Responses of presumed cholinergic mesopontine tegmental neurons to carbachol microinjections in freely moving cats

Summary The effects of microinjections of a cholinergic agonist, carbachol (0.2 g/0.2 l), were examined on three different types of rostrally projecting tonic neurons that we have reported previously in the dorsal part of the pontomesencephalic tegmentum known to contain numerous cholinergic cell bodies: 1) tonic type I slow (Type I-S); 2) tonic type I rapid (Type I-R); and 3) tonic type II (Type II) (El Mansari et al. 1989). Microinjections of carbachol near unit recording sites in freely moving cats induced within a few minutes a complete suppression of the spontaneous activity and a marked reduction in orthodromic excitation of identified and non-identified type I-S neurons. These effect lasted for approximately 90–120 min and were reversed by local (0.4 g/0.2 l) or systemic (0.1–0.2mg/kg, i.m.) administration of atropine sulfate. In contrast, the cholinergic agonist had no consistent effects on tonic type II nor on tonic type I-R neurons. In the light of these and other recent findings, we suggested the direct inhibition of central cholinergic neurons via muscarinic receptors, on the one hand, and the cholinergic nature of type I-S, but not type I-R nor type II neurons, on the other.     

Evidence for the presence of PS-OFF neurons in the ventromedial medulla oblongata of freely moving cats

Summary Recordings were made from 24 PS-OFF neurons, characterized by a slow rhythmic discharge rate during waking and slow wave sleep and a marked decrease in the firing rate during paradoxical sleep, in the ventromedial medulla oblongata of freely moving cats. These neurons were located in either the nuclei raphe magnus and pallidus or the neighboring reticular formation where serotonincontaining neurons are found in the cat. Two types of medullary PS-OFF neurons are described, and the descending projection and slow conduction velocity of some of these neurons are demonstrated.Supported by INSERM (U 52), CNRS (LA 162), and DGRST (Contract no. 79.7.1077)     

Effect of optic nerve stimulation on neurons in pericruciate cortex of cats

The distribution of optic chiasm input to different types of neurons in pericruciate cortex of cats agreed with previous work using light flashes. Neuron response times served to differentiate the input pathways to pericruciate cortex, and the types of neurons they influence. Input from the optic chiasm arrived in three distinct surges: the first via the superior colliculus, the second via an unidentified pathway, and the third via the visual cortex. A fourth, diffuse surge arrived in the postcruciate cortex via some unidentified pathway. Stimulation of the contralateral side of the optic chiasm had a weaker effect than stimulation of the ipsilateral side; it evoked activity at a higher threshold, with fewer spikes per response, and at a longer latency. The difference in response latency between the two sides was largest on neurons responding to the first surge, decreasing in later surges, and being least on those neurons responding to the last surge. About 2.3% of the postcruciate and 15% of the precruciate neurons responded only to optic chiasm stimulation; they were isolated in the granular layers, and their responses could not be influenced by prior cutaneous input. It is suggested that much of the visual input to pericruciate cortex serves to modulate on-going cortical output and, thereby, the behavior of the animal.     

The responses of neurons in subdivisions of the inferior colliculus of cats to tonal,noise and vocal stimuli

The aim of this study was to gain information from anesthetized cats about the differential coding properties of neurons in the three major subdivisions of the inferior colliculus: the central (CNIC) and external (EN) nuclei and dorsal cortex (DC). Stimuli were presented in the free field from a speaker facing the contralateral pinna. For each unit, the characteristic frequency (CF, where threshold was lowest) was determined, and impulse rates to CF tone bursts, noise bursts and four feline vocal stimuli were measured as a function of increasing sound pressure level (rate/level functions). Peristimulus-time histograms were computed for responses to all stimuli. Sustained firing patterns to CF stimuli were observed for 81% of units in CNIC, for 50% of units in EN and 27% of units in DC. Sustained discharges were evoked by noise in 78–100% of units in all regions, and by at least one vocal stimulus in 86% of units in CNIC, 82% in EN and 55% in DC. In the CNIC, non-monotonic rate/level functions to CF stimuli were more common (41%) than either monotonie or plateau functions, whereas the reverse was the case with noise and vocal stimuli. Non-monotonic functions were uncommon to any stimulus in EN and DC (21–24%). Vocal stimuli were more effective in terms of higher firing rates than noise or CF stimuli in 27% of units in CNIC, 82% in EN and 72% in DC. There were no units that responded exclusively to one vocal stimulus, but a high proportion of units in EN responded strongly to broad band stimuli, and some of these showed clear preferences for one vocal stimulus over others.     

