4-aminopyridine improves evoked potentials and ambulation in the taiep rat: A model of hypomyelination with atrophy of basal ganglia and cerebellum

The taiep rat is a tubulin mutant with an early hypomyelination followed by progressive demyelination of the central nervous system due to a point mutation in the Tubb4a gene. It shows clinical, radiological, and pathological signs like those of the human leukodystrophy hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC). Taiep rats had tremor, ataxia, immobility episodes, epilepsy, and paralysis; the acronym of these signs given the name to this autosomal recessive trait. The aim of this study was to analyze the characteristics of somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) in adult taiep rats and in a patient suffering from H-ABC. Additionally, we evaluated the effects of 4-aminopyridine (4-AP) on sensory responses and locomotion and finally, we compared myelin loss in the spinal cord of adult taiep and wild type (WT) rats using immunostaining. Our results showed delayed SSEPs in the upper and the absence of them in the lower extremities in a human patient. In taiep rats SSEPs had a delayed second negative evoked responses and were more susceptible to delayed responses with iterative stimulation with respect to WT. MEPs were produced by bipolar stimulation of the primary motor cortex generating a direct wave in WT rats followed by several indirect waves, but taiep rats had fused MEPs. Importantly, taiep SSEPs improved after systemic administration of 4-AP, a potassium channel blocker, and this drug induced an increase in the horizontal displacement measured in a novelty-induced locomotor test. In taiep subjects have a significant decrease in the immunostaining of myelin in the anterior and ventral funiculi of the lumbar spinal cord with respect to WT rats. In conclusion, evoked potentials are useful to evaluate myelin alterations in a leukodystrophy, which improved after systemic administration of 4-AP. Our results have a translational value because our findings have implications in future medical trials for H-ABC patients or with other leukodystrophies.

Enhanced astroglial Ca2+ signaling increases excitatory synaptic strength in the epileptic brain

The fine-tuning of synaptic transmission by astrocyte signaling is crucial to CNS physiology. However, how exactly astroglial excitability and gliotransmission are affected in several neuropathologies, including epilepsy, remains unclear. Here, using a chronic model of temporal lobe epilepsy (TLE) in rats, we found that astrocytes from astrogliotic hippocampal slices displayed an augmented incidence of TTX-insensitive spontaneous slow Ca(2+) transients (STs), suggesting a hyperexcitable pattern of astroglial activity. As a consequence, elevated glutamate-mediated gliotransmission, observed as increased slow inward current (SICs) frequency, up-regulates the probability of neurotransmitter release in CA3-CA1 synapses. Selective blockade of spontaneous astroglial Ca(2+) elevations as well as the inhibition of purinergic P2Y1 or mGluR5 receptors relieves the abnormal enhancement of synaptic strength. Moreover, mGluR5 blockade eliminates any synaptic effects induced by P2Y1R inhibition alone, suggesting that the Pr modulation via mGluR occurs downstream of P2Y1R-mediated Ca(2+)-dependent glutamate release from astrocyte. Our findings show that elevated Ca(2+)-dependent glutamate gliotransmission from hyperexcitable astrocytes up-regulates excitatory neurotransmission in epileptic hippocampus, suggesting that gliotransmission should be considered as a novel functional key in a broad spectrum of neuropathological conditions.

A new rapid kindling variant for induction of cortical epileptogenesis in freely moving rats

Kindling, one of the most used models of experimental epilepsy is based on daily electrical stimulation in several brain structures. Unlike the classic or slow kindling protocols (SK), the rapid kindling types (RK) described until now require continuous stimulation at suprathreshold intensities applied directly to the same brain structure used for subsequent electrophysiological and immunohistochemical studies, usually the hippocampus. However, the cellular changes observed in these rapid protocols, such as astrogliosis and neuronal loss, could be due to experimental manipulation more than to epileptogenesis-related alterations. Here, we developed a new RK protocol in order to generate an improved model of temporal lobe epilepsy (TLE) which allows gradual progression of the epilepsy as well as obtaining an epileptic hippocampus, thus avoiding direct surgical manipulation and electric stimulation over this structure. This new protocol consists of basolateral amygdala (BLA) stimulation with 10 trains of biphasic pulses (10 s; 50 Hz) per day with 20 min-intervals, during 3 consecutive days, using a subconvulsive and subthreshold intensity, which guarantees tissue integrity. The progression of epileptic activity was evaluated in freely moving rats through electroencephalographic (EEG) recordings from cortex and amygdala, accompanied with synchronized video recordings. Moreover, we assessed the effectiveness of RK protocol and the establishment of epilepsy by evaluating cellular alterations of hippocampal slices from kindled rats. RK protocol induced convulsive states similar to SK protocols but in 3 days, with persistently lowered threshold to seizure induction and epileptogenic-dependent cellular changes in amygdala projection areas. We concluded that this novel RK protocol introduces a new variant of the chronic epileptogenesis models in freely moving rats, which is faster, highly reproducible and causes minimum cell damage with respect to that observed in other experimental models of epilepsy.

