Excitability changes in non-specific thalamic nuclei during cortical spreading depression in the rat

73

ELECTROENCEPHALOGRAPHY A N D CLINICAL NEUROPHYSIOLOGY

EXCITABILITY CHANGES IN NON-SPECIFIC THALAMIC NUCLEI DURING CORTICAL SPREADING DEPRESSION

IN THE RAT t

J. BuRE.~, M.D., O. BURE/IOV~,M.D., T. WEISS, M.D. AND E. FWKOV.~, M.D. Institute of Phys,.'olagy, Czechoslovak Academy of Sciences, Prague (Czechoslovakia) (Received for p u b l i c a t i o n : M a y 18, 1962)

Spreading depression (SD) of Lena (Lelio 1944; Marshall 1959; Bureg 1962) was recently used in research on the functional organisation of the brain as a technique for the reversible functional elimination of the cerebral cortex, and of some other structures (Bureg and Buregov~i 1960; Weiss and Fitkov/t 1960, 1961; Bureg et al. 1961 a, b, ¢; Buregov/t et al. 1961). During SD, evoked in the neocortex or the hippocampus, the electrical activity of remote brain structures was studied. A temporary and reversible decrease of the spontaneous EEG activity and evoked responses in the non-specific thalamic regions was demonstrated during cortical SD (Weiss and Fifkovtt 1961). The present paper describes changes: (a) in the spontaneous unit activity in non-specific thalamic nuclei in unanesthelized and anesthetized rats: (b) in the threshold for eliciting recruiting responses in the cortex or caudate nucleus, caused by cortical SD elicited on the ipsi- or contralateral side.

taxically (according to the atlases of Krieg 1946 and of Fifkov/t and Margala 1960) into *+henonspecific thalamus by means of a microdriv¢, in most cases the electrode position was verified histologically in Nissl stained serial sections (Fig. I). The activity of well isolated units with an amplitude of 100-300 pV, and e".ceeding two or three times the maximal noise, was amplified by an AC amplifier and recorded on one channel of a double beam CRO. The fi, ing rate was counted at I-rain intervals, as described by Bureg et al. (1961a), using a decade counter connected to the output of the CRO amplifier. Unilateral SD was evoked only when the firing rate during a 10-rain control interval was sufficiently stable. The unit w,.s a~bi-

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Adult Wistar albino rats were used in acute experiments. Two trephine openings, 5 mm in diameter, were made under light ether anesthesia above the occipital cortex. After cannulation of the trachea, the rats were immobilized with dtubocurarin¢, fixed in a stereotaxic apparatus and maintained under artificial respiration. In two groups of animals 40-50 mg/kg of intraperitoneal Dial or chloralose was also administered. Steel micro-electrodes (electrolytically sharpened to tips of 2-5 microns and insulated with acetone nail varnish) were introduced stereo-

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FiJ. I Examples of the localization of electrodes in the nonspecific thalamic nuclei. Abbreviations: AD: no. anterodorsalis; AHA: area hypothalaraicaanterior; AHL: area hypothalamica lateralis; AM: no. anteromedialis; AV: no. anteroventralis;CE: ©iaustrum; F: fomix; IAM: no. t A preliminary report of a part of this paper was inter.anteromedialis; LA: nc. lateralis anterior; PT: no. given at a meet'mj .of the Czechoslovak Physiological parataenialis; PV: no. paraventricularis;RE: no. reuniens; SO: no. supraopticus; TO: tractus optieus. Society (Weiss et al. 1961). Eleetroenceph. olin. NeurophysloL, 1963, 15:73-83

74

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Fig, 2 Demonstrations ol" various types of' unit reactionsduring SD. Above: firing rate (absolute number of spikes/rain). Below: steady potential changes accompanying SD, H: ip~ilateral (homolateral) SD; C: contralateral SD (steadypotentials r~ordcd with two calomelcell electrodeslocalized in symmetrical poi~lts of both hem~phe,ra),

