Vincenzo Perciavalle

Differences in H-reflex between athletes trained for explosive contractions and non-trained subjects

SummaryThe efficacy of type la synapse on alpha-motoneurons of soleus and lateral gastrocnemius muscles has been investigated, using the H-reflex technique, in athletes engaged in sports requiring very rapid and intense contractions (sprinters and volley-ball players) as well as in non-trained subjects. It has been observed, in both muscles, that the ratio between the mean value of the maximal reflex response (Hmax) and the mean value of the maximal direct response (Mmax) elicited upon electrical stimulation of the tibial nerve is significantly smaller in athletes trained for explosive-type movements than in non-trained subjects. This difference in the Hmax:Mmax ratio was dependent on a smaller amplitude of Hmax and not on a greater amplitude of Mmax. No significant differences were observed between sprinters and volley-ball players. In both trained and non-trained subjects, soleus and lateral gastrocnemius muscles displayed significant differences in Hmax: Mmax ratio and Mmax amplitude but not in Hmax amplitude. Since the H-response is considered to be due mainly to activation of the smallest motoneurons in the motoneuronal pools, the difference in Hmax amplitude and Hmax:Mmax ratio between athletes and non-trained subjects could have been dependent on a lower incidence of these motoneurons in the athletes. This is in accord with the mechanical needs of muscles during explosive-type power training. Although this difference ,ay have been wholly determined genetically, the possibility is discussed as to whether the lower incidence in sprinters and volley-ball players of small motoneurons could have been related to a training-induced transformation of small and slow motoneurons into large and fast ones.

Interleukin 2 modifies the bioelectric activity of some neurosecretory nuclei in the rat hypothalamus

Introduction of 15-30 U of interleukin-2 (IL-2) into the 3rd ventricle of Wistar rats was followed by a marked and significant decrease in neuron discharge frequency in the ventromedial nucleus of hypothalamus and a marked increase in the supraoptic and paraventricular nuclei. The monoclonal antibody ART62 partly blocked these effects. The conventional anti-IL-2 receptor monoclonal antibody ART18 had only a non-significant influence on the effects of IL-2. Since the supraoptic and paraventricular nuclei secrete the antidiuretic hormone, their excitation may offer a partial explanation of the considerable water retention observed during IL-2 therapy against neoplasia.

Elevated blood lactate is associated with increased motor cortex excitability.

No information has yet been provided about the influence of blood lactate levels on the excitability of the cerebral cortex, in particular, of the motor cortex. The aim of the present study was to examine the effects of high blood lactate levels, induced with a maximal cycling or with an intravenous infusion, on motor cortex excitability. The study was carried out on 17 male athletes; all the subjects performed a maximal cycling test on a mechanically braked cycloergometer, whereas 6 of them were submitted to the intravenous infusion of a lactate solution (3 mg/kg in 1 min). Before the exercise or the injection, at the end, as well as 5 and 10 min after the conclusion, venous blood lactate was measured and excitability of the motor cortex was evaluated by using the transcranial magnetic stimulation. In both of these experimental conditions, it was observed that an increase of blood lactate is associated with a decrease of motor threshold, that is, an enhancement of motor cortex excitability. We conclude by hypothesizing that in the motor cortex the lactate could have a protective role against fatigue.

Synaptic plasticity modulates the spontaneous recovery of locomotion after spinal cord hemisection

Several evidences have demonstrated that adult mammals could achieve a wide range of spontaneous sensory-motor recovery after spinal cord injury by means of various forms of neuroplasticity. In this study we evaluated the possibility that after low-thoracic spinal cord hemisection in the adult rat, significant hindlimb locomotor recovery could occur, and that this recovery may be driven, at least in part, by mechanisms of synaptic plasticity. In order to address these issues, we measured the expression levels of synapsin-I and brain-derived neurotrophic factor by Western blotting, at various time points after hemisection and correlated them with the motor performance on a grid walk test. Regression analysis showed that the expression of synapsin-I was strongly correlated with the spontaneous recovery of hindlimb locomotion (R=0.78). Conversely, neither the expression levels of synapsin-I nor the locomotor recovery were associated with the expression of brain-derived neurotrophic factor. Overall results indicate that after spinal cord hemisection, substantial recovery of hindlimb locomotion could occur spontaneously, and that synaptic plasticity within spinal circuitries below the level of the lesion, could be an important mechanism involved in these processes.