Glutamate released spontaneously from astrocytes sets the threshold for synaptic plasticity

Astrocytes exhibit spontaneous calcium oscillations that could induce the release of glutamate as gliotransmitter in rat hippocampal slices. However, it is unknown whether this spontaneous release of astrocytic glutamate may contribute to determining the basal neurotransmitter release probability in central synapses. Using whole-cell recordings and Ca(2+) imaging, we investigated the effects of the spontaneous astrocytic activity on neurotransmission and synaptic plasticity at CA3-CA1 hippocampal synapses. We show here that the metabolic gliotoxin fluorocitrate (FC) reduces the amplitude of evoked excitatory postsynaptic currents and increases the paired-pulse facilitation, mainly due to the reduction of the neurotransmitter release probability and the synaptic potency. FC also decreased intracellular Ca(2+) signalling and Ca(2+) -dependent glutamate release from astrocytes. The addition of glutamine rescued the effects of FC over the synaptic potency; however, the probability of neurotransmitter release remained diminished. The blockage of group I metabotropic glutamate receptors mimicked the effects of FC on the frequency of miniature synaptic responses. In the presence of FC, the Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N ',N '-tetra-acetate or group I metabotropic glutamate receptor antagonists, the excitatory postsynaptic current potentiation induced by the spike-timing-dependent plasticity protocol was blocked, and it was rescued by delivering a stronger spike-timing-dependent plasticity protocol. Taken together, these results suggest that spontaneous glutamate release from astrocytes contributes to setting the basal probability of neurotransmitter release via metabotropic glutamate receptor activation, which could be operating as a gain control mechanism that regulates the threshold of long-term potentiation. Therefore, endogenous astrocyte activity provides a novel non-neuronal mechanism that could be critical for transferring information in the central nervous system.

Asynchronic transmission in the CA3–CA1 hippocampal synapses in the neurological mutanttaiep rat

For the taiep rat, a neurological mutant with severe astrogliosis secondary to demyelination, we have described alterations in spinal cord synaptic transmission. Asynchronous responses result from phasic action potential-derived glutamate release in this mutant. To evaluate whether this anomalous transmission is also produced in other regions of the taiep CNS and whether its nature involves a presynaptic or postsynaptic disruption, we studied the CA3-CA1 hippocampal synapses. Excitatory postsynaptic currents (EPSC) evoked by stimulation of Schaffer collaterals were recorded from CA1 pyramidal cells on picrotoxin-treated slices. Initial fast and time-locked EPSCs were evoked by conventional stimulation in both control and taiep neurons, showing similar latency and amplitude values unimodally distributed. In a high percentage of taiep neurons (47%), the initial EPSC was frequently followed by additional asynchronous synaptic currents (EPSC(ASYN)) with latencies ranging from 10 to 300 msec. As with initial EPSCs, EPSC(ASYN) were action potential dependent, sensitive to tetrodotoxin, and blocked by D-2-amino-5-phosphonovaleric acid and 6-cyano-7-nitroquinoxaline-2,3-dione. The occurrence probability of these events decayed monoexponentially as a function of poststimulus time. The elevation of extracellular Ca(2+) induced a reduction of amplitudes and a rate increase of EPSC(ASYN), in parallel with a reduction of paired pulse facilitation of initial EPSCs. The presynaptic fiber volley, extracellularly recorded, showed no significant differences between groups, with similar mean values of area and decay time. These findings in hippocampal circuitry suggest that, in taiep, the asynchronous evoked activity represents a rather generalized phenotype of the glutamatergic synapses and that EPSC(ASYN) seems to be determined by presynaptic alterations.