£1ectroenceph. olin, NeurophysioL, 1963, 13:7~--85

EXCITABILITYIN THALAMICNUCLEI trarily considered as responding to SD when its firing rate in any l-min period of the 2 min after or before the maximum of the cortical slow potential (accompanying SD) differed by more than three standard deviations from the average of the control period. The duration of the reaction was expressed as the time during which the frequency of the unit exceeded this statistical criterion, Only reversible reactions were evaluated, The recruiting response was studied in rats anesthetized with Dial (40-50 mg/kg). The concentric stimulating electrodes (0.5 mm outer sheath diameter, 0.5 mm interelectrode distance) were stereotaxically placed in the nonspecific thalamus (stereotaxi¢ co-ordinates AP2; L i ; V4-5, atlas of Fif,:ov~i and Margala, 1960). The recruiting response was znonopolarly recorded with wick calomel cell electrodes from the frontoparietal cortex exposed by the trephine opening, while the indifferent electrode was placed on the frontal bone, In some experiments concentric electrodes were used to record the recruiting response also from the caudate nucleus. The recruiting response was elicited by trains of rectangular pulses (0.2 msee, 7 c/see, $ sec) applied at 20-see intervals, in some rats bipolar records of the cortical recruiting response were made with a multiple electrode consisting of 5 con. stantan wires (diameter 0.2 ram, distance between the first and fifth tip 2 mm) introduced to various depths in the cortex. Cortical SD was elicited by local application of filter papers (3 × 3 mm) soaked with 1 per cent KCI solution on the dural surface of either hemisphere. The slow potential changes accompany-

75

ing SD were led off with calomel cell electrodes from the pariet~.! cortex. Monopolar recording was used, the indifferent electrode being placed on the frontal bone or on a symmetrical cortical point, the steady potential of which was not affected by contralateral spreading depression. A mechanical chopper transformed this slow potential into rectangular pulses amplified by the AC amplifier or the CRO or EEG apparatus. RESULTS !. The unit activity in the non-specific thalamic nuclei during ipsi- or contralaterai cortical SD (a) Unanesthetized curarized rats. In 27 rats 59 reactions of thalamic units to unilateral cortical SD were recorded. Results are summarized in Table I and Fig. 3. The typical reactions are illustrated by Fig. 2. The activ;ty of more units was changed during cortical SD ipsilateral to the recording (91.97o) than with contralateral SD (63.6%) (P < 0.003). The commonest reaction was a decrease of the spontaneous firing of the unit, especially during ipsilateral SD. The du. ration of changes in unit activity (exceeding three standard deviations), and their statistical comparison are shown in Table II. The most prolonged decrease of unit firing was also observed during ipsilateral SD. The difference between the behaviour of the thalami¢ units during ipsi- or contralaterai SD indicates a more intensive ipsilaterai cortico-thalamic influence, it seems that the changes in the activity of thalamic units are more closely related to the depression of the eleetrocorticogram during SD, and to the see. ondary changes in the spontaneous thalami¢ EEG activity (lasting approximately 10 min).

TABLE ! Changes of unit activity in the non-specific thalamus during unilateral SD Total No

lpsilateral SD

II

Chloralose n ~- 49

6 !2

Cerveau isold÷n --- 12

2

No

Con'~alateral SD

Reaction reaction Decrease Increase reaction Decrease Increase reaction Decrease Increase

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Reaction

37 18

1i 17

29

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29

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10 19

9 3

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+ From the paper by gtldiger et al. 1962

Eiectroenceph. olin. Ne,rophysiol., 1963, 13:7].-83

76

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than to the potential wave of SD (lasting about 2-3 min). The reaction of the units does not depend on the we-depression firing rate. No statistically significant difference was found between the mean pre-depression frequencies in Fig. 3 Hatched columns = percentage of neurons reacting with significant decrease; white columns --- significant increase of spontaneous unit activity during ipsilateral SD (first column), ccntralatcral SD (second column), and the total (third column). CU: in unanesthetized curarised rats. The difference between the percentage of reacting neurons during ipsilateral and contralateral SD is significant (P < 0.003). In the case of ipsilateral SD (in contradiction to ¢ontralateral SD) the decrease reactions occur siip~ificantiy ( P < 0.003) more frequently. D: in rats anestbelized with Dial. No significant difference exists either between the percentage of reacting neurons or between the incidence of decrease and increase reactions, during ipsilateral and contralateral SD. CH: in rats anesthetized with chloralose. The number of reacting neurons is higher during ipsilateral th~n during contralateral SD (P < 0.003). During ipsilateral SD a decrease of firing rate can be .teen mare frequently than an increase (P <~. 0.003). El: in unanesthetized rats with "cer~eau isold" (according to R0diger et al. 1962). The results were not evaluated in a more detailed manner (for the small number of experiments). 'there was no statistically significant difference be. tween the total number of reacting neurons in unanes, thetized rats and in animals with Dial and chloralose anesthesia, In rats anesthetized with Dial during ipsUat, SD the decrease reaction occurs less frequently (P ~: 0.003) than in anesthetized curarized rats. or in animals with chloralose.

