2. THE PINEAL ORGAN
97
transferase (HIOMT) which is responsible for the formation of melatonin within the pineal of Salmo irideus. Working with the same species,
Oguri et al. (1968) found that a melatonin precursor, 5-hydroxytryptophan is taken up by the pineal organ in greater quantities than it is by
other parts of the brain studied; they infer from this finding that the
pineal of fish may also be concerned with melatonin synthesis. These
studies have now been substantiated by Fenwick (1970a) who isolated
melatonin from the pineal organs of the Pacific salmon Oncorhyncus
tshawytscha. Thus, the pineal organ of fish is responsive to light,
has a high cellular metabolism, and shows an active tryptophan
metabolism which is capable of producing the mammalian hormone
metatonin.
A. The Pineal Body as a Sensory Organ
There remains little doubt that the pineal body of some, if not all fish,
functions as a sensory organ. Krabbe (1916) and Walter (1923) and
more recently Van de Kamer (1952) as well as Hafeez and Ford (1967)
have suggested that the fish pineal is associated with the detection of
the pressure or chemical composition of the CSF. Evidence favoring this
hypothesis includes the reported open connection between the pineal
lumen and the ventricles of the brain, the changing shape of the pineal
body of Esox lucius in relation to the pressure of the CSF, and the
cytoplasmic extensions of the primary sensory cells toward the lumen
of the body thus suggesting a functional relationship with the CSF.
Hafeez and Ford (1967) go on to suggest that the similarities between
the pineal body and the subcommissural organ with regard to the chemical nature of their secretions and the common direction of release
into the ventricles support the view of a CSF-pineal relationship. There
have been no reported studies of the effect of pinealectomy on either
the pressure or composition of the CSF.
Although the hypothesis that the pineal gland is associated with the
limbic system or visceral brain (Relkin, 1966) suffers from the same
paucity of experimental evidence, some suggestive findings have been
reported. Both Le Gros Clarke (1932) and Boon (1938) noted a close
anatomical relationship between the pineal body and the olfactory
system of fishes; the latter has been shown to have at least some connection with hypothalamic nuclei responsible for pituitary hormone
release (Jasinski et al., 1966; Peter and Gorbman, 1968). Moreover,
Hoffman and Reiter (1965) reported that olfactory stimuli are capable
of interfering with the primary inhibitory effects which the active
97
transferase (HIOMT) which is responsible for the formation of melatonin within the pineal of Salmo irideus. Working with the same species,
Oguri et al. (1968) found that a melatonin precursor, 5-hydroxytryptophan is taken up by the pineal organ in greater quantities than it is by
other parts of the brain studied; they infer from this finding that the
pineal of fish may also be concerned with melatonin synthesis. These
studies have now been substantiated by Fenwick (1970a) who isolated
melatonin from the pineal organs of the Pacific salmon Oncorhyncus
tshawytscha. Thus, the pineal organ of fish is responsive to light,
has a high cellular metabolism, and shows an active tryptophan
metabolism which is capable of producing the mammalian hormone
metatonin.
A. The Pineal Body as a Sensory Organ
There remains little doubt that the pineal body of some, if not all fish,
functions as a sensory organ. Krabbe (1916) and Walter (1923) and
more recently Van de Kamer (1952) as well as Hafeez and Ford (1967)
have suggested that the fish pineal is associated with the detection of
the pressure or chemical composition of the CSF. Evidence favoring this
hypothesis includes the reported open connection between the pineal
lumen and the ventricles of the brain, the changing shape of the pineal
body of Esox lucius in relation to the pressure of the CSF, and the
cytoplasmic extensions of the primary sensory cells toward the lumen
of the body thus suggesting a functional relationship with the CSF.
Hafeez and Ford (1967) go on to suggest that the similarities between
the pineal body and the subcommissural organ with regard to the chemical nature of their secretions and the common direction of release
into the ventricles support the view of a CSF-pineal relationship. There
have been no reported studies of the effect of pinealectomy on either
the pressure or composition of the CSF.
Although the hypothesis that the pineal gland is associated with the
limbic system or visceral brain (Relkin, 1966) suffers from the same
paucity of experimental evidence, some suggestive findings have been
reported. Both Le Gros Clarke (1932) and Boon (1938) noted a close
anatomical relationship between the pineal body and the olfactory
system of fishes; the latter has been shown to have at least some connection with hypothalamic nuclei responsible for pituitary hormone
release (Jasinski et al., 1966; Peter and Gorbman, 1968). Moreover,
Hoffman and Reiter (1965) reported that olfactory stimuli are capable
of interfering with the primary inhibitory effects which the active