Abstract

Various stressors on the one hand and psychological interventions on the other are known to modulate immunity, mainly via the hypothalamus and the question arises as to whether pleasure might also have a role to play. The lateral hypothalamus (LH) is a potent reward centre, sometimes known as the pleasure centre, where given the opportunity, rats will prefer to self stimulate at the expense of all else. Electrical stimulation of the LH through precisely inserted electrodes is a convenient way of administering a standard dose of "reward/pleasure".
Natural Killer cell (NK) activity in WKA and SD rats was found to be significantly higher following 30 mins. of electrical stimulation of the LH compared to sham operated rats. However there was no such difference between the NK activity of sham operated rats and those who had received electrical stimulation in the frontal cortex as a control. All operations were performed under nembutal anesthetic and NK activity measured 20 hours later using the 51Cr release assay.
It is NK activity which is thought to be most relevant to tumour destruction and that stimulation of the LH resulted in increased NK activity leads one to speculate that pleasure might play a role in the protection against cancer.

Introduction

Even as far back as 1954(1), stress has long been considered to be implicated in immunity, which is why psychological intervention has aimed at reducing the causes of stress in order to allow the body to heal itself. Various therapy programmes including relaxation and(2) psychotherapy(3), (4), have been found to be effective in reducing the negative immunological effects of stress. Indeed, even the fight against cancer has been found to benefit from psychotherapy(5) but little is known exactly why. If stress can be defined as a perceived unavoidable cause of discomfort, then its antithesis and therefore antidote, might lie in a sense of well-being.
While it has been well established that the hypothalamic-pituitary-adrenal axis provides a pathway where stress leads to immune modulation(6), little is known about well-being, probably because emotions such as hope, happiness and a sense of controllability are hard to define. However, thanks originally to a fortuitous accident by Olds and Milner(7), a number of areas along the A10 nerve, notably the lateral hypothalamus (LH) have been found to exhibit "reward" characteristics when electrically stimulated, that is to say, given the chance, a rat would self- stimulate this area in preference to all else until starvation. This has led to the speculative concept of pleasure centres which can be conveniently stimulated by quantifiable schedules and intensities.
So far, it has been found that stimulation of the medial forebrain bundle-posterior lateral hypothalamus (MFB-PLH) in rats can attenuate the formation of gastric lesions (8) and age related decline in cold tolerance can be retarded by stimulation of the LH. (9) But more relevant was the finding that electrical stimulation of the LH was found to enhance rat's plaque forming cell response (PFC) and increase their anti-sheep red blood cell (SRBC) antibody titer(10).
Early in infection, the immune system can respond in at least two ways, either the antibody associated humourer response based on Th2 activity, or the cellular response based on Th1 activity. The above mentioned enhancement of the PFC response requires Th2 generated activity, but does the LH always favour a Th2 response, even if that reaction is inappropriate, as stress is thought to do(11,12) or does it enhance effectiveness of both responses?
Thus the question now arises as to what effect the lateral hypothalamus has on cellular immunity.
In mice, destruction of the tuberoinfundibular part of the hypothalamus was found to permanently abrogate NK activity(3). NK cells are those thought to be effective against cancer and are an indication of a Th1 shift. What is more, Sahs et al. (14) concluded that NK cells are the most susceptible to emotions and Fawzy et al. (5) even found psychotherapy to be effective against cancer, which makes NK activity a likely candidate for investigating the role of the LH on cellular immunity.
Therefore the present experiment aimed to study the effect of acute electoral stimulation on NK activity in WKA and SD rats.

