Jaime R. Villablanca

The electrocorticogram in the chronic cerveau isolé cat

1. 1. The ECoG of cerveau isole preparations was studied in 16 high mesencephalic, chronic cats which survived for an average of 48 days. Relationships were sought between ECoG and the level of behavioral arousal and with the electrical activity at the brain-stem caudal to the transection. 2. 2. In the acute stage, two ECoG patterns could be distinguished: spindle bursts or discontinuous slow waves; and continuous, high voltage slow activity. In chronicity, this pre-collicular forebrain exhibited low voltage, fast desynchronized rhythms (ECD) which lasted for several hours and which were similar to the ECD patterns of an intact cat. 3. 3. Periods (mean duration 60 ± 4 min) of high voltage, continuous slow synchronized rhythms (ECS) alternated with ECD in the chronic preparation. These cyclical lapses exhibited electrocortical synchronization; i.e., sleep period (ECSP), which closely resembled the ECoG of slow sleep in the normal cat. 4. 4. Since both ECD and ECS persisted following visual and olfactory deafferentation of the cerveau isole, both patterns probably have an autochthonous origin in the structures of the rostral forebrain. 5. 5. Olfactory stimulation desynchronized the ECoG according to the stage of the ECSP during which stimulation was presented. Maximal desynchronization was observed during the onset stage of the ECSP. 6. 6. The EEG patterns of the cerveau isole showed no systematic relationship with the level of arousal of the animal, nor with the electrical activity in the brain-stem. However, the effect of nociceptive and proprioceptive stimulation revealed the possibility of an extraneural pathway which affected the ECoG of the isolated cerebrum. 7. 7. The possibility of the existence in the forebrain of the cat of an autochthonous tonic, mechanism capable of independently evoking a cyclic alternation between wakefulness and slow sleep is discussed.

Behavioral and polygraphic study of “sleep” and “wakefulness” in chronic decerebrate cats

Abstract 1. 1. Behavioral and physiological analyses were performed in 21 high mesencephalic and in three pontine chronic cats maintained chronically for an average of 43 days in order to ascertain their sleep-wakefulness capabilities. Relationships were sought between the findings in this preparation and the electrical and behavioral patterns of the cerveau isole rostral to the mesencephalic transection. 2. 2. Periods of activity with postural and ocular patterns similar to those displayed by intact cats during wakefulness were observed, which alternated with periods of rest and showed elevated excitability threshold and ocular patterns similar to those of intact cats during sleep. Episodes were identified of atonia with muscular twitches and of fissured myosis with rapid eye movements which could not be distinguished from that occurring during paradoxical sleep lapses of intact cats. During these episodes, heart rate increased in high decerebrate cats and irregularities in respiratory movements were noted in all animals. 3. 3. In high decerebrate cats, the brain-stem exerted control over pupil and ocular activity during wakefulness and sleep, whereas in pontine animals only a fragmentary caudal brain-stem control of rapid eye movements was retained. 4. 4. The time course for wakefulness and sleep after decerebration was studied as well as the relative amount of time which cats spent in deep sleep before and after the operation. Quantitative changes in the duration of these behavioral states after mesencephalic transection were found. 5. 5. After decerebration EEG from the brain-stem exhibited a permanent pattern of low voltage fast activity which was not altered in chronicity nor by suprathreshold doses of Metrazol, atropine or eserine. The implication of this finding in the genesis of the ECoG of the intact animal is discussed. During paradoxical sleep episodes, brain-stem EEG exhibited phasic discharges of grouped, high voltage monophasic waves. The physiological meaning of these events is also discussed. 6. 6. The behavioral and physiological manifestations of sleep and wakefulness in decerebrate animals showed no systematic relationship with the ECoG and behavioral manifestations of the rostral cerveau isole. 7. 7. On the basis of previous as well as the present findings the existence is postulated of an independent dual control for sleep and wakefulness by the rostral brain (“brain sleep and wakefulness”) and caudal brain-stem structures (“body sleep and wakefulness”).