Developmental impairment of compound action potential in the optic nerve of myelin mutant taiep rats

The taiep rat is a myelin mutant with an initial hypomyelination, followed by a progressive demyelination of the CNS. The neurological correlates start with tremor, followed by ataxia, immobility episodes, epilepsy and paralysis. The optic nerve, an easily-isolable central tract fully myelinated by oligodendrocytes, is a suitable preparation to evaluate the developmental impairment of central myelin. We examined the ontogenic development of optic nerve compound action potentials (CAP) throughout the first 6 months of life of control and taiep rats. Control optic nerves (ON) develop CAPs characterized by three waves. Along the first month, the CAPs of taiep rats showed a delayed maturation, with lower amplitudes and longer latencies than controls; at P30, the conduction velocity has only a third of the normal value. Later, as demyelination proceeds, the conduction velocity of taiep ONs begins to decrease and CAPs undergo a gradual temporal dispersion. CAPs of control and taiep showed differences in their pharmacological sensitivity to TEA and 4-AP, two voltage dependent K+ channel-blockers. As compared with TEA, 4-AP induced a significant increase of the amplitudes and a remarkable broadening of CAPs. After P20, unlike controls, the greater sensitivity to 4-AP exhibited by taiep ONs correlates with the detachment and retraction of paranodal loops suggesting that potassium conductances could regulate the excitability as demyelination of CNS axons progresses. It is concluded that the taiep rat, a long-lived mutant, provides a useful model to study the consequences of partial demyelination and the mechanisms by which glial cells regulate the molecular organization and excitability of axonal membranes during development and disease.

Immature developmental pattern of the monosynaptic reflex in isolated spinal cord of glial mutant taiep rats

There is increasing evidence suggesting that glial cells play a crucial role in the formation and maturation of neural circuits. However, little is known about the effects of glial alterations on the establishment of functional circuitry in vivo during the development. The taiep rat, a long-lived neurological mutant characterized by early astrogliosis and demyelination affecting selectively the CNS, provides an interesting model to study the glia-neuron interaction in situ. In the present study, we evaluated the functional development of segmental neural circuits recording the monosynaptic reflex responses (MSR) in the isolated spinal cord of neonatal taiep rats. To evaluate the developmental changes during the first two postnatal weeks, we measured the latency of MSR, the magnitude of depression to paired pulses and the time course of post-tetanic recovery. During the early postnatal period, the MSR of control rats reduced their latency and decreased their sensitivity to depression, as a function of age. By contrast, the MSR of taiep rats failed to develop further from neonatal stage. Near the end of the second postnatal week, the MSR latencies were still prolonged, and the MSR showed a significantly stronger paired pulse depression, and higher post-tetanic recovery times than the age-matched controls. The lack of MSR maturation in taiep rats suggests an early alteration of functional mechanisms underlying the maturation of the spinal reflexes, probably due to the characteristic glial dysfunction(s) of this mutant.

Altered synaptic and electrical properties of lumbar motoneurons in the neurological glial mutant taiep rat

Maturation and differentiation of electrical properties of neurons and synaptic transmission are modulated by neuronal interaction. In vitro experiments have shown that these processes also seem to be regulated by signals from non-neuronal elements such as glial cells. It is not known, however, whether glial alterations in intact neural networks may also affect the maturation of electrical properties and synaptic transmission during development. We used the taiep rat, a neurological mutant with a progressive demyelination and astrogliosis, as an experimental model to study the postnatal development of motoneurons in an altered glial environment. Using the patch-clamp technique, we made intracellular recording from motoneurons of Rexed's lamina IX in spinal cord slices of neonatal rats (postnatal day P4-P10). The electrical properties of normal motoneurons changed significantly with age, showing decreasing input resistance (R(in)) and increasing membrane capacity (C(m)). The rheobase increased with age, accompanied by an increase of the amplitude and a decrease of the duration of action potentials (APs). In contrast, mutant neurons showed no age-dependent changes of R(in), C(m), or AP characteristics. After blocking inhibitory transmission, intralaminar bipolar stimulation elicited, in both control and taiep motoneurons, fast glutamatergic excitatory postsynaptic potentials (EPSPs). Two types of taiep motoneurons were identified according to the temporal patterns of synaptic responses; (1). taiep(SYN) neurons, which showed no significant differences to control motoneurons, and (2). taiep(ASYN) neurons, in which the initial EPSP was followed by a variable number of delayed, asynchronous EPSP responses (for up to 300 ms). All these electrophysiological findings suggest that the mutation in taiep rats interfered with the development of the electrical properties of neurons and with the maturation of synaptic transmission, probably due to alterations in the neuron-glia interactions.

