RESUMO
Synaptosomal-associated protein of 25kDa (SNAP25), vesicle-associated membrane protein 1 (VAMP1) and 2 (VAMP2) are components of soluble N-ethylmaleimide-sensitive fusion attachment protein receptors (SNARE) complex which is involved in synaptic vesicle exocytosis, a fundamental step in neurotransmitter release. SNARE expression in cerebellum correlates with specific neurotransmitter pathways underlying synaptic diversification and defined synaptic properties. In this study we firstly characterized the distribution of SNAP25, VAMP1 and VAMP2 in the nerve terminals of a defined cerebellar region, the deep cerebellar nuclei (DCN), of adult and newborn rats. Then, given the pivotal role of estradiol (E2) in the synaptic organization of the cerebellar circuitry in early postnatal life, we examined whether administration of E2 in the newborn DCN affected synaptic density and changed the distribution of the presynaptic proteins SNAP25, VAMP1 and VAMP2, together with post synaptic density protein 95 (PSD95). Results showed that: (1) distribution of SNAP25, VAMP1 and VAMP2 in adult DCN differs significantly from that found in newborn DCN; (2) administration of E2 in the newborn DCN affected synaptic density and also changed the distribution of the pre- and postsynaptic proteins. The differential distribution of SNAP25, VAMP1 and VAMP2 in nerve terminals of adult and newborn rats may correlate with specific stages of neuronal phenotypic differentiation. The effects of E2 on SNAP25, VAMP1, VAMP2, PDS95 and synaptic density suggest that pre- and postsynaptic proteins are under estrogenic control during development and that synaptic maturation can also be related with the activity of this steroid.
Assuntos
Núcleos Cerebelares/metabolismo , Estradiol/farmacologia , Proteína 25 Associada a Sinaptossoma/biossíntese , Proteína 1 Associada à Membrana da Vesícula/biossíntese , Proteína 2 Associada à Membrana da Vesícula/biossíntese , Animais , Animais Recém-Nascidos , Western Blotting , Núcleos Cerebelares/efeitos dos fármacos , Núcleos Cerebelares/crescimento & desenvolvimento , Imunofluorescência , Microscopia Confocal , Neurogênese/efeitos dos fármacos , Neurogênese/fisiologia , Ratos , Ratos Wistar , Sinapses/efeitos dos fármacos , Sinapses/metabolismoRESUMO
We investigated in the rat whether hypoglossal innervation extended to facial muscles other than the extrinsic musculature of the mystacial pad. Results showed that hypoglossal neurons also innervate the masseter muscle. Dil injected into the XII nucleus showed hypoglossal axons in the ipsilateral main trunk of the trigeminal nerve. After Gasser's ganglion crossing, the axons entered into the infraorbital division of the trigeminal nerve and targeted the extrinsic muscles of the mystacial pad. They also spread into the masseter branch of the trigeminal nerve to target the polar portions of the masseter muscle spindles. Retrograde double labelling, performed by injecting Dil into the pad and True Blue into the ipsilateral masseter muscle, showed labelled hypoglossal neurons in the medio-dorsal portion of the XII nucleus. The majority of these neurons were small (15-20 microm diameter), showed fluorescence for Dil and projected to the mystacial pad. Other medium-size neurons (25 microm diameter) were instead labelled with True Blue and projected to the masseter muscle. Finally, in the same area, other small hypoglossal neurons showed double labelling and projected to both structures. Functional hypotheses on the role of these hypoglossal projections have been discussed.