Metabolic Maturation of the Brain: A Study of Local Cerebral Glucose Utilization in the Developing Cat

Previously, using positron emission tomography (PET), we showed that local cerebral metabolic rates for glucose (lCMRglc) in children undergo dynamic maturational trends before reaching adult values. In order to develop an animal model that can be used to explore the biological significance of the different segments of the lCMRglc maturational curve, we measured lCMRglc in kittens at various stages of postnatal development and in adult cats using quantitative [14C]2-deoxyglucose autoradiography. In the kitten, very low lCMRglc levels (0.14 to 0.53 μmol min−1 g−1) were seen during the first 15 days of life, with phylogenetically older brain regions being generally more metabolically mature than newer structures. After 15 days of age, many brain regions (particularly telencephalic structures) underwent sharp increases of lCMRglc to reach, or exceed, adult rates by 60 days. This developmental period (15 to 60 days) corresponds to the time of rapid synaptic proliferation known to occur in the cat. At 90 and 120 days, a slight decline in lCMRglc was observed, but this was followed by a second, larger peak occurring at about 180 days, when sexual maturation occurs in the cat. Only after 180 days did lCMRglc decrease to reach final adult values (0.21 to 2.04 μmol min−1 g−1). In general, there was good correlation between the metabolic maturation of various neuroanatomical regions and the emergence of behaviors mediated by the specific region. At least in the kitten visual cortex, which has been extensively studied with respect to developmental plasticity, the “critical period” corresponded to that portion of the lCMRglc maturational curve surrounding the 60-day metabolic peak. These normal maturational lCMRglc data will serve as baseline values with which to compare anatomical and metabolic plasticity changes induced by age-related lesions in the cat.

Effects of caudate nuclei or frontal cortex ablations in cats. II. Sleep-wakefulness, EEG, and motor activity ☆

Abstract The effects of caudate nuclei ablation or frontal cortex removal on the percentages of wakefulness and sleep stages, spontaneous motor activity, and the EEG were studied in cats by means of 24-hr polygraphic recordings for a 6-month period. A significant, permanent, reduction of sleep (particularly REM sleep) and an increase in motor activity were observed in cats with removal of most of the frontal tissue in front of the A22 stereotaxic plane. A similar decrease in sleep was also observed in animals with bilateral, almost total, removal of the caudate nuclei, but this reduction almost fully recovered after the second postlesion month. Motor hyperactivity was more marked in cats with caudate ablations than in cats with frontal ablations and persisted indefinitely. No marked or lasting effects on the EEG were observed. Sham-operated cats and those with unilateral caudate removal behaved like intact cats. It is concluded that both the frontal cortex and the caudate nuclei are parts of a postulated, complex, forebrain system modularing brain stem activating-deactivating central nervous system mechanisms.

Developmental neuroplasticity in a model of cerebral hemispherectomy and stroke.

Cerebral hemispherectomy, a last resort treatment for childhood epilepsy, is a standard procedure which dramatically illustrates the resilience of the brain to extensive damage. If this operation, also mimicking long-term, extensive unilateral capsular stroke, is performed in postnatal cats of up to 60 days of age, there is a remarkable recovery/sparing of neurological functions that is not seen when the lesion occurs during late fetal life or in adulthood. A long-term effect at all ages is loss of neurons in bilateral brain areas remote from the resection site. This is pronounced in adult cats and shows intriguing, paradoxical features in fetal animals, but is substantially attenuated in neonatal cats. Similarly, large-scale reinnervation of subcortical sites (sprouting) by neurons of the remaining, intact hemisphere is prominent in young cats, but not in fetal or adult animals. These and other restorative processes (described herein) in young postnatal animals are matched by relatively higher rates of local cerebral glucose utilization, supporting the notion that they underlie the improved behavioral outcome. Thus, during a critical, defined stage of maturation, presumably common to higher mammals including humans, the brain entirely remodels itself in response to extensive but focal injury. Perhaps the molecular environment allowing for rescue of neurons and enhanced reinnervation at a specific developmental stage could be recreated in subjects with brain lesions at less favorable ages, thereby helping to restore circuitry and spare neurons. However, replacement via transplantation of neurons eliminated by the damage appears to be crucial in attempts to further preserve cells located remotely but yet destined to die or decrease in size. This article presents abundant evidence to show that there is a surprisingly comprehensive long-term morphological remodeling of the entire brain after extensive unilateral damage and that this occurs preferentially during a discrete period of early life. Additional evidence strongly suggests that the remodeling underlies the outstanding behavioral and functional recovery/sparing following early cerebral hemispherectomy. We argue that this period of reduced brain vulnerability to injury also exists in other higher mammals, including man, and suggest ways to enhance restorative processes after stroke/hemispherectomy occurring at other ages.