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T A B L E II Average duration of siptfieant changes of unit firing during unilateral SD (in min)

Decrease (a) lpsilateral SD (b) Contralateral SD 1¢1 Total I Unanesthetized curarized 2 Dial 3 Chloralose

6.6 i

Increase (d) Ipsilateral SO (e) ContralateralSD

if) Total

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Remark: Only experiments in which a single wave of SD occurred were counted, Signiflcances between: (a)l and (a)2 for P < 0,05; (a)2 and (a)3 for P < 0.05; (¢)1 and (f)! for P < 0,05: (a)3 and (b)3 for P < 0,003, Eleetmeneepb, ella.Neuro,elo,~ioL, 1~3, I$ : 73-83

LXCITABILITY IN THALAMIC NUCLEI TABLE

77

llI

Average absolute values of unit firing in I-min intervals before and during unilateral SD

Unit frequency

Average frequency/1 rain during Average frequency/I rain during the 10-rain control interval before maximal change (increase or decrea~) SD of unit activity

Unanesthetized curarized

Decrease Inc,'ease

477 -I- 63 399 -4- 84

154 -4- 141 723 :t: 126

Dial

Decrease Increase

310 -t- 69 298 :t: 60

107 ± 29 559 :[: 11 I

Chloralose

Decrease

451 :]: 37 x 274:1:73 x

147 ± 3! 602 :t: 319

Increase

Remark: Significance between values marked with ~ for P < 0.05, the groups showing decreased and increased "eactions. In some cases (16.6% of reactions)a biphasic response occurred, with a brief (I-2 rain) acceleration of unit activity, followed by a longlasting decrease (in Fig. 3 and Tables I and 11 these reactions are included in the group "decrease"). Histological control demonstrated that no correlation could be found between the exact localization of the micro-electrode (mostly in ncl. antero-ventralis, medio-dorsalis, para-faseieularis, ret,~.ularis, antero-mcdialis) and the type or magnitude of the reaction. (b) Rats anesthetized with Dial or chloralose. In eighteen rats anesthetized with Dial, 41 experimoms, and in eighteen animals anesthetized with chloralose, 49 experiments, were performed in a similar manner. The results are summarized in Tables !, II, Ill and Fig. 3. In the chloralose group (40-50 mg/kg) the results were very similar to the findings in unanesthetized animals, The number of reacting neurons and the percentage of long-lasting decrease reactions were greater during ipsilateral than during contralateral SD. In dialized (40-50 mg/kg) rats the decrease and increase reactions were equally frequent and the difference between the effects of ipsi- and contralateral SD disappeared. The shorter duration of the decrease reactions during ipsilateral SD in these rats, in comparison with unanesthetized animals, is also remarkable. The total percentage of reacting neurons .was not changed, however. A biphasic reaction was also seen in some anesthetized animals (with chloralose, 10.2~o, and with Dial, 19.5%). The pre-depression frequency was slightly higher in units displaying decrease

