4. CHEMORECEPTION
97
second component had a comparatively long (about 30 msec) refractory
period and would not follow repeated stimulation at a frequency higher
than about l/sec without undergoing a reduction in amplitude. The third
component ( positive-directed afterpotentials ) disappeared after section
of the olfactory tract. It has therefore been concluded that the first
component is of synaptic origin, the second component represents the
activity in the second-order neurons, and that the third component is
centrifugal origin.
When microelectrodes were inserted into the olfactory bulb, spontaneous unitary activities were recorded in different layers of the olfactory bulb of the goldfish. Oshima and Gorbman ( 1966b) observed three
different types of discharge patterns of single cells in the glomerular and
subglomerular layers of the olfactory bulb. These spontaneous and evoked
unitary activities in response to chemical stimulation were easily influenced by treating with thyroxine and steroid hormones. In the layers
about 300-400 p under the surface, large biphasic action potentials were
frequently detected ( Hara, 1967a). The discharge frequently varied from
cell to cell, but most cells of this type had an average discharge frequency
of about 2-6 impulses/sec. Probably much of the activity in this layer is
derived from the mitral cells. Different individual neurons responded in
different ways to chemical stimulation of the olfactory cavity. The variety
of observed responses to 5 x
M NaCl from different individual cells
included the following: (1) inhibition (decrease in the firing rate) during
or after the period of stimulation, ( 2 ) excitation (increase in firing rate)
which could outlast for a few seconds the duration of the stimuli, ( 3 )
excitation during stimulus followed by a short inhibition when the stimulus ceased, ( 4 ) excitation at the beginning of the stimulus and inhibition
afterward, ( 5 ) a short inhibition at the very beginning of the stimulation
followed by excitation, and ( 6 ) no response. More than 60% of the neurons
tested were of types (1) and ( 3 ) , which represent opposite patterns of
response. Similar spontaneous activity from single units in the olfactory
bulb was recorded with microelectrodes in the burbot Lota lota (Dkiving,
1966a,b).
4. ELECTRICAL ACTIVITY OF THE OLFACTORY TRACT AND
CENTRAL REGULATORY SYSTEM
Olfactory information filtered in the first relay station, the olfactory
bulb, is transferred through the olfactory tract to higher nervous centers.
In some teleosts the olfactory tract runs as a long nerve bundle (see Section 11, D ) between the bulb and telencephalon. Such a unique anatomical
feature of the olfactory system provides a convenient preparation for elec-
97
second component had a comparatively long (about 30 msec) refractory
period and would not follow repeated stimulation at a frequency higher
than about l/sec without undergoing a reduction in amplitude. The third
component ( positive-directed afterpotentials ) disappeared after section
of the olfactory tract. It has therefore been concluded that the first
component is of synaptic origin, the second component represents the
activity in the second-order neurons, and that the third component is
centrifugal origin.
When microelectrodes were inserted into the olfactory bulb, spontaneous unitary activities were recorded in different layers of the olfactory bulb of the goldfish. Oshima and Gorbman ( 1966b) observed three
different types of discharge patterns of single cells in the glomerular and
subglomerular layers of the olfactory bulb. These spontaneous and evoked
unitary activities in response to chemical stimulation were easily influenced by treating with thyroxine and steroid hormones. In the layers
about 300-400 p under the surface, large biphasic action potentials were
frequently detected ( Hara, 1967a). The discharge frequently varied from
cell to cell, but most cells of this type had an average discharge frequency
of about 2-6 impulses/sec. Probably much of the activity in this layer is
derived from the mitral cells. Different individual neurons responded in
different ways to chemical stimulation of the olfactory cavity. The variety
of observed responses to 5 x
M NaCl from different individual cells
included the following: (1) inhibition (decrease in the firing rate) during
or after the period of stimulation, ( 2 ) excitation (increase in firing rate)
which could outlast for a few seconds the duration of the stimuli, ( 3 )
excitation during stimulus followed by a short inhibition when the stimulus ceased, ( 4 ) excitation at the beginning of the stimulus and inhibition
afterward, ( 5 ) a short inhibition at the very beginning of the stimulation
followed by excitation, and ( 6 ) no response. More than 60% of the neurons
tested were of types (1) and ( 3 ) , which represent opposite patterns of
response. Similar spontaneous activity from single units in the olfactory
bulb was recorded with microelectrodes in the burbot Lota lota (Dkiving,
1966a,b).
4. ELECTRICAL ACTIVITY OF THE OLFACTORY TRACT AND
CENTRAL REGULATORY SYSTEM
Olfactory information filtered in the first relay station, the olfactory
bulb, is transferred through the olfactory tract to higher nervous centers.
In some teleosts the olfactory tract runs as a long nerve bundle (see Section 11, D ) between the bulb and telencephalon. Such a unique anatomical
feature of the olfactory system provides a convenient preparation for elec-