Classical eyeblink conditioning in the bilaterally hemispherectomized cat

Abstract The classically conditioned eyeblink response was studied in cats with various forebrain lesions. The most extreme of these were three chronically prepared “diencephalic” cats in which the cerebral hemispheres were separated from the thalamus and removed bilaterally. Other animals studied included two animals with frontal cortex ablation, one neodecorticate cat, two animals with bilateral lesions of the caudate nucleus, and one cat with extensive bilateral damage to the thalamic nucleus ventralis posteromedialis. Conditioning was established using a 400-msec duration auditory conditioning stimulus (CS) followed by a brief cutaneous shock to the eyelid as the reinforcing stimulus (US). The EMG was recorded bipolarly from orbicularis oculi, and integrated EMG for the CS interval served as an additional objective measure of conditioned response (CR) magnitude. The conditioned responses were characterized by a burst of EMG activity toward the end of the CS interval (latency 100 msec) which occurred as a result of systematic pairing of CS and US, and did not occur during random presentation of the CS and US, or CS alone. All of the experimental animals learned a conditioned blink response which appeared qualitatively similar to that obtained in the normal animals. All preparations acquired a response, showed extinction when reinforcement was discontinued, discriminated between two stimuli within the same sensory modality, showed discrimination reversal, and retained the acquired response over days. Our results are compatible with a growing body of evidence that telencephalic structures are not necessary for the acquisition and maintenance of a classically conditioned response. Further studies in this laboratory are aimed at investigating conditioning in the chronic decerebrate cat.

Reorganization of Pericruciate cortical projections to the spinal cord and dorsal column nuclei after neonatal or adult cerebral hemispherectomy in cats

This is a quantitative study of changes in distribution and density of terminals of the corticospinal tract in the cervical spinal cord and dorsal column nuclei (DCN) in cats with left cerebral hemispherectomy performed neonatally or in adulthood. Kittens received hemispherectomy at a mean of 12.1 postnatal days and were compared, as adults, to adult-lesioned cats of similar survival time. All animals, including controls, received injections of [3H]leucine-proline and were sacrificed 5 days later. Injection sites and terminal fields were reconstructed from autoradiography-processed tissue. The label filled comparable extents of areas 4 gamma and 3a of the right cerebral cortex. Coronal sections from upper and lower cervical cord levels, and from the brainstem (cuneate and gracile nuclei) were studied. Computer-image processing procedures were used to count labeled particles from multiple sites of the dorsal horn and DCN, bilaterally. In the spinal cord of intact and adult-hemispherectomized cats, most terminals were found in lamina VI, and adjacent laminae V and VII contralateral to the injection side. The major finding was that neonatal-lesioned cats showed a significant increase in axon terminals in areas ipsilateral to the injection. The topography of distribution of the novel terminals was similar to that in the contralateral side and the originating fibers appeared to have crossed the midline from that side. A similar reorganization occurred in the gracile nucleus where, in intact and adult-lesioned cats, the cortical terminals also predominated in the side contralateral to the injection. In contrast, neonatal-lesioned animals showed a significant increase in terminal density ipsilateral to the cortical injection. These findings are discussed as an alternative mechanism for postlesion remodeling of the corticospinal tract in animals with the pyramidal crossing completed at the time of birth.

Counterpointing the functional role of the forebrain and of the brainstem in the control of the sleep-waking system.

