Effects of stimulation of the dorsocaudal claustrum on activities of striate cortex neurons in the cat

Brain Research, 240 (1982) 345-349

345

Elsevier Biomedical Press

Effects of stimulation of the dorsocaudal claustrum on activities of striate cortex neurons in the cat TADAHARU TSUMOTO and KOUHEI SUDA Department of Physiology, Kanazawa University Medical School, Kanazawa, 920 (Japan)

(Accepted February 1lth, 1982) Key words: visual cortex -- claustrum -- claustro-cortical projection - - reverberating circuit - - cat

In the cat striate cortex, single electrical shocks applied to the dorsocaudal claustrum (CLdc) elicited bimodal excitatory responses with about 12 and 26 ms latencies. About one-fourth of the cortical cells observed had CLdc-induced inhibitions with onset latencies longer than the excitations. On cortical field responses to geniculate stimulation, CLdc conditioning shocks exerted early facilitatory and late inhibitory effectswhich were shown to be not transmitted through the mesencephalicreticular formation. Recent anatomical studies using various tracers demonstrated a dense, reciprocal connection between the striate cortex and the dorsocaudal sector of the claustrum (CLdc)1,3-5,7,9,10,12,14,19. Physiological investigations showed that cells in the CLdc respond to visual stimuli and the cortico-claustral projection is organized in a precise retinotopical manner2,6,1°, ~5. Until now, however, only little is known about the functional significance of the claustro-cortical projection, although Ptito and Lassonde 11 very recently reported that repetitive electrical stimulation of the claustrum produced a decrease in the spontaneous activity and visual responses of striate cortex cells. The present study was undertaken to determine whether action of the claustrocortical projection is excitatory or inhibitory on cortical neuron activities and to elucidate neuronal circuits transmitting such an action to cortical neurons. The experiments were done on 13 normal, adult cats. Except for anesthesia, experimental procedures for preparing and maintaining the animals were essentially the same as described before2L Initially, the trachea and the femoral vein were cannulated under ketamine anesthesia (i.m., 35-40 mg/kg). In order to place stimulating and recording electrodes during the operation, a small dose of Nembutal (5-10 mg/kg) was added via the femoral vein. Endtidal CO2 concentration and body temperature was 0006-8993/82/0000-0000/$02.75© Elsevier Biomedical Press

kept at 3.8-4.2 ~ and 37-38 °C, respectively. Recordings were done under 70 ~ N20-30 ~ Oz anesthesia with continuous infusion of Flaxedil. All wound margins were carefully covered with 2 ~ Xylocaine jelly. The animal's ECG and EEG, which were monitored continuously, indicated that they were sufficiently anesthetized. A bipolar, stimulating electrode was inserted stereotaxically into the dorsal lateral geniculate nucleus (LGN). The part of the visual fields projecting to the vicinity of the L G N electrode was determined by listening to the mass unit responses to small light spots projected to the tangent screen in front of the animal. The final position of the L G N electrodes was adjusted so that the tips were located in the area representing the central or paracentral visual field. Compensated by any mismatch between the stereotaxic coordinates of the L G N electrode and those of the equivalent site of the L G N map of Sanderson 1~, another stimulating electrode of the same type was placed in the CLdc (Horsley-Clarke: F 9.5-10.5; L 11.5-12.0; H 2.53.0). Later, the positions of these stimulating electrodes were examined histologically. The present report deals only with the data obtained from 11 animals in which the electrode tips were found to be located in the CLdc and LGN, respectively. To record cortical-evoked potentials elicited by L G N and CLdc stimulation, a bipolar electrode of the same type as above was inserted into area 17 of the

346 hemisphere ipsilateral to the stimulating sites. Usually, the intensity of LGN stimulation was 0.50.8 mA for 0.1 ms pulses, which was just maximal for postsynaptic responses of the cortex (see Fig. 2A). The intensity of CLdc stimulation was adjusted in the way described below. In 5 experiments a glass pipette filled with 2 M potassium citrate was inserted into the cortex through a closed chamber. Amplification and display techniques for extra- and intracellular recordings were described previously 21. Single pulses applied to the CLdc consistently elicited a positive-negative biphasic potential followed by a slow positive potential (Fig. 1A, records 1 and 2). The onset and peak latency of the initial positive potential (PI wave) were 5.3 ± 0.6 (S.D.) and 9.7 ~ 0.6 ms on the average, respectively. A negative deflection following the P1 wave seemed to

