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Query: UMLS:C0011570 (depression)
 172,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The responses of 302 neurons in the medial medullary reticular formation (MRF) to a variety of noxious and innocuous somatic stimuli were studied in anesthetized and awake rats. In addition, the effects of analgesic electrical stimulation in the mesencephalon (MES) on unit responses were examined. Tail shock was the most effective stimulus, exciting more than 80% of all units recorded. This stimulus was considered separately during data analysis, since it could not be classified as noxious or innocuous. Noxious somatic stimuli (including pinch, firm pressure, pin prick, and radiant heating of the tail above 45 degrees C were especially effective in eliciting discharge in a significant fraction of all cells in both awake (123/205) and anesthetized (45/97) animals. Nociceptive neurons could be classified as nociceptive specific (NS) or wide dynamic range (WDR) depending on their responses to all somatic stimuli tested. Nociceptive neurons showed no preferential anatomical distribution. Most neurons, including those responsive to noxious inputs, exhibited large, often bilateral receptive fields which frequently covered the tail, one or more limbs, and extensive areas of the body or head. Electrical stimulation within or adjacent to the mesencephalic periaqueductal gray matter depressed the spontaneous and evoked discharge of MRF neurons in both acute and chronic preparations. This inhibition showed a significant preference (p less than 0.001, chi-square statistic) for units that were excited by somatic and especially noxious stimuli. No units were facilitated by MES stimulation. In the awake rat, unit suppression closely followed the time course and level of MES-induced analgesia. Excitability data from the acute experiments suggest that this response inhibition may be the result of a direct action on MRF neurons. Anesthesia severely depressed the spontaneous discharge of MRF neurons as well as the activity evoked by innocuous somatic stimulation. Our data suggest that analgesia produced by MES stimulation is at least in part due to the depression of MRF unit activity, and support the hypothesis that MRF neurons play a critical role in the mediation of behavioral responses to noxious stimuli.
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PMID:Suppression of bulboreticular unit responses to noxious stimuli by analgesic mesencephalic stimulation. 667 18

Excitability and discharge behavior of neurons depends on the highly variable expression pattern of voltage-dependent potassium (Kv) channels throughout the nervous system. To learn more about distribution, development, and activity-dependent regulation of Kv channel subunit expression in the rodent hippocampus, we studied the protein expression of members of the Kv1 subfamily in mouse hippocampus in situ and in primary cultures. In adult hippocampus, Kv1 (1-6) channel alpha-subunits were present, whereas at postnatal day 2, none of these proteins could be detected in CA1-CA3 and dentate gyrus. Kv1.1 was the first channel to be observed at postnatal day 6. The delayed postnatal expression and most of the subcellular distribution observed in hippocampal sections were mimicked by cultured hippocampal neurons in which Kv channels appeared only after 10 days in vitro. This developmental upregulation was paralleled by a dramatic increase in total K(+) current, as well as an elevated GABA release in the presence of 4-aminopyridine. Thus, the developmental profile, subcellular localization, and functionality of Kv1 channels in primary culture of hippocampus closely resembles the in situ situation. Impairing secretion by clostridial neurotoxins or blocking activity by tetrodotoxin inhibited the expression of Kv1.1, Kv1.2, and Kv1.4, whereas the other Kv1 channels still appeared. This activity-dependent depression was only observed before the initial appearance of the respective channels and lost after they had been expressed. Our data show that hippocampal neurons in culture are a convenient model to study the developmental expression and regulation of Kv1 channels. The ontogenetic regulation and the activity-dependent expression of Kv1.1, Kv1.2, and Kv1.4 indicate that neuronal activity plays a crucial role for the development of the mature Kv channel pattern in hippocampal neurons.
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PMID:Expression of Kv1 potassium channels in mouse hippocampal primary cultures: development and activity-dependent regulation. 1068 88

Long-term depression (LTD) of synaptic transmission is reliably induced by low-frequency stimulation (LFS) of presynaptic nerve fibers in vitro. Many experiments suggest that LTD of basal transmission is not readily induced either in awake or anesthetized animals in vivo. In order to fill the gap between the in vitro cell studies and the in vivo situation, the effect of LFS on trigeminal somatosensory processing in healthy volunteers was investigated. Excitability of trigeminal sensory neurons was tested by applying the blink reflex (BR) elicited by electric stimulation of supraorbital nerve afferents. LFS of these afferents induced a significant reduction of the BR integral, a significant increase of the BR onset latency and a significant decrease of the stimulus intensity ratings. This depressive effect on the BR lasted for at least 1 h after the end of LFS. Thus, this study documented for the first time a long-term depression of trigeminal somatosensory processing in healthy volunteers.
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PMID:Long-term depression of the human blink reflex. 1244 87