Discharges of superior colliculus neurons during head and eye movements of the alert cat

Summary 452 single neurons from the superior colliculus were recorded in awake and non-paralysed cats. 75 neurons were obtained from cats with unrestrained horizontal head movements.228 neurons remained unaffected by saccadic eye movements. Eye movement related discharge followed the onset of saccades in 156 neurons either only in the presence of a visual pattern (92 neurons) or in darkness, too (64 neurons). The latter reaction type probably depends on eye muscle afferents.In 48 neurons eye movement related activity preceded the onset of eye movements. 12 neurons fired in synchrony with eye movements of any direction (type I). 30 neurons were excited during contralaterally directed eye versions within or into the contralateral head related hemifield. They were inhibited when the eyes moved within or into the ipsilateral head related hemifield (type II). 6 neurons with constant maintained activity during fixation were inhibited by ipsilaterally directed saccades, but remained unaffected by contralateral eye movements.Head movement related discharge followed the onset of head movements in 20 neurons only in presence of a visual pattern and also in darkness in 6 neurons. Ipsilateral head movements or postures strongly suppressed maintained activity and visual responsiveness of some neurons.15 neurons discharged in synchrony with and prior to contralateral head movements. Ipsilateral head movements inhibited these neurons. Activation or inhibition were usually related to movement and to posture, exceptionally to movement or to posture.Electrical stimulation of recording sites of these neurons through the recording microelectrode elicits contralateral head movements.     

Firing rates and patterns of midbrain reticular neurons during steady and transitional states of the sleep-waking cycle

Summary Spontaneous firing of midbrain reticular formation (MRF) neurons was recorded extracellularly in chronically implanted, behaving cats during steady and transitional states of the sleep-waking cycle. Physiological identification of receiver and/or projection MRF neurons was achieved through orthodromically and antidromically elicited discharges.Discharge rates of MRF neurons were more than double in waking (W) and active sleep (D) without phasic motor events, as compared to synchronized sleep (S). During behavioral states associated with EEG activation, the increased firing was essentially due to cells exhibiting high discharge rates, located at relatively ventral levels of the midbrain core. MRF neurons with identified rostrally projecting axons were more active during W and D states; their discharge rates were significantly higher than those of caudally projecting cells. The discharge patterns of MRF neurons increasing their firing rates from S to W and D were of the tonic type. First-order analyses showed a negligible proportion of both very short and long interspike intervals in all states, large interval density around the mode especially in W and D, and the smallest variation coefficients in W. Rhythmic firing with a period near the modal interval was detected during W by autocorrelations.The increase in firing rate of MRF neurons from S to W or D took place before overt EEG desynchronization and behavioral manifestations that define stable W or D states. In our sample a statistically significant increase in discharge rate was found about 15 s before the end of S sleep epochs that developed into awakening.The differences between discharge features of MRF neurons during waking and sleep states and those of neurons in other brainstem reticular fields are emphasized. Taken together, these data support, at a cellular level, Moruzzi and Magoun's concept of a rostral reticular substrate that gives rise to impulses leading to tonic activation of the thalamocortical systems.Supported by grant MT-3689 from the Medical Research Council of CanadaPart of the results was incorporated in the Ph. D. thesis of N. Ropert     

Microinjected clonidine inhibits noradrenergic neurons of the locus coeruleus in freely moving cats

Microinjection of the alpha 2-adrenoceptor agonist, clonidine (CLON; 1.0 microgram/0.1 microliter) effected a virtually complete suppression of the spontaneous activity of noradrenergic neurons of the locus coeruleus in freely moving cats. This effect lasted for approximately 90 min and was reversible by systemic administration of the alpha 2-adrenoceptor antagonist, yohimbine. In contrast, CLON had no consistent effect on the activity of neighboring non-noradrenergic neurons. These results provide additional evidence for the direct inhibition of central noradrenergic neurons by CLON by demonstrating such effects independent of anesthesia or the behavioral effects of systemic drug administration. More generally, these findings demonstrate the usefulness of a technique in which small amounts of drug can be applied in small volumes to produce a neuropharmacologically specific effect upon locally recorded neurons in behaving animals.     

