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.

0134 Circadian variation of absence seizures in an animal model of human leukodystrophy (H-ABC)

Introduction

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a human leukodystrophy is due to a mutation in the tubulin b 4a (TUBB4A) and the taiep rats is the only available model of this human disease with similar signs in the magnetic resonance imaging and a mutation in the TUBB4 that induced an accumulation of microtubules in the cytoplasm and its processes in the oligodendrocytes. Taiep rats had spike-wave discharges (SWD) that are similar to absence epilepsy with a progressive increase with the age of the subjects. The aim of this study is to analyze the circadian distribution of SWD on male taiep.

Methods

We used 16 male taiep rats at 6 and 9 months of age. All rats were kept in standard conditions with a 12/12 light-dark cycle (lights on at 0700) and free access to rodent food pellets and purified water and were implanted for EEG, EMG and EOG recordings to characterize the frequency and duration of SWD. All procedures followed the NIH rules, and the protocol was approved by BUAP-IACUC.

Results

The number of SWD are higher in male rats at 9 with respect to 6 months of age (P≤0.05), and also had higher incidence during the light phase with respect to the dark phase (P≤0.05). The duration of SWD had also a greater duration during the light period than the dark phase (P≤0.05).

Conclusion

Our results showed that SWD has higher incidence of SWD and of longer duration during the light period when the rats had more sleep suggesting that the neurotransmitters that are released during sleep facilitate the discharge in the thalamo-cortical circuit that support SWD.

Support (If Any)

Partially supported by PRONACES-CONACYT grant 194171, and VIEP-BUAP 2021 to CA in Neuroendocrinología. JMI is fellowship from CONACYT No. 735813.

Mating-induced analgesia is dependent of copulatory male pattern in high- and low- yawning male rats

Mating behavior in rodents can modulate pain sensations in both sexes. In males, the execution of mounts, intromissions, and ejaculations induced a progressive increase in their vocalization thresholds induced by tail shocks and other types of noxious stimuli. We selectively inbred two sublines from Sprague-Dawley (SD) rats that differed in their spontaneous yawning frequency. The high-yawning (HY) subline had a mean of 20 yawns/h and a different pattern of sexual behavior characterized by longer interintromission intervals and more sexual bouts that delayed ejaculation. The low-yawning (LY) subline and SD rats yawned as a mean 2 and 1 yawns/h, respectively. So, we determine mating-induced analgesia in HY, LY, and SD male rats by measuring vocalization thresholds in response to noxious electric tail shocks. Our results showed that the magnitude of mating-induced analgesia was lower in HY and LY rats with respect to SD rats. When the rats performed different components of male sexual pattern, both sublines exhibited a significantly lower increase in their vocalization thresholds with respect to SD rats-being sublines less responsive regarding mating-induced analgesia. Pain modulation mechanisms depend on responses to stress, so the low levels of analgesia obtained in the yawning sublines may be due either to differences in their response to stress in other paradigms, or to atypical performance of male sexual behavior during mating, an event which as a stressful event in rats. Therefore, the yawning sublines are a suitable model for analyzing how a different temporal pattern in the display of male sexual behavior affects analgesia mechanisms. Our results concur with Wistar rats with different endophenotypes that could apply to humans as well.

Longitudinal Evaluation of Cerebellar Signs of H-ABC Tubulinopathy in a Patient and in the taiep Model

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a central neurodegenerative disease due to mutations in the tubulin beta-4A (TUBB4A) gene, characterized by motor development delay, abnormal movements, ataxia, spasticity, dysarthria, and cognitive deficits. Diagnosis is made by integrating clinical data and radiological signs. Differences in MRIs have been reported in patients that carry the same mutation; however, a quantitative study has not been performed so far. Our study aimed to provide a longitudinal analysis of the changes in the cerebellum (Cb), corpus callosum (CC), ventricular system, and striatum in a patient suffering from H-ABC and in the taiep rat. We correlated the MRI signs of the patient with the results of immunofluorescence, gait analysis, segmentation of cerebellum, CC, and ventricular system, performed in the taiep rat. We found that cerebellar and callosal changes, suggesting a potential hypomyelination, worsened with age, in concomitance with the emergence of ataxic gait. We also observed a progressive lateral ventriculomegaly in both patient and taiep, possibly secondary to the atrophy of the white matter. These white matter changes are progressive and can be involved in the clinical deterioration. Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) gives rise to a spectrum of clinical signs whose pathophysiology still needs to be understood.

