1. ANATOhlY AND PHYSIOLOGY OF THE CENTRAL NERVOUS SYSTEM
15
differ from species to species. In goldfish, Carassius auratus, the spontaneous activity of the surface of the olfactory bulb was consistently
of relativc~ly high amplitude ( Hara and Gorbman, 1967). Frequencies of
1.016 Hz with amplitudes of 70-100 pV peak to peak were obtained
from the olfactory bulb. Infusion of salt solutions into the nasal cavity
evoked synchronous waves of comparatively high amplitude ( 150-200
p V ) . This synchronous pattern of discharge decreased and was subsequently followed by desynchronous wave patterns with relatively higher
frequencies and lower amplitudes ( Hara and Gorbman, 1967). However, spontaneous activity in the olfactory bulb of homing and juvenile
salmon of the species Oncorhynchus tshawytscha and 0 . kisutch had
discharges of relatively lower frequency, 7-9 Hz with amplitudes of
35-65 p V (Hara et al., 1965). In contrast to this, young hatchery-reared
salmon of the same spccies exhibited consistently higher frequencies of
8-10 Hz with amplitudes of 35-65 pV (Hara et al., 1965).
The evoked response of the olfactory bulb increased in magnitude
(linearly) with the infusion of the nasal cavity with sodium chloride solutions of increasing concentrations ( Hara and Gorbman, 1967). Transection of the ipsilateral medial bundle of the olfactory tract resulted in
augmentation of the synchronized electrical activity of the olfactory
bulb in response to sodium chloride infusion. If the lateral bundle of the
ipsilateral olfactory tract was sectioned there was no change either in
the spontaneous discharge pattern or in the evoked synchronized activities within the bulb. When the olfactory bulb was stimulated electrically,
transection of one of the olfactory tracts augmented the efferent-induced
activity and accelerated the excitability cycle, resulting in reduction of
the threshold for electrically evoked potentials in the olfactory bulb.
These data indicate that centrifugal tonic depressive influences are
normally exerted on the excitability of the olfactory bulb and that this
is mediated through the medial bundle of the olfactory tract (Hara and
Gorbman, 1967).
Repetitive electrical stimulation to the ipsilateral olfactory bulb depressed spontaneous activity in the contralateral olfactory bulb ( Hara
and Gorbman, 1967). This activity was also depressed after the application of strong olfactory stimuli but was facilitated and synchronized by
weaker olfactory stimuli. These phenomena indicate that there is an
inhibitory action derivcd from the activity of the contralateral bulb via
the olfactory tract. Furthermore, since no recognizable change occurred
after sectioning of the contralateral olfactory tract, it is likely that the
inhibitory influence in the contralateral bulb is not of a tonic nature but
may be triggered only when the stimulation to the ipsilateral bulb is of
relatively greater magnitude in comparison to the stimulation of the
15
differ from species to species. In goldfish, Carassius auratus, the spontaneous activity of the surface of the olfactory bulb was consistently
of relativc~ly high amplitude ( Hara and Gorbman, 1967). Frequencies of
1.016 Hz with amplitudes of 70-100 pV peak to peak were obtained
from the olfactory bulb. Infusion of salt solutions into the nasal cavity
evoked synchronous waves of comparatively high amplitude ( 150-200
p V ) . This synchronous pattern of discharge decreased and was subsequently followed by desynchronous wave patterns with relatively higher
frequencies and lower amplitudes ( Hara and Gorbman, 1967). However, spontaneous activity in the olfactory bulb of homing and juvenile
salmon of the species Oncorhynchus tshawytscha and 0 . kisutch had
discharges of relatively lower frequency, 7-9 Hz with amplitudes of
35-65 p V (Hara et al., 1965). In contrast to this, young hatchery-reared
salmon of the same spccies exhibited consistently higher frequencies of
8-10 Hz with amplitudes of 35-65 pV (Hara et al., 1965).
The evoked response of the olfactory bulb increased in magnitude
(linearly) with the infusion of the nasal cavity with sodium chloride solutions of increasing concentrations ( Hara and Gorbman, 1967). Transection of the ipsilateral medial bundle of the olfactory tract resulted in
augmentation of the synchronized electrical activity of the olfactory
bulb in response to sodium chloride infusion. If the lateral bundle of the
ipsilateral olfactory tract was sectioned there was no change either in
the spontaneous discharge pattern or in the evoked synchronized activities within the bulb. When the olfactory bulb was stimulated electrically,
transection of one of the olfactory tracts augmented the efferent-induced
activity and accelerated the excitability cycle, resulting in reduction of
the threshold for electrically evoked potentials in the olfactory bulb.
These data indicate that centrifugal tonic depressive influences are
normally exerted on the excitability of the olfactory bulb and that this
is mediated through the medial bundle of the olfactory tract (Hara and
Gorbman, 1967).
Repetitive electrical stimulation to the ipsilateral olfactory bulb depressed spontaneous activity in the contralateral olfactory bulb ( Hara
and Gorbman, 1967). This activity was also depressed after the application of strong olfactory stimuli but was facilitated and synchronized by
weaker olfactory stimuli. These phenomena indicate that there is an
inhibitory action derivcd from the activity of the contralateral bulb via
the olfactory tract. Furthermore, since no recognizable change occurred
after sectioning of the contralateral olfactory tract, it is likely that the
inhibitory influence in the contralateral bulb is not of a tonic nature but
may be triggered only when the stimulation to the ipsilateral bulb is of
relatively greater magnitude in comparison to the stimulation of the