Activity of neurons in Forel's field H during orienting head movements in alert head-free cats

Single unit activities were recorded in Forel's field H (FFH) at the mesodiencephalic junction during orienting head movements in two alert cats under headfree conditions. Recordings were made of 63 neurons of which 20 showed phasic firing that preceded the onset of head movements by 20–100 ms and was temporally related to the dynamic phase of the orienting head movement. Nineteen of these neurons showed a preference for upward movements, while the remaining neuron preferred downward movements. Activities during orienting movements in eight different directions (each separated by 45°) were systematically analyzed for 12 of the 19 upward-preferring neurons. The activities were broadly tuned; in most of the neurons, maximum activity was observed for direct upward movements (+90°), but significant activity was also observed for ipsilateral and contralateral oblique upward movements (+45° and +135°). In these cases, the increase in activity preceded the onset of the movement. Some increase in activity was also observed for ipsilateral and contralateral horizontal, oblique downward and downward movements. However, the increase in activity in the latter cases occurred simultaneously with or lagged behind the onset of the movement and was often preceded by a decrease in activity. The same pattern of directional tuning was observed in the EMG of the biventer cervicis muscle, a target of FFH neurons. The preferred directions of the 12 upward-preferring neurons were estimated by calculating the vector sum of the activity and were distributed between +68° and +108°. The same amount of activity was observed for ipsilateral and contralateral oblique upward movements, suggesting that FFH neurons on both sides of the brainstem are equally activated even during oblique orienting. Input from the ipsilateral superior colliculus was investigated in 18 neurons, all of which were orthodromically activated with a latency of 0.8–1.8 ms, suggestive of a mono- or disynaptic excitatory connection. Seven neurons were identified as descending projection neurons by antidromic activation from the ipsilateral medullary reticular formation. Repetitive microstimulation of unilateral FFH induced oblique upward head movements and an accompanying torsional component, while simultaneous bilateral stimulation at comparable stimulus strength induced purely upward head movements. These results strongly suggest that the vertical component of orienting head movements is encoded by equal bilateral activation of the FFH.     

Modulation of unit activity in the amygdala of unrestrained cats during the sleep-waking cycle

Recordings of amygdaloid unit activity were performed in unrestrained cats during the sleep-waking cycle. Discharge rates of most units studied in the central part of the amygdala were related to the sleep-wakefulness cycle. Out of 30 units, 18 had decreased discharge rates during slow-wave-sleep (SWS), compared to the waking state. In 12 of these 18 units discharge rates became higher during desynchronized sleep (DS). A similar relationship was seen when studying units in basal amygdala.     

Microinjected morphine suppresses the activity of locus coeruleus noradrenergic neurons in freely moving cats

Microinjection of morphine (1.0 microgram/0.1 microliter) produced a significant suppression (approximately 60%) of the single unit activity of locus coeruleus noradrenergic neurons in freely moving cats. This effect was reversible by systemic administration of the opioid receptor antagonist, naloxone (1.0 mg/kg i.v.). The microinjection of naloxone (1.0 microgram/0.1 microliter), however, was without effect on the spontaneous activity of noradrenergic neurons in the locus coeruleus. Non-noradrenergic neurons recorded in the same vicinity showed no consistent response to the microinjection of morphine. These results suggest that the direct effect of opioids in the locus coeruleus is an inhibition of noradrenergic neuronal activity. Furthermore, it appears that opioid influences upon these neurons are not tonically active.     

