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Query: UMLS:C0030193 (pain)
 261,466 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Neuronal responses to noxious stimulation applied on the skin of the limbs or of the tail were studied in the somatosensory cortex of rats under Fluothane/nitrous oxyde anesthesia. Among 694 neurons, 56 responded to noxious stimulation only and 35 to noxious as well as non-noxious stimulation. The receptive fields of these neurons were often larger than those of neurons recorded during the same penetration but unresponsive to noxious stimulation. They were able to encode stimulus parameters such as temperature of a hot water bath or size of the skin area stimulated. They were more frequently found in the deepest half of the cortex. These results suggest that the cerebral somatosensory cortex plays a role in pain mechanisms.
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PMID:Neuronal responses to noxious stimulation in rat somatosensory cortex. 707 Jul 11

The rabbit dorsal root ganglion is an important model of pain mechanisms in the human spine. A morphometric model of the normal rabbit dorsal root ganglion was constructed to provide quantitative comparisons with injured ganglia. Lumbar ganglia were studied under light and electron microscopy using simple stereologic methods. Neuronal diameter ranged from 18 to 85 microns, with 60% between 30 and 50 microns. Neurons constituted approximately 30% of dorsal root ganglion volume, and neuronal nuclei accounted for 14% of neuronal volume and 4% of dorsal root ganglion volume. Contributions from organelles to dorsal root ganglion volume were: mitochondria, 1.5%; rough endoplasmic reticulum, 9.4%; lysosomes, 0.2%; golgi, 0.5%. This morphometric model facilitates quantitative analysis of ganglia exposed to direct or indirect stimuli, providing important information on the structural changes that influence pain production.
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PMID:Morphometric model of normal rabbit dorsal root ganglia. 769 77

In anaesthetized rats, the influence of an acute inflammation (2-8 h duration) of the gastrocnemius-soleus (GS) muscle on the excitability of dorsal horn neurones was studied using a mapping procedure. One of the main effects of the myositis was that the neurone population responding to GS A-fibre input increased in size. The increase was most marked in the lateral segments L6-L3 which received little input from the GS muscle in control animals. Excitability testing showed a myositis-induced lowering in threshold, combined with an increase in latency, jitter and input convergence. This suggests that new oligo- or polysynaptic connections become functional under the influence of a myositis. Neuronal effects induced by C fibres in the GS nerves were not significantly altered by a myositis, but C fibre-induced activations from the peroneal and sural nerves increased in the lateral dorsal horn. The results show that an acute myositis leads to marked changes in the functional connectivity of the dorsal horn within a few hours. The main increase in excitability took place in the lateral dorsal horn, where many neurones acquired a new input from the GS muscle. This mechanism may be involved in the spread or referral of muscle pain.
Pain 1994 Oct
PMID:Functional reorganization in the rat dorsal horn during an experimental myositis. 785 91

Recent investigations have shown that non-steroidal antiinflammatory drugs (NSAIDs) may exert an antinociceptive effect when administered at or within the central nervous system (CNS). This might be due to the engagement of CNS substrates that support the analgesic effects of opiates, including the periaqueductal gray matter (PAG) and the rostral ventromedial medulla (RVM). The off- and on-cells of the RVM have been proposed to inhibit and facilitate, respectively, nociceptive transmission. Accordingly, upon heating of a rat's tail the tail-flick (TF) reflex occurs only after off-cells have decreased, and on-cells have increased, their activity. In the present study, i.v. administration (200 and 400 mg/kg) or PAG microinjection (25, 50, 100 and 250 micrograms) of dipyrone (metamizol) to lightly anesthetized rats caused a dose-related retardation of the heat-elicited off-cell pause, on-cell discharge and corresponding TF. Neuronal response and TF retained their mutual time relationship but shifted pari passu toward longer latencies. This antinociception was apparent already 5 min post-injection and reached a maximum in 50-60 min for i.v. administration and 30-35 min for PAG microinjection. These results confirm other authors' findings of the direct antinociceptive action of NSAIDs upon PAG, and provide the first evidence for a plausible involvement of RVM off- and on-cells in such antinociceptive effect.
Pain 1994 May
PMID:Putative role of medullary off- and on-cells in the antinociception produced by dipyrone (metamizol) administered systemically or microinjected into PAG. 809 May 17