Electrophysiological properties of retinal Müller glial cells from myelin mutant rat

The structural and functional similarities between Müller cells and oligodendrocytes prompted the present study of the electrophysiological properties of Müller (glia) cells obtained from the retinae of control and myelin mutant taiep rats during the postnatal developmental period (P12-P180). The whole-cell configuration of the patch-clamp technique was used to characterize the general properties and the K+ currents from dissociated Müller cells. During the first 3 weeks of life, a decrease of the membrane resistance and an increase of the membrane potential were observed in Müller cells from both control and taiep rats. However, Müller cells from taiep rats never achieved the very negative membrane potential (-50 mV vs -80 mV) and the low membrane resistance characteristic for control cells. Furthermore, Müller cells displayed increased inward and outward K+ currents during postnatal development up to P30/60 in controls; however, in taiep rats, this increase ceased at P20/30, and low-amplitude currents persisted into adulthood. These results provide first evidence of physiological changes in retinal Müller cells as a consequence of a myelin mutation causing a progressive deterioration of the central nervous system (CNS) due to a disturbance of the microtubule network of oligodendrocytes. We hypothesize that the progressive dysmyelination process of the optic nerve, accompanied by functional deficits of retinal neurons (e.g., ganglion cells), induces physiological alterations of Müller cells.

The retinal anatomy and function of the myelin mutant taiep rat

PURPOSE

To study the histology and the physiological function of the retina in the neurological myelin mutant, taiep rats during the postnatal developmental period (P20-P360).

METHODS

Electroretinography (ERG) was applied to evaluate intensity dependence and spectral sensitivity of the responses to light. Retinal histology, morphometry, and immunocytochemistry were used to characterize the structure of the retina, with particular emphasis on the Müller (glial) cells.

RESULTS

In the taiep rats of all ages studied, the scotopic ERG showed normal a- and b-wave amplitudes and latencies; likewise, the scotopic spectral sensitivity function was the same for control and taiep animals, with a maximal sensitivity (lambda(max)) at 500 nm. However, in adult taiep rats (P90 to P360) a secondary cornea-positive wave ('b(2)') was observed in response to high stimulus intensities, which never occurred in controls. This correlated with the observation that in the photopic ERG responses of the taiep rats, the b-wave was reduced in amplitude, and was followed by a rapid cornea-negative after-potential. After 1 year of life, in taiep rats the outer plexiform layer (OPL) became slightly thinner and the inner plexiform/ganglion cell layers (IPL/GCL) appeared to be swollen, and increased in thickness; in addition, the number of retinal neurons (particularly, of photoreceptor cells) slightly decreased. Increased GFAP immunoreactivity revealed a hypertrophy and reactivity of the Müller cells in 1-year-old taiep rats.

CONCLUSIONS

The present results suggest the occurrence of a relatively mild and slowly progressing neural retinal alteration in taiep rats, which becomes histologically and functionally evident at the end of the first year of life, and mainly affects the circuit(s) of the photopic ON-response. It is speculated that this alteration is due to missing/altered signals from demyelinated optic nerve.

Dysmyelination, demyelination and reactive astrogliosis in the optic nerve of the taiep rat

Taiep is an autosomal recessive mutant rat that shows a highly hypomyelinated central nervous system (CNS). Oligodendrocytes accumulate microtubules (MTs) in association with endoplasmic reticulum (ER) membranes forming MT-ER complexes. The microtubular defect in oligodendrocytes, the abnormal formation of CNS myelin and the astrocytic reaction were characterized by immunocytochemical and ultrastructural methods during the first year of life. Optic nerves of both control and taiep rats were processed by the immunoperoxidase method using antibodies against tubulin, myelin basic protein (MBP) and glial fibrillary acidic protein (GFAP). Taiep oligodendrocytes are strongly immunoreactive against tubulin, indicative of a significant accumulation of microtubules. Early differentiated oligodendrocytes observed with electron microscopy show that MT-ER complexes are mainly present in the cell body. This defect increases during the first year of life; oligodendrocytes show large MT-ER complexes projected within oligodendrocyte processes. Using anti-MBP, there was a progressive reduction of immunolabeling in the myelin sheaths as taiep rats grew older. Ultrastructural analysis revealed severely dysmyelinated axons with a frequently collapsed periaxonal collar. However, through age the myelin sheath became gradually infiltrated by MTs, suggesting their contribution to premature loss of myelin in the taiep rat. Axons of one-year-old taiep rats were severely demyelinated. Modifications in astrocytes revealed by the GFAP antibody showed a strong hypertrophy with increased immunostaining in their processes. As demyelination of axons progressed, taiep rats developed a strong astrogliosis. The present findings suggest that in taiep rats the early abnormal myelination of axons affects the adequate maintenance of myelin, leading to a progressive loss of myelin components and severe astrogliosis, features that should be considered in the pathogenesis of dysmyelinating diseases.