reactions in comparison with those showing increase reactions, but this difference is statistically significant only in rats under chloralose anesthesia. 2. Recruiting responses to thalamic stimulation, recorded from the contralateral cortex or caudate nucleus during cortical SD The recruiting response in rats is similar to that in other rodents (Kerr and O'Leary 1957; Do Carmo 1960). Although no exact check of electrode location was attempted in our experiments, the active thalamic recruiting areas corresponded approximately with ncl. para-taenialis, paravcntricularis, antero-medialis, mediodorsalis sad para-ccnt~alis. This is in good agreement with the findings of Bradley et al. (1961), who obtained rec, uiting responses in rats by stimulation of nucleus medio.dorsalis and adjacent structures. With unilateral thalamic stimulation the responses were equally well developed in both ipsi- and contralateral cortex. The maximal amplitude was usually obtained after 5-10 stimuli, with decrease of the response towards the end of the train. Using slightly supramaximal stimuli the responses were well reproducible and constant for tens of minutes. After this level of responsiveness was established, SD was evoked by application of 1 per cent KCI to either the ipsilateral or contralateral cortex, while thalamic stimulation was continued at regular intervals. A typical experiment is shown in Fig. 4. SD evoked in the cortex overlying the point of thalamie stimulation caused a clear-cut reduction of the reccuiting responses in Electroenceph. olin. Neurophysiol., 1963, 15:"/343

78

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Fig. 4 The efl'~t of cortical SD on recruitin8 responses evoked by stimulation of nonapeciflc thalamus. A,B: trephine openlnp for KCI application. 1,2: cortical electrodes for EEG, 3,4 cortical electrodes for slow potential. 2,1,~: stereotaxic coordinates of the thaktmic stimulating electrodes. Cortical SD elicited from the occipital cortex. ,4: ipsilateral, B: contralateral SD. Short horizontal lines denote trains of thalamtc stimult. TABLE IV The effect of unilateral cortical spreading depression on recruiting responses evoked by lateralized thalamic stimulation SD evoked in the hemisphere

No effect

Local decrease

Bilateral decrease Intensity •1 + o~ + + ~to

lpsilateral to thalamic stimulation Contralateral to thalamic stimulation

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both hemispheres. On the contrary, SD in the contralateral hemisphere did not even reduce the recruiting response in the depressed cortex. In thirteen rats the effect of 43 SD waves was studied in the above way. The results are summarized in Table IV. In all experiments ipsilateral

3

28

latency

Duration

1.8 ± 0.2 rain

5.0 i 0.6 rain

SD was more effective than contmlateral. It seems that the effect of SD on recruiting responses is not due to cortical unresponsiveness, but to changes in excitability in the stimulated region. During SD the excitability of ipsi-lateral non-specific thalamic nuclei is reduced, and the Electroeneeph. ella, Neurophysiol., 1963, L~: 73-83

EXCITABILITY I N THALAMICNUCLEI

constant stimulus becomes sub-maximal or even subthreshold, and recruiting responses are reduced or abolished in both hemispheres. This assumption is also supported by several experiments in which SD ipsilateral to the stimulated thalamus suppressed the recruiting response recorded in the caudate nucleus. The delay between the passage of the negative maximum of the

79

recruiting response is masked by the persisting, more diffuse, and partly extracortical components. Similarly Arduini and Terzuolo (1951) were able to record recruiting responses from the subcortical white matter after local cortical ablations or from cocainized cortical areas. In bipolar i'ecordings from different de.ph'~s of cortex the local component is better expressed;

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FiB. $ Bipolar records of recruiting responses from various depths (leads 1-4) in the right frontoparietal cortex, evok~ by nonsl~ifl¢ thalami¢ stimulation on the left side durins cortical SD. DC: unipolar DC potential record from the neighbourhood of the multi.lead cortical electrode. ST: interruption of the line =~ stimulation of thalamus. A, before; B, during; C, after SD on the right cortex.

slow potential wave through the parietal cortex and the or/set of reduction of the recruiting response was usually 1.8 ±0.2 rain. Because SD was evoked from the occipital cortex,-this delay indicates that the thalamic excitability is markedly decreased only after SD has covered nearly the whole cortex. On the contrary clear-cut recruiting responses were recorded in the depressed cortex contralateral to stimulation (Fig. 4; see also Weiss and Burei 1958). This is probably due to the monopolar recording technique, with which the depression of the local cortical component of the

as Fig. 5 shows, recruiting responses in all the cortical layers are effectively suppressed by SD. DISCUSSION