We describe microelectrode recording and stimulation techniques to delineate the cellular boundaries and neural projections of stereotactic brain targets. These techniques have applications in the surgery for pain, movement disorders and in psychosurgery. Neuronal records from stereotactic operations including thalamotomy, pallidotomy, cingulotomy and anterior capsulotomy are discussed. These tools are used to distinguish gray matter from white matter, to obtain direct measures of cellular activity in the target, to identify the physiological properties and receptive fields of the subpopulation of neurons at the electrode tip and to avoid lesion making induced injury to adjacent structures. Microelectrode recording and stimulation techniques improve physiological localization and decrease the possibility of unwanted neurological complications with functional stereotactic procedures.
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PMID:Microelectrode monitoring of cortical and subcortical structures during stereotactic surgery. 874 79

Behavioral and electrophysiological methods were used to investigate the hyperalgesia and allodynia, and functional changes in lumbar spinal dorsal horn neurons, in a model of neuropathic pain (Selzer et al. 1990) involving ligation of one-third to one-half of one sciatic nerve in rats. One and 5 weeks following ligation, there was a significant reduction in hind limb withdrawal latency to noxious radiant heat on the operated side and, to a lesser degree, on the unoperated side. By 16 weeks, heat withdrawal latencies were reduced about equally (approximately 40%) on both sides. Withdrawal threshold to mechanical pressure was markedly reduced within 1 week on the operated side, and decreased in a time-dependent manner on the unoperated side. Heat withdrawal latency and von Frey withdrawal thresholds were not significantly affected in sham-operated rats. The same rats were tested in a paradigm measuring the isometric force of hind limb withdrawals elicited by graded noxious contact heat stimuli (38-52 degrees C, 5 sec). Withdrawal force increased monotonically with stimulus temperature starting at a threshold of approximately 40 degrees C. Stimulus-response functions were not significantly different between a sham-operated group and groups tested 5 (acute) and 16 weeks (chronic) after partial sciatic nerve ligation. Following behavioral testing, the animals were deeply anesthetized with pentobarbital sodium to allow electrophysiological recording of responses of single lumbar dorsal horn wide-dynamic range-type neurons to mechanical and noxious thermal stimulation of the hind paw. Recordings were made from 6 sham-operated rats (26 neurons ipsilateral and 31 contralateral to the operated leg), from 7 rats receiving partial sciatic nerve ligation 5 weeks previously (29 ipsilateral and 29 contralateral to ligation), and from 7 rats receiving partial sciatic ligation 16 weeks previously (18 ipsilateral, 29 contralateral to ligation). In several ligated rats we were unable to find heat-responsive neurons with cutaneous receptive fields on the hind paw ipsilateral to the ligation. For the neurons that were sensitive to heat, responses increased monotonically from a threshold of 40-42 degrees C. Neuronal stimulus-response functions for heat were not significantly different between ipsi- and contralateral (to operated) sides in the sham, 5-week or 16-week post-ligation groups, or between sham and 5- or 16-week post-ligation groups. Mechanical receptive field areas were not significantly different between ipsi- and contralateral sides in the sham and 5-week post-ligation groups, or between sham and 5-week post-ligation groups. However, receptive field areas were significantly larger in the 16-week post-ligation group (both ipsi- and contralateral to ligation) compared to sham and 5-week post-ligation groups. The results suggest that allodynia may be associated with a chronic enhancement of neuronal mechanosensitivity, but that the thermal hyperalgesia is not associated with enhanced neuronal responsiveness or force of withdrawal.
Pain 1996 Aug
PMID:Behavioral and electrophysiological assessment of hyperalgesia and changes in dorsal horn responses following partial sciatic nerve ligation in rats. 888 Aug 53