Assuntos
Nervo Hipoglosso/citologia , Músculo Masseter/inervação , Mastigação/fisiologia , Bulbo/citologia , Sistema Estomatognático/citologia , Animais , Benzofuranos , Carbocianinas , Tamanho Celular , Músculos Faciais/inervação , Músculos Faciais/fisiologia , Nervo Hipoglosso/fisiologia , Músculo Masseter/fisiologia , Nervo Maxilar/citologia , Nervo Maxilar/fisiologia , Bulbo/fisiologia , Neurônios Motores/citologia , Neurônios Motores/fisiologia , Contração Muscular/fisiologia , Fusos Musculares/inervação , Fusos Musculares/fisiologia , Vias Neurais/citologia , Vias Neurais/fisiologia , Ratos , Ratos Wistar , Coloração e Rotulagem , Sistema Estomatognático/fisiologia , Nervo Trigêmeo/citologia , Nervo Trigêmeo/fisiologia , Vibrissas/inervação , Vibrissas/fisiologiaRESUMO
Years of effort have failed to establish a generally-accepted mechanism of thyroid hormone (TH) action in the mature brain. Recently, both morphological and pharmacological evidence have supported a direct neuroactive role for the hormone and its triiodinated metabolites. However, no direct physiological validation has been available. We now describe electrophysiological studies in vivo in which we observed that local thyroxine (T4) administration promptly inhibited field excitatory postsynaptic potentials recorded in the dentate gyrus (DG) with stimulation of the medial perforant pathway, a result that was found to be especially pronounced in hypothyroid rats. In separate in vitro experiments, we observed more subtle but statistically significant responses of hippocampal slices to treatment with the hormone. The results demonstrate that baseline firing rates of CA1 pyramidal cells were modestly reduced by pulse-perfusion with T4. By contrast, administration of triiodothyronine (T3) was often noted to have modest enhancing effects on CA1 cell firing rates in hippocampal slices from euthyroid animals. Moreover, and more reliably, robust firing rate increases induced by norepinephrine were amplified when preceded by treatment with T3, whereas they were diminished by pretreatment with T4. These studies provide the first direct evidence for functional, nongenomic actions of TH leading to rapid changes in neuronal excitability in adult rat DG studied in vivo and highlight the opposing effects of T4 and T3 on norepinephrine-induced responses of CA1 cells studied in vitro.
Assuntos
Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Hipocampo/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Tiroxina/farmacologia , Tri-Iodotironina/farmacologia , Potenciais de Ação/fisiologia , Agonistas alfa-Adrenérgicos/farmacologia , Animais , Antitireóideos/farmacologia , Giro Denteado/citologia , Giro Denteado/efeitos dos fármacos , Giro Denteado/fisiologia , Relação Dose-Resposta a Droga , Eletrofisiologia , Potenciais Pós-Sinápticos Excitadores/fisiologia , Hipocampo/citologia , Hipotireoidismo/induzido quimicamente , Masculino , Neurônios/citologia , Norepinefrina/farmacologia , Propiltiouracila/farmacologia , Ratos , Ratos Sprague-Dawley , Ratos Wistar , Glândula Tireoide/efeitos dos fármacos , Glândula Tireoide/metabolismo , Tiroxina/metabolismo , Tri-Iodotironina/metabolismoRESUMO
Recently, we showed that extra-trigeminal axons, originating from the hypoglossal nucleus, travel with the infraorbital division of the trigeminal nerve (ION), which is known to innervate the rat mystacial pad. Dil was monolaterally injected into the rat XII nucleus to analyse the peripheral distribution of hypoglossal axons to the mystacial pad, to evaluate their involvement in facial sensory-motor control. Electromyographic responses of mystacial pad motor units to electrical stimulation of the ION were recorded, along with the evoked responses to electrical stimulation of the ipsilateral XII nucleus. The results showed that hypoglossal axon terminals target the ipsilateral extrinsic musculature of the mystacial pad, but they do not have any contact with the intrinsic muscles. ION electrical stimulation increased electromyographic activity in the ipsilateral pad extrinsic muscles, even following VII nerve transection. Hypoglossal nucleus electrical stimulation induced field potentials and monosynaptic responses in the same motor units that persisted even following VII nerve transection, these disappearing after cooling the ION. We suggest that the small hypoglossal neurons projecting to the extrinsic musculature of the mystacial pad are part of a hypoglossal-trigeminal loop that participates in the sensory-motor control of the rat vibrissae system.