The above results agree well with our earlier findings (Weiss and Fitkov/t 1961) which ~howed that, in curarized unanesthetized rats and in animals anesthetized with Dial, the spontaneous EEG activity and evoked responses in the nonspecific thalamic nuclei are reversibly decreased during cortical SD. Slow potential recording demonstrated that these changes are not due to the spreading of SD to the thalamus, but that £1ectroenceph. din. Neurophysiol., 1963, I J: 73-83

80

J. BURE~et al.

they are secondary effects of cortical elimination. it is evident that non-specific thalamic regions depend greatly on tonic cortical influences. It seems clear that not only does cortical EEG activity depend on stimuli coming from the diencephalon but also that normaicortical function is necessary for maintaining diencephalic activity. The findings of Verzeano and Calma (1954) and Verzeano e: al. (1955) on synchronization of thalamic unit activity with cortical spindles also support this conclusion. Elimination of the cortex by SD may interrupt the reverberating circuits between the cortex and the non-specific thalamus which possibly play a part, not only in the generation of the normal bio-electric activity, but also in maintaining the level of excitability in both structures. Similar results were obtained when the unit activity and excitability changes were studied in other diencephalic structures, especially in the hypothalamus (Bureg el al. 1961b; Rtldiger et al. 1962: Rtidiger 1962; Rfidiger, Bure~ 1962). Usu. ally a decrease of both was seen. Sometimes, however, an increase of unit activity in the thalamus was recorded. This could be a consequence of a corticofugal discharge related to the short burst of unit activity which accompanies the beginning of depolarization of cortical neurons during SD (Grafstein 1956), An alternative explanation is that in these cases a release phenomenon may take place, which is due to elimination of a hypothetical tonic cortico-dien. cephalic inhibitory influence, Thalamic (and in general diencephalic) units are affected by cortical spreading depression in a different way than are neurons in the tegmental or bulbo-pontine reticular formation (Bure~ et al. 1961a, Buregov~t et aL 1961), In the reticular formation a prevalence of increased firing was found, without any lateralization of the effect. In the thalamus a clear-cut lateralization was seen except in the Dial group, A great difference probably exists between non-specific diencephalic centers and brain,stem structures from the point of view of the cortical descending effect. The effect of anesthesia on thalamic units was not systematically studied. According to Verzeano and Calma (1954) a tendency to synchronized firing can be observed in thalamic

neurons after low doses of Nemb.tal. AlbeFessard and Kr0ger (1961) and Albe-Fessard and Gillet (1961) observed a decrease of spontaneous activity of centrum medianum units after chioralose. In our experiments also it was usually more dit~cult to find units in a.esthetized rats. Although the thalamic neuronal populations studied in unanesthetized and anesthetized animals may be different, the total percentage of units reacting to cortical SD is not changed. Chloralose anesthesia does not even change the relative incidence of various types of thalamic reactions. A similar distribution (predominance of decreased firing) of reticular unit responses to cortical SD was found in rats anesthetized witlb chloralose (Buregov~t el ai. 1962). On the contrary dial anesthesia, which did not influence the relative incidence of increase and decrease reactions in the reticular formation (Bure~ov~ el al. 1962), not only causes an important reduction of the percentage of decrease reactions during ipsilateral SD, but it also shortens their duration and abolishes the lateralization of the cortico-thalamic influence, in conclusion, it may be pointed out that in anesLhetized animals the normally clearly cut difference between the behaviour ofdiencephalic and reticular units is lost. Under chloralose the reticular neurons arc "copying" the reaction of diencephalic elements during SD, while under Dial the thalamic neurons resemble the reticular ones in their behavi. our. This may indicate different affinities of the two drugs for various systems. Our earlier findings (Weiss 1961; Weiss and FiP~ov/t 1961), according to which the spontaneous EEG activity in non-specific thalamus and tegmental retieul~r formation is affected by cortical SD in the same way in rats anesthetized with Dial, but in different ways in animals without anesthesia (depression in thalamus, no change in tegmentum), are in good agreement with these results. The persistence of the influence of cortical SD in thalamic neurons in "cerveau isolt" preparations (RUdiger el eL 1962) shows that the cortico-thalamic influence is a direct one and is not mediated through the brain-stem reticular formation, The effect of cortical SD on the recruiting response, demonstrated in our experiments, conEleclroenceph. olin. NewophysioL, 1963, 13:73-83