Progressive deterioration of central components of auditory brainstem responses during postnatal development of the myelin mutant taiep rat

Auditory brainstem responses (ABRs) were evaluated during the postnatal development (P10-P180) of taiep rats, neurological mutants characterized by early abnormal myelin development and subsequent demyelination of the CNS. The disorder is produced by an autosomal recessive mutation trait that affects the oligodendrocytes but not the Schwann cells. After onset of ABRs (P12-P14), taiep rats and their nonaffected heterozygous littermates that served as controls showed a similar pattern of maturation for wave I. The central waves (In-IV) showed significantly longer latencies in the mutants. By P60-P180, the later waves (III and IV) were frequently difficult to discern. From the onset of ABRs, the interpeak latency I-IV, corresponding to the central conduction time (CCT) of the auditory pathway, showed in taiep rats significantly longer values than controls. After an initial reduction, proportional to that of control rats, the CCT value increased progressively during the second month of the mutants' lives. The electrophysiological results of the present study strongly support the hypothesis that mutation in the taiep rat impairs neuromaturation of the central auditory pathway in the brainstem by affecting the myelination process in the CNS.

Evidence of altered central nervous system development in infants with iron deficiency anemia at 6 mo: delayed maturation of auditory brainstem responses

Iron deficiency anemia has long been thought to have effects on the central nervous system (CNS). Finding direct evidence of this in human infants, however, has been challenging. Auditory brainstem responses (ABRs) provide a noninvasive means of examining an aspect of the CNS that is rapidly maturing during the age period when iron deficiency is most common. ABRs represent the progressive activation of the auditory pathway from the acoustic nerve (wave I) to the lateral lemniscus (wave V). The central conduction time (CCT, or wave I-V interpeak latency) is considered an index of CNS development because myelination of nerve fibers and maturation of synaptic relays lead to an exponential reduction in the CCT from birth to 24 mo. In 55 otherwise healthy, 6-mo-old Chilean infants (29 with iron deficiency anemia and 26 nonanemic control infants), the CCT was longer in those who had been anemic at 6 mo, with differences becoming more pronounced at 12- and 18-mo follow-ups despite effective iron therapy. The pattern of results--differences in latencies but not amplitudes, more effects on the late ABR components (waves III and V), and longer CCTs (as an overall measure of nerve conduction velocity)--suggested altered myelination as a promising explanation, consistent with recent laboratory work documenting iron's essential role in myelin formation and maintenance. This study shows that iron deficiency anemia in 6-mo-old infants is associated with adverse effects on at least one aspect of CNS development and suggests the fruitfulness of studying other processes that are rapidly myelinating during the first 2 y of life.

Binding of microtubules to transitional elements in oligodendrocytes of the myelin mutant taiep rat

The presence of microtubules physically bound to smooth endoplasmic reticulum profiles of oligodendrocytes constitutes the most conspicuous feature observed in the myelin mutant taiep rat. The endoplasmic reticulum membranes associated with microtubules were morphologically characterized as transitional elements that constitute the intermediate compartment according to their topographic location close to the cis-Golgi apparatus. The development of this surprising microtubular defect appears to be associated with the early events of myelination. Transitional elements associated with microtubules operate in protein transport from endoplasmic reticulum to cis-Golgi. This microtubular defect could explain the dysmyelination and neurologic alterations observed in taiep rats. Moreover, these findings allow us to propose that there is a blockage of protein traffic at the intermediate compartment of taiep oligodendrocytes, a situation that could explain the hypomyelinated axons observed in this myelin mutant. The binding of microtubules to membranous organelles promotes the stabilization of microtubules, a feature that has important implications regarding its accumulation within the cytoplasm of oligodendrocytes during the temporal evolution of this neurologic disorder. The taiep rat is a myelin mutant with a long survival and could be a useful model for understanding dysmyelinating diseases in which the intracellular transport of myelin components is affected.

