Systems-level organization of non-alcoholic fatty liver disease progression network.

Non-Alcoholic Fatty Liver Disease (NAFLD) is a complex spectrum of diseases ranging from simple steatosis to Non-Alcoholic Steatohepatitis (NASH) with fibrosis, which can progress to cirrhosis and hepatocellular carcinoma. The pathogenesis of NAFLD is complex, involving crosstalk between multiple organs, cell-types, and environmental and genetic factors. Dysfunction of the adipose tissue plays a central role in NAFLD progression. Here, we analysed transcriptomics data obtained from the Visceral Adipose Tissue (VAT) of NAFLD patients to understand how the VAT metabolism is altered at the genome scale and co-regulated with other cellular processes during the progression from obesity to NASH with fibrosis. For this purpose, we performed Weighted Gene Co-expression Network Analysis (WGCNA), a method that organizes the disease transcriptome into functional modules of cellular processes and pathways. Our analysis revealed the coordination of metabolic and inflammatory modules (termed "immunometabolism") in the VAT of NAFLD patients. We found that genes of arachidonic acid, sphingolipid and glycosphingolipid metabolism were upregulated and co-expressed with genes of proinflammatory signalling pathways and hypoxia in NASH/NASH with fibrosis. We hypothesize that these metabolic alterations might play a role in sustaining VAT inflammation. Furthermore, immunometabolism related genes were also co-expressed with genes involved in Extracellular Matrix (ECM) degradation. Our analysis indicates that upregulation of both ECM degrading enzymes and their inhibitors (incoherent feedforward loop) potentially leads to the ECM deposition in the VAT of NASH with fibrosis patients.

Evaluation of palatal rugae pattern in establishing identification and sex determination in Nalgonda children.

BACKGROUND: Establishing individual identification of a decedent only by dental means is a mammoth task in forensic odontology. Palatal rugae's uniqueness, its resistance to heat, and stability throughout life have been proved by its use as an alternative aid in individual identification where comparison of fingerprints and other records is difficult. AIMS AND OBJECTIVES: The aim of the present study was to analyze the role of palatal rugoscopy in personal identification and sex determination of Nalgonda pediatric population. MATERIALS AND METHODS: The study group consisted of 100 children having mixed dentition within the age range of 8-11 years, residing in Nalgonda district. Palatal rugae pattern, shape of the incisive papillae, length of the median palatal raphae, and shape of the dental arches were analyzed using Chi-square and Mann-Whitney tests between males and females. RESULTS: Wavy and curved patterns appeared to be most prevalent in both males and females but with no significant difference. The number of primary rugae in females and secondary rugae in males, on left side of the palate, was significantly more than their counterparts (P < 0.05). When rugae unification was observed, diverging type was significantly more in males than in females. Parabolic dental arch form, elliptical type of incisive papilla, and medium length of median palatal raphae was observed in majority of the subjects. CONCLUSION: The present study hypothesizes the uniqueness of the rugae in personal identification as no two palates showed similar type of rugae in either of the genders. The rugae pattern also contributes minimally towards sex determination as there was no significant difference observed between the two variables.

Timing of developmental sequences in different brain structures: physiological and pathological implications.

The developing brain is not a small adult brain. Voltage- and transmitter-gated currents, like network-driven patterns, follow a developmental sequence. Studies initially performed in cortical structures and subsequently in subcortical structures have unravelled a developmental sequence of events in which intrinsic voltage-gated calcium currents are followed by nonsynaptic calcium plateaux and synapse-driven giant depolarising potentials, orchestrated by depolarizing actions of GABA and long-lasting NMDA receptor-mediated currents. The function of these early patterns is to enable heterogeneous neurons to fire and wire together rather than to code specific modalities. However, at some stage, behaviourally relevant activities must replace these immature patterns, implying the presence of programmed stop signals. Here, we show that the developing striatum follows a developmental sequence in which immature patterns are silenced precisely when the pup starts locomotion. This is mediated by a loss of the long-lasting NMDA-NR2C/D receptor-mediated current and the expression of a voltage-gated K(+) current. At the same time, the descending inputs to the spinal cord become fully functional, accompanying a GABA/glycine polarity shift and ending the expression of developmental patterns. Therefore, although the timetable of development differs in different brain structures, the g sequence is quite similar, relying first on nonsynaptic events and then on synaptic oscillations that entrain large neuronal populations. In keeping with the 'neuroarcheology' theory, genetic mutations or environmental insults that perturb these developmental sequences constitute early signatures of developmental disorders. Birth dating developmental disorders thus provides important indicators of the event that triggers the pathological cascade leading ultimately to disease.

Outcomes 5 years after response to rituximab therapy in children and adults with immune thrombocytopenia.

Treatments for immune thrombocytopenic purpura (ITP) providing durable platelet responses without continued dosing are limited. Whereas complete responses (CRs) to B-cell depletion in ITP usually last for 1 year in adults, partial responses (PRs) are less durable. Comparable data do not exist for children and 5-year outcomes are unavailable. Patients with ITP treated with rituximab who achieved CRs and PRs (platelets > 150 × 10(9)/L or 50-150 × 10(9)/L, respectively) were selected to be assessed for duration of their response; 72 adults whose response lasted at least 1 year and 66 children with response of any duration were included. Patients had baseline platelet counts < 30 × 10(9)/L; 95% had ITP of > 6 months in duration. Adults and children each had initial overall response rates of 57% and similar 5-year estimates of persisting response (21% and 26%, respectively). Children did not relapse after 2 years from initial treatment whereas adults did. Initial CR and prolonged B-cell depletion predicted sustained responses whereas prior splenectomy, age, sex, and duration of ITP did not. No novel or substantial long-term clinical toxicity was observed. In summary, 21% to 26% of adults and children with chronic ITP treated with standard-dose rituximab maintained a treatment-free response for at least 5 years without major toxicity. These results can inform clinical decision-making.

Contribution of 5-HT to locomotion - the paradox of Pet-1(-/-) mice.

Serotonin (5-HT) plays a critical role in locomotor pattern generation by modulating the rhythm and the coordinations. Pet-1, a transcription factor selectively expressed in the raphe nuclei, controls the differentiation of 5-HT neurons. Surprisingly, inactivation of Pet-1 (Pet-1(-/-) mice) that causes a 70% reduction in the number of 5-HT-positive neurons in the raphe does not impair locomotion in adult mice. The goal of the present study was to investigate the operation of the locomotor central pattern generator (CPG) in neonatal Pet-1(-/-) mice. We first confirmed, by means of immunohistochemistry, that there is a marked reduction of 5-HT innervation in the lumbar spinal cord of Pet-1(-/-) mice. Fictive locomotion was induced in the in vitro neonatal mouse spinal cord preparation by bath application of N-methyl-d,l-Aspartate (NMA) alone or together with dopamine and 5-HT. A locomotor pattern characterized by left-right and flexor-extensor alternations was observed in both conditions. Increasing the concentration of 5-HT from 0.5 to 5 µm impaired the pattern in Pet-1(-/-) mice. We tested the role of endogenous 5-HT in the NMA-induced fictive locomotion. Application of 5-HT(2) or 5-HT(7) receptor antagonists affected the NMA-induced fictive locomotion in both heterozygous and homozygous mice although the effects were weaker in the latter strain. This may be, at least partly, explained by the reduced expression of 5-HT(2A) R as observed by means of immunohistochemistry. These results suggest that compensatory mechanisms take place in Pet-1(-/-) mice that make locomotion less dependent upon 5-HT.

Developmental up-regulation of the potassium-chloride cotransporter type 2 in the rat lumbar spinal cord.

The classical GABA/glycine hyperpolarizing inhibition is not observed in the immature spinal cord. GABA(A) and glycine receptors are anions channels and the efficacy of inhibitory transmission in the spinal cord is largely determined by the gradient between intracellular and extracellular chloride concentrations. The concentration of intracellular chloride in neurons is mainly regulated by two cation-chloride cotransporters, the potassium-chloride cotransporter 2 (KCC2) and the sodium-potassium-chloride co-transporter 1 (NKCC1). In this study, we measured the reversal potential of IPSPs (E(IPSP)) of lumbar motoneurons during the first postnatal week and we investigated the expression of KCC2 and NKCC1 in the ventral horn of the spinal cord from the embryonic day 17 to the postnatal day 20 in the rat. Our results suggest that the negative shift of E(IPSP) from above to below the resting membrane potential occurs during the first postnatal week when the expression of KCC2 increases significantly and the expression of NKCC1 decreases. KCC2 immunolabeling surrounded motoneurons, presumably in the plasma membrane and NKCC1 immunolabeling appeared outside this KCC2-labeled fine strip. Taken together, the present results indicate that maturation of chloride homeostasis is not completed at birth in the rat and that the upregulation of KCC2 plays a key role in the shift from depolarizing to hyperpolarizing IPSPs.

Serotonin refines the locomotor-related alternations in the in vitro neonatal rat spinal cord.

Serotonergic projections from raphe nuclei arrive in the lumbar enlargement of the spinal cord during the late fetal period in the rat, a time window during which the locomotor-related left/right and flexor/extensor coordinations switch from synchrony to alternation. The goal of the present study was to investigate the role played by serotonin (5-HT) in modulating the left/right and flexor/extensor alternations. Fictive locomotion was induced by bath application of N-methyl-D,L-aspartate (NMA) in the in vitro neonatal rat spinal cord preparation. By means of cross-correlation analysis we demonstrate that 5-HT, when added to NMA, improves left/right and flexor/extensor (recorded from the 3rd and 5th lumbar ventral roots, respectively) alternations. This effect was partly reproduced by activation of 5-HT(2A/2C) receptors. We then tested the contribution of endogenous 5-HT to NMA-induced fictive locomotion. Reducing the functional importance of endogenous 5-HT, either by inhibiting its synthesis with daily injections of p-chloro-phenylalanine (PCPA), starting on the day of birth, or by application of ketanserin (a 5-HT(2) receptor antagonist) or SB269970 (a 5-HT(7) receptor antagonist), disorganized the NMA-induced locomotor pattern. This pattern was restored in PCPA-treated animals by adding 5-HT to the bath. Blocking 5-HT(7) receptors disorganized the locomotor-like rhythm even in the absence of electrical activity in the brain stem, suggesting that NMA applied to the spinal cord does not cause 5-HT release by activating a spino-raphe-spinal loop. These results demonstrate that 5-HT is critical in improving the locomotor-related alternations in the neonatal rat.

The in vitro neonatal rat spinal cord preparation: a new insight into mammalian locomotor mechanisms.

The in vitro neonatal rat spinal cord preparation is the first mammalian nervous system isolated from the brainstem to the caudal end of the spinal cord. It permits the study of the cellular properties of mammalian locomotor networks and is unique in containing all the nervous structures related to locomotion. Although being a very immature system, this model has been considered as an adult preparation in which mammalian locomotor central pattern generators can be studied in detail. Nevertheless, one can also follow the development of locomotor functions during the perinatal period. Contrary to the adult, all neuroactive substances can directly reach the cellular structures in the brainstem-spinal cord preparation. When a neuroactive substance is applied to the bath, a single rhythmic activity is recorded along the cord. In fact, three rhythms can be isolated: one at the cervical level for the forelimbs, one at the lumbar level for the hind limbs and one in the sacrococcygeal region for the tail. Studies carried out on this preparation deal with three major areas: (1) relations between spontaneous activity and maturation of spinal network, (2) organisation of the different spinal networks, (3) key role of the descending pathways.

Gravity influences the development of inputs from the brain to lumbar motoneurons in the rat.

We investigated the influence of gravity on the maturation of electrical properties of lumbar motoneurons and the development of their inputs from ventral descending pathways, which are important for the control of posture and locomotion. Using electrophysiological approaches in the in vitro brain stem-spinal cord preparation of neonatal rats born and reared in hypergravity field we demonstrate that: (1) the postnatal development of descending inputs to lumbar enlargement was reduced in animals submitted to hypergravity; (2) similar developmental pattern of basic electrical properties observed between motoneurons of hypergravity and control animals could not account for the changes in descending inputs. We concluded that gravity was critical to shape development of the supraspinal afferents in the lumbar spinal cord throughout the postnatal period.

Close relationship between motor impairments and loss of functional motoneurons in a Charcot-Marie-Tooth type 1A model.

Charcot-Marie-Tooth disease type 1A is the most frequent hereditary neuropathy affecting the peripheral nervous system. A partial duplication of chromosome 17 (17p11.2) involving the PMP22 gene is responsible for dysmyelination-demyelination processes leading to motor and sensory impairments. Murine models of this disease are now widely used to investigate the mechanisms occurring at the behavioural and physiological levels. In this study, adult transgenic mice (6 months old) having integrated 7 copies of the human PMP22 gene were used to compare the motor performance, evaluated by using a complex locomotor test (the rotarod test), with both the number of functional motoneurons innervating the soleus muscle and the level of myelination in the sciatic nerve. Two levels of motor deficits were detected and led us to divide the population into two subgroups. In both impaired groups, the level of motor deficit was strongly correlated with the number of functional motoneurons evaluated by retrograde labeling from the muscle, but not with the number of myelinated fibers or the thickness of the myelin sheath (g-ratio). It therefore appears that the number of motor units may be a key element in motor impairments observed in Charcot-Marie-Tooth disease type 1A disease. These findings may have implications for therapeutic procedures, which should focus on the survival of the motoneuronal pool and/or the maintenance of functional neuro-muscular connexions to reduce motor impairments in humans.

PMP22 overexpression causes dysmyelination in mice.

Charcot-Marie-Tooth (CMT) disease is the most frequent hereditary peripheral neuropathy in humans. Its prevalence is about one in 2500. A subform, CMT1A, is transmitted as an autosomal dominant trait. An estimated 75% of patients are affected. This disorder has been shown to be associated with the duplication of a 1.5 Mb region of the short arm of chromosome 17, in which the PMP22 gene has been mapped. We have constructed a murine model of CMT1A by inserting into the murine genome a human YAC containing peripheral myelin protein 22 (PMP22) and its flanking controlling elements. We describe the behaviour of the C22 line (seven copies of YAC, 2.1 times PMP22 overexpression) during the myelination process. Electron microscopy, morphometry, electrophysiology, nerve conduction and expression of specific markers (e.g. Krox20) in normal and pathological Schwann cells demonstrated that PMP22 overexpression leads to a defect in the myelination of axons. The largest axons are the most affected. Only a few demyelination/remyelination processes were observed. Moreover, PMP22 overexpression probably enhances collagen synthesis by fibroblasts, before myelination, demonstrating that structures other than Schwann cells are affected by PMP22 overexpression. Classically, CMT1A was thought to be induced by a demyelination process following a phase of normal myelination, yet our data suggest that dysmyelination should be considered as a major factor for the disease.

Differential maturation of motoneurons innervating ankle flexor and extensor muscles in the neonatal rat.

The first postnatal week is a critical period for the development of posture in the rat. The use of ankle extensor muscles in postural reactions increases during this period. Changes in excitability of motoneurons are probably an important factor underlying this maturation. The aim of this study was to identify whether variations in the maturation exist between motor pools innervating antagonistic muscles. Intracellular recordings in the in vitro brain stem-spinal cord preparation of neonatal rats (from postnatal day 0-5) were used to examine the developmental changes in excitability of motoneurons innervating the ankle flexors (F-MNs) and the antigravity ankle extensors (E-MNs). No significant difference in resting potential, action potential threshold, input resistance or rheobase was observed at birth. The age-related increase in rheobase was more pronounced for F-MNs than for E-MNs. The development of discharge properties of E-MNs lagged behind that of F-MNs. More F-MNs than E-MNs were able to fire repetitively in response to current injection at birth. F-MNs discharged at a higher frequency than E-MNs at all ages. Differences in the duration of action potential afterhyperpolarization accounted, at least partly, for the differences in discharge frequency between E-MNs and F-MNs at birth, and for the age-related increase in firing rate. These results suggest that E-MNs are more immature at birth than F-MNs and that there is a differential development of motoneurons innervating antagonistic muscles. This may be a critical factor in the development of posture and locomotion.

Spontaneous and locomotor-related GABAergic input onto primary afferents in the neonatal rat.

The in vitro brain stem-spinal cord preparation of neonatal rats (0-5 days old) was used to examine the contribution of GABAA (gamma-aminobutyric acid) receptors to the spontaneous and locomotor-related antidromic firing in the dorsal roots of neonatal rats. Spontaneous bursts of antidromic discharges were generated by the underlying afferent terminal depolarizations reaching spiking threshold. The number of antidromic action potentials increased significantly in saline solution with Cl- concentration reduced to 50% of control. Bath application of the GABAA receptor antagonist bicuculline, at low concentrations (1-2 microM), or picrotoxin blocked the antidromic discharges in the dorsal roots almost completely. The increase in Cl- conductance was therefore mediated by an activation of GABAA receptors. Increasing the concentration of bicuculline to 10-20 microM never blocked these discharges further. On the contrary, in half of the preparations, the number of antidromic action potentials was higher in the presence of high concentrations of bicuculline (10-20 microM) than in the presence of picrotoxin or low concentrations of bicuculline. This suggests that bicuculline, at high concentrations, may have other effects, in addition to blocking GABAA receptors. Dorsal root firing was observed during fictive locomotion induced by bath application of excitatory amino acids and serotonin. A rhythmical pattern was often demonstrated. Bicuculline at low concentrations caused a decrease of the antidromic discharge whereas, at high concentrations, bursts of discharges appeared. A double-bath with a barrier built at the L3 level was then used to separate the mechanisms which generate locomotion from those mediating primary afferent depolarizations. Excitatory amino acids and serotonin were perfused in the rostral pool only. Decreasing the concentration of chloride in the caudal bath caused a sharp increase in the number of antidromic action potentials recorded from the L5 dorsal root. These discharges, which were modulated in phase with the locomotor rhythm, were blocked by bicuculline. These data demonstrate the existence of a locomotor-related GABAergic input onto primary afferent terminals in the neonatal rat.

Perinatal development of lumbar motoneurons and their inputs in the rat.

The rat is quite immature at birth and a rapid maturation of motor behavior takes place during the first 2 postnatal weeks. Lumbar motoneurons undergo a rapid development during this period. The last week before birth represents the initial stages of motoneuron differentiation, including regulation of the number of cells and the arrival of segmental and first supraspinal afferents. At birth, motoneurons are electrically coupled and receive both appropriate and inappropriate connections from the periphery; the control from supraspinal structures is weak and exerted mainly through polysynaptic connections. During the 1st postnatal week, inappropriate sensori-motor contacts and electrical coupling disappear, the supraspinal control increases gradually and myelin formation is responsible for an increased conduction velocity in both descending and motor axons. Both N-methyl-D-aspartate (NMDA) and non-NMDA receptors are transiently overexpressed in the neonatal spinal cord. The contribution of non-NMDA receptors to excitatory amino acid transmission increases with age. Activation of gamma-aminobutyric acid(A) and glycine receptors leads to membrane depolarization in embryonic motoneurons but to hyperpolarization in older motoneurons. The firing properties of motoneurons change with development: they are capable of more repetitive firing at the end of the 1st postnatal week than before birth. However, maturation does not proceed simultaneously in the motor pools innervating antagonistic muscles; for instance, the development of repetitive firing of ankle extensor motoneurons lags behind that of flexor motoneurons. The spontaneous embryonic and neonatal network-driven activity, detected at the levels of motoneurons and primary afferent terminals, may play a role in neuronal maturation and in the formation and refinement of sensorimotor connections.

Antidromic discharges of dorsal root afferents in the neonatal rat.

Presynaptic inhibition of primary afferents can be evoked from at least three sources in the adult animal: 1) by stimulation of several supraspinal structures; 2) by spinal reflex action from sensory inputs; or 3) by the activity of spinal locomotor networks. The depolarisation in the intraspinal afferent terminals which is due, at least partly, to the activation of GABA(A) receptors may be large enough to reach firing threshold and evoke action potentials that are antidromically conducted into peripheral nerves. Little is known about the development of presynaptic inhibition and its supraspinal control during ontogeny. This article, reviewing recent experiments performed on the in vitro brainstem/spinal cord preparation of the neonatal rat, demonstrates that a similar organisation is present, to some extent, in the new-born rat. A spontaneous activity consisting of antidromic discharges can be recorded from lumbar dorsal roots. The discharges are generated by the underlying afferent terminal depolarizations reaching firing threshold. The number of antidromic action potentials increases significantly in saline solution with chloride concentration reduced to 50% of control. Bath application of the GABA(A) receptor antagonist, bicuculline (5-10 microM) blocks the antidromic discharges almost completely. Dorsal root discharges are therefore triggered by chloride-dependent GABA(A) receptor-mediated mechanisms; 1) activation of descending pathways by stimulation delivered to the ventral funiculus (VF) of the spinal cord at the C1 level; 2) activation of sensory inputs by stimulation of a neighbouring dorsal root; or 3) pharmacological activation of the central pattern generators for locomotion evokes antidromic discharges in dorsal roots. VF stimulation also inhibited the response to dorsal root stimulation. The time course of this inhibition overlapped with that of the dorsal root discharge suggesting that part of the inhibition of the monosynaptic reflex may be exerted at a presynaptic level. The existence of GABA(A) receptor-independent mechanisms and the roles of the antidromic discharges in the neonatal rat are discussed.

Development of hindlimb postural control during the first postnatal week in the rat.

The development of the postural control of hindlimbs was investigated during the first postnatal week in the rat. The whole body was tilted in a vertical plane with the nose up. The proportion of animals producing a complete extension of both hindlimbs increased with age until the end of the first postnatal week. Motor responses were evoked by the pitch tilt already at birth with a slight extension of the hips, the knees and the ankles remaining bent in most cases. The extension produced at the ankle level increased gradually during the first postnatal week. This was correlated with a change in the EMG activity recorded from the triceps surae muscles (ankle extensors) during this postural reaction. There was a gradual acquisition of a tonic pattern. Characteristics of EMG responses changed significantly with age demonstrating an important increase in the use of triceps surae muscles in this postural task. These data demonstrate that the first postnatal week is a critical period for the development of postural reactions in the hindlimbs. They also suggest the existence of a proximo-distal gradient in the maturation of postural control. The mechanisms responsible for this reflex and for the maturation of posture are discussed.

Gradual development of the ventral funiculus input to lumbar motoneurons in the neonatal rat.

The in vitro brainstem-spinal cord preparation of newborn rats (0 to six-days-old) was used to investigate the development of pathways descending ventrally from the brainstem, which are important for the control of posture and locomotion. The ventral funiculus of the spinal cord was stimulated at the cervical (C1) level. Responses were recorded at the lumbar level from either motoneurons or ventral roots using intracellular microelectrodes or suction electrodes, respectively. Responses consisted of a pure excitation lasting 15 ms, followed by mixed excitatory/inhibitory responses. The inhibition was, at least partly, mediated by glycine. Excitatory amino acid transmission appears to be responsible for the excitation. The characteristics of the ventral funiculus-evoked postsynaptic potentials and ventral root potentials changed significantly with age. Their latency decreased whereas the slope and the area, measured over the first 15 ms, increased. The increase of the ventral funiculus input to motoneurons was slightly more pronounced than that of the monosynaptic dorsal root-evoked potentials from day 0 to day 4. These data suggest a gradual arrival of ventral descending axons in the lumbar enlargement which may be responsible for the gradual acquisition of postural control that takes place during the first days after birth. This is a prerequisite for the development of the adult pattern of quadrupedal locomotion, with elevated trunk.

Antidromic discharges of dorsal root afferents and inhibition of the lumbar monosynaptic reflex in the neonatal rat.

The in vitro brain stem-spinal cord preparation of neonatal (0- to five-day-old) rats was used to establish whether pathways descending from the brain stem are capable of modulating synaptic transmission from primary afferents to lumbar motoneurons within the first few days after birth. We stimulated the ventral funiculus of the spinal cord at the cervical (C1-C2) level. Single-pulse stimulations evoked both excitatory and inhibitory postsynaptic potentials in ipsilateral lumbar (L2-L5) motoneurons which were recorded intracellularly. Twin-pulse stimulations evoked bursts of action potentials in ventral roots. The amplitude of the monosynaptic dorsal root-evoked excitatory postsynaptic potential decreased when a conditioning stimulation was applied to the ventral funiculus 50-300 ms prior to the stimulation of the ipsilateral dorsal root. A decreased input resistance of the motoneurons during the early part (25-100 ms after the artifact) of the ventral funiculus-evoked postsynaptic potentials could account, at least partly, for the decreased amplitude of the dorsal root-evoked response. However, the duration of the inhibition of the dorsal root-evoked excitatory postsynaptic potential was longer than that of the decrease in input resistance. Ventral funiculus stimulation evoked antidromic discharges in dorsal roots. Recordings of dorsal root potentials showed that these discharges were generated by the underlying afferent terminal depolarizations reaching firing threshold. The dorsal root discharge overlapped with most of the time-course of the ventral funiculus-evoked inhibition of the response to dorsal root stimulation, suggesting that part of this inhibition may be exerted at a presynaptic level. The number of antidromic action potentials evoked in dorsal roots by ventral funiculus stimulation increased significantly in saline solution with chloride concentration reduced to 50% of control. Bursts of action potentials disappeared when chloride was removed completely. Antidromic discharges were therefore due to chloride conductance. The number of action potentials evoked in ventral roots was increased in low-chloride saline solutions. Removing chloride from the bathing solution resulted in an unstable ventral root activity. Bath application of the GABA(A) receptor antagonist, bicuculline (5-10 microM), blocked the ventral funiculus-evoked antidromic discharges in the dorsal roots. The increase in chloride conductance which generated the depolarizations underlying the dorsal root discharges was therefore mediated by an activation of GABA(A) receptors. In contrast, bursts of action potentials in the ventral roots were increased in both amplitude and duration under bicuculline. Our data demonstrate that pathways running in the ventral funiculus of the spinal cord exert a control on interneurons mediating presynaptic inhibition at birth.