To determine which alpha 2-adrenergic receptor subtypes are present in primary afferent and sympathetic postganglionic neurons we have performed in situ hybridization and immunohistochemistry experiments on rat dorsal root and superior cervical ganglia. Reverse transcriptase polymerase chain reaction was used as a preliminary screen for the presence of mRNA encoding alpha 2-adrenergic subtypes in dorsal root and superior cervical ganglia; polymerase chain reaction primers amplified distinct regions of the rat alpha 2A-(RG20), alpha 2B-(RNG) and alpha 2C-(RG10) adrenergic receptor subtypes in mRNA extracted from lumbar dorsal root and superior cervical ganglia. To localize receptors to cell types in the ganglia, in situ hybridization was performed on cryosections of dorsal root and superior cervical ganglia with oligonucleotide probes designed to distinguish between mRNA encoding for alpha 2-adrenergic receptor subtypes. Immunohistochemistry was performed with a polyclonal antibody against the alpha 2A-adrenergic receptor subtype. Our results with reverse transcriptase polymerase chain reaction indicate that all three alpha 2-adrenergic receptor subtypes are expressed in dorsal root and superior cervical ganglia. Data from the in situ hybridization experiments indicated that the mRNA detected with the reverse transcriptase polymerase chain reaction was present in neuronal cell bodies, except for the mRNA encoding the alpha 2A-adrenergic receptor which was not detectable in dorsal root ganglia. The distribution of mRNA encoding alpha 2B- and alpha 2C-adrenergic receptor subtypes among dorsal root ganglion neurons and alpha 2A-, alpha 2B- and alpha 2C-adrenergic receptor subtypes among superior cervical ganglion neurons suggests that multiple adrenergic receptor subtypes are present in a single neuron. Neuronal cell bodies in both the dorsal root and superior cervical ganglion consistently demonstrated alpha 2A-adrenergic receptor-like immunoreactivity. The apparent co-expression of multiple alpha 2-adrenergic receptor subtypes in dorsal root and superior cervical ganglion neurons enables a single transmitter to produce a number of effects in the same neuron; which receptors are functionally active may vary with the presence of nerve injury, inflammation or other physiological and pathophysiological conditions.
Pain 1997 Jan
PMID:Alpha 2-adrenergic receptor subtypes in rat dorsal root and superior cervical ganglion neurons. 906 29

To investigate the spinal processing of cutaneous pruritic and algesic stimuli, single-unit recordings were made from wide-dynamic-range-type lumbar spinal dorsal horn neurons in pentobarbital-sodium-anesthetized rats. Neuronal responses were recorded to mechanical and noxious thermal stimuli, as well as to microinjection (1 microl) of histamine (0.01-10% = 9 x 10(-1)-9 x 10(-4) M), capsaicin (0.1% = 3.3 x 10(-3) M), or other algesic chemicals into skin within the receptive field via intracutaneously placed needles. Most (84%) of the 89 neurons responded to intracutaneous (i.c.) microinjection of histamine with a brief phasic discharge followed by an afterdischarge of variable (s to min) duration. Ten minutes after i.c. microinjection of histamine (but not NaCl), there was a significant increase in the mean area of the low-threshold (but not high-threshold) portion of unit mechanical receptive fields. However, responses to graded pressure stimuli were not significantly affected after histamine. Responses did not exhibit significant tachyphylaxis when histamine microinjections were repeated at 5- or 10-min intervals. Unit responses significantly increased in a dose-related manner to microinjection of histamine at concentrations ranging across 4 orders of magnitude. Within 30 s after i.c. microinjection of the H1 antagonist cetirizine, unit responses to i.c. histamine delivered at the same skin site were significantly attenuated. Unit responses to histamine, as well as to noxious thermal stimulation, were significantly reduced after systemic administration of morphine (3.5 mg/kg i.p.) in a naloxone-reversible manner. Application of a mechanical rub, scratch, or a noxious heat stimulus during the unit's ongoing response to i.c. histamine produced a brief and marked excitation, often followed by a period of reduced ongoing discharge. Unit responses to histamine were markedly suppressed by electrical stimulation in the midbrain periaqueductal gray. Most (79%) histamine-responsive units tested also responded to i.c. microinjection of capsaicin. After the initial microinjection of capsaicin, subsequent responses to histamine and capsaicin microinjections were significantly reduced. Units also responded to i.c. ethanol (capsaicin vehicle) in a dose-related manner, and showed tachyphylaxis to repeated i.c. ethanol at 80% but not at 8%. The mean response to 80% ethanol was significantly smaller than to 0.1% capsaicin. All units tested also responded to topical application of mustard oil (50%) and i.c. serotonin (30 microg). The results are discussed in terms of theories that attempt to reconcile psychophysical and clinical observations of pain and itch sensation.
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PMID:Responses of rat spinal dorsal horn neurons to intracutaneous microinjection of histamine, capsaicin, and other irritants. 916 72

