Characterization of sperm motility and testosterone secretion in the taiep myelin mutant, a model of demyelination

Presently, demyelinating diseases have been reported to affect the reproductive life of patients who suffer from them, but the progression of the alterations is unknown, especially in men. To better understand these effects, it is necessary to perform studies in animal models, such as the male taiep rat, which exhibits progressive demyelination of the central nervous system, altered kisspeptin expression at the hypothalamic level, and decreased luteinizing hormone, which could alter sperm quality and testicular diameter. Thus, the objective of the present study was to analyze the diameter of the seminiferous tubules, the sperm motility, and the testosterone levels of 90-day-old male taiep rats. The obtained results indicate that male taiep rats show an increase in testicular size accompanied by an increase in the diameter of the seminiferous tubules of the left testicle. There was also a decrease in progressive motility in sperm samples from the left epididymis of male taiep rats compared to the control group, with no changes in serum testosterone concentration. Therefore, we conclude that male taiep rats with central demyelination show altered testicular diameter and decreased motility in sperm from the left side. This type of studies serves as a basis for proposing possible reproductive strategies to improve the fertility and testicular function of men with demyelinating diseases of the central nervous system.

The deficiency of myelin in the mutant taiep rat induces a differential immune response related to protection from the human parasite Trichinella spiralis

Taiep rat is a myelin mutant with a progressive motor syndrome characterized by tremor, ataxia, immobility episodes, epilepsy and paralysis of the hindlimbs. Taiep had an initial hypomyelination followed by a progressive demyelination associated with an increased expression of some interleukins and their receptors. The pathology correlated with an increase in nitric oxide activity and lipoperoxidation. In base of the above evidences taiep rat is an appropriate model to study neuroimmune interactions. The aim of this study was to analyze the immune responses in male taiep rats after acute infection with Trichinella spiralis. Our results show that there is an important decrease in the number of intestinal larvae in the taiep rat with respect to Sprague-Dawley control rats. We also found differences in the percentage of innate and adaptive immune cell profile in the mesenteric lymphatic nodes and the spleen that correlated with the demyelination process that took place on taiep subjects. Finally, a clear pro-inflammatory cytokine pattern was seen on infected taiep rats, that could be responsible of the decrement in the number of larvae number. These results sustain the theory that neuroimmune interaction is a fundamental process capable of modulating the immune response, particularly against the parasite Trichinella spiralis in an animal model of progressive demyelination due to tubulinopathy, that could be an important mechanism for the clinical course of autoimmune diseases associated with parasite infection.

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.

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.