Materials and method

Rats
Inbred and specific pathogen-free Wister.King-Aptekman (WKA) and Sprague Downey (SD) male rats were used, 8 weeks old, weighing approx. 350 gms from Nihil Clea (Tokyo, Japan). All were handled similarly, given sodium pentobarbital anesthetic (50mg/kg) and put on stereotaxic apparatus (Narishige Instruments, Tokyo, Japan) with the incisor bar lowered 3.3 mm below the horizontal. The operations took place in the afternoon. A time delay of 20 hours post operation was chosen before measuring NK activity as out of several time delays, this gave the most marked result and ample time fOF the anesthetic to wear off.
Sham operated : had an electrode inserted into the LH area.
LH stimulated : had an electrode inserted into the LH area - and then given electrical stimulation.
Cx stimulated : had an electrode inserted into the cortical area - 1.5mm posterior to bregma, 1.5mm lateral and 2mm deep - and then given electrical stimulation. The electrodes were bipolar, 0.5mm wide and stimulation was at 100 uAX0.5 secsX50 Hz every 3 secsX30 mins using a Nihon Kohden sen-3301 stimulator.

NK activity
NK activity was measured by the 51Cr release assay. 20 hours post treatment, the rats were sacrificed by CO2 asphyxiation, their slpeen cells isolated and used as effector cells against 51Cr absorbed YAC- 1 target cells for a 6 hour incubation period.

Slides
After extraction of the spleen cells, the rats brains were preserved in 10% formalin, 20% sucrose solution for minimum 10 days. They were then frozen and sections put onto slides and dyed with toluidin blue for confirmation of electrode tip position (Paxinos and Watson(15)). Data from rats whose tip did not fall within the LH area was not used.

Groups
Expt. a:
WKA rats: LH sham operated (n=3), Cx control stimulated (n=2)
Expt. b:
WKA rats: LH sham operated (n=5), LH stimulated (n=5)
Expt. c:
SD rats: LH sham operated (n=3), Cx control stimulated (n=3)
Expt. d:
SD rats: LH sham operated (n=5), LH stimulated (n=5)

Expt. a
No significant difference in NK activity between LH sham operated and Cx control stimulated groups was found based on standard error plot.

Expt. b
The NK activity in the LH stimulated group was found to be signficantly higher than that in the LH sham operated group based both on the standard error plots and using a paired t test. For effector:target ratio of 100:1, 50:1 and 25:1 the 1 values were t(4)=28.85 <0.001, t(4)=9.174<0.001, and t(4)=6.7<0.001 respectively.

Expt. c
No significant difference in NK activity between LH sham operated and Cx control stimulated groups was found based on standard error plot.

Expt. d
The NK activity in the LH stimulated group was found to be significantly higher than that in the LH sham operated group based both on the standard error plots and using a paired t test. For effector:target ratio of 100:1, 50:1 and 25:1 the t values were t(4)=3.39 <O.O5, t(4)=3.93<O.O5, and t(4)=2.43 <0.1

Summary results

Therefore while there was no significant difference in NK activity between the LH sham operated and cortex control groups, there was a significant difference between the LH sham operated and the LH stimulated groups.

Discussion

The nature of the 51Cr release assay precludes large numbers of subjects and only values for NK activity within each experiment can be compared relative to each other. Nevertheless, though the numbers are small, there is still a distinct effect where acute stimulation of the Lateral Hypothalamus increases NK activity compared to LH sham operated, while stimulation of the cortex as a control does not.
On top of this functional information as to the NK modulatorial role of the LH, it would also be tempting to speculate as to its assumed role of pleasure and well-being on NK activity. However, the "emotion" associated with the LH still remains conjecture, not only because we are dealing with animals, but especially because they were anesthetized during stimulation. The next step would require chronic electrode implantation where not only are the rats conscious during electrical stimulation, but where the fact that the rats self stimulate argues for its rewarding "pmeasurable" properties. Also, research is planned combining stimulation of the lateral hypothalamus and various stressors to see if LH stimulation may indeed be a possible antidote to stress.
That it is NK "activity" which increased is more meaningful than had it been a simple cell count and implies that the helper T cell balance was tipped towards a Th1 response (since it is the Th1 response which is associated with enhanced NK activity). However it might not necessarily have been the stimulation of the LH which tipped the balance, one can only say that somehow it resulted in enhanced NK activity following cancer cell presentation. Since LH stimulation also increased the plaque forming cell response in Sakes and Vlajkovic's above mentioned experiment, which requires a Th2 response, it seems more likely that the LH does something which enables subsequent responses, both Thl and Th2, to be more effective.
NK activity is particularly relevant to tumour apoptosis and its enhanced reactivity following stimulation of the LH leads one to speculate that maybe pleasure can increase the organism's protection against foreign cells, tumours and intracellular micro-organisms such as viruses. The mechanism for such modulation is not known and requires further study, but the effect has important implications for the treatment of such diseases and argues that enjoyment is not just a pleasant epiphenomenon, but has an essential biological function for life. After all, if pleasure exists, there must be a good biological reason for it being here.

References

(1) Selye, H.: An experimental model illustrating the pathogenesis of the deseases off adaptation. J.C.E.M. 14:997-1005, 1954.
(2) Kiecolt-Glaser, J. K., Glazer, R., Williger, D., Stout, J., Messik, G., Sheppard, S., Ricker, D., Romisher, S. C., Briber, W., Bonnell, G. and Donnerberg, R.: Psychosocial enhancement of immunocompetence in a geriatric population. Health Psychol., 4:25-41, 1985.
(3) Jones, K. and Vischi, T.: Impact of alcohol, drug abuse and mental health treatment of medical health care utilization: a review of the literature. Medical Care, 17 (suppl.2): 1-82, 1980.
(4) Mumford, E., Schlesinger, H. J. and Glass, G. V.: Reducing medical costs through mental health treatment: Research problems and recommendations. In Linking health and mental health Beverly Hills. Broskowski, A., Marks, E. and Budman, S. H. (eds.), P257-273, CA: Sage, 1981.
(5) Fawzy, F. I., Fawzy, N. W., Arndt, L. A. and Pascal, R. O.: Critical review of psychosocial interventions in cancer care. Arch. Geen. Psychiat. (US), 52: 100-113, Feb, 1995.
(6) Bullock, J. E.: The syntax of immune-neuroendocrine communication. Immunol. Today, 15:504-511, 1994.
(7) Milner, P.: Discovery of Self Stimulation and other stories. Neurosci. Biobehav. Rev., 13: 61-67, 1989.
(8) McCutcheon, N. B., Guile, M. N. and McCormick, R.: Electrical stimulation of Medial Forebrain bundle-posterior lateral hypothalamus auenuates gastric lesions. Physics. Behav., 37:4335-4340, 1986.
(9) Talon, M. I., Engel, B. T. and Whitaker, J. R.: Age related decline in cold tolerance can be retarded by brai stimulation. Physics. Behav., 33:969-973, 1984.
(10) Sakes, B. and Vlajkovic, S.: Self stimulation behaviour: consequences upon immunity ? Brain Behav., 4:255-264, 1990.
(11) Rook, G. A. W., Hernandez-Pando, R. and Lightman, S. L.: Hormones, peripherally activated prohormones and regulation of the Th Irrh2 balance. Immunol. Today, 15(7): 1994.
(12) Namiki, M.: Aged people and stress. Nippoon Rosen Igakkai Zasshi, 31: 85-95, Feb, 1994.
(13) Form, G., Binding, M., Santoni, A., Belluardo, N., Marchers, A. and Giovarelli, M.: Radiofrquency destruction of the tuberinfundibular region of hypothalamus permanently abrogates NK cell activity in mice. Nature, 306: 181-184, 1983.
(14) Sahs, J. A., Goetz, R., Ruddy, M., Rabkin, J., Williams, J. B. W., Kertzner, R. and German, J. M.: Psychological distress and natural killer cells in gay men with & without HIV infection. Am. J. Psychiat., 151: 14479-14484, 1994.
(15) Paxinos, G. and Watson, C.: The rat brain in stereotaxic coordinates. Academic Press, San Diego, 1982.