EXCITABILITY IN THALAMIC NUCLEI

firms the assumption that depression of EEG and unit activity is accompanied by a corresponding decrease of excitability. The relationship between electrical activity and excitability is not, however, necessarily a direct one. The threshold of a complex reaction may also rise when the firing rate of most neurons in the areas concerned is accelerated (Riidiger and Bure~ 1962). This explanation also applies to changes in evoked responses (Weiss and Fifkov~t 1961), the depression of which may be due either to inhibition or occlusion. The decrease of recruiting responses during ipsilateral cortical SD can also be explained in a different way. The recruit;ng reaction is maintained by complex feedback connections between the cortex, thalamus and caudate nucleus and the effect of SD may be due to disorganisation of this system. Of course this possibility does not contradict the first explanation, and both mechanisms are possibly important~ it is hardly possible to design an experiment which will allow us to study them independently. The lateralized effect of cortical SD on recruiting supports the assumption that this generalized response has a quite local origin. As Kerr and O'Leary (1957) showed, even a small parasagittal displacement of the stimulating electrodes results in a signiticant latency difference between the recruiting waves i~1 the ipsi. lateral and contralateral cortices, It seems that the recruiting reaction is built up in the stimulated half of the thalamus and conducted from there across the midline. Cortical SD evoked ispilateral to the point of thalamic stimulation considerably impairs the development of the recruiting reaction. On the contrary, contralateral SD neither impairs the development of the recruiting responses nor affects their conduction to the depressed hemisphere. This points to the conclusion that ipsilateral cortico-thalamic interaction is essential for the development of recruiting in the stimulated hemisphere, while coaduction of recruiting response to the contralateral hemisphere is rather independent of the functional state of the overlying neocortex.

81

cortical spreading depression (SD) were studied in 150 experiments in curarized unanesthetized, or anesthetized, rats (Dial or chloraiose 40-50 mg/kg i.p.). In total 81.3 per cent of units in unanesthetized, 85.3 per cent in those anesthetized with Dial, and 75.3 per cent in animals anesthetized with chloralose changed their activity significantly in this condition. In rats without anesthesia or with chloralose a clear-cut lateralization of the effect exists. During ipsilateral SD the percentage of reacting cells is significantly greater than during contralateral ~,o/. chioraSD (unanesthetized: 91.9To and 6a,,.,,/o, lose 96.0°,~, and 57.6~o). The most frequent reaction is a reversible decrease of the firing rate, lasting about 6 rain. In rats with Dial no lateralization of the SD effect could be seen, the occurrence of reacting neurons being similar during ipsi- and contralateral SD (86.4°~ and 84.2°,~,). The percentage of neurons reacting to ipsilateral SD with a long.lasting decrease of activity is reduced. These findings indicate the existence of descending cortical influences on non-specific thalamic regions. 2. Recruiting responses evoked by stimulation of the non-specific thalamus, recorded in the cortex or in the caudate nucleus, are reversibly reduced during SD elicited in the cortex overlying the point of the thalamic stimulation. This effect is due to decrease of the thalamic excitability which accompanies the functional decortication. Recruiting responses in the cortex contralateral to thalamic stimulation are not significantly diminished by cortical SD in monopolar records, while recruiting responses from different cortical layers are depressed in bipolar records.

R~SUM~ MODIFICATIONS D'EXCITABILITI~ DES NEURONES THALAMIQUES NON-SP,~CIFIQUI'~, I~VOQUI~ES PAR LA "SPREADING DEPRF,&~ION"CORTICALE

I. Les modifications de, ractivitl spontan/~e des unit~s thalamiques non.sp~cifiques pendant la "spreading depression" (SD) de l'~corce c~.r~brale ont 6t6 6tudi~es au cours de 150 exl~riences SUMMARY chez des rats non anesthi~si~s immobililes au I, The changes in the spontaneous firingrate d-tubocurarine ou anesth~si6s au Dial ou au of non-specific thalamic units during unilateral chloralose i.p. (40-50 mg/kg). L'activit6 de 81.3 Electroenceph. clin. Neurophysiol., 1963, 15:73-83

82

j.