Short-term homeostasis of active sleep and the architecture of sleep in the rat

1. Sixteen rats were recorded continuously for 3 days using an automated system that detected, quantified, and stored the incidence of cortical delta waves, cortical sigma spindles, hippocampal theta rhythm, and electromyographic activity. A time series then was constructed wherein 15-s epochs were ascribed to one behavioral state: wakefulness (W), quiet sleep (QS), or active sleep (AS, a state also referred to as REM sleep). From those series, AS episodes and non-AS intervals could be determined. Episodes and intervals were defined as lasting at least two epochs and the one-epoch episodes and intervals were incorporated to the ongoing state. 2. Having established the length of each AS episode and non-AS interval, pairings were made, on the one hand between episodes and their preceding intervals, and on the other, between episodes and the intervals that followed. 3. Highly significant correlations were found between the length of AS episodes and the length of the non-AS intervals that followed. Correlations were also significant when calculated separately versus the amount of QS and of W within the following interval. Correlations improved when they were performed against the log of the interval and when only intervals with a predominance of QS were selected. 4. No significant correlation was found between the length of AS episodes and the length of the preceding non-AS intervals, except for a negative one that was present only when the statistical analysis was performed in the unsmoothed array where the one-epoch episodes and intervals were preserved. 5. These results suggest that there is a short-term homeostasis operating within the spontaneous architecture of sleep in rats. This homeostatic mechanism is not manifested by the regulation of the length of AS episodes. Instead, there is a forward regulatory mechanism that, given the duration of an AS episode, permissively controls the interval that the animal may abstain from AS, and hence the timing of the triggering of a new AS episode.

Measures of location and dispersion of sleep state distributions within the circular frame of a 12:12 light: dark schedule in the rat

Distributions within a 12:12 light:dark schedule of wakefulness (W), active sleep (AS), quiet sleep (QS) and of QS rich in delta (QSD) and in spindle (QSS) activities were evaluated for 52 days from 15 rats. Angular statistics were applied for each state by equating their hourly incidence to data distributed around a circle. Measures of location (mean angle, median angle, mode angle, maximum semicircle), dispersion (mean vector, standard deviation, quartile deviation), skewness and kurtosis were computed and their intra- and interindividual variabilities were compared. Mean angles (in hours and after lights-on) averaged 5.5 for QS, 8.6 for AS, 18.4 for W, 1.9 for QSD and 10.6 for QSS. Length of vectors, representing concentration around the mean angle, averaged 0.22 for QS, 0.36 for AS, 0.22 for W, 0.38 for QSD and 0.23 for QSS. Distributions of QS and W were closely related to the light-dark step function. QSD had a leptokurtic distribution, sharply rising at the beginning of the sleep-predominant phase, whereas AS and QSS had smoother distributions reaching maxima in its second half. In rodents as in humans, QSS and AS have opposite distributions to QSD. QSS may contribute to maintain sleep through the resting phase of the light-dark schedule after restorative function associated with delta activity has been fulfilled.

Auditory brainstem responses of children with developmental language disorders

Brainstem auditory evoked potentials (BAEPs) were recorded from 48 children with language disorders (aged four to nine years old, IQs normal to borderline, normal audiometric thresholds and attending special school) and 20 healthy children (four to eight years old, with normal IQs, audiometry and school-level). The language-disabled group showed significantly lower absolute latency values of the BAEPs than controls. There were no significant differences in the central conduction time of the auditory pathway (I-V interval). Therefore, the only significant difference corresponded to a minor value for the first wave (auditory nerve discharge) of the BAEP. A reduction in the control mechanisms of the sensory inputs at the peripheral level, or a disturbance in the inhibitory mechanisms of cortico-subcortical modulation, might explain these findings.

Time course of rat sleep variables assessed by a microcomputer-generated data base

A microcomputer-based system is described that detects, counts and stores cortical delta and sigma waves, hippocampal theta waves and electromyographic activities in the rat by building matrices with the incidence of those four variables (columns) in 15-second bins (rows). Data tables are submitted to statistical, graphics and spread-sheet software to assess internal organization of sleep episodes and 24-hour distribution of sleep variables. Within sleep episodes, cross-correlograms reveal a delta-sigma-theta sequence, while autocorrelograms quantify clustering and periodicity of variables. Sleep accumulates in the lights-on phase, with high concentration of delta at the beginning of this sleep-predominant phase and of sigma and theta in its second half. These are notable similarities with human sleep architecture. Simple procedures for data reduction into standard behavioral state diagnosis are demonstrated. The low cost of personal computers and data acquisition interfaces facilitates the automation of complex paradigms by ad hoc on-line programs that produce as output a data base that can be processed by standard software, providing a fluid pathway of automated acquisition, analysis and presentation of data.