Patients with primary headache syndromes often describe a distribution of pain that involves both frontal and occipital parts of the head. Such a distribution of pain does not respect the cutaneous sensory innervation of the head which would divide it into anterior (trigeminally innervated) and posterior (spinal nerve root innervated) regions. Studies of pain-producing intracranial structures, such as the superior sagittal sinus, have demonstrated that second order neurons as caudal as C2 are activated after either electrical or mechanical stimulation. For this study cats were anaesthetised with halothane (during surgery) and alpha-chloralose (60 mg/kg, i.p., then 20 mg/kg intravenous maintenance), paralysed (gallamine 6 mg/kg) and ventilated. The greater occipital nerve was isolated bilaterally and stimulated unilaterally using hook electrodes with stimuli of 100 V at 0.3 Hz. Metabolic activity in the caudal brain stem and upper cervical cord was measured using 2-deoxyglucose autoradiography and quantitative densitometry. Stimulation of the greater occipital nerve increased metabolic activity by 220% ipsilateral to stimulation and by a lesser amount contralaterally. Increases in metabolic activity were seen in the dorsal horn at the level of C1 and C2 as might be predicted from the cervical origin of the nerve. Neuronal activation appeared contiguous with the trigeminal nucleus caudalis and was in the same distribution as is seen when trigeminally-innervated structures are stimulated. These data suggest that the well recognised clinical phenomenon of pain at the front and back of the head and in the upper neck are likely to be a consequence of overlap of processing of nociceptive information at the level of the second order neurons.
Pain 1997 Oct
PMID:Stimulation of the greater occipital nerve increases metabolic activity in the trigeminal nucleus caudalis and cervical dorsal horn of the cat. 941 53

Neural proliferative processes are regarded as a contributing factor in chronic inflammatory diseases and chronic pain. To elucidate whether neural proliferations occur in tissues surrounding chronic anal fissures and in the normal anal canal, the nerve fibre density was examined with the pan-neural marker protein gene product 9.5 (PGP) and the neural proliferative marker growth-associated protein 43 (GAP) by immunohistochemistry. GAP-immunoreactive nerve fibres in the uninflamed anal canal were distributed region specifically. The proportion of GAP-immunoreactive nerves in relation to the PGP-immunoreactive innervation exhibited regional differences. In tissue sections of chronic anal fissures, a marked increase in the density of PGP- and GAP-immunoreactive nerve fibres was noted, and PGP- and GAP-immunopositive nerve fibres displayed a neuroma-like appearance. Image analysis revealed that PGP- and GAP-immunoreactive innervation represented an area fraction of 0.5% (0.49 +/- 0.052; mean and SEM) and 0.1% (0.11 +/- 0.013) in the normal anal canal, respectively. In tissue sections of chronic anal fissures, PGP- and GAP-immunostained nerve fibres represented area fractions of 1.3% (1.32 +/- 0.12) and 0.6% (0.56 +/- 0.15), respectively. The increases in PGP- and GAP-immunopositive area fractions were highly significant (P > 0.01). The mean ratio of GAP to PGP immunoreactivities was not significantly increased in chronic anal fissures. The increase in pan-neural innervation and neuronal GAP immunoreactivity in tissues of anal fissures may imply that neuronal proliferation is involved in the pathogenesis of anal fissures. Neuronal proliferations may also be responsible for pruritus and severe pain in chronic anal fissures.
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PMID:Elevated density and plasticity of nerve fibres in anal fissures. 968 64


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