The projections of the retrorubral field A8 to the hippocampal formation in the rat

The dopaminergic neurons in the midbrain of the rat are located in three groups: the ventral tegmental area (VTA-A10), substantia nigra (SN-A9), and retrorubral field (RRF-A8). We have recently examined the organization of the projections from the VTA and the SN to the hippocampal formation (HF) in the rat. In the present study we characterize the projections of the RRF to the HF by using anterograde tracing, retrograde tracers, and tyrosine hydroxylase (TH) immunohistochemistry. Following iontophoretical injections of Phaseolous vulgaris leucoagglutinin (PHA-L) into the RRF, anterograde labeling was observed primarily in the ipsilateral subiculum and adjacent CA1 cell field. Sparse labeling was also observed in the CA3 cell field and dentate gyrus. The distribution of RRF neurons projecting to the HF was examined by injecting retrograde fluorescent tracers (fluorogold, fast blue, and nuclear yellow) into several hippocampal areas. The retrograde tracer findings indicate that the medial aspects of the RRF project to the subiculum and adjacent CA1 cell field of both the septal and temporal HF. In order to evaluate the percentage of dopaminergic cells of the RRF projecting to the HF, the retrograde neuronal tracer fluorogold was used in combination with TH immunohistochemistry. The quantitative evaluation of retrograde labeled and TH-immunoreactive (IR) cells showed that RRF projections to the HF are partially (10–18%) dopaminergic. The findings suggest that the general pattern of distribution and organization of the RRF-A8 projections to the HF is similar to that observed in our previous studies examining hippocampal afferents from the VTA and SN. The data also suggest a crude topographical organization of RRF afferents to the HF and a more prominent input to the temporal than to the septal HF.

Projections from the intracerebellar nuclei to the ventral midbrain tegmentum in the rat.

The present study was undertaken to provide anatomical evidence, in the rat, for a direct projection from the cerebellum towards structures, other than the red nucleus, which belong to the ventral midbrain tegmentum, by using the retrograde as well as the anterograde horseradish peroxidase transport method. Following unilateral injection in the ventral midbrain tegmentum of horseradish peroxidase, free or conjugated to wheat germ agglutinin, sparing the red nucleus, retrogradely labeled neurons were found in the contralateral cerebellar lateral nucleus and, at lower density, in the interpositus nucleus. No labeled neurons were found in the fastigial nucleus of either side. Anterogradely labeled axons from lectin coupled horseradish peroxidase injection sites in the lateral and interpositus nuclei reached the contralateral ventral midbrain tegmentum. Terminal labeling was observed in the entire red nucleus as well as in the lateral division of the ventral tegmental area of Tsai, in the dorsal region of the substantia nigra pars compacta, and in the medial part of the retrorubral field. No terminal labeling was found in the caudal linear nucleus, interfascicular nucleus, peripeduncular nucleus, rostral linear nucleus of the raphe, substantia nigra pars lateralis and the substantia nigra pars reticulata. Terminal labeling was also not observed in the ventral midbrain tegmentum following horseradish peroxidase injection in lateral and interpositus nuclei of rats pretreated with kainic acid. In conclusion, it is noteworthy that, besides the red nucleus, the sole structures of ventral midbrain tegmentum receiving cerebellar efferents are those with a higher density of dopaminergic cells.

