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during 60 minutes daily session for 14 consecutive days) in rats caused an increase
in NK cell cytotoxicity (measured by chromium release assay) in the spleen but not
in the peripheral blood; there was no simultaneous effect on the number of LGLs
(measured by the morphological method) or plasma level of prolactin (PRL), growth
hormone (GH), corticosterone (COR), and testosterone (TST).
Thus, we now have enough data to assume that pleasure or reward behavior evoked
by electrical stimulation in the LH and VTA is linked with augmentation of NK cell
activity. These findings might give some insight into the underlying mechanisms by
which psychological intervention that enables recovery from depressive symptoms or
improvement of coping ability can ameliorate the repression of NK cell activity.
13.3.3 Reward Center and T Cell
As described earlier, T-cell and Th1 cell functions are sensitive to stress. However,
we have not obtained any data that illustrate the correlation of reward center with
T cells and with their function. Recently we tried to investigate whether T-cell
cytokine production via CD3 stimulation is modulated by LH electrical stimulation.
13.3.3.1 Methods
We used inbred and pathogen-free WKA male rats (Clea Japan, Tokyo, Japan), 7-9
weeks old, weighing approximately 380 g. On the date of the operation, they were
anesthetized with sodium pentobarbital (50 mg/kg) and fixed on a stereotaxic appara-
tus (Narishige Instruments, Tokyo, Japan).
The rats were divided into four groups (
n
11 each); the LH-stimulated rats had
an electrode inserted into the unilateral LH area, 3 mm posterior to bregma, 1.7 mm
lateral to the right side, and 8.5 mm below dura. These animals received acute electri-
cal stimulation at 100 mA 0.5 seconds 50 Hz every 3 seconds for 30 minutes.
The LH sham-stimulated rats had an electrode inserted into the same LH area but
were given no stimulation. The cortex-stimulated rats had an electrode inserted into
the unilateral cortex area, 1.5 mm posterior to bregma, 1.5 mm lateral to the right, and
2 mm below dura and were given acute electrical stimulation as for the LH-stimulated
rats. The cortex sham-stimulated rats had an electrode inserted into the same cortex
area but were given no stimulation.
Additional rats were divided into four groups (
n
6 each): LH-ablated rats had
electrodes inserted into the same positions bilaterally as the LH-stimulated rats, and
were subjected to local ablation by electrical current of 2 mA, 50 Hz for 15 seconds.
The LH sham-ablated rats had electrodes inserted into the same LH area bilaterally,
but underwent no actual ablation. The cortex-stimulated rats were subjected to the
same local ablation as the LH-ablated rats. The cortex sham-operated rats had an
electrode inserted into the same cortex areas but were given no current. All treat-
ments were carried out under sterile conditions. The operations were performed from
10:00 AM to 2:00 PM.
The rats were sacrificed by CO
2
asphyxiation 24 hours after the operation and
their spleens were collected for immunological analyses. Single-cell suspensions