The effect of electrolytic thalamic lesions on the NADPH-diaphorase activity of neurons of the laterodorsal tegmental and pedunculopontine nuclei in rats

Cholinergic neurons of the mesopontine complex have extensive ascending projections to the forebrain: the laterodorsal tegmental nucleus extensively innervates the anterior thalamus, the anteroventral nucleus in particular, whereas the pedunculopontine nucleus has widespread projections to both the thalamus and extrapyramidal structures. Most of their neurons express nitric oxide synthase (NOS) activity. Following electrolytic lesions of the anteroventral thalamic nucleus, nicotinamide adenine dinucleotide phosphate-diaphorase (NADPHd) activity in neurons of the laterodorsal tegmental nucleus changed drastically. The intensity of NADPH-diaphorase staining increased in laterodorsal tegmental neurons ipsilateral to the lesion side, but decreased contralaterally. The intensity of the NADPH-diaphorase staining of neurons of the pedunculopontine nucleus, however, remained unchanged bilaterally. After partial lesions of the anteroventral thalamic nucleus a similar effect was noted. In contrast, large electrolytic lesions involving other thalamic nuclei or extrapyramidal structures did not change the number of NADPH-diaphorase neurons or their intensity of staining in the laterodorsal tegmental nuclei. These data show that electrolytic lesions of target areas can lead to an upregulation of NOS expression in the parent cell bodies, provided that there is no wide collateralization as found for the pedunculopontine nucleus.     

Synaptic mechanisms acting on lumbar motoneurons during postural augmentation induced by serotonin injection into the rostral pontine reticular formation in decerebrate cats

Intrapontine microinjections of serotonin in acutely decerebrated cats resulted in the bilateral augmentation of the postural muscle tone of the hindlimbs. Optimal injection sites were located in the dorsomedial part of the rostral pontine reticular formation corresponding to the nucleus reticularis ponds oralis (NRPo). In this study, attempts were made to elucidate the cellular basis for the serotoninergically induced augmentation of postural muscle tone by recording the electromyographic (EMG) activity of hindlimb extensor muscles, the monosynaptic reflex responses evoked by electrical stimulation of group Ia muscle afferent fibres and the membrane potentials of hindlimb alpha-motoneurons (MNs). Serotonin injections resulted not only in the augmentation of the EMG activity of gastrocnemius soleus muscles, but also in the restoration of EMG suppression, which was induced by previous injection of carbachol into the NRPo. Extensor and flexor monosynaptic reflex responses were facilitated by serotonin injections into the NRPo. Such reflex facilitation was not induced by serotonin injections into the mesencephalic or the medullary reticular formation. Intrapontine serotonin injections resulted in membrane depolarization of extensor and flexor MNs with decreases in input resistance and rheobase. Spontaneous depolarizing synaptic potentials (EPSPs) increased in both frequency and amplitude. Peak voltage of Ia monosynaptic EPSPs also increased. Serotonin injections which followed carbachol injections resulted in membrane depolarization of MNs along with an increase in the frequency of spontaneous EPSPs and a decrease in carbachol-induced inhibitory postsynaptic potentials. Following pontine carbachol injections, antidromic and orthodromic responses in MNs were suppressed. Discharges of MNs evoked by intracellular current injections were also suppressed, but were restored following serotonin injections. These results indicate that postsynaptic excitation, presynaptic facilitation and disinhibition (withdrawal of postsynaptic inhibition) simultaneously act on the hindlimb MNs during serotonin-induced postural augmentation and restoration.     

Discharge properties of medullary reticulospinal neurons during postural changes induced by intrapontine injections of carbachol,atropine and serotonin,and their functional linkages to hindlimb motoneurons in cats