Assuntos
Músculos Faciais/inervação , Músculos Faciais/fisiologia , Nervo Hipoglosso/fisiologia , Vibrissas/fisiologia , Animais , Axônios/fisiologia , Estimulação Elétrica , Eletrofisiologia , Face/inervação , Face/fisiologia , Músculos Faciais/anatomia & histologia , Nervo Facial/anatomia & histologia , Nervo Facial/fisiologia , Nervo Hipoglosso/anatomia & histologia , Masculino , Neurônios Motores/fisiologia , Fibras Musculares Esqueléticas/fisiologia , Ratos , Ratos Wistar , Vibrissas/inervaçãoRESUMO
An important defence against free radicals is represented by plasma low molecular weight (LMW) thiols that compose a dynamic system of reduced and oxidized forms able to act as a buffer redox system. This study examined the effect of an acute graded exercise bout on LMW thiols in 16 young subjects (six sedentaries and 10 athletes). Blood analysis was performed before and immediately after the exercise and total and reduced thiols were measured in order to evaluate the thiol redox status. Findings suggested that the exercise test proposed was not enough to imbalance the redox status of all LMW thiols. However, when the redox status was evaluated for each thiol, it was evident that homocysteine (Hcy) redox status was significantly different after physical activity. In particular, we found a lower level of reduced Hcy after the exercise test both in sedentaries and in athletes. We concluded that duration and intensity of the proposed exercise were not enough to promote a reactive oxygen species production able to imbalance the redox thiols status and that the lowering of the reduced Hcy form may be due to the effect produced during the effort on the synthesis and/or removal processes of Hcy.
Assuntos
Exercício Físico/fisiologia , Peso Molecular , Esforço Físico , Plasma , Compostos de Sulfidrila/análise , Adulto , Humanos , Itália , Masculino , Compostos de Sulfidrila/fisiologiaRESUMO
Spinning is a type of indoor fitness activity performed on stationary bikes by participants who pedal together to the rhythm of music and the motivating words of an instructor. Despite worldwide popularity of this type of recreational activity, to date there have been few, mainly non-scientific, studies of the impact of spinning on metabolic, respiratory, and cardiovascular functions. The main aim of this study was to evaluate a number of metabolic and cardiovascular variables during a standard 50-min class performed by Spinning instructors of both sexes: six males (age 30 +/- 4.8 years, body mass index 24 +/- 2.5 kg x m(-2); mean +/- s) and six females (age 34 +/- 6.3 years, body mass index 21 +/- 1.9 kg x m(-2)). The mean power output, heart rate, and oxygen uptake during the performance were 120 +/- 4 W, 136 +/- 13 beats x min(-1), and 32.8 +/- 5.4 ml x kg(-1) x min(-1) respectively for males, and 73 +/- 43 W, 143 +/- 25 beats x min(-1), and 30 +/- 9.9 ml x kg(-1) x min(-1) respectively for females. Analysis of individual performances showed that they were compatible with physical exercise that ranged from moderate-to-heavy to very heavy, the latter conditions prevailing. The results show that this type of fitness activity has a high impact on cardiovascular function and suggest that it is not suitable for unfit or sedentary individuals, especially the middle aged or elderly, who are willing to begin a recreational physical activity programme.
Assuntos
Ciclismo/fisiologia , Monitorização Fisiológica , Análise e Desempenho de Tarefas , Adulto , Teste de Esforço , Feminino , Humanos , Itália , MasculinoRESUMO
The effects of chronic exposure (90 days) to Aluminum chloride (AlCl(3)) were analyzed in 3, 10 and 24 month old male rats (n=270) by investigating the function of the VOR (vestibulo-ocular reflex) in correlation with Aluminum (Al) concentrations in blood and brain. The VOR was chosen and tested in basal conditions (pre-exposure measures) and during the continuous administration of three different concentrations of AlCl(3) (0.5, 1, 2 g/l in drinking solution): the control animals being exposed to NaCl (0.125, 0.25 and 5 g/l in drinking solution). Results showed that LOAEL (Lowest Observed Adverse Effect Level) was 43.1+/-11.4 mg Al/kg-day. At this concentration the Al induced significant VOR impairment in all exposed rats, regardless of animal age. Neuroanatomical analysis showed that VOR impairment was not dependent on astrocyte damage nor evidences of amyloid deposits in the exposed rats was found. Significant changes of Al concentrations were observed in nervous tissue, while its concentration in whole blood was unaffected. Furthermore, results show that it is possible to identify an individual neurotoxic threshold for each animal and therefore hypothesize the clinical use of the VOR test for the evaluation of individual risk toxicity to chronic Al exposure.
Assuntos
Alumínio/farmacologia , Reflexo Vestíbulo-Ocular/efeitos dos fármacos , Alumínio/sangue , Alumínio/metabolismo , Animais , Encéfalo/metabolismo , Eletrofisiologia , Movimentos Oculares/fisiologia , Imuno-Histoquímica , Microeletrodos , Nistagmo Optocinético/fisiologia , Ratos , Ratos WistarRESUMO
INTRODUCTION: The physiopathogenetic mechanisms possibly involved in sudden unexplained epileptic death (SUDEP), were investigated in the hemispherectomized rat. METHODS: For this purpose, paroxysmal activity, vagal nerve firing, systemic blood pressure (BP), pulmonary artery pressure, and ECG were simultaneously recorded in an experimental animal model of epilepsy. Recordings were performed in basal conditions and during paroxysmal activity induced by topical application of penicillin-G at hypothalamic and mesencephalic level. During the experiment were also performed hemogas analysis and at end, samples of lung tissue were processed for histology. RESULTS: Activation of hypothalamic (HEF) and mesencephalic (MEF) epileptic foci induced a significant increase of spontaneous vagal nerve firing that was strictly correlated to ECG impairments and hypotension. When paroxysmal activity extinguished, vagal nerve activity and cardiovascular parameters returned to basal conditions. However, in 25% of the animals, co-activation of HEF and MEF always triggered a vagal hypertone which was temporally correlated to cardiac arrhythmias, but also to hyperkalemia, acidosis, pulmonary hypertension and to animal death. Histological control in lungs of deceased animals showed an alveolar and perivessel oedema with an oedematous infiltration in the alveolar and bronchial spaces and mucous secretion. During ictal activity, comparison between survived and deceased animals showed significant differences in the incidence of ECG impairment of pulmonary artery pressures, pO2, and pCO2 pressures, and [K+], [HCO3-], and [pH], concentrations. DISCUSSION: A possible explanation of the above observations is discussed in relationship to SUDEP physiopathogenesis.
Assuntos
Arritmias Cardíacas/fisiopatologia , Morte Súbita/etiologia , Convulsões/fisiopatologia , Nervo Vago/fisiopatologia , Animais , Modelos Animais de Doenças , Eletrocardiografia , Eletroencefalografia , Eletrofisiologia , Feminino , Hemisferectomia , Hipotálamo/patologia , Masculino , Mesencéfalo/patologia , Penicilina G , Ratos , Ratos Wistar , Convulsões/induzido quimicamente , Convulsões/complicaçõesRESUMO
Synaptic plasticity was studied in the lateral vestibular nuclei (LVN) of the guinea pig in vivo. High frequency stimulation (HFS) of increasing or decreasing frequencies was applied to the ipsilateral vestibular nerve. Vestibular field potentials (VFPs) and extracellular single unit activity evoked in the LVN by electrical stimulation of the ipsilateral vestibular nerve, were analyzed before and after the application of different protocols of HFS. Results show that the monosynaptic component of the VFPs undergo long-term potentiation (LTP) with stimulation of 100 Hz applied for 20 s lower frequencies, applied for shorter periods, induce only a transient post-tetanic potentiation. This potentiation, although long lasting, is not permanent since it is susceptible of a reversal or cancellation by opposite patterns of HFS that determine a depression or depotentiation of the previously acquired potentiation. The results demonstrate that the plasticity phenomena that take place at the level of the LVN neurons are not steady but undergo continuous adjustment of their sign and gain depending on the variable flow of vestibular information that reach the nuclei from the labyrinthine receptors.
Assuntos
Potenciação de Longa Duração/fisiologia , Inibição Neural/fisiologia , Núcleo Vestibular Lateral/fisiologia , Animais , Estimulação Elétrica , Potenciais Evocados Auditivos/fisiologia , Feminino , Cobaias , Masculino , Plasticidade Neuronal/fisiologia , Nervo Vestibulococlear/fisiologiaRESUMO
In the present study the possible derangement of the autonomic system and its influence in life threatening arrhythmias were analysed during paroxysmal activity. In hemispherectomized rats a paroxysmal activation of the hypothalamic and mesencephalic cardioarrhythmogenic triggers was performed by topical application of penicillin-G. Blood gas parameters and electrical activity of the thalamus, hypothalamus, vagal nerve fibre, ECG and arterial blood pressure were simultaneously monitored in basal conditions and repeated after the appearance of paroxysmal activity. Temporal correlation analysis was carried out. Results showed that during activation of these triggers, the spontaneous vagal nerve fibre activity significantly increased and triggered the appearance of cardiac arrhythmias which could become life threatening and induce animal death when blood gas and electrolytic parameters were simultaneously impaired. These experiments suggest that fatal evolution of the heart impairment is related not only to an autonomic cardiac trigger, but also to a concomitant metabolic derangement, which most likely shares the same autonomic origin.
Assuntos
Arritmias Cardíacas/complicações , Arritmias Cardíacas/fisiopatologia , Sistema Nervoso Autônomo/fisiopatologia , Encéfalo/fisiopatologia , Modelos Animais de Doenças , Epilepsia/complicações , Epilepsia/fisiopatologia , Animais , Gasometria , Pressão Sanguínea , Eletrocardiografia , Eletroencefalografia , Eletrólitos/sangue , Feminino , Hipotálamo/fisiopatologia , Masculino , Mesencéfalo/fisiopatologia , Fibras Nervosas/fisiologia , Ratos , Ratos Wistar , Tálamo/fisiopatologia , Nervo Vago/fisiopatologiaRESUMO
The effects of lead exposure at low concentrations were evaluated by studying the post-rotatory nystagmus (PRN) in two groups of rats exposed for 3 months to 50 parts per million (ppm) of sodium acetate and 50 ppm of lead acetate, respectively, in the drinking water. Only animals treated with lead acetate showed changes of the PRN parameters which were significantly related to the concentration of lead in the blood and in brain structures. The patterns of PRN responses were characterized and classified into four types: progressively inhibitory (40%), prematurely inhibitory (25%), late inhibitory (25%), and excitatory-inhibitory (10%). No alterations of the PRN parameters were observed in the animals treated with sodium acetate. The results show that exposure to lead, even at low concentrations, impairs both sensory and motor functions. The findings also point out that the vestibular system and brain stem structures which generate and control the PRN represent targets of the action of this heavy metal. Finally, the results indicate that the evaluation of the vestibulo-ocular-reflex can provide a test suited for the screening of the neurotoxic effects of lead even in the absence of clinical signs typical of lead intoxication.
Assuntos
Intoxicação do Sistema Nervoso por Chumbo/fisiopatologia , Chumbo/toxicidade , Neurotoxinas/toxicidade , Nistagmo Fisiológico/efeitos dos fármacos , Reflexo Vestíbulo-Ocular/efeitos dos fármacos , Núcleos Vestibulares/efeitos dos fármacos , Animais , Relação Dose-Resposta a Droga , Exposição Ambiental/efeitos adversos , Feminino , Intoxicação do Sistema Nervoso por Chumbo/patologia , Masculino , Nistagmo Fisiológico/fisiologia , Ratos , Ratos Long-Evans , Reflexo Vestíbulo-Ocular/fisiologia , Núcleos Vestibulares/patologia , Núcleos Vestibulares/fisiopatologia , Poluentes Químicos da Água/toxicidadeRESUMO
The disposition of propofol in the blood and brain of New Zealand rabbits was studied in three groups of six rabbits. One group received a single anaesthetic dose; a second group received a 1-h infusion; and a third group was studied after the rabbits were judged to have recovered from a 1-h infusion. There was a high concentration of propofol in the red blood cell fraction and in the brain, however, the red blood cell concentration largely exceeded the one found in the brain in all groups of animals. This is consistent with the high fat solubility of diisopropylphenol. The possible effects of propofol sequestered in red blood cells is discussed.
Assuntos
Anestésicos Intravenosos/farmacocinética , Encéfalo/metabolismo , Eritrócitos/metabolismo , Propofol/farmacocinética , Acidose/induzido quimicamente , Análise de Variância , Período de Recuperação da Anestesia , Anestésicos Intravenosos/administração & dosagem , Anestésicos Intravenosos/sangue , Anestésicos Intravenosos/líquido cefalorraquidiano , Animais , Cromatografia Líquida de Alta Pressão , Hipotensão/induzido quimicamente , Infusões Intravenosas , Injeções Intravenosas , Masculino , Fenol/sangue , Plasma/metabolismo , Propofol/administração & dosagem , Propofol/sangue , Propofol/líquido cefalorraquidiano , Coelhos , SolubilidadeRESUMO
The sensitivity and electrophysiological patterns of paroxysmal activity induced in different brain structures by topical application of penicillin-G were evaluated in the rat. Recordings were carried out in five groups of animals, in telencephalon, diencephalon, mesencephalon, rombencephalon and spinal cords. The following analysis were carried out: frequency distribution histograms, latency and time course duration of paroxysmal activity, duration and amplitude of epileptic bursts. The results obtained showed that the nervous structures tested with penicillin-G had a different epileptogenic sensitivity and response pattern which significantly changed along the cerebral cortex-spinal cord axis. The highest epileptic sensitivity was observed in somatosensory cortex (SI) at 500-600 microns depth; in the other cortical layers, a significant lenghtening in latency was observed. Among the other structures, the spinal cord seemed to be the most sensitive target to the epileptogenic action of penicillin-G, whereas in the remaining structures, sensitivity significantly decreased in rostro-caudal direction. As far as the features of the paroxysmal activity are concerned, significant differences among tested structures were observed. In particular, within the SI cortex, the main differences were represented by the gradual increase in burst frequency and voltage from the surface to the IVth layer and by their subsequent decrease in deeper layers (V-VI). In the diencephalon, the paroxysmal activity was similar to that observed in more superficial and deeper cortical layers even though epileptic bursts showed a lower amplitude. Mesencephalon and rombencephalon displayed a paroxysmal activity with a distinctive feature, characterized by long lasting bursts of low amplitude, although bulbar outbursts showed a shorter duration than the mesencephalic ones. In the spinal cord, the epileptiform activity displayed a different paroxysmal pattern, characterized by the longest duration and the highest amplitude. The different sensitivities of the investigated brain structures to penicillin-G and the characteristics of the induced paroxysmal activity have been extensively discussed.
Assuntos
Ventrículos Cerebrais/fisiopatologia , Convulsivantes/toxicidade , Epilepsias Parciais/fisiopatologia , Colículos Inferiores/fisiopatologia , Neurônios/fisiologia , Penicilina G/toxicidade , Córtex Somatossensorial/fisiopatologia , Medula Espinal/fisiopatologia , Teto do Mesencéfalo/fisiopatologia , Tálamo/fisiopatologia , Animais , Ventrículos Cerebrais/efeitos dos fármacos , Eletroencefalografia/efeitos dos fármacos , Epilepsias Parciais/induzido quimicamente , Colículos Inferiores/efeitos dos fármacos , Especificidade de Órgãos , Penicilina G/administração & dosagem , Ratos , Ratos Wistar , Córtex Somatossensorial/efeitos dos fármacos , Teto do Mesencéfalo/efeitos dos fármacos , Tálamo/efeitos dos fármacos , Ácido gama-Aminobutírico/fisiologiaRESUMO
beta-endorphin and cortisol were measured in cerebrospinal fluid (CSF) and plasma by radioimmunological method (RIA) in two groups of rabbits with spinal cord traumatic injuries at cervical and lumbar levels, respectively with and without concomitant spinal shock and arterial hypotension, and in a group of sham operated animals as controls. The two groups with spinal lesions displayed a significant beta-endorphin increase in CSF, whereas the cortisol level remained unchanged both in the spinal traumatized rabbits and in controls. Both the opioid and the cortisol concentration rose significantly in plasma in all three groups and in particular resulted significantly higher in the cervical traumatized group where spinal trauma was associated with spinal shock and hypotension. However, no significant difference was found when beta-endorphin concentrations in plasma were compared between the sham operated animals and the spinal lumbar traumatized animals without concomitant spinal shock. The results seem to suggest that the beta-endorphin increase in CSF is related to the nervous tissue lesion, while its increase in plasma, like that of cortisol, is due to surgery or other stress factors inherent in the experiment. This independent behaviour of beta-endorphin in plasma and in CSF suggests its different origin in these two compartments.
Assuntos
Nível de Alerta/fisiologia , Hidrocortisona/metabolismo , Traumatismos da Medula Espinal/fisiopatologia , beta-Endorfina/metabolismo , Animais , Feminino , Hipotensão/fisiopatologia , Masculino , Coelhos , Radioimunoensaio , Choque/fisiopatologia , Medula Espinal/irrigação sanguíneaRESUMO
It has been shown that tetanic stimulation of area 2 of the somatosensory cortex produces long-term potentiation in neurons in area 4gamma, and this has been suggested as the basis of learning new motor skills. The purpose of this study was to further elucidate the characteristics of this projection by the use of evoked potentials in area 4gamma elicited by intracortical microstimulation of area 2. The experiments were carried out in cats and the following results were obtained. 1) In six animals, stimulation of a given site in area 2 elicited evoked potentials in a restricted region of area 4gamma, the size of which ranged from 1 to 1.5 mm2. These responses were labeled "localized responses." The evoked potentials were recorded from the superficial layers of the cortex, and were positive monophasic in shape. 2) In 16 animals, stimulation of a given site in area 2 elicited a focal response that was surrounded by smaller positive and monophasic potentials of <50% amplitude that spread broadly over area 4gamma. These responses were labeled "graded responses." 3) The sites that produced focal evoked potentials in area 4gamma extended along the direction of the radial fibers in area 2. These sites were defined as most effective segments (MESs). 4) The receptive fields of neurons along the MES in area 2 were similar to those of neurons recorded at the foci of the evoked potentials in area 4gamma. The results demonstrate that some of the projections from area 2 to area 4gamma are highly specific and that the somatosensory and motor areas that are connected by these specific projections receive functionally related peripheral input. These results are discussed in relation to possible mechanisms underlying motor learning.
Assuntos
Potenciação de Longa Duração/fisiologia , Córtex Motor/fisiologia , Córtex Somatossensorial/fisiologia , Transmissão Sináptica/fisiologia , Animais , Mapeamento Encefálico , Gatos , Potencial Evocado Motor/fisiologia , Potenciais Somatossensoriais Evocados/fisiologia , Feminino , Membro Anterior/inervação , Membro Posterior/inervação , Articulações/inervação , Masculino , Destreza Motora/fisiologia , Vias Neurais/fisiologiaRESUMO
Long-term potentiation (LTP) was studied in the lateral vestibular nucleus (LVN-Deiters' nucleus) in guinea-pigs in vivo. Field potentials and extracellular single unit discharges were recorded in the LVN following electrical stimulation of the ipsilateral VIIIth nerve. High-frequency stimulation (HFS) of the VIIIth nerve fibres produced LTP of the monosynaptic component of the vestibular field potential. The LTP of the field potentials was paralleled by an increase of the evoked spike activity. Intranuclear administration of the NMDA antagonist MK-801 prevented LTP of the monosynaptic component of the vestibular field potentials and significantly suppressed the spontaneous firing of lateral vestibular neurones in a dose-dependent fashion. These results demonstrate that synapses between primary afferent fibres and second order LVN neurones undergo long lasting changes following HFS of the ipsilateral vestibular nerve.
Assuntos
Cobaias/fisiologia , Potenciação de Longa Duração , Núcleo Vestibular Lateral/fisiologia , Animais , Maleato de Dizocilpina/farmacologia , Estimulação Elétrica , Antagonistas de Aminoácidos Excitatórios/farmacologia , Feminino , Potenciação de Longa Duração/efeitos dos fármacos , Masculino , Núcleo Vestibular Lateral/efeitos dos fármacos , Nervo Vestibulococlear/fisiologiaRESUMO
Experiments performed in the guinea pig were aimed at evaluating the effect of electric or caloric stimulations of the vestibular afferents on the electrical activity of the jaw-closing and jaw-opening trigeminal motoneurons. Results showed that masseter and digastric motoneurons mainly responded to vestibular ampullar activation with excitatory responses, with latencies being shorter for contralateral than ipsilateral ampullar stimulation. Differences in latencies between the jaw-closing and jaw-opening trigeminal motoneurons were observed: the masseter motoneurons constantly responded about 2 msec earlier than the digastric motoneurons. These results suggest that the vestibular-trigeminal relationship is quite complex and uses multiple systems to connect the vestibular apparatus with the trigeminal motor nuclei. From the functional point of view, the vestibular-trigeminal relationship may play a role in the dynamic control of the jaw muscle tone during head movements.