Role of gravity in the development of posture and locomotion in the neonatal rat.

This report describes the early motor behaviour in the neonatal rat in relation with the maturation of sensory and motor elements of the central nervous system (CNS). The role of vestibular information during the week before (E14-21) and the 2 weeks after (P0-15) birth will be considered. There is a rostro-caudal gradient in the maturation of posture and locomotion with a control of the head and forelimbs during the first postnatal week and then a sudden acceleration in the functional maturation of the hindlimb. At birth, the neonatal rat is blinded and deaf; despite the immaturity of the other sensory systems, the animal uses its olfactory system to find the mother nipple. Vestibular development takes place between E8 and P15. Most descending pathways from the brainstem start to reach the lumbar enlargement of the spinal cord a few days before birth (reticulo-, vestibulospinal pathways as well as the serotonergic and noradrenergic projections); their development is not completed until the end of the second postnatal week. At birth, in an in vitro preparation, a locomotor activity can be evoked by perfusing excitatory amino acids and serotonin over the lumbar region. The descending pathways which trigger the activity of the CPG are also partly functional. At the same age both air stepping and swimming can be induced. Complex locomotion such as walking, trotting and galloping start later because it requires the maturation of the vestibular system, descending pathways and postural reflex regulation. The period around birth is critical to properly define how the vestibular information is essential for the structuring of the motor behaviour. Different types of experiments (hypergravity, microgravity) are planned to test this hypothesis.

Spinal inputs from lateral columns to reticulospinal neurons in lampreys.

This study characterizes the inputs from the lateral columns of the spinal cord to reticulospinal neurons in the lampreys, using the in vitro isolated brainstem and spinal cord preparation. Synaptic responses to the electrical stimulation of the lateral columns were recorded in reticulospinal neurons of the posterior and middle rhombencephalic reticular nuclei. The responses consisted of a mixture of excitation and inhibition. They were markedly potentiated when using trains of two to five pulses, suggesting that the larger part of these synaptic responses was mediated via an oligosynaptic pathway. An early component, however, persisted when using twin pulses at 10-20 Hz on the ipsilateral side, suggesting the presence of an early mono- or disynaptic component. When increasing the stimulation strength, an early fast rising excitatory component appeared. It most likely resulted from an antidromic activation of vestibulospinal axons in the lateral tracts, which make en passant synaptic contacts with reticulospinal neurons. Responses were practically abolished by adding CNQX and AP5 to the Ringer's solution. The late component of excitatory responses was decreased by AP5, suggesting that NMDA receptors were activated. The NMDA receptor-mediated component was larger when using trains of stimuli or in Mg2+-free Ringer's. The application of NMDA depolarized reticulospinal neurons. The glycinergic inhibitory component was markedly increased in Mg2+-free Ringer's. Moreover, GABAB-receptor activation with (-)-baclofen abolished both excitatory and inhibitory responses. Taken together, the present results indicate that ascending lateral column axons generate large excitatory and inhibitory synaptic potentials in reticulospinal neurons. The possible role of these inputs in modulating the activity of reticulospinal neurons during locomotion is discussed.