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be cut off by the second positive potential (P~ wave) which had an average onset and peak latency of 15 1.0 and 30 i 2.5 ms, respectively. When the intensity of CLdc stimulation was increased, a sharp positive-negative potential with two notches in the positive stroke was elicited prior to the P1 wave (Fig. 1A, record 3). Those short-latency responses with an onset latency less than 1 ms were judged to be potentials evoked by concomitant stimulation of the optic radiation fibers which pass considerably close to the caudal end of the claustrum 16, on the bases of the following 3 observations. (1) Their wave forms were very similar to those of cortical potentials evoked by LGN stimulation (see Fig. 2A). (2) Their latencies were only slightly shorter than those of the corresponding peaks of the LGN-evoked potentials. (3) The CLdc stimulation strong enough to elicit these

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1-~m~smV Fig. 1. Striate cortical responses to single electrical shocks applied to the CLdc. A: cortical-evoked potentials to CLdc stimulation. Five responses were superimposed. Negativity, upward. 1 and 2, slower and faster sweeps respectively. Stimulus intensity was 0.9 mA for 0.1 msec pulses. 3, stimulus intensity was increased to 1.6 mA. Scales are the same as in 2. B: excitatory responses of a cortical cell to CLdc stimulation. 1, extracellular records. Superimposition of 5 sweeps. 2, peristimulus time histogram of spikes followi ng CLdc single shocks which were given at the arrow. Number of sweeps, 50. Bin width, 0.3 ms. C: inhibitory responses of cortical cells. I, peristimulus time histogram of spikes of a cortical cell following CLdc shocks given at the arrow. Number of sweeps, 50. Ordinate, same as in B-2. Bin width, 0.5 ms. 2, intracellularly recorded responses of the same cell as above. Superimposition of 5 sweeps. Membrane potential was 50 mV when this cell was penetrated. 3, peristimulus time histogram of spikes of another cell. Number of sweeps, 100. Ordinate and abscissa, same as in 1.4, intracellularly recorded responses of the same cell as in 3. Superimposition of 5 sweeps. Membrane potential was 45 mV when this cell was penetrated.

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Fig. 2. CLdc-induced effects on cortical responses evoked by LGN stimulation. A: cortical evoked potentials to LGN stimulation. Superimposition of 5 sweeps. Scales at the bottom apply to all the records. 1, control responses to single LGN shocks. Only Cx and C5 components are indicated by arrows. 2, and 3, LGN shocks were preceded by conditioning CLdc shocks by 20 and 100 msec, respectively. B: time course of the effects of conditioning shocks of CLdc (open symbols) and MRF (filled symbols) on LGNevoked potentials. Amplitudes of Cz (triangles) and C5 (circles) components of the LGN-evoked potentials were measured from the initial small negative to the succeeding positive peaks and from the largest positive to the succeeding negative peaks, respectively. Each symbol represents an average value of 20 responses and the bar represents twice the standard deviation. short-latency responses evoked antidromic field responses in the L G N , while a weaker stimulation which did not elicit these responses also did not evoke the antidromic L G N response. Therefore, we adjusted the intensity of CLdc stimulation to 80 ~o of the threshold of the short-latency, contaminated response. Usually, the stimulus intensity was 0.8-1.0 m A for 0.1 ms pulses. In several experiments we moved the CLdc electrode systematically in the vertical direction to see whether the P1 and P2 waves could be obtained only from the CLdc. When the electrode tip was 2 m m above or below the point where the maximal responses were obtained, the Pz wave became indistinguishable and the P2 wave was remarkably reduced in amplitude. When the electrode was moved 1 m m further away from the maximal point, the P2 wave also disappeared. Unitary activities were recorded from 63 cells, of which 20 were reliably excited by single shocks applied to the CLdc. Examples of the CLdc-induced