Assuntos
Neurônios Motores/fisiologia , Gânglio Trigeminal/fisiologia , Vestíbulo do Labirinto/fisiologia , Animais , Estimulação Elétrica , Eletromiografia , Espaço Extracelular/fisiologia , Cobaias , Temperatura Alta , Músculos da Mastigação/inervação , Microeletrodos , Neurônios Aferentes/fisiologia , Gânglio Trigeminal/citologiaRESUMO
Recent findings have shown that olfactory stimulation by brief puffs of air odorized with amyl acetate induces several patterns of response in rabbit hypoglossal neurons. It has been argued that the functional role of the olfactory input may be the modulation of tongue muscular tone during the oral phase of digestion. In the present research, the peripheral effect of olfactory-hypoglossal modulation was analyzed. Both the spike traffic along the fibers of the hypoglossal nerve and the electromyographic activity of single tongue muscles (genioglossus, styloglossus, superior longitudinal and hyoglossus) were recorded before, during and after olfactory stimulation. Results showed that brief puffs of air odorized with amyl acetate induced a significant change in the efferent volleys along the hypoglossal nerve, as well as a substantial modulation of tongue muscle activity. Olfactory stimulation induced a significant increase in the spontaneous activity of both type I and type II genioglossal fibers; excitation followed by inhibition both in tonic and phasic styloglossal fibers; excitatory responses in tonic and phasic superior longitudinal fibers and short-lasting excitatory responses in the hyoglossal fibers. The diverse patterns of activation of the tested muscle and the significant differences between fibers, tonically or phasically controlled by the XIIth neurons, indicate that olfaction may be strongly involved in tongue reflex regulation. Different functional hypothesis are discussed about the role played by olfaction in the economy of tongue muscle activity.
Assuntos
Nervo Hipoglosso/fisiologia , Odorantes , Olfato/fisiologia , Língua/fisiologia , Potenciais de Ação/efeitos dos fármacos , Animais , Deglutição/fisiologia , Músculos da Mastigação/efeitos dos fármacos , Músculos da Mastigação/fisiologia , Contração Muscular/efeitos dos fármacos , Fibras Nervosas/fisiologia , Pentanóis/farmacologia , Coelhos , Língua/inervaçãoRESUMO
This report describes the changes of the spontaneous firing rate due to an acute non-toxic dose of phenytoin (PHT), a drug commonly used in antiepileptic therapy, in the pre-motor neurons involved in saccadic movement. The drug (500 mg/kg of a 10% PHT suspension in arabic gum) was orally administered, and plasma and brain levels were regularly evaluated (EMIT assay). Results show that PHT significantly modifies the spontaneous electrical activity of the pre-motor neurons localized in the paramedian pontine reticular formation by inducing excitation, inhibition, or a biphasic effect. PHT action was observed 10-15 min after drug administration, when plasma and brain concentrations were still very low. The oculomotor system neurons appear to be a more specific target to this drug in comparison to the cerebellum and the vestibular system. Since the PHT action was observed 1 hour after drug administration in the vestibular nuclei and the cerebellum, which are extensively connected with the oculomotor neurons, it is possible to hypothesize that PHT can affect the oculomotor neurons directly and, with longer latency, indirectly through the vestibular nuclei and the cerebellum.
Assuntos
Anticonvulsivantes/farmacologia , Neurônios Motores/fisiologia , Fenitoína/farmacologia , Formação Reticular/fisiologia , Animais , Eletrofisiologia , Potenciais da Membrana/efeitos dos fármacos , Neurônios Motores/efeitos dos fármacos , Ratos , Ratos WistarRESUMO
The protective effect of nimodipine, a calcium entry blocker, and MK-801, an excitatory amino acid antagonist, on the cortical electrobiogenesis of hypertensive SHR-Charles-River adult rats during a 90-s session of acute hypoxia, was tested either with a single treatment or with a therapeutic association. Pretreatment with nimodipine alone (0.1 mg kg-1, i.v.) was particularly effective in increasing the rat brain resistence to hypoxia when compared to the controls. MK-801 pretreatment alone (3 mg kg-1, subcutaneous), improved significantly the recovery of brain electrical activity from hypoxia, as it not only shortened the recovery time but also abolished the post-hypoxic burst activity. The combined pretreatment with both drugs, using the same doses, displayed a more powerful brain protective effect on the cortical electrobiogenesis than the single drug pretreatment, suggesting the existence of a synergy between nimodipine and MK-801.