Long-term taurine administration improves motor skills in a tubulinopathy rat model by decreasing oxidative stress and promoting myelination

The taiep rat undergoes hypomyelination and progressive demyelination caused by an abnormal microtubule accumulation in oligodendrocytes, which elicits neuroinflammation and motor behavior dysfunction. Based on taurine antioxidant and proliferative actions, this work explored whether its sustained administration from the embryonic age to adulthood could prevent neuroinflammation, stimulate cell proliferation, promote myelination, and relieve motor impairment. Taurine (50 mg/L of drinking water = 50 ppm) was given to taiep pregnant rats on gestational day 15 and afterward to the male offspring until eight months of age. We measured the levels of nitric oxide (NO), malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA), CXCL1, CXCR2 receptor, growth factors (BNDF and FGF2), cell proliferation, and myelin content over time. Integral motor behavior was also evaluated. Our results showed that taurine administration significantly decreased NO and MDA + 4-HDA levels, increased cell proliferation, and promoted myelination in an age- and brain region-dependent fashion compared with untreated taiep rats. Taurine effect on chemokines and growth factors was also variable. Taurine improved vestibular reflexes and limb muscular strength in perinatal rats and fine movements and immobility episodes in adult rats. These results show that chronic taurine administration partially alleviates the taiep neuropathology.

Auditory impairment in H-ABC tubulinopathy

Hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC) is a neurodegenerative disease due to mutations in TUBB4A. Patients suffer from extrapyramidal movements, spasticity, ataxia, and cognitive deficits. Magnetic resonance imaging features are hypomyelination and atrophy of the striatum and cerebellum. A correlation between the mutations and their cellular, tissue and organic effects is largely missing. The effects of these mutations on sensory functions have not been described so far. We have previously reported a rat carrying a TUBB4A (A302T) mutation and sharing most of the clinical and radiological signs with H-ABC patients. Here, for the first time, we did a comparative study of the hearing function in an H-ABC patient and in this mutant model. By analyzing hearing function, we found that there are no significant differences in the auditory brainstem response (ABR) thresholds between mutant rats and WT controls. Nevertheless, ABRs show longer latencies in central waves (II-IV) that in some cases disappear when compared to WT. The patient also shows abnormal AEPs presenting only Waves I and II. Distortion product of otoacoustic emissions and immunohistochemistry in the rat show that the peripheral hearing function and morphology of the organ of Corti are normal. We conclude that the tubulin mutation severely impairs the central hearing pathway most probably by progressive central white matter degeneration. Hearing function might be affected in a significant fraction of patients with H-ABC; therefore, screening for auditory function should be done on patients with tubulinopathies to evaluate hearing support therapies.

MRI Features in a Rat Model of H-ABC Tubulinopathy

Tubulinopathies are a group of recently described diseases characterized by mutations in the tubulin genes. Mutations in TUBB4A produce diseases such as dystonia type 4 (DYT4) and hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC), which are clinically diagnosed by magnetic resonance imaging (MRI). We propose the taiep rat as the first animal model for tubulinopathies. The spontaneous mutant suffers from a syndrome related to a central leukodystrophy and characterized by tremor, ataxia, immobility, epilepsy, and paralysis. The pathological signs presented by these rats and the morphological changes we found by our longitudinal MRI study are similar to those of patients with mutations in TUBB4A. The diffuse atrophy we found in brain, cerebellum and spinal cord is related to the changes detectable in many human tubulinopathies and in particular in H-ABC patients, where myelin degeneration at the level of putamen and cerebellum is a clinical trademark of the disease. We performed Tubb4a exon analysis to corroborate the genetic defect and formulated hypotheses about the effect of amino acid 302 change on protein physiology. Optical microscopy of taiep rat cerebella and spinal cord confirmed the optical density loss in white matter associated with myelin loss, despite the persistence of neural fibers.

0427 Bicuculine Increased the Cataplexy in the Male Taiep Rats: An Animal Model of Narcolepsy with an Inherent Tubulopathy

Introduction

Narcolepsy is a hypersomnolence that is characterized by sleep fragmentation, sleep paralysis, hypnagogic hallucinations and cataplexy that is characterized by atonia induced by strong emotions. The amygdala is the trigger for cataplexy through GABAergic mechanisms. Taiep is a myelin mutant with TUBB4A tubulopathy which showed spontaneous episodes of atonia or induced by manipulations from the tail or the thorax. EEG recordings during immobility episodes (IE′s) had a cerebral cortex desynchronized associated to theta rhythm in the hippocampus. The aim of this sturdy was to analyze the effects of bicuculine administration on IE′s and sleep-wake pattern on adult male taiep rats.

Methods

We used 6 taiep male rats at 9 months of age. The subjects (Ss) lived in individual acrylic cages with water and food pellets available ad libitum, under a 12:12 light-dark cycle (lights on at 0700), with controlled temperature and humidity recording room. All Ss were implanted to record EEG, EMG and EOG to characterize EI′s. We evaluated a basal 24 h EEG recording and then after bicuculine i.p. administration of 0.5, 1 y 1.5 mg/Kg every 48h. We measured the number, mean duration and latency to the first IE′s.

Results

The duration of IE′s increased 527% with 1 mg/Kg and reach 700% with 1.5 mg/Kg of bicuculine (P<0.01) with respect to saline-treated control group. Importantly, the frequency of IEs did not differ among the groups and did not affect the number of awake, slow wave or rapid eye movements sleep phases.

Conclusion

Bicuculine, a specific GABA antagonist, modify the duration of IES but not their frequency supporting a role of GABAergic mechanism on IE′s. It is relevant because sodium oxybate, an indirect GABA agonist, reduced cataplexy and improved sleep quality on narcoleptic patients.