REPETITIVE MECHANICAL STIMULATION CAUSES DEPRESSION OF EXCITABILITY IN ISOLATED PACINIAN CORPUSCLES: the mechanical threshold of the sense organ for producing nerve impulses increases progressively with time of repetitive stimulation. The effect is completely reversible; it can be elicited with repetitive stimuli of less than threshold strength. Within certain limits, the depression increases as a function of strength and frequency of the repetitive stimuli.
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PMID:After-effects of repetitive activity in a nerve ending. 1441 17

The exact pathogenesis of migraine remains to be determined. In particular there is increasing evidence for the neural basis of migraine. We now have a body of data supporting the concept of central neuronal hyperexcitability as a pivotal physiological disturbance predisposing to migraine. The reasons for increased neuronal excitability may be multifactorial. Most recently, abnormality of calcium channels has been introduced as a potential mechanism of interictal neuronal excitability. Mutant voltage gated P/Q type calcium channel genes likely influence presynaptic neurotransmitter release, possibly of excitatory amino-acid systems or inhibitory. It could therefore be hypothesised that genetic abnormalities result in a lowered threshold of response to trigger factors. There is also evidence from spectroscopic studies that magnesium is low in migraine. We currently conceive of a migraine attack as originating in the brain. Triggers of an attack initiate a depolarising neuroelectric and metabolic event likened to the spreading depression of Leao. This event activates the headache and associated features of the attack by mechanisms that remain to be determined, but appear to involve either peripheral trigeminovascular or brain stem pathways, or both. Excitability of cell membranes, perhaps in part genetically determined, is the brain's route of susceptibility to attacks. Factors that increase or decrease neuronal excitability constitute the threshold for triggering attacks.
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PMID:Pathophysiology of migraine. 1554 46

In this study, we investigated the effect of ascorbic acid (AA) administration on goat excitability due to transportation. Ten goats administered AA (p.o.) at 100 mg/kg of body weight before transportation served as the experimental group, and seven goats administered only 10 ml/kg of sterile water (p.o.) served as controls. Excitability scores were recorded for each goat; when weighed, before, immediately after, and 3 h after 8 h of transportation. A score of one to four was allocated to each goat; higher scores represent greater excitability. Immediately after transportation, excitability scores decreased significantly, especially those of control goats (p < 0.001). At 3 h posttransportation, the excitability scores of animals in the experimental group were not significantly (p > 0.05) different from their pre-transportation normal values, whereas those of control goats were significantly lower (p < 0.01). The correlation i.e. the relationship between excitability score values and percent excitability (percentage of goat with particular excitability score) for different excitability score group 3 h post-transportation was positive and highly significant (p < 0.001), in both experimental and control goats. Our results indicate that road transportation induces considerable stress (depression) in goats as evidenced by a lower excitability score posttransportation. Moreover, the administration of AA pretransportation facilitated the transition from a state of depression to excitation. In conclusion, AA administration to animals prior to transportation may ameliorate the depression often encountered after road transportation.
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PMID:Excitability scores of goats administered ascorbic acid and transported during hot-dry conditions. 1664 36

Different phases of motor skill learning appear to involve different physiological processes, with long-term potentiation (LTP) occurring at existing synapses in early and cortical reorganization involving synaptogenesis in later phases. Here, we test the evolution of skill learning-dependent changes in motor plasticity and excitability in six subjects trained to perform rapid thumb abductions over 5 d. Plasticity was examined using paired-associative stimulation (PAS) of the median nerve and motor cortex to induce LTP-like "PAS given with an interstimulus interval of 25 ms (PAS25)" or long-term depression (LTD)-like "PAS given with an interstimulus interval of 10 ms (PAS10)" plasticity. Excitability was tested by measuring recruitment of motor-evoked-potentials "input-output (IO) curve" and of short-latency intracortical inhibition (SICI curve), and sensorimotor organization (SMO). Task performance improved continuously over 5 d. After practice on day 1, the PAS25 effect reversed from facilitation to inhibition whereas the slope of the IO curve increased and the level of SICI decreased. These effects on IO curve and SICI were still present or even enhanced before the last practice on day 5, and were not changed by it. The effect of proprioceptive input from the trained muscle on SMO was also strengthened before practice on day 5. In contrast, PAS-induced plasticity was not influenced by motor practice on day 5, and had returned to prepractice values. The interference with PAS-induced plasticity suggests that the initial performance improvement relies on increasing the efficacy of existing synaptic connections. However, the long-lasting changes in the IO curve, SICI curve, and SMO suggest that continued practice enhances performance by changing Motor cortical organization. We hypothesize that new synaptic connections might have formed that allow LTP/LTD-susceptibility to be restored without reducing synaptic strength and performance skill.
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PMID:Differential modulation of motor cortical plasticity and excitability in early and late phases of human motor learning. 1797 47

