Limbic structures, including the hippocampus, are thought to be involved in pain though not much is known of their neuronal responses to noxious stimuli. Experiments were therefore performed in lightly anaesthetized rats to determine the effect of noxious heat stimuli on the excitability of dorsal hippocampal field CA1 pyramidal neurones. A prolonged and substantial depression of the CA1 population spike was produced by a brief but intense noxious stimulus applied to the tail. This depression was temperature-dependent and habituated to subsequent noxious stimuli applied more than 1 hr later. In other animals, a similar depression and habituation was also obtained with noxious heat stimuli applied to the left hind paw. However, following this habituation of the hind paw, a persistent depression of the CA1 population spike was seen if the tail was exposed to a noxious heat stimulus. The persistent depression was absent when noxious heat was applied in the presence of hippocampal theta rhythm. If, however, the hippocampal electroencephalographic ( EEG ) activity was in an irregular pattern at the time noxious heat was applied, a 4-6 Hz theta rhythm was produced along with the depression of the population spike. The latency and intensity of the reflex response was combined into a reflex-reaction score. There appeared to be a relationship between the reflex-reaction score and the duration of theta rhythm induced by different intensities of noxious heat stimuli but there was no habituation to these responses. The CA1 population spike evoked either by ipsilateral or contralateral CA3 stimulation was similarly depressed following a noxious stimulus. Concomitantly, the persistent depression and habituation of the commissural CA1 population spike was also accompanied by similar changes in the corresponding dendritic field excitatory postsynaptic potential ( EPSP ). However, the amplitude of the CA1 antidromic spike was increased in the majority of cases. These findings suggest that a presynaptically mediated decrease in synaptic transmission may account for the depression of the population spike and dendritic field EPSP. There is evidence to suggest that the noxious stimulus-induced persistent depression of CA1 pyramidal cell synaptic excitability is due to a cholinergic projection from the medial septal-vertical limb of the diagonal band of Broca complex ( MS-VLDBB ). Thus, atropine sulphate ( 40 mg/kg, i.p. ) prevented the persistent depression of the CA1 population spike to a noxious stimulus. It also antagonized the septal tetanus-evoked, cholinergic mediated facilitation of the CA1 commissural population spike but had no effect on the corresponding paired-pulse facilitation. Atropine, applied iontophoretically to the cell body region antagonized the iontophoretic acetylcholine-induced facilitation of the CA1 population spike but not its depression to a noxious stimulus. On the other hand, apical dendritic application of atropine antagonized iontophoretic acetylcholine and noxious stimulus-induced depression of the CA1 dendritic field EPSP. However, such iontophoretic application of atropine had no effect on dendritically applied gamma aminobutyric acid ( GABA )-induced depression of the CA1 dendritic field EPSP. These results support the notion that acetylcholine release in the dendritic region of CA1 neurones is involved in the depression of synaptic excitability of these neurones evoked by a noxious stimulus. / Pharmaceutical Sciences, Faculty of / Graduate

No description available.

Thesis (doctoral)--Lund University, 1992. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1992. / Added t.p. with thesis statement inserted.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 6 uppsatser.

Thesis (Ph. D.)--University of Chicago, Division of the Biological Sciences, Committee on Neurobiology. / Includes bibliographical references. Also available on the Internet.

Rapid and efficient escape behaviors in response to noxious sensory stimuli are essential for protection and survival. In Drosophila larvae, the class III (cIII) and class IV (cIV) dendritic arborization (da) neurons detect low-threshold mechanosensory and noxious stimuli, respectively. Their axons project to modality-specific locations in the neuropil, reminiscent of vertebrate dorsal horn organization. Despite extensive characterization of nociceptors across organisms, how noxious stimuli are transformed to the coordinated behaviors that protect animals from harm remains poorly understood. In larvae, noxious mechanical and thermal stimuli trