Psychopharmacologia (Berl.) 42, 95-97 (1975) �9 by Springer-Verlag 1975

Effects of Early Post-Natal a-Methyl-Dopa Treatment on Behavior in the Rat

P. JUVANCZ* and T. NOWACZYK

Ddpartement de M6decine Exp6rimentale, Universit6 Claude Bernard, Lyon, France

Received September 17, 1974; Final Version December 9, 1974

Abstract. 250 mg/kg of L-alpha-methyl-Dopa (a-m-Dopa) or saline were administered to rats for three weeks after birth. Subsequent tests revealed an increased locomotor ac-

tivity and greater rate of acquisition but no disturbance in shuttle-box conditioning. The whole brain content of nor- epinephrine, dopamine and serotonin was not affected.

Key words: a-Methyl-Dopa- Paradoxical Sleep Deprivation - Maturation of Central Nervous System (CNS).

One of the hypothetical functions of paradoxical sleep (PS) is to participate in the maturation of the CNS. Newborn animals or humans have more PS than adults and the greatest amount occurs during intrauterine life (Astic and Jouvet-Mounier, 1969) decreasing during ontogenetic development. Moreover, the more mature the animal is at birth, the less PS it has (Jou- vet-Mounier, 1968). Therefore, it seemed of interest to deprive animals of PS after birth and examine the behavioral consequences.

We have failed to find any studies in the literature concerning long-term deprivation of PS in early post- natal life. Only pharmacological deprivation is prac- tical for a long period. We have utilized a-m-Dopa because of its relatively selective PS depriving action on the cat (Delorme, 1966), the mouse (Kitahama, 1973) and on the adult and newborn rat (Carlier et al., 1974). In the latter work, in baby rats isolated from

~eir mother, maintained in an incubator and fed by a gastric catheter, a -m-Dopa produced a long-lasting and strong deprivation (75 %) of PS, when adminis- tered with a schedule similar to the present study.

Method

The litters of OFA rats were received 2 days after birth. 38 rats (18 males and 20 females) were given subcutane- ous injections of 250 mg/kg L-a-m-Dopa (Calbiochem) daily for 21 days, from 4-24 days of age. The daily dose

* With IUPHAR fellowship. Present address: Institut of Pharmacology, Semmetweis University, Budapest.

was divided unequally in two parts: 100 mg/kg at 9 a.m. and 150 mg/kg at 17 p.m. Control animals (7 males and 6 females) were injected with the same volume of saline with an identical schedule. Litter-mates were used for con- trol and treated group. Locomotor activity was recorded with an open field test at 5 weeks of age. Rats were placed in a 123 • 135 cm floor divided into 36 equal squares. The number of squares crossed during 30 rain was recorded.

From 41 days of age the rats were trained in a shuttle- box. The shuttle-box consisted of a 20 • 40 cm chamber with a grid floor, divided into two equal parts by a barrier 5 cm height. After habituation, the conditioned stimulus- a shrill bell-was presented. The conditioned stimulus con- tinued until the rat crossed to the opposite compartment. If it did not cross within 5 sec a footshock was delivered (110 V, 50 Hz), which terminated when the animal escaped. One session consisted of 30 trials with 5-10 sec inter-trial intervals. The animals were tested throughout the day in a random manner.

At 53 days of age 6 treated and 6 control males were sacrified and the serotonin (5 HT), dopamine (DA) and nor- epinephrine (NE) contents of their whole brains were de- termined spectrofluorometrically, by the methods of Bog- dansky et al. (1957), Fleming et al. (1965) and Euler and Lishajko (1961), respectively.

Results

Increased excitability was observed in the a-m- Dopa-group.

The body weightof the treated animals was signifi- cantly lower than that of the controls, with a 1 -2 day lag. After the end of injection-period, they regained their weight loss. There is a sex-related difference in body weight beginning from the third postnatal week.

96 Psychopharmacologia (Bed.), Vol. 42, Fasc. 1 (1975)

o l A ~1oo

504

0/ / /

m ......... contr0[ (n=13) =. �9 �9 o~IDQPI~ (n=381

t ~ t-

J. m~'mQ==~=~=l=,t

Succesive 10min periods 30 minutes Fig. l. Effects of a-m-Dopa injections on locomotor activ- ity. The number of squares crossed during the total session (30 rain) is represented by the vertical bars in part A (means _+ S.E.); the habituation in both groups in successive

10 rain in part B

30

82O

-~ 15

Z

l J ' - - .5/" l / ) / i ) I / I ~ - ~

/ / I [ / " r / .--. 0~H00PA~(n--20! / / / , / t . - - . ~MOOPA~(o=lSj

, ' .--. control (n=7) ~ l } / ~ .__. contr01~(n=,)

. . . . . . . . ,

I 2 3 L 5 6 7 8 9 10 Sessions

Fig. 2. The effect of a-m-Dopa treatment on shuttle-box conditioning. Mean + S.E.

Male and female rats have a decrease in body weight during the drug-treatment and displayed a similar re- covery.

In the open field the treated animals were signifi- cantly more active than the control ones. Both groups exhibited the phenomenon of habituation. Sex-differ- ences at this age were negligable (Fig. 1).

Marked differences in shuttle-box conditioning were found. Females have generally more avoidance responses than males, but this difference was only sig- nificant at the 4th session in the control group and never in the treated one. However, during the first half of the training, the a-m-Dopa-rats learned their task more rapidly in both sex groups. These differ- ences were found to be highly significant with the Stu- dent non-paired t-test. From the 7th session the differ- ence decreased gradually and finally the control

Table 1. The effect of ,-m-Dopa treatment on whole brain 5HT, DA and NE

5HT DA NE (Pg/g) (Pg/g) (gg/g)

Control 0.259 0.646 0.256 (n = 6) +0.039 +_0.022 +0.01

~-m-Dopa 0.220 0.624 0.228 (n = 6) +0.014 _+0.014 -+0.014

animals displayed a performance similar to the treated ones (Fig. 2).

No marked differences in endogenous brain levels of 5HT, DA and NE were seen (Table 1).

Discussion

The results demonstrate an increased excitability and locomotor activity due to early postnatal a-m-Dopa treatment. The superior performance on the shuttle- box does not reflect the capacitY of learning but in- dicates a higher rate of acquisition which is very likely the consequence of the increased locomotor activity and not of any specific process of learning. It is evident, however, that treatment did not cause any deficit in learning.

These results are in agreement with the ex- periments of Pappas and Sobrian (1972) and of Schaeffer etal. (1973). They administered 6- hydroxy-dopamine (6-OHDA) and p-chlorophenyl- alanine (PCPA) respectively to baby rats, two drugs which cause selective or non-selective PS deprivation, if injected in adult rats (Matsuyama et al., 1973; Mou- ret and Jouvet, 1968). None of them have found gross behavioral disturbances.

Smith et al. (1973) used 6-OHDA administration in immature rats in a manner which reduced brain NE preferentially. Their results are similar to ours: in- creased locomotor activity and shuttle-box acquisi- tion. However, with other types of administration which reduced DA or both NA and DA, both activities mentioned above were reduced. In our case, brain 5HT, DA and NE levels were not changed. It is possi- ble that turnover might be affected, but the dynamics of these biogenic amine systems were not studied.

The present findings might be explained by the following alternatives: either the relationship be- tween PS and the maturation of the CNS might not operate or at least not in this simple form, or we have not sufficiently deprived PS. Unfortunately, the problem of continuous recording on the newborn with the mother is not resolved yet. If it is separated from its mother, its environmental conditions are highly un-

P. Juvancz and T. Nowaczyk: Early a-Methyl-Dopa Treatment 97

natural, and its spontaneous sleep patterns are mod- ified (Carlier et al., 1974). The pharmacological data resulting from this condition might be extrapolated to the present experimental conditions with some re- servations.

The increased excitability and locomotor activity also deserve some attention. This might be due to PS deprivation but other specific or nonspecific actions (e.g. hypotension, decreased heart rate, reduced body weight) of this drug have to be considered, too.

Acknowledgements. The authors wish to express their ap- preciation to Marthe Pinatel and Chantal Blondaux for the biochemical determinations.

This work has been supported by grants from INSERM (U52), CNRS (L.A. 162) and DRME (Contract 72-108).

References

Astic, L., Jouvet-Mounier, D.: Mise en 6vidence du som- meil paradoxal in utero chez le Cobaye. C. R. Acad. Sci. (Paris) 264, 2578-2581 (1969)

Bogdansky, D. F., Pletscher, A., Brodie, B. B., Udenfriend, S.: Identification and assay of serotonin in the brain. J. Pharmacol. exp. Ther. 117, 82-88 (1957)

Carlier, E., Nowaczyk, T., Valatx, J. L., Juvancz, P.: Etude du sommeil du raton nouveau-n6 isol6 de sa m6re. Effets de L-alpha-m6thyl-Dopa. Psychopharmaeologia (Berl.) 37, 205-215 (1974)

Delorme, F.: Monoamines et sommeils. Etude polygra- phique neuropharmacologique et histochimique des 6tats de sommeil chez le chat. Thbse de M6decine, Lyon, p. 168 (1966)

von Euler, U. S., Lishajko, F.: Improved technique for the fiuorometric estimation of catecholamines. Acta Phys- iol. Scand. 51, 348-355 (1961)

Fleming, R. M., Clark, W. G., Fenster, E. D., Towne, J. C.: Single extraction method for the simultaneous fluoro- metric determination of serotonin, dopamine and nor- epinephrine in the brain. Analyt. Chem. 37, 692-696 (1965)

Jouvet-Mounier, D.: Ontog6n6se des 6tats de vigilance chez quelques mammif6res. Th6se de Sciences, Lyon, Tixier, p. 231 (1968)

Kitahama, K.: Contribution ~ l'6tude de la relation som- meil-apprentissage. Effets de la privation de sommeil paradoxal par L-alpha-m6thyl-Dopa. Th6se Doctorat d'Universit6, Lyon, p. 98 (1973)

Matsuyama, S., Coindet, J., Mouret, J.: 6-Hydroxydopa- mine intracisternale et sommeil chez le rat. Brain Res. 57, 85-95 (1973)

Mouret, J., Jouvet, M.: Insomnia following para- chlorophenylalanine in the rat. Europ. J. Pharmacol. 5, 17-22 (1968)

Pappas, B. A., Sobrain, S. K.: Neonatal sympathectomy by 6-hydroxydopamine in the rat: no effects on behavior but changes in endogenous brain norepinephrine. Life Sci. 11, 653-659 (1972)

Schaeffer, G. J., Bunchan, D. C., Ray, O. S.: The effects of early p-chlorophenylalanine administration and post- weaning housing conditions on serotonin and behavior in rats. Life Sci. 12, 401-411 (1973)

Smith, R. D., Cooper, B. R., Breese, G.R.: Growth and behavioral changes in developing rats treated in- tracisternally with 6-hydroxydopamine: evidence for involvement of brain dopamine. J. Pharmacol. exp. Ther. 185, 609-619 (1973)

Peter Juvancz, Institute of Pharmacology, Semmelweis University H-1085 Budapest VIII., Ull6i Ut 26, Hungary