BURE~el ai.

pourcent des un[t~s chez les animaux non anesth6si6s, de 85.3 pourccnt chcz lcs rats anesth6si6s au Dial et de 75.3 pourcent chez les animaux chloralos~s est chang6e de faqon significative darts ces conditions. On constate une lat6ralisation distinct© de cat effet chez les rats non anesth6si6s ou chloralos6s. La SD ipsi]at6rale 6voque une r6action des unit6s thalamiques dans un pourcentage significativcment plus 61ev6 qua la SD contralat6rale (non anesth6si6s, 91.9% ct 63.6%; chloralos~s, 96.0% et 57.6%). La r6action la plus fr6quente est la r6duction r6versible de la fr6quence des d6charges, dont la dur6e est d'environ 6 rain. Une lat6ralisation de l'effet de la SD n'est pas d6montr(:e chez les rats sous anesth6sie barbiturique, le pourcentage des neurones r6pondants 6tant semblable pendant la SD ipsi- et contralat~rale (86.4% et 84.2%). On constate aussi une diminution du pourcentage des neurones r6pondants ~t la SD ipsilat6rale par une diminution prolong6e de I'activitd spontan6c. Ces donnC:es sugg6rent que ractivit6 corticofugale influence les r6gions thalamiques non-sp6cifiques, 2, Le "recruitment" 6voqu~ par la stimulation du thalamus non-sl~cilique et enregistr~ dans r~corce c6rt~brale ou dans le noyau caud(: est rt~duit r~versiblement pendant la " S D " produite dans I'~corce ipsilat~rale au thalamus sti. mul~. Cet effet est dO A la diminution de I'excitabilit~ thalamique pendant la d~cortication fonctionnelle, Le "recruitment" enregistr6 par la d/~rivation monopolaire dans l'~cor~e contralat~rale au thalamus stimul~ n'@rouve aucune r~duction significative pendant la SD, tandis que le "recruitment" enregistr~ sous la meme condition par la d6rivation bipolairt: dans los diff~rentes couches cortica!es est abaiss~. REFERENCES ALBE-FIEssARD,D. et GILLF:r, E. Conver~Doc$ v~rs |~ centre n~lian. Eleeteoenceph. din. Neuropk~!e!., 1962, 13: 257-269. ALBI~-FI~SSARD,D. and KRUGER, L. Duality of unit discharscs from the cat tantrum medianum in response to natural and electrical stimulation. J. Neurol~ysiol.,

1961, 25: 3-20. ARDUINI, A. and TERZUOLO,C. Cortical and subcortical components in the recruitin~ responses.Electroeneeph. din. Neurophysioi., 1951, 3: 189-196. BRADLEY,P. B., E^vas, J. T., GLASs,A. and He^T~, R. W.

The maturational and metabolic consequences of neonatal thyroid.~tomy upon the recruiting rcsponscin the rat. Electrocnceph. din. Neurophysiol., 1961, 13:

577-586. Buerdi,J. [Spreadingcorticaldepression---itsmechanismand application.] SZN, Prague, 1962 (in Czech). BuRr~, J. and BuRr:.~vJ,,O. The use of ~ ' s spreading cortical depression in research on conditioned reflexas. Electrocnceph. clin. Neurophysiol., 1960, 12: Suppl. 13: 359--396. Btza~, J., BUREiOVJL,O. and FIFKOVI,,E. The effect of cortical and hippocampal spreading depression on activity of bulbopontine reticular units in the rat. Arch. ital. Biol., 1961a, 99: 23-32. BUREt, J., BURE~v/~, O., FIeKOV,t,E., OLDS, J., OLDS, M. E., and TRAvm,R. P. Spreading depression and subcortical drive centers. Phydol. bohemoslov., 1961b, 10: 321-330. BuRE~t,J., BuRE~v/~,O.,WEms,T.and FIFKOVI~,E. Experimental study of the role of hippocampus in conditioning and memory functions. Coll. Int. du CNRS, No. 107, Montpellier, 1961c. BuRE.~vI,, O., BURE~I,J. and FIFKOV,t,O. An analysis of the influenceof cortical spreading depression on the activity of reticular neurons. PhysioL bohemoslov., 1962, in press. BURE~V~, O., BURE.~,J., Weiss, T. and FIFKOVJ~,E. The useof spreadingdepressionas a ncuronographic method. Vth. Int. Congr. of EEG and Clln. Neurophysiol., Rome, 1961. Do C^RMO, R, J. Direct cortical and recruiting responses in postnatal rabbit. J. NeurophysloL, 1960, 23: 496-504.