Long-term potentiation (LTP) and long-term depression (LTD) are regulated by homeostatic control mechanisms to maintain synaptic strength in a physiological range. Although homeostatic metaplasticity has been demonstrated in the human motor cortex, little is known to which extent it operates in other cortical areas and how it links to behavior. Here we tested homeostatic interactions between two stimulation protocols -- paired associative stimulation (PAS) followed by peripheral high-frequency stimulation (pHFS) -- on excitability in the human somatosensory cortex and tactile spatial discrimination threshold. PAS employed repeated pairs of electrical stimulation of the right median nerve followed by focal transcranial magnetic stimulation of the left somatosensory cortex at an interstimulus interval of the individual N20 latency minus 15 msec or N20 minus 2.5 msec to induce LTD- or LTP-like plasticity, respectively [Wolters, A., Schmidt, A., Schramm, A., Zeller, D., Naumann, M., Kunesch, E., et al. Timing-dependent plasticity in human primary somatosensory cortex. Journal of Physiology, 565, 1039-1052, 2005]. pHFS always consisted of 20-Hz trains of electrical stimulation of the right median nerve. Excitability in the somatosensory cortex was assessed by median nerve somatosensory evoked cortical potential amplitudes. Tactile spatial discrimination was tested by the grating orientation task. PAS had no significant effect on excitability in the somatosensory cortex or on tactile discrimination. However, the direction of effects induced by subsequent pHFS varied with the preconditioning PAS protocol: After PAS(N20-15), excitability tended to increase and tactile spatial discrimination threshold decreased. After PAS(N20-2.5), excitability decreased and discrimination threshold tended to increase. These interactions demonstrate that homeostatic metaplasticity operates in the human somatosensory cortex, controlling both cortical excitability and somatosensory skill.
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PMID:Homeostatic metaplasticity in the human somatosensory cortex. 1830 76

Transcranial stimulation techniques have revealed homeostatic-like metaplasticity in the hand area of the human primary motor cortex (M1(HAND)) that controls stimulation-induced changes in corticospinal excitability. Here we combined two interventional protocols that induce long-term depression (LTD)-like or long-term potentiation (LTP)-like plasticity in left M1(HAND) through different afferents. We hypothesized that the left M1(HAND) would integrate LTP- and LTD-like plasticity in a homeostatic fashion. In ten healthy volunteers, low-intensity repetitive transcranial magnetic stimulation (rTMS) of the left dorsal premotor cortex (PMD) was first applied to produce an LTP-like increase (5 Hz rTMS) or LTD-like decrease (1 Hz rTMS) in corticospinal excitability in left M1(HAND) via premotor-to-motor inputs. Following PMD rTMS, paired-associative stimulation (PAS) was applied to the right median nerve and left M1(HAND) to induce spike-time-dependent plasticity in sensory-to-motor inputs to left M1(HAND). We adjusted the interstimulus interval to the N20 latency of the median nerve somatosensory-evoked cortical potential to produce an LTP-like increase (PAS(N20+2ms)) or an LTD-like decrease (PAS(N20-5ms)) in corticospinal excitability. The amplitude of motor-evoked potentials was recorded from intrinsic hand muscles to assess stimulation-induced changes in corticospinal excitability. Premotor-to-motor preconditioning triggered a homeostatic response to subsequent sensory-to-motor PAS. After facilitatory 5 Hz rTMS, "facilitatory" PAS(N20+2ms) suppressed corticospinal excitability. Likewise, "inhibitory" PAS(N20-5ms) facilitated corticospinal excitability after "inhibitory" 1 Hz rTMS. There was a negative linear relationship between the excitability changes induced by PMD rTMS and those elicited by subsequent PAS. Excitability changes were not paralleled by changes in performance during a finger-tapping task. These results provide evidence for a homeostatic response pattern in the human M1(HAND) that integrates acute plastic changes evoked through different "input channels."
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PMID:Inducing homeostatic-like plasticity in human motor cortex through converging corticocortical inputs. 1972 23

Sensory experience can elicit long-lasting plasticity of both single neurons and ensemble neural circuit response properties during embryonic development. To investigate their relationship, one must image functional responses of large neuronal populations simultaneously with single-cell resolution. In this protocol, we describe a noninvasive approach to assay functional plasticity of individual neurons and neuronal populations in vivo using targeted infusion of calcium-sensitive dyes, two-photon microscopy and synchronized visual stimuli presentations. This technique allows visualization of approximately 200 neurons while probing visual responses in the optic tectum of awake, immobilized Xenopus laevis tadpoles. The protocol includes visual training paradigms that elicit long-lasting potentiation or depression of functional responses, allowing investigations of population and single-neuron plasticity induced by natural sensory stimuli in the awake, intact, developing brain. Setup time for this protocol, including dye injection and chamber preparation, is approximately 2 h. Excitability probing experiments can then be performed for at least 3 h.
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PMID:In vivo single-cell excitability probing of neuronal ensembles in the intact and awake developing Xenopus brain. 2037 39


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