), we conclude that, in our material, noradrenaline leakage did not cause the electrical events.…”

“…In this context, the spiking cells may monitor extracellular neurotransmitter and hormone levels in the pineal gland and adapt their firing accordingly, as suggested for the rat [37,38]. Indeed, the spiking cells in avian pineal glands are principally capable of subserving such a function, as has been demonstrated in the pigeon pineal, in which firing is affected by noradrenaline, acetylcholine, k-aminobutyric acid, melatonin and 5-methoxytryptophol [24].…”

Physiology of the epiphysis: Modern concepts

“…At the same time, in the studies of the effects of microelectrophoretic applications of melatonin, noradrenaline, acetylcholine, GABA, testosterone, estrone, and prolactin on the circadian rhythms of pinealocyte electrical activity in pigeons and guinea pigs [56 ] it was found that the above hormones and transmitters effectively change the discharge frequency in these cells. These data indicated that electrical activity of pinealocytes is also determined by the influence of humoral factors [57 ].…”

Mechanisms responsible for autocrine regulation of the epiphysis function

“…Pev~t emphasized the capability of the epiphysis to uptake from the circulation system melatonin synthesized in other organs, as well as the role of this hormone as a stimulator of epiphyseal functions (synthesis of epiphyseal hormones). Therefore, an increase in the background electrical activity of the pinealocytes evoked by microapplication of melatonin, as found by Serum et al [2][3][4], could be just due to activation of peptide biosynthesis.…”

“…Serum et al [2][3][4] found that following microelectrophoretic application of melatonin to the pineal cells in birds and guinea pigs many pinealocites intensified their background electrical activity. Based on this observation, the authors suggested that an increase in the concentration of the proper hormone (melatonin) may enhance functional activity of the organ, i.e., a positive feedback principle is realized.…”