The present study was aimed at elucidating the pontomedullary and spinal cord mechanisms of postural atonia induced by microinjection of carbachol and restored by microinjections of serotonin or atropine sulfate into the nucleus reticularis pontis oralis (NRPo). Medullary reticulospinal neurons (n=132) antidromically activated by stimulating the L1 spinal cord segment were recorded extracellularly. Seventy-eight of them were orthodromically activated with mono- or disynaptic latencies by stimulating the NRPo area at the site where carbachol injections effectively induced postural atonia. Most of these reticulospinal neurons (71 of 78) were located in the nucleus reticularis gigantocellularis (NRGc). Following carbachol injection into the NRPo, discharge rates of the NRGc reticulospinal neurons (29 of 34) increased, while the activity of soleus muscles decreased bilaterally. Serotonin or atropine injections into the same NRPo area resulted in a decrease in the discharge rates of the reticulospinal neurons with a concomitant increase in the levels of hindlimb muscle tone. Membrane potentials of hindlimb extensor and flexor alpha motoneurons (MNs) were hyperpolarized and depolarized by carbachol and serotonin or atropine injections, respectively. In all pairs of reticulospinal neurons and MNs (n=11), there was a high correlation between the increase in the discharge rates and the degree of membrane hyperpolarization of the MNs. Spike-triggered averaging during carbachol-induced atonia revealed that inhibitory postsynaptic potentials (IPSPs) were evoked in 15 MNs by the discharges of nine reticulospinal neurons. Four of them evoked IPSPs in more than one MN. The mean segmental delay and the mean time to the peak of IPSPs were 1.6 ms and 2.0 ms, respectively. Axonal trajectories of reticulospinal neurons (n=6), which evoked IPSPs in MNs, were investigated in the lumbosacral segments (L1-S1) by antidromic threshold mapping. The stem axons descended through the ventral (n=2) and ventrolateral (n=4) funiculi in the lumbar segments. All axons projected their collaterals to the intermediate region (laminae V, VI) and ventromedial part (laminae VII, VIII) of the gray matter. All these results suggest that the reticulospinal pathway originating from the NRGc is involved in postural atonia induced by pontine microinjection of carbachol, and that the pathway is inactivated during the postural restoration induced by subsequent injections of serotonin or atropine. It is further suggested that the pontine inhibitory effect is mediated via segmental inhibitory interneurons projecting to MNs.     

Callosal responses of fast-rhythmic-bursting neurons during slow oscillation in cats

The cortically generated slow oscillation consists of long-lasting hyperpolarizations associated with depth-positive electroencephalogram (EEG) waves and neuronal depolarizations accompanied by firing during the depth-negative EEG waves. It has previously been shown that, during the prolonged hyperpolarizations, the transfer of information from prethalamic pathways to neocortex is impaired, whereas the intracortical dialogue is maintained. To study some of the factors that may account for the maintenance of the intracortical information transfer during the hyperpolarization, intracellular recordings from association areas 5 and 7 were performed in anesthetized cats, and the synaptic responsiveness of fast-rhythmic-bursting, regular-spiking and fast-spiking neurons was tested using single pulses to the homotopic sites in the contralateral areas. During the long-lasting hyperpolarizations callosal volleys elicited in fast-rhythmic-bursting neurons, but not in regular-spiking or fast-spiking neurons, large-amplitude excitatory post-synaptic potentials crowned by single action potentials or spike clusters. Our data show that callosal volleys excite and lead to spiking in fast-rhythmic-bursting neurons during prolonged hyperpolarizations, thus enabling them to transmit information within intracortical networks during slow-wave sleep.     

Activity of dorsal respiratory group inspiratory neurons during laryngeal-induced fictive coughing and swallowing in decerebrate cats

Membrane potential changes and/or discharges from 36 inspiratory neurons were recorded intracellularly in the dorsal respiratory group (DRG; i.e., the ventrolateral subdivision of the nucleus tractus solitarii) in decerebrate, paralyzed, and ventilated cats. Electrical activities were recorded from both somata (n=10) and axons (n=26). Activities during quiet breathing were compared with those observed during fictive coughing and swallowing evoked by repetitive electrical stimulation of afferent fibers of the superior laryngeal nerve (SLN). These nonrespiratory behaviors were evident in paralyzed animals as characteristic discharge patterns of the phrenic, abdominal, and hypoglossal nerves. Twenty-six neurons exhibiting antidromic action potentials in response to electrical stimuli applied to the cervical (C3–5) spinal cord were classified as inspiratory bulbospinal neurons (IBSNs). These neurons were considered as premotoneurons. The remaining 10 inspiratory neurons (INAA) were not antidromically activated by electrical stimuli applied to either cervical spinal cord or ipsilateral cervical vagus. These neurons are thought to be propriobulbar neurons. We recorded the activity of 31 DRG inspiratory neurons (24 IBSNs and 7 I-NAA) during coughing. All but one (a late-recruited IBSN) discharged a burst of action potentials during the coughing-related phrenic nerve activity. Typically, ramp-like membrane depolarization trajectories and discharge frequencies during coughing were similar to those observed during inspiration. We recorded the activity of 33 DRG inspiratory neurons (23 IBSNs and 10 I-NAA) during swallowing. Most (28/33) neurons were briefly activated, i.e., discharged a burst of action potentials during swallowing, but peak discharge frequency decreased compared with that measured during inspiration. The membrane potentials of nine somata exhibited a brief bell-shaped depolarization during swallowing, the amplitude of which was similar to that observed during inspiration. These results suggest that some inspiratory premotoneurons and propriobulbar neurons of the DRG might be involved in nonrespiratory motor activities, even if clearly antagonistic to breathing (e.g., swallowing). We postulate the existence in the medulla oblongata of adult mammals of neurons exhibiting a functional flexibility.     