FIFKOV£,E. and MARIALA,J. Stereotaxic atlas for thecat rabbit and rat. In: J. BuaE[l, M. P~Ta/~N ^Nt) J, ZAClIAa (Editors), Electrophyslological methods tn biological research. PuhUshing Hou~ of the Czechoslov. Acad. Sci,, Prague, 1960, p. 426, GRA~STI'.IN, B, Mechanisms of spreading cortical de, pression, J, NeurophysloL, 1956, 19: 154-171, KeR#, F, W, and O'L~^RY,J. The thalami¢ soureeof ¢oro tical recruiting in the rodent. F2eefroeneeph. cliH. NeurophysioL, 1957, 9: 461-476. Knl~o, W. J. S. Accurate placement of minute lesions in the brain of the albino rat. Quart. Bull. Northw. Univ. nwd. Sch., 1946, 20: 199-208. L~^o, A. A. P. Spreading depression of activity in the cerebral cortex. J. NeurophysioL, 1944, 7: 359-390. MARmAt.L,W. H. Spreading cortical depression of kdo. Physiol. Ray., 1959, 39: 239-279. RODIoeR,W, Interfering sub©ortical stimulation and cortical spreading depression.PhysioL bo~moslov., 19~, in press. gODIO~, W. and BuRI~,J. Cortical spreading depression and threshold of tegm~ntal and hypothalamic stimulation producing a locomotor flight. Phys~ol,bohe~lov., 1962, in press. RODIGER,W., BUR~[IOV~,O. und FIFKOV~, E. Die Wirkun$ der sich ~rbreitenden EEG-Depression in der Grosshirnrinde auf die gpontanaktivit~t yon einzc'nen Nervenzcllcn in Hypothalamus der Ratte. Acre Biologica Germanic¢, 1962, in press.

Electroew~reph. eli& Ne~mophysiol., 1963, 15:73-83

EXCITABILITY IN THALAMIC NUCLEI

VERZEANO, M. and CALMA,I. Unit activity in spindle bursts. J. Neurophysiol., 1954, 17: 417428. VILN.ZEANO,M., NAQUET,R. and KING, E. E. Action of barbiturates and convulsants on unit activity of diffusely projecting nuclei of thalamus. J. Neurophysiol., 1955, 18:502-5 ! 2. WEISS, T. The spontaneous EEG activity of the mesencephalic reticular formation during cortical spreading depression. Physiol. bohemoslov., 1961,10:109-116. Weiss, T. and BUREt,J. [Nonspecific projections from subcortical regions to the cerebral cortex during spreading EEG depression.]~s. Fysiol,, 1958, 7:186 (in Czech).

83

WEISS,T., BUREI,J., B u ~ v A , O. and FIFKOVA,E. [The use of conical spreading depression to ap.~lysis of corticothalamic relationships.] Cs. Fy~ioi., 1961, !0: 298 (in Czech). WEISS, T. and FtFKOV~, E. The use of spreading EEG depression for analysing the mutual relationships between the cortex and the hippocampus. Electroenceph, clin. Neurophys:'o!., 1960, 12: 841-850. WEISS,T. and FtFgOVJ,,E. Bioelectric activity in the thalamus and hypothalamus of rats during cortical spreading EEG depression. Electroencepl.. c:7~. Neurw physiol., 1961, 13: 734-744.

Reference: Boad, J., BuRr~ov/~, O., Wrdss, T. and Ftegov/~, E. Excitability changes in non.specific thalamic nuclei durin8 cortical spreading depression in the rat. Electroenceph. din, Neurophysiol., 1963, 15: 'i3-83.