Support

CONACYT grants 243333 and 243247 to CC and JRE, respectively and from VIEP-BUAP 2019 to CA in Neuroendocrinología BUAP-CA-288.

0428 Taiep Rats Had Normal Levels of Orexin Neurons in the Lateral Hypothalamus But Their Cataplexy Attacks are Sensible to Specific Orexin B Agonist

Introduction

Narcolepsy is characterized by sleep fragmentation, sleep paralysis, hypnagogic hallucinations and cataplexy. The cataplexy is a sudden loss of muscle tone triggered by emotions in humans, as well as in animal models. It is stablished that most of the patients had a significant decrease of orexin neurons in the lateral hypothalamus. Taiep rats had a mutation in tubulin TUBB4A and suffer immobility episodes (IE′s) that had a desynchronized activity in the cortex associated with theta rhythm in the hippocampus similar to narcolepsy patients. The aim of this study was to analyze the effects of central administration of an orexin B agonist and determination by immunohistochemistry of the number of orexin neurons on adult male taiep rats.

Methods

We used 14 male taiep rats of 9 months of age. The subjects (Ss) lived 3-4 in acrylic cages with water and food pellets ad libitum, under a 12:12 light-dark cycle (lights on at 0700), whit-controlled temperature and humidity in the recording room. All Ss were implanted to record EEG, EMG and EOG to characterize immobility episodes (IE′s) in a control 8 h recording and after i.c.v. administration of [Ala 11, D-Leu 15]-orexin B with 1, 3 and 10 nmol/1 μL. We measured the number, mean duration and latency to the first IE′s.

Results

The administration of [Ala 11, D-Leu 15]-orexin B significantly reduced the number of IE′s (P<0.01), from 4.28 ± 1.5 IE′s to just 0.25 ± 0.17 with 10 nmol/1 μL dose, but did not change the amount of awakening, slow wave or rapid eye movement sleep. Importantly, the number or orexins neurons were similar between taiep and Sprague-Dawley rats.

Conclusion

The myelin mutant taiep rats is a model of narcolepsy with cataplexy with normal number of orexin neurons in the lateral hypothalamus. Additionally, a specific orexin B agonist reduced IE′s without any effect the sleep pattern. This could be useful for the design of new treatments.

Support

CONACYT grants 243333 and 243247 to CC and JRE, respectively. Grants from VIEP-BUAP 2019 and CA in Neuroendocrinología BUAP-CA-288.

Yawning and Penile Erection Frequencies Are Resilient to Maternal Care Manipulation in the High-Yawning Subline of Sprague-Dawley Rats

Yawning is a stereotyped behavioral pattern characterized by wide opening of the mouth associated with deep inspiration followed by short expiration. All vertebrate species yawn, but with low frequencies. We obtained two sublines of Sprague–Dawley (SD) rats by a strict inbreeding process: one with a high-yawning frequency (HY) of 20 yawns/h, which is one order of magnitude higher with respect to the low-yawning frequency (LY) subline, with 2 yawns/h. Outbred SD rats had a yawning frequency of 1 yawn/h. HY dams had a different organization of maternal care with respect to that displayed by LY and SD dams because HY dams constructed lower quality nests and had more re-retrieving and atypical retrieving. The aim of this study was to analyze the changes in maternal care using in- and cross-fostering between the sublines and SD dams and to measure spontaneous and dopaminergic-induced yawning, penile erections, grooming and scratching bouts. We also measured the expression of dopamine D₂ receptors in the striatum using Western blot analysis. Our results showed that HY male rats reared by SD or LY dams did not significantly differ in yawning frequencies with respect to HY male rats reared by mothers of their own phenotype. Maternal care did not differ between sublines and SD dams independent of the litter they reared. However, LY rats reared by HY dams showed a significant increase in the number of spontaneous penile erections. Importantly, in-fostered HY male rats had the highest number of yawns induced by systemic administration of (−)-quinpirole supporting that higher maternal care display can influence the frequency of dopaminergic-induced yawning. In fact HY male rats in all conditions yawned more than did LY and SD male rats independent of the dam that raised them supporting a strong influence of genetic background. However SD male rats raised by LY dams showed significantly increased the dopamine D₂ receptor expression. In conclusion, maternal care and the environmental nest conditions during the lactation period did not change the phenotypic characteristics of the yawning sublines supporting that their genetic background is fundamental for the expression of spontaneous or dopaminergic-induced yawning.

Brain Processing of Complex Geometric Forms in a Visual Memory Task Increases P2 Amplitude

We study the cognitive processing of visual working memory in three different conditions of memory load and configuration change. Altering this features has been shown to alter the brain's processing in memory tasks. Most studies dealing with this issue have used the verbal-phonological modality. We use complex geometric polygons to assess visual working memory in a modified change detection task. Three different types of backgrounds were used to manipulate memory loading and 18 complex geometric polygons to manipulate stimuli configuration. The goal of our study was to test whether the memory load and configuration affect the correct-recall ratios. We expected that increasing visual items loading and changing configuration of items would induce differences in working memory performance. Brain activity related to the task was assessed through event-related potentials (ERP), during the test phase of each trial. Our results showed that visual items loading and changing of item configuration affect working memory on test phase on ERP component P2, but does not affect performance. However frontal related ERP component-P3-was minimally affected by visual memory loading or configuration changing, supporting that working memory is related to a filtering processing in posterior brain regions.