responses are shown in Fig. lB. In response to CLdc stimulation this unit fired with a slightly fluctuated latency of about 10 ms. These initial responses were followed by more fluctuated responses with an average latency of 35 ms (Fig. 1B, record 1). This bimodal excitatory response was clearly seen in the peristimulus time histogram of spikes (Fig. 1B, record 2). It is to be noted that each peak latency of the excitatory responses roughly corresponds to the respective value of the Pz and P2 waves of the CLdcevoked potentials. Eight cells had only the initial responses while 10 had the secondary responses only. Two had the bimodal excitatory responses. The average latency values of the initial and secondary responses for the 10 and 12 cells were 12.1 43.0 and 25.9 4- 5.5 ms, respectively. In 15 cells a clear suppression of spike discharges was seen following CLdc stimulation (Fig. 1C, records 1 and 3). In most cases this suppression was not preceded by distinguishable excitatory responses. Intracellular

348 records support our presumption that the discharge suppression seen in these cells may be for the most part ascribable to an inhibitory post-synaptic potential (IPSP) (Fig. I C, records 2 and 4). There were two types of IPSPs or discharge suppressions. In 9 cells the onset latency of the IPSPs or discharge suppressions was relatively short (17.0 ~_ 4.8 ms), while in the other 6 cells it was long (40.5 ± 11.5 ms), as exemplified in Fig. 1C, records 2 and 4, respectively. However, the duration of the 1PSPs or discharge suppressions was approximately the same in the two groups and consistent with that of IPSPs evoked by L G N stimulation2L The average onset latencies of these early and late inhibitions were significantly (P < 0.05, t-test) longer than those of the initial and secondary excitations, respectively. Next, we studied effects of CLdc stimulation on cortical field potentials evoked by L G N stimulation. An example of the cortical evoked potentials to a single L G N stimulus is given in Fig. 2A, record 1. For the components of the cortical responses we used the terminology of Malis and Kruger s. As a representative of the pre- and post-synaptic components we analyzed the C1 and C5 components, respectively, because the other pre-synaptic component, Cz, was practically indistinguishable and the post-synaptic ones, C3 and C4, behaved in the same way as C517,2°. When single CLdc shocks preceded testing LGN stimuli by 20 ms, the post-synaptic components were enhanced while the pre-synaptic component seemed unchanged (Fig. 2A, record 2). A clear suppression of the post-synaptic components was observed when CLdc stimulation preceded testing L G N shocks by 100 ms (Fig. 2A, record 3). The time courses of the CLdc-induced effects on the cortical evoked potentials are shown in Fig. 2B where the amplitudes of the C1 and Ca components are plotted as functions of the interval between conditioning CLdc and testing L G N stimuli (open symbols). It is seen that the facilitatory effect lasted from 15 to 25 ms after the conditioning CLdc stimulation, whereas the suppressive effect lasted from 60 to 200 ms. These early facilitatory and late suppressive effects might be transmitted through the mesencephalic reticular formation (MRF), since electrical stimulation of this site is known to exert facilitatory effects on striate cortex activities17, is. Thus, we compared the effects of