Activity of serotonin-containing nucleus centralis superior (raphe medianus) neurons in freely moving cats

Summary Presumed serotonin-containing neurons in the nucleus centralis superior (NCS) in freely moving cats showed a slow, rhythmic discharge rate during quiet waking (X = 2.41 ± 0.12 spikes/s), and displayed a strong positive correlation with level of behavioral arousal. Unit activity during phasic and tonic arousal, as elicited by acoustic stimuli, was increased by 76% and 31%, respectively, and unit activity decreased to active waking levels as the arousal response habituated. During active waking, unit activity was significantly increased by 18% as compared to quiet waking, but there was no correlation between unit activity and phasic body movements. NCS unit activity showed a significant decrease of 15% during drowsiness (first appearance of EEG synchronization) as compared to quiet waking, and then progressive decreases during the early (–27%), middle (–41%) and late (–67%) phases of slow wave sleep. During all phases of slow wave sleep, the occurrence of sleep spindles was frequently associated with a transitory decrease in unit activity. The discharge rate would typically decrease during the few seconds immediately preceding the spindle, remain at this low level during the occurrence of the spindle, and then increase immediately after the spindle. NCS unit activity showed decreases of 73% during Pre-REM (the 60 s immediately before REM onset) and 84% during REM, as compared to quiet waking. Unit activity reappeared on the average 2.7 s before the end of REM with significant increases in activity of 60% and 28% during the first second and first 10 s of unit activity, respectively, as compared to quiet waking. NCS neurons showed no significant changes in activity across the 24-h light-dark cycle, when behavioral state was held constant. Seventy-eight % of NCS units were excited by phasic auditory stimulation, with a mean latency of 41 ± 3 ms and a mean duration of 34 ± 4 ms. The response to repetitive auditory stimulation showed no evidence of habituation and was even present during sleep. A similar response was evoked by phasic visual stimulation in 68% of the cells tested. A small subset of cells (12%) were inhibited by phasic auditory and visual stimuli. NCS neurons were inhibited by low doses of 5-methoxy-N,N-dimethyltryptamine (50 g/kg, i.m.) or LSD (50 g/kg, i.p.). These data demonstrate that serotonin-containing NCS neurons exhibit properties very similar to those in the nucleus raphe dorsalis, but are different in many respects from medullary serotonergic neurons.     