Juvenile Taiep rats have shorter dendritic trees in the dorsal field of the hippocampus without spatial learning disabilities

Myelin mutant taiep rats show a progressive demyelination in the central nervous system due to an abnormal accumulation of microtubules in the cytoplasm and the processes on their oligodendrocytes. Demyelination is associated with electrophysiological alterations and the mutant had a progressive astrocytosis. The illness is associated with change in cytokine levels and in the expression of different nitric oxide synthase and concomitantly lipoperoxidation in several areas of the brain. However, until now there has been no detailed anatomical analysis of neurons in this mutant. The aim of this study was to analyze the dendritic morphology in the hippocampus using Golgi-Cox staining and spatial memory through Morris water maze test in young adult (3 months old) taiep rats and compare them with normal Sprague-Dawley. Our results showed that taiep rats have altered dendritic tree morphology in pyramidal neurons in the CA1 field of the hippocampus, but not in the CA3 region. These morphological changes did not produce a concomitant deficit in spatial memory acquisition or recall at this early stage of the disease. Our results suggest that impairment of dendritic morphology in the CA1 field of the hippocampus is a landmark of the pathology of this progressive multiple sclerosis model.

Thermal imaging reveals sizable shifts in facial temperature surrounding yawning in budgerigars (Melopsittacus undulatus)

Accumulating comparative and interdisciplinary research supports a brain cooling function to yawning. In particular, previous research has shown significant decreases in both brain and skull temperature following yawning in mammals. In a recent study using a thermal imaging camera, significant reductions in both the cornea and concha temperature were observed following yawns in the high-yawning subline of Sprague-Dawley rats. Here, we performed a similar experiment to investigate shifts in facial temperature surrounding yawning in an avian species with more typical yawning patterns: budgerigars (Melopsittacus undulatus). In particular, we took maximal surface temperature recordings from the face (cere or eye) from 13 birds over a one-hour period to track changes before and after yawns. Similar to previous findings in high-yawning rats, we identified significant cooling (-0.36°C) of the face 10-20 seconds following yawning in budgerigars. Consistent with the hypothesis that yawns serve a thermoregulatory function, facial temperatures were slightly elevated just prior to yawning and then decreased significantly below baseline levels immediately thereafter. Similarly, birds that yawned during the trials had consistently higher facial temperatures compared to those that did not yawn. Moreover, yawn latency and overall yawn frequency were strongly correlated with the highest facial temperature recorded from each bird across trials. These results provide convergent evidence in support of a brain cooling function to yawning, and further validate the use of thermal imaging to monitor changes in skull temperature surrounding yawning events.

Yawning reduces facial temperature in the high-yawning subline of Sprague-Dawley rats

BACKGROUND

Yawning is a stereotyped behavior that enhances blood flow to the skull, and the resulting counterflow has been hypothesized as a mechanism for brain cooling. Studies have shown that yawns are strongly associated with physiological and pathological conditions that increase brain temperature, and that they are followed by equivalent decreases in brain temperature. However, measured reductions in cranial or facial temperatures following yawning have yet to be reported, to our knowledge. To accomplish this, we used a subline of Sprague-Dawley rats that yawn at a much greater rate (20 yawns/h) than do outbred Sprague-Dawley rats (2 yawns/h).

RESULTS

Using an infrared camera, we effectively evaluated thermal changes in the cornea and concha of these rats before, during, and after yawns. The maximum temperature in both regions significantly decreased 10 s following yawns (concha: -0.3 °C, cornea: -0.4 °C), with a return to basal temperatures after 20 s.

CONCLUSIONS

This study is the first clear demonstration of yawning-induced thermal cooling on the surface of the face, providing convergent evidence that this behavior plays a functional role in thermoregulation. As other studies have demonstrated that yawning is capable of reducing cortical brain temperature, our current data support the idea that yawning functions as a thermoregulator, affecting all structures within the head.

Differential organization of male copulatory patterns in high- and low-yawning-frequency sublines versus outbred Sprague-Dawley rats

The temporal organization of masculine sexual behavior in rats is highly stereotyped; involving a sequence of mounts, intromissions and ejaculations. Sexual behavior has been described in exogamic and genetically manipulated rodent species. In this work, we compare the male sexual behavior of outbred Sprague-Dawley (SD) to those of rats inbred for high (HY)- and low (LY)- spontaneous yawning frequency. In the first experiment, the percentage of inexperienced rats' ejaculatory behavior is significantly lower in the HY and LY respect to Sprague-Dawley rats. The latency to ejaculate for inexperienced HY was shorter than the LY and SD rats. In the second experiment, we examined the differences between inbred sublines and Sprague-Dawley rats once the subjects had become sexually experienced after four copulatory sessions. HY rats still have slower proportion of ejaculators respect to LY and SD rats. Additionally, postejaculatory latencies were longer for HY rats, with longer intercopulatory intervals and higher number of copulatory bouts that delayed ejaculation. Both sublines show lower copulatory efficiency respect to SD rats. In conclusion, both sublines show alterations in the temporal organization of sexual motor pattern that are due at least partially to strong inbreeding process to select them.

Copulation and ejaculation in male rats under sexual satiety and the Coolidge effect

Sexually satiated males cease copulating after several ejaculations with the same female; and the presence of an unknown receptive female renews copulation including ejaculation, a process named the Coolidge effect. It is believed that the Coolidge effect has the aim to impregnate another female, although it is known that the sperm count gradually decreases after consecutive ejaculations. The main goal was to investigate if sexually satiated males during the Coolidge effect can reestablish seminal expulsion associated to the ejaculation behavior and/or penile erection associated to the intromission behavior. The results show that during the Coolidge effect, most of the sexually satiated males showed the motor ejaculatory behavior, however, no sperm in the uterine horns or seminal plug in the vagina were detected. Such lack of sperm was not related with the number of ejaculations required to achieve sexual satiety nor with the number of intromissions needed for ejaculating (experiment 1: 2.4.1.). After the behavioral ejaculation, during the Coolidge effect, there was a 44% decrease in sperm count in the epididymal caudae (experiment 1: 2.4.2.). Males that mated for 8 behavioral ejaculations (close to sexual satiety) deposited tiny seminal plugs but no sperm in the female reproductive tract (experiment 1: 2.4.3.). Interestingly, sexually satiated and non-satiated-animals displayed similar number of intromissions and spent a similar time in dislodging the seminal plug from the vagina deposited by other males (experiment 2). These results suggest that sexually satiated males during the Coolidge effect have the capacity for penile erection and vaginal insertion, because they are able to dislodge seminal plugs; but are unable to expel seminal fluid, because neither form seminal plugs nor deposit sperm in the female genital tract.

Comparative analysis of maternal care in the high-yawning (HY) and low-yawning (LY) sublines from Sprague-Dawley rats

High- and low-yawning rats (HY and LY) were selectively bred as a function of their spontaneous yawning frequency with the LY subline about 2 yawns/hr and the HY 20 yawns/hr. The HY rats have more grooming bouts and travel longer distances in an open field. HY dams spent less time in the nest, retrieved their pups faster, and show a longer latency to licking and mouthing the pups than the LY or outbred Sprague-Dawley (SD) animals. The percentage of HY dams that had atypical retrieving was higher, with a lower nest quality, and produced offspring whose weights were lower than those from the LY subline. We also showed that the pregnant HY dams have fewer pups and the percentage that had lost at least three pups during lactation was higher than the SD and LY dams. In conclusion, HY dams are motivated to take care of their pups, but the "fine tuning" of maternal care is disturbed.

Neurophamacology of yawning

Yawning is a common behavioral event that is observed in humans, as well as other mammals, birds and reptiles. In humans, yawning often occurs just before bed and upon waking up, and is also associated with tedious or boring situations. Although the physiologic roles of yawning have yet to be fully elucidated, the past 50 years of research has led to a much greater understanding of the neuropharmacologic regulation of yawning. While many of the early studies concluded that yawning was primarily driven by changes in cholinergic neurotransmission, we now know that numerous neurotransmitters and neurohormones are involved in the mediation of yawning, including acetylcholine, dopamine, glutamate, serotonin, oxytocin, GABA, opioids, adrenergics, nitric oxide, as well as the proopiomelanocortin-derived peptides ACTH and alpha-MSH. Furthermore, antagonist interaction studies have clearly defined at least 3 distinct neural pathways involved in the induction of yawning, as well as the hierarchical order through which these different neurotransmitter systems interact to regulate yawning. The following sections will discuss the state of knowledge for each of the major neurotransmitters and neurohormones involved in the regulation of yawning, their interactions with one another, and their place in the hierarchical organization of yawning.

Regional and temporal progression of reactive astrocytosis in the brain of the myelin mutant taiep rat

Reactive astrocytosis in taiep rats was shown by glial fibrillary acidic protein (GFAP) immunoreactivity measured by means of enzyme-linked immunosorbent assay and indirect immunofluorescence. Increased GFAP immunoreactivity was first observed in the brainstem of 15-day-old taiep rats and was widespread throughout all brain regions at 6 months of age. Characteristically, astrocytes were hypertrophic and displayed strong GFAP fluorescence. The pattern of these reactive cells may correlate with the process of dysmyelination in the taiep rat.

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.

Inhibition of grooming by pilocarpine differs in high- and low-yawning sublines of Sprague-Dawley rats

A comparative study of the effect of pilocarpine, a muscarinic receptor agonist, on grooming, scored during 45 min via a time-sampling procedure, was carried out on two sublines of male rats selectively bred for high-(HY) and low-yawning (LY) frequency. In one condition, we introduced rats in a novel cage and observed them immediately after receiving an I.P. injection of pilocarpine (0.5-3.75 mg/Kg) or an equivalent volume of saline. Besides grooming, the occurrence of yawns was continuously recorded. In the other condition, we immersed rats in water for 60 s, then they received an I.P. injection of pilocarpine (3.75 mg/Kg) or an equivalent volume of saline and we placed them in an open field, in which we recorded the number of crossed squares. Grooming scores were significantly higher in the condition after water immersion than in the novel situation; in both conditions HY had a grooming response higher than that of LY rats. Pilocarpine produced a dose-dependent inhibition of novelty-induced grooming in HY rats, whereas LY grooming was reduced only with the highest dose. In contrast, yawning increased in a dose-dependent manner with HY rats curve over that of LY animals, except for the highest dose. Pilocarpine inhibited water immersion-induced grooming in both sublines of rats, but it did not reduce grooming as much as it did in the novel condition. Pilocarpine affected distinctly each of the components of grooming, without inhibiting animals locomotor activity. The results indicate that HY rats also have a higher number of grooms than LY rats, and because grooming and yawning can appear after stressful circumstances, HY rats may be used to study the role that both behaviors could have in counteracting the effects of stress. Similarly, HY animals might be utilized to study the underlying neurochemical mechanisms of grooming. This study also indicates that the cholinergic systems exert an inhibitory influence on grooming which contrasts with the excitatory effect on yawning.

Patterns of connectivity of spinal interneurons with single muscle afferents

A technique was developed to measure, in the anesthetized and paralyzed cat under artificial ventilation, changes of excitability to intraspinal stimulation simultaneously in two different afferent fibers or in two collaterals of the same afferent fiber. Intraspinal stimulation reduced the threshold of single muscle afferent fibers ending in the intermediate nucleus. This effect was seen with strengths below those required to activate the afferent fiber tested (1.5-12 microA), occurred at a short latency (1.5-2.0 ms), reached a maximum between 15 and 30 ms, and lasted up to 100 ms. The effects produced by graded stimulation applied at the shortest conditioning-testing stimulus time intervals increased by fixed steps, suggesting recruitment of discrete elements, most likely of last-order interneurons mediating primary afferent depolarization (PAD). The short-latency increases in excitability produced by the weakest effective intraspinal stimuli were usually detected only in the collateral closest to the stimulating micropipette, indicating that the stimulated interneurons mediating PAD have spatially restricted actions. The short-latency PAD produced by intraspinal stimuli, as well as the PAD produced by stimulation of the posterior biceps and semitendinosus (PBSt) nerve or by stimulation of the bulbar reticular formation (RF), was depressed 19-30 min after the i.v. injection of 0.5 mg/kg of picrotoxin, suggesting that all these effects were mediated by GABAergic mechanisms. The PAD elicited by stimulation of muscle and/or cutaneous nerves was depressed following the i.v. injection of (-)-baclofen, whereas the PAD elicited in the same collateral by stimulation of the RF was baclofen-resistant. The short-latency PAD produced by intraspinal stimulation was not always depressed by i.v. injections of (-)-baclofen. Baclofen-sensitive and baclofen-resistant monosynaptic PADs could be produced in different collaterals of the same afferent fiber. The results suggest that the intraspinal terminals of single muscle afferents receive synapses from more than one PAD-mediating GABAergic interneuron and that a single last-order interneuron has synaptic connections with a restricted number of intraspinal terminals and/or collaterals of the same afferent fiber. In addition, they support the existence of separate subsets of last-order baclofen-sensitive and baclofen-resistant interneurons that respond predominantly to segmental and to descending inputs. It is suggested that the restricted nature of the PAD plays an important role in the central control of the synaptic effectiveness of group I muscle afferents.

Selective cortical and segmental control of primary afferent depolarization of single muscle afferents in the cat spinal cord

This study was primarily aimed at investigating the selectivity of the cortico-spinal actions exerted on the pathways mediating primary afferent depolarization (PAD) of muscle spindle and tendon organ afferents ending within the intermediate nucleus at the L6-L7 segmental level. To this end we analyzed, in the anesthetized cat, the effects produced by electrical stimulation of sensory nerves and of the cerebral cortex on (a) the intraspinal threshold of pairs of single group I afferent fibers belonging to the same or to different hindlimb muscles and (b) the intraspinal threshold of two collaterals of the same muscle afferent fiber. Afferent fibers were classified in three categories, according to the effects produced by stimulation of segmental nerves and of the cerebral cortex. Twenty-five of 40 fibers (62.5%) were depolarized by stimulation of group I posterior biceps and semitendinosus (PBSt) or tibialis (Tib) fibers, but not by stimulation of the cerebral cortex or of cutaneous and joint nerves, which instead inhibited the PBSt- or Tib-induced PAD (type A PAD pattern, usually seen in Ia fibers). The remaining 15 fibers (37.5%) were all depolarized by stimulation of the PBSt or Tib nerves and the cerebral cortex. Stimulation of cutaneous and joint nerves produced PAD in 10 of those 15 fibers (type B PAD pattern) and inhibited the PBSt- or Tib-induced PAD in the 5 remaining fibers (type C PAD pattern). Fibers with a type B or C PAD pattern are likely to be Ib. Not all sites in the cerebral cortex inhibited with the same effectiveness the segmentally induced PAD of group I fibers with a type A PAD pattern. With the weakest stimulation of the cortical surface, the most effective sites that inhibited the PAD of individual fibers were surrounded by less effective sites, scattered all along the motor cortex (area 4gamma and 6) and sensory cortex (areas 3, 2 and 1), far beyond the area of projection of group I fibers from the hindlimb. With higher strengths of cortical stimulation, the magnitude of the inhibition was also increased, and previously ineffective or weakly effective sites became more effective. Maps obtained when using the weakest cortical stimuli have indicated that the most effective regions that produced PAD of group I fibers with a type B or type C PAD pattern were also scattered throughout the sensory-motor cortex, in the same general area as those that inhibited the PAD of group I afferents with a type A PAD pattern. In eight fibers with a type A PAD pattern it was possible to examine the intraspinal threshold of two collaterals of the same single afferent fiber ending within the intermediate nucleus at the L7 segmental level. In six fibers, stimulation of the PBSt nerve with trains of pulses between 1.5 and 1.86 times threshold (xT) produced a larger PAD in one collateral than in the other. In seven fibers, stimulation of the sensory-motor cortex and of cutaneous nerves produced a larger inhibition of the PBSt-induced PAD in one collateral than in the other. The ratio of the cortically induced inhibition of the PAD elicited in the two collaterals could be modified by changing the strength of cortical and of PBSt stimulation. In three fibers it was possible to inhibit almost completely the background PAD elicited in one collateral while having little or no effect on the PAD in the other collateral. Changes in the intraspinal threshold of pairs of collaterals following electrical stimulation of segmental nerves and of the somato-sensory cortex were examined in three fibers with a type B and two fibers with a type C PAD pattern. In four fibers the PAD elicited by stimulation of cutaneous (4-20xT) and muscle nerves (1.54-3.7xT), or by stimulation of the sensory-motor cortex, was of different magnitude in the two collaterals. In two experiments it was possible to find cortical sites in which weak surface stimulation produced PAD in one collateral only. (ABSTRACT TRUNCATED)

Raphe magnus and reticulospinal actions on primary afferent depolarization of group I muscle afferents in the cat

1. In the anaesthetized cat, electrical stimulation of the bulbar reticular formation produced a short latency (2.1 +/- 0.3 ms) positive potential in the cord dorsum. In contrast, stimulation of the nucleus raphe magnus with strengths below 50 microA evoked a slow negative potential with a mean latency of 5.5 +/- 0.6 ms that persisted after sectioning the contralateral pyramid and was abolished by sectioning the ipsilateral dorsolateral funiculus. 2. The field potentials evoked by stimulation of the bulbar reticular formation and of the nucleus raphe magnus had a different intraspinal distribution, suggesting activation of different sets of segmental interneurones. 3. Stimulation of these two supraspinal nuclei produced primary afferent depolarization (PAD) in single Ib fibres and inhibited the PAD elicited by group I volleys in single Ia fibres. The inhibition of the PAD of Ia fibres produced by reticulospinal and raphespinal inputs appears to be exerted on different interneurones along the PAD pathway. 4. It is concluded that, although reticulospinal and raphespinal pathways have similar inhibitory effects on PAD of Ia fibres, and similar excitatory effects on the PAD of Ib fibres, their actions are conveyed by partly independent pathways. This would allow their separate involvement in the control of posture and movement.

Selective cortical control of information flow through different intraspinal collaterals of the same muscle afferent fiber

We have analyzed in the anesthetized cat the effects of electrical stimulation of the cerebral cortex on the intraspinal threshold of two collaterals belonging to the same muscle spindle or tendon organ afferent fiber. The results obtained provide, for the first time, direct evidence showing that the motor cortex is able to modify, in a highly selective manner, the synaptic effectiveness of individual collaterals of the same primary afferent fiber. This presynaptic control could function as a mechanism that allows funneling of information to specific groups of spinal neurons in the presence of extensive intraspinal branching of the afferent fibers.

Presynaptic modulation of spinal reflexes

Recent evidence suggests that independent sets of interneurons mediate presynaptic inhibition of primary and secondary muscle spindles and of tendon organ afferents. There is also evidence that the information which flows through different intraspinal collaterals of a single muscle spindle or tendon organ afferent fiber is selectively affected by electrical stimulation of the motor cortex. These studies suggest that presynaptic inhibition plays an important role in the selection of the sensory signals required for the execution of a specific motor task.