CLdc stimulation on LGN-evoked potentials with those of MRF stimulation (Fig. 2B, filled circles). It is obvious that the CLdc-induced effects are quite different from the MRF-induced effects. This indicates that the M R F is not directly involved in the CLdc-induced effects, at least the early facilitatory effect, on cortical evoked activities. The present results support recent anatomical findings that there is a direct projection from the CLdc to the striate cortex 1,3,5,7,9,1°,12, and suggest that synapses between the projection fibers and cortical cells are primarily excitatory in nature. Onset latencies of the CLdc-evoked IPSPs or discharge suppressions were longer than those of the excitatory responses, suggesting that the inhibition may be induced through intracortical inhibitory circuits. Very recently, Ptito and Lassonde 11 reported that electrical stimulation of the claustrum produced a decrease in the spontaneous and visually evoked responses of cortical cells. Their stimulation was continuously given at 2 Hz for a time during which visual responses or spontaneous firing were observed. Such a continuous stimulation might result in a decrease of the total number of spikes simply because the duration of the late suppression is much longer than that of the early excitation in most cells. In fact, we observed that visually evoked responses of cortical cells innervated mono-synaptically by LGN axons were reduced in the total number of spikes during 2 Hz LGN stimulation (Tsumoto and Suda, unpublished observation) despite the fact that the LGN axons make excitatory connections with those cells. There is a possibility that CLdc stimulation might activate cortical cells through recurrent collaterals of cortico-claustral cells. This possibility seems unlikely, however, for the following reasons: in case of L G N stimulation a possibility of activation of cells through collaterals of cortico-genicutate cells is practically negligible '4, and cortico-claustral cells have less extensive axon collaterals than cortico-geniculate cells 5. The relatively long latency of the early excitation (12 ms on the average) of cortical cells suggests that the claustro-cortical projection is slow-conducting system. If the distance between CLdc and the cortex is assumed to be 26 mm and synaptic delay is of the order of 1.0 ms 23, the conduction velocity of the projection fibers is calculated at 2.4 m/s on the average.

349 Creutzfeldt a n d his colleagues 2 reported that the

up a reverberating circuit t h r o u g h which impulses

cortical s t i m u l a t i o n elicited bursts of spikes of CLdc cells with 3-5 ms latency. Very recently, LeVay a n d Sherk 5 reported that the majority o f cortico-clau-

circulate. The f u n c t i o n a l significance of this reverberating circuit is to be investigated in future experiments.

stral fibers contacted the large, spiny dendrite neurons which may project back to the cortex. Therefore, it seems reasonable to assume that the recipro-

We express m a n y t h a n k s to Prof. C. Y a m a m o t o

cal connections between the cortex a n d CLdc makes

for his valuable criticism of the manuscript.

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lateral geniculate and medial interlaminar nuclei in the cat, J. camp. Neural., 143 (1971) 101-118. 14 Sanides, D. and Buchholtz, C. S., Identification of the projection from the visual cortex to the claustrum by anterograde axonal transport in the cat, Exp. Brain Res., 34 (1979) 197-200. 15 Sherk, H. and LeVay, S., The visual claustrum of the cat. III. Receptive field properties, J. Neurosci., 1 (1981) 993-1002. 16 Shoumura, K., Pathway from dorsal lateral genieulate nucleus to visual cortex (visual radiation) in cats, Brain Research, 49 (1973) 277-290. 17 Singer, W., The effect of mesencephalic reticular stimulatin on intracellular potentials of cat lateral genieulate neurons, Brain Research, 61 (1973) 35-54. 18 Singer, W., Tretter, F. and Cynader, M., The effect of reticular stimulation on spontaneous and evoked activity in the cat visual cortex, Brain Research, 102 (1976) 71-90. 19 Squatrito, S., Battaglini, P. P., Galletti, C. and Sansaverino, E. R., Autoradiographic evidence for projections from cortical visual areas 17 18, 19 and the ClareBishop area to the ipsilateral elaustrum in the eat, Neurosci. Lett., 19 (1980) 265-269. 20 Tsumoto, T. and Suzuki, D. A., Effects of frontal eye field stimulation upon activities of the lateral geniculate body of the cat, Exp. Brain Res., 25 (1976) 291-306. 21 Tsumoto, T., Inhibitory and excitatory binocular convergence to visual cortical neurons of the cat, Brain Research, 159 (1978) 85~97. 22 Tsumoto, T. and Suda, K., Three groups of cortico-geniculate neurons and their distribution in binocular and monocular segments of cat striate cortex, J. camp. NeuraL, 193 (1980) 223-236. 23 Tsumoto, T. and Suda, K., Laminar differences in afferent innervation to visual cortical neurons of the cat. In M. Ira et al. (Eds.), Integrative Control Function of the Brain, Vol. 3, Kodansha, Tokyo, 1980, pp. 75-78. 24 Tsumoto, T. and Suda, K., Laminar differences in development of afferent innervation of striate cortex neurones in kittens, Exp. Brain Res., 45 (1982) 433-446.