This paper reviews the lifetime contributions of the author to the field of sleep–wakefulness (S–W), reinterprets results of the early studies, and suggests new conclusions and perspectives. Long‐term cats with mesencephalic transection show behavioral/polygraphic rapid eye movement sleep (REMS), including the typical oculo‐pupillary behavior, even when the section is performed in kittens prior to S–W maturation. REMS can be induced as a reflex. Typical non‐rapid eye movement S (NREMS) is absent and full W/arousal is present only after a precollicular section. The isolated forebrain (IF) rostral to the transection exhibits all features of W/arousal and NREMS [with electroencephalographic (EEG) spindles and delta waves], arousal to olfactory stimuli, and including the appropriate oculo‐pupillary behaviors. These features also mature normally after neonatal transection. REMS is absent from the IF. After deprivation there is NREMS pressure and rebound in the IF, but the decerebrate cat only shows pressure for REMS. Most IF reactions to pharmacologic agents are within expectations, except for the tolerance/withdrawal effects of long‐term morphine use which are absent. In contrast, these effects are supported by the brainstem (i.e. seen in the decerebrate cat). In cats with ablation of the telencephalon, or diencephalic cats, delta waves are absent in the thalamus. EEG thalamic spindle waves are seen triggering S for only 4–5 days after ablation. Therefore, true NREMS is absent in chronic diencephalic cats although pre‐ and postsomniac behaviors persist. These animals are hyperactive and show a pronounced, permanent insomnia; however, a low dose of barbiturate triggers a dramatic REMS/atypical NREMS rebound. Cats without the thalamus (athalamic cats), initially show a dissociation between behavioral hyperactivity/insomnia and the neocortical EEG, which for 15–20 days exhibits only delta and slower oscillations. Fast, low‐voltage W rhythms appear later on, first during REMS, but spindle waves and S postures are absent from the start, such that these cats also display only atypical NREMS. Athalamic cats also show barbiturate‐sensitive insomnia. Cats with ablation of the frontal cortices or the caudate nuclei remain permanently hyperactive. They also show a mild, but significant hyposomnia, which is permanent in afrontal cats, but lasts for about a month in acaudates. The polygraphic/behavioral features of their S–W states remain normal. We conclude and propose that: (a) the control of the S–W system is highly complex and distributed, but is organized hierarchically in a well‐defined rostro‐caudal manner; the rostral‐most or highest level (telencephalon), is the most functionally complex/adaptative and regulates the lower levels; the diencephalic/basal forebrain, or middle level, has a pivotal role in inducing switching between S and W and in coordinating the lowest (brainstem) and highest levels; (b) W can occur independently in both the forebrain and brainstem, but true NREMS‐ and REMS‐generating mechanisms exist exclusively in the forebrain and brainstem, respectively; (c) forebrain and brainstem S–W processes can operate independently from each other and are preprogrammed at birth; this helps understanding normal and abnormal polygraphic/behavioral dissociations in humans and normal dissociations/splitting in aquatic mammals; (d) NREMS homeostasis is present in the IF, but only REMS pressure after deprivation persists in the decerebrate cat; (e) the thalamus engages in both NREMS and W; (f) insomnia in diencephalic cats is the result of an imbalance between antagonistic W‐ and S‐promoting cellular groups in the ventral brain (normally modulated by the telencephalon); (g) the EEG waves, which are signature for each S–W state, appear to truly drive the concomitant behaviors, e.g. a hypothetical human IF could alternate between behavioral NREMS and W/arousal/awareness; (h) a role for REMS is to keep the individual sleeping at the end of the self‐limiting NREMS periods. The need for accelerating research on telencephalic S–W processes and downstream control of the lower S–W system levels is emphasized.

A quantitative study of temporal and spatial response patterns in a thalamic cell population electrically stimulated.

Summary In locally anesthetized cats, unit activity was recorded in the immediate vicinity of a stimulating electrode implanted in nucleus ventralis lateralis of the thalamus (VL). Three classes of cells were distinguished: (I) non-responsive, (II) immediately silenced, and (III) initially fired by the VL stimulus. The latter were also silenced following the initial discharged. Quantitative estimates of their relative proportions are given as a function of distance of the cells from the stimulated site. Immediately silenced cells were found preferentially located at more than 2 mm from the stimulated site. These results concern VL-identified neurons as well as other cells. Upon repetition of the VL stimuli at 100 msec intervals, the responses were changed in such a way that, globally, the second pulse produced a more intense firing, by more neurons, but with a slightly longer latency (augmentation). Similar observations were made while stimulating the VL in decorticate preparations and the medial geniculate nucleus (GM) in intact animals. This is in sharp contrast with the response patterns of mesencephalic cells locally stimulated. None of them were immediately silenced, and repetition of the stimuli at 100 msec intervals produced no systematic changes. The quantitative data gathered in this study are used to reconstruct a picture of the events occurring in a thalamic cell population submitted to local electrical stimulation.

Cortical control of thalamic spindle waves

Abstract The EEG activity of the thalamus was studied in acute cat preparations in which the diencephalon was deprived of all neocortical and most archicortical and striatal connections. Waves (8–12/sec) waxing and waning, similar to electrocortical spindles, were recorded in all cases. They persisted after interruption of the interhemispheric commissures, and were enhanced by mesencephalic transection, lesion of the optic chiasma or injection of a small dose of barbiturate (3 mg/kg, iv). Spindles occurred more than twice as frequently in a decorticate thalamus than in the thalamus of a contralateral intact hemisphere. Producing lesions in the region of the inferior thalamic peduncle (ITP) in an intact hemisphere abolished both thalamic and cortical spindles. This effect persisted after complete mesencephalic transection, but the spindles reappeared after complete decortication. It is postulated that EEG spindles are basically thalamic in origin and that their occurrence is controlled by antagonistic corticothalamic influences which operate independently from influences of the caudal brain stem.