Primary afferent depolarization of muscle afferents elicited by stimulation of joint afferents in cats with intact neuraxis and during reversible spinalization

1. In the anesthetized and artificially ventilated cat, stimulation of the posterior articular nerve (PAN) with low strengths (1.2-1.4 x T) produced a small negative response (N1) in the cord dorsum of the lumbosacral spinal cord with a mean onset latency of 5.2 ms. Stronger stimuli (> 1.4 x T) produced two additional components (N2 and N3) with longer latencies (mean latencies 7.5 and 15.7 ms, respectively), usually followed by a slow positivity lasting 100-150 ms. With stimulus strengths above 10 x T there was in some experiments a delayed response (N4; mean latency 32 ms). 2. Activation of posterior knee joint nerve with single pulses and intensities producing N1 responses only, usually produced no dorsal root potentials (DRPs), or these were rather small. Stimulation with strengths producing N2 and N3 responses produced distinct DRPs. Trains of pulses were clearly more effective than single pulses in producing DRPs, even in the low-intensity range. 3. Cooling the thoracic spinal cord to block impulse conduction, increased the DRPs and the N3 responses produced by PAN stimulation without significantly affecting the N2 responses. Reversible spinalization also increased the DRPs produced by stimulation of cutaneous nerves. In contrast, the DRPs produced by stimulation of group I afferents from flexors were reduced. 4. Conditioning electrical stimulation of intermediate and high-threshold myelinated fibers in the PAN depressed the DRPs produced by stimulation of group I muscle and of cutaneous nerves. 5. Analysis of the intraspinal threshold changes of single Ia and Ib fibers has provided evidence that stimulation of intermediate and high threshold myelinated fibers in the posterior knee joint nerve inhibits the primary afferent depolarization (PAD) of Ia fibers, and may either produce PAD or inhibit the PAD in Ib fibers, in the same manner as stimulation of cutaneous nerves. In 7/16 group I fibers the inhibition of the PAD was increased during reversible spinalization. 6. The results obtained suggest that intermediate and high-threshold myelinated fibers in the PAN have the same actions on Ia and Ib fibers as intermediate and high-threshold cutaneous afferents and may therefore be considered as belonging to the same functional system. They further indicate that in anesthetized preparations the pathways mediating the PAD of group I fibers, as well as the pathways mediating the inhibition of the PAD, may be subjected to a descending control that is removed by spinalization.

Differential action of (-)-baclofen on the primary afferent depolarization produced by segmental and descending inputs

The purpose of the present series of experiments was to analyze, in anesthetized and paralyzed cats, the effects of (-)-baclofen and picrotoxin on the primary afferent depolarization (PAD) generated in single Ib afferent fibers by either intraspinal microstimulation or stimulation of the segmental and descending pathways. PAD was estimated by recording dorsal root potentials and by measuring the changes in the intraspinal activation threshold of single Ib muscle afferent fibers. The PAD elicited by stimulation of group I muscle or cutaneous afferents was readily depressed and often abolished 20-40 min after the intravenous injection of 1-2 mg/kg (-)-baclofen. In contrast, the same amounts of (-)-baclofen produced a relatively small depression of the PAD elicited by stimulation of the brainstem reticular formation (RF). The monosynaptic PAD produced in single Ib fibers by intraspinal microstimulation within the intermediate nucleus was depressed and sometimes abolished following the i.v. injections of 1-2 mg/kg (-)-baclofen. Twenty to forty minutes after the i.v. injection of picrotoxin (0.5-1 mg/kg), there was a strong depression of the PAD elicited by stimulation of muscle and cutaneous afferents as well as of the PAD produced by stimulation of the RF and the PAD produced by intraspinal microstimulation. The results obtained suggest that, in addition to its action on primary afferents, (-)-baclofen may depress impulse activity and/or transmitter release in a population of last-order GABAergic interneurons that mediate the PAD of Ib fibers. The existence of GABAb autoreceptors in last-order interneurons mediating the PAD may function as a self-limiting mechanism controlling the synaptic efficacy of these interneurons.

Genotypic dependency of spontaneous yawning frequency in the rat

By inbreeding we have obtained two sublines of Sprague-Dawley rats which differ significantly in spontaneous mean yawning frequency (MYF). In generation F21 of the high-yawning (HY) subline MYF was 21.5 yawns/h (y/h) in males and 1.95 y/h in females, at the age of 2 months. In the low-yawning (LY) subline, in generation F16 the MYF was 0.9 y/h in males and only 0.5 y/h in females. During the first 15 days there are no differences in yawning frequency between HY and LY rats. Thereafter yawning increases with age, more steeply in the HY subline. The results of reciprocal crosses between both sublines indicate that the LY character is partially dominant over the HY one.

GABAergic modulation of yawning behavior

The hypothetical modulation by GABAergic neurons of yawning behavior in the rat was explored with GABA-active drugs. Gamma-acetylenic-GABA, a specific inhibitor of GABA-T, increases yawning frequency when injected at a dose of 7 mg/kg. Baclofen, a GABAB agonist (3 mg/kg), inhibits yawning completely; GABA antagonists, bicuculline and picrotoxin, at subconvulsant doses, also decrease yawning. All drugs were injected intraperitoneally with the exception of apomorphine, which was injected subcutaneously. It is suggested that GABAB receptors play a role in yawning behavior by modulating ACh release, and that GABAA receptors may modify yawning frequency by modulating inhibitory influences on ACh neurons.