Brain research
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To further understand how tactile information is carried in somatosensory cortex (S1) and the thalamus (VPL), and how neuronal plasticity after neuroprosthetic stimulation affects sensory encoding, we chronically implanted microelectrode arrays across hand areas in both S1 and VPL, where neuronal activities were simultaneously recorded during tactile stimulation on the finger pad of awake monkeys. Tactile information encoded in the firing rate of individual units (rate coding) or in the synchrony of unit pairs (synchrony coding) was quantitatively assessed within the information theoretic-framework. We found that tactile information encoded in VPL was higher than that encoded in S1 for both rate coding and synchrony coding; rate coding carried greater information than synchrony coding for the same recording area. ⋯ The percent change of mutual-information after stimulation was increased with closed-loop stimulation, but decreased with random stimulation. The underlying mechanisms during closed-loop stimulation might be spike-timing-dependent plasticity, while frequency-dependent synaptic plasticity might play a role in random stimulation. Our results suggest that VPL could be a promising target region for somatosensory stimulation with closed-loop brain-machine-interface applications.
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The trigeminovascular system has a pivotal role in the pathomechanism of migraine. The aim of the present study was to further develop existing models of migraine making them more suitable for testing the effects of compounds with presumed antimigraine activity in anaesthetised rats. Simultaneous recording of ongoing activity of spontaneously active neurons in the trigeminocervical complex as well as their discharges evoked by electrical stimulation of the dura mater via activation of A- and C-sensory fibres were carried out. ⋯ Nevertheless, inhibitory effect of propranolol and topiramate was evident when considering A- or C-fibre responses. Findings do not support the view that electrically evoked responses are useful for the measurement of trigeminal sensitization. It is proposed however, that inhibition of enhanced firing (immediate and/or delayed) evoked by inflammatory mediators as an endpoint have higher predictive validity regarding the clinical effectiveness of compounds.
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The α7 nicotinic acetylcholine (nACh) receptor expressed in microglia has a crucial role in neuroprotection. Simulation of α7 nACh receptor leads to increased expression of glutamate/aspartate transporter (GLAST), which in turn decreases synaptic glutamate levels. However, the upregulation of GLAST in cultured rat cortical microglia appears long after (over 18 h) stimulation of the α7 nACh receptor with nicotine. ⋯ Conversely, pretreatment with PD173074, an inhibitor of FGF receptor (FGFR) tyrosine kinase, significantly prevented the nicotine-induced expression of GLAST mRNA, its protein and (14)C-glutamate uptake. Reverse transcription polymerase chain reaction confirmed FGFR1 mRNA expression was confined to cultured cortical microglia. Together, the current findings demonstrate that the neuroprotective effect of activation of microglial α7 nACh receptors could be due to the expression of FGF-2, which in turn increases GLAST expression, thereby clearing glutamate from synapse and decreasing glutamate neurotransmission.
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The lateral parabrachial nucleus (LPBN) and the central nucleus of the amygdala (CeA) are important central areas for the control of sodium appetite. In the present study, we investigated the importance of the facilitatory mechanisms of the CeA on NaCl and water intake produced by the deactivation of LPBN inhibitory mechanisms. Male Holtzman rats (n=7-14) with stainless steel cannulas implanted bilaterally in the CeA and LPBN were used. ⋯ Euhydrated rats treated with muscimol (0.5 nmol/0.2 μl) into the LPBN also ingested 0.3M NaCl (19.1 ± 6.4 ml/4h) and water (8.8 ± 3.2 ml/4h). Muscimol (0.5 nmol/0.2 μl) into the CeA also abolished 0.3M NaCl (0.1 ± 0.04 ml/4h) and water intake (0.1 ± 0.02 ml/4h) in euhydrated treated with muscimol into the LPBN. The present results show that neuronal deactivation of the CeA abolishes NaCl intake produced by the blockade of LPBN inhibitory mechanisms, suggesting an interaction between facilitatory mechanisms of the CeA and inhibitory mechanisms of the LPBN in the control of NaCl intake.
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A virtual ball-tossing game called Cyberball has allowed the identification of neural structures involved in the processing of social exclusion by using neurocognitive methods. However, there is still an ongoing debate if structures involved are either pain- or exclusion-specific or part of a broader network. In electrophysiological Cyberball studies we have shown that the P3b component is sensitive to exclusion manipulations, possibly modulated by the probability of ball possession of the participant (event "self") or the presumed co-players (event "other"). ⋯ Questionnaire data indicate that social need threat is only induced when the expectancy for involvement in the ball-tossing game is violated. Similarly, the P3b amplitude of both "self" and "other" events was a correlate of expectancy violation. We conclude that both the subjective report of exclusion and the P3b effect induced in the Cyberball paradigm are primarily based on a cognitive process sensitive to expectancy violations, and that the P3b is not related to the activation of an exclusion-specific neural alarm system.