Sodium L-Lactate Differently Affects Brain-Derived Neurothrophic Factor, Inducible Nitric Oxide Synthase, and Heat Shock Protein 70 kDa Production in Human Astrocytes and SH-SY5Y Cultures

The present study analyzed the in vitro effects induced by sodium L‐lactate on human astrocytes and the SH‐SY5Y cell line, when added at concentrations of 5, 10, and 25 mmol/liter. Expression of brain‐derived neurotrophic factor (BDNF), inducible nitric oxide synthase (iNOS), and heat shock protein 70 kDa (HSP70) was evaluated by Western blot analysis. Cell viability with MTT, release of nitric oxide (NO) through the Griess reaction, and production of BDNF by enzyme‐linked immunoassay was determined. Data indicate that, in SH‐SY5Y as well as in cortical astrocytes, after 4 hr sodium L‐lactate increases the expression and release of BDNF, iNOS, and NO; after 24 hr, it turns is ineffective for the production of the neurotrophin in SH‐SY5Y and not in astrocytes, but the expression of iNOS and release of NO appear to be further increased compared with those after 4 hr. Sodium L‐lactate influences differently the expression of HSP70 in SH‐SY5Y compared with astrocytes. We propose, based on these findings, that sodium L‐lactate affects the expression of BDNF in SH‐SY5Y and astrocytes in a different manner: high levels of iNOS and NO expressed in SH‐SY5Y have a profound inhibitory effect on the release of BDNF related to a more limited production of HSP70 by SH‐SY5Y. In conclusion, the results demonstrate differences in the responses of SH‐SY5Y and astrocytes to stimulation by high levels of sodium L‐lactate. Sodium L‐lactate differently and dose and time dependently influences the expression and release of BDNF, iNOS, NO, and HSP70 depending on the cell type.

Influences of pyramidal tract on the subthalamic nucleus in the cat.

In adult cats, with mesencephalic decerebration sparing the cerebral peduncles and ablation of the sensorimotor cortex, changes in firing of single cells of subthalamic nucleus (STN) were analyzed upon stimulation of ipsilateral medullary pyramidal tract (PT). Twenty-two out of 44 of the STN cells exhibited, following PT stimulation, discharge changes that in the greatest part of cases (91%) were excitatory in nature. Excitations, always followed by inhibitory rebound, appeared with latency values compatible with a monosynaptic linkage.

Attentional processes and blood lactate levels

The accumulation of lactate in the blood after a high-intensity exercise is associated to an increase of lactate extractions by the brain. However, no information has been provided about the influences of blood lactate on cognitive performances and, in particular, on attention. The present study was carried out to examine the association of high blood lactate levels, induced with a maximal cycling, with two different attentional tasks. The study was carried out on 17 male sprinters who performed exhaustive exercise. Before the exercise, as well as 5 and 10 min after the exhaustion, blood lactate was measured and intensity as well as selectivity of attention of each subject were evaluated. Same measurements were performed on 6 out of 17 subjects who accepted to receive an intravenous infusion of a lactate solution. In both experimental conditions, an inverse relation between scores in both aspects of attention and blood lactate levels was observed.

Levels of brain-derived neurotrophic factor and neurotrophin-4 in lumbar motoneurons after low-thoracic spinal cord hemisection.

Neuroplasticity represents a common phenomenon after spinal cord (SC) injury or deafferentation that compensates for the loss of modulatory inputs to the cord. Neurotrophins play a crucial role in cell survival and anatomical reorganization of damaged spinal cord, and are known to exert an activity-dependent modulation of neuroplasticity. Little is known about their role in the earliest plastic events, probably involving synaptic plasticity, which are responsible for the rapid recovery of hindlimb motility after hemisection, in the rat. In order to gain further insight, we evaluated the changes in BDNF and NT-4 expression by lumbar motoneurons after low-thoracic spinal cord hemisection. Early after lesion (30 min), the immunostaining density within lumbar motoneurons decreased markedly on both ipsilateral and contralateral sides of the spinal cord. This reduction was statistically significant and was then followed by a significant recovery along the experimental period (14 days), during which a substantial recovery of hindlimb motility was observed. Our data indicate that BDNF and NT-4 expression could be modulated by activity of spinal circuitry and further support putative involvement of the endogenous neurotrophins in mechanisms of spinal neuroplasticity.