Canal-neck interaction in vestibular nuclear neurons of the cat

Summary The convergence and interaction of horizontal semicircular canal and neck proprioceptive inputs were studied in neurons of the caudal two thirds of the vestibular nuclear complex. Extracellular neuron activity was recorded under muscle relaxation and slight anesthesia in chronically prepared cats. The following stimulations were applied: horizontal rotations of (a) the whole body (labyrinth stimulation), (b) the trunk vs. the stationary head (neck stimulation), and (c) the head vs. the stationary trunk (combined labyrinth and neck stimulation).Of 152 neurons investigated, 83 (55%) showed convergence of the two inputs. In about half of these neurons, the neck input was very weak and hardly affected the labyrinthine response during head rotation. Judged from the response pattern, several of these neurons presumably were related to vestibulo-oculomotor function (i.e., vestibular nystagmus). In the other half (i.e., 27% of all neurons), sensitivity of the two inputs was similar. Both labyrinthine and neck responses contained a dynamic (velocity) component; neck responses of more than half of these neurons had, in addition, a static (position) component. The dynamic components were either antagonistic or synergistic as to their convergence during head rotation. When applying this combined stimulation, the dynamic components summed linearly, yielding subtraction in case of antagonistic convergence and addition in case of synergistic convergence. In contrast, the static components of the neck responses remained largely unchanged during head rotation. However, the static head-to-trunk deflection determined the tonic discharge level in such neurons and thus facilitated or disfacilitated the dynamic responses to superimposed labyrinth stimulation.We suggest that the two patterns of labyrinthine-neck interaction observed in vestibular nuclear neurons, i.e., subtraction and addition, may be involved in the postural control of the trunk and head, respectively. In contrast, interference of the neck input with vestibule-oculomotor function appears to be almost negligible in the intact cat.Supported by Deutsche Forschungsgemeinschaft, SFB 70     

Attack,grooming, and threat elicited by stimulation of the pontine tegmentum in cats

Predatory-like biting attack and associated prey-kicking, grooming, and components of threat behavior were elicited by electrical stimulation of different, but partly overlapping areas of the pontine tegmentum in cats. Electrodes producing biting attack and prey-kicking were located in the central tegmentum. The effective area for grooming was located in the dorsolateral tegmentum and extended, with the superior cerebellar peduncle, into the deep fibers of the cerebellum. Electrodes producing threat responses were more widely distributed, but tended to be located ventrally or laterally. The results support the view that the lower brainstem may play an important role in the production of complex species-typical behaviors.     

Single unit recordings in the nuclei raphe dorsalis and magnus during the sleep-waking cycle of semi-chronic prepared cats

Single unit recordings were performed in the nuclei raphe dorsalis (RD) and raphe magnus (RM) of semi-chronic prepared cats during spontaneous or cryogenically induced sleep. Of the RD neurons 75% showed a discharge pattern which decreased during slow wave sleep and paradoxical sleep (PS); such a decrease in spiking was related to the occurrence of ponto-geniculo-occipital (PGO) waves. To the contrary, 78% of the RM neurons demonstrated a discharge pattern which significantly increased during PS, and especially when PGO waves were present.     

Neuronal activity during eye movements in a visual association area of cat cerebral cortex

Summary 270 single neurons from the anterior part of the middle suprasylvian gyrus (AMSS) were recorded in awake and non-paralyzed cats (Chronic preparation).10% were unresponsive to visual stimulation, the remainder reacted well to moving visual stimuli. Half of the units tested were directionally selective. Horizontal, or downward preferred directions predominated. Most neurons were relative insensitive to changes of shape, orientation, contrast, and velocity of the visual stimulus. Some neurons preferred rapid (100°/sec) jerky movements, others required complex motions of irregular shapes, a few strongly preferred objects moving towards the animal in the midsagittal plane. 40% of neurons yielded phasic On-Off reaction to flashing stationary spots.Habituation to repeated stimulation was a common feature and occured in 50% of AMSS neurons. In 19% of neurons tested the discharge rate was not affected by saccadic eye movements, when the animal faced a patterned background. Among the remainder two types of saccade associated responses could be distinguished. Type I discharged prior to or simultaneously with the onset of saccades. This early response was usually associated with saccades of particular directions. Saccades in total darkness yielded weaker and less consistent responses. Type II discharged subsequent to the onset of the saccades after a latency of 40 msec (type IIa), 40–80 msec (type IIb) and 80 msec (type IIc). Responses of type IIa are probably consequences of the retinal effects of eye movements.The saccade associated responses of type Ia, IIb and IIc are tentatively interpreted as results of an eye movement-synchroneous subcortical input, which facilitates transmission in AMSS neurons. Presaccadic facilitation, which generates type Ia responses, may be functionally related to shifts of attention prior to eye movements. It is suggested that postsaccadic facilitation, which underlies the reactions of type IIb and IIc, may be a correlate of visual attention during the fixation period.