Circadian Activity Rhythm in the CNS and its Control
259
units but also to the appearance of larger units [4]. One could observe a
similar diurnal rhythm in the activity of the mesosomatic segmental nerves
which supply the legs [8].
Similar changes in the electrical activity of the VNC have been noticed
in the cockroach (RAG, 1967, unpublished).
These results indicated that the diurnal changes in the locomotor activity noticed in the organism follow from the changes in the electrical
activity of the CNS. That the state of excitability of the CNS also varies
with the time of the day is indicated by the quantitative measurements made
in our laboratory on the "defensive strike" reflex [3].
The neurosecretory cells in the brain of scorpions have been shown to
exhibit diurnal changes in their secretory activity [2]. Therefore it was
thought possible that there might be some relation between this cyclic activity
of the neurosesecretory cells and the diurnal variation in the motor activity
of the CNS. This possibility was investigated by measuring the effects of
blood and the extracts of the cephalothoracic nerve mass (CTNM) made at
different times of the day on the electrical activity of the isolated ventral
nerve cord.
Such an experiment revealed that there was a great increase in the
electrical activity of the VNC when either blood or the CTNM extract
from the 5 p.m. or the 8 p.m. scorpions was applied. On the other hand
there was a marked depression of activity when the blood or CTNM extract
from the 11 p.m. or 2 a.m. scorpions is applied to the VNC. These effects
are maintained for long periods if the nerve cord is bathed in perfusion
fluid containing the active substance [6]. Similar results were obtained in
the cockroach (RAO, 1967 unpublished). In the cockroach extracts of the
supra-oesophageal ganglion alone were adequate to obtain these effects.
Injection of these extracts into intact scorpion results in modification of
the activity associated with "the defensive strike reflex". 8 p.m. blood or
CTNM extract enhances the excitability, while the 8 a.m. blood or extract
depresses the activity considerably (Table 1).
Now the question would arise as to how merely an increase or decrease
in the electrical activity and the excitability of the CNS would result in the
natural diurnal behaviour of the animal. Such behaviour consists of emerging from a place of hiding in the evening and returning to a place of hiding
in the night (about midnight).
It has been shown in our laboratory that the scorpion exhibits also a
rhythm in the photo-kinetic response, which involves a reversal of the sign
of the photo-kinetic response. Using a standard choice chamber technique,
it has been shown that there is a change from photonegativity during the
day to photopositivity in the evening. The change from photonegativity to
photopositivity occurs at about 4 p.m. and it reverts back to photonegativity at about 11 p.m. or 12 midnight [3].
17*
259
units but also to the appearance of larger units [4]. One could observe a
similar diurnal rhythm in the activity of the mesosomatic segmental nerves
which supply the legs [8].
Similar changes in the electrical activity of the VNC have been noticed
in the cockroach (RAG, 1967, unpublished).
These results indicated that the diurnal changes in the locomotor activity noticed in the organism follow from the changes in the electrical
activity of the CNS. That the state of excitability of the CNS also varies
with the time of the day is indicated by the quantitative measurements made
in our laboratory on the "defensive strike" reflex [3].
The neurosecretory cells in the brain of scorpions have been shown to
exhibit diurnal changes in their secretory activity [2]. Therefore it was
thought possible that there might be some relation between this cyclic activity
of the neurosesecretory cells and the diurnal variation in the motor activity
of the CNS. This possibility was investigated by measuring the effects of
blood and the extracts of the cephalothoracic nerve mass (CTNM) made at
different times of the day on the electrical activity of the isolated ventral
nerve cord.
Such an experiment revealed that there was a great increase in the
electrical activity of the VNC when either blood or the CTNM extract
from the 5 p.m. or the 8 p.m. scorpions was applied. On the other hand
there was a marked depression of activity when the blood or CTNM extract
from the 11 p.m. or 2 a.m. scorpions is applied to the VNC. These effects
are maintained for long periods if the nerve cord is bathed in perfusion
fluid containing the active substance [6]. Similar results were obtained in
the cockroach (RAO, 1967 unpublished). In the cockroach extracts of the
supra-oesophageal ganglion alone were adequate to obtain these effects.
Injection of these extracts into intact scorpion results in modification of
the activity associated with "the defensive strike reflex". 8 p.m. blood or
CTNM extract enhances the excitability, while the 8 a.m. blood or extract
depresses the activity considerably (Table 1).
Now the question would arise as to how merely an increase or decrease
in the electrical activity and the excitability of the CNS would result in the
natural diurnal behaviour of the animal. Such behaviour consists of emerging from a place of hiding in the evening and returning to a place of hiding
in the night (about midnight).
It has been shown in our laboratory that the scorpion exhibits also a
rhythm in the photo-kinetic response, which involves a reversal of the sign
of the photo-kinetic response. Using a standard choice chamber technique,
it has been shown that there is a change from photonegativity during the
day to photopositivity in the evening. The change from photonegativity to
photopositivity occurs at about 4 p.m. and it reverts back to photonegativity at about 11 p.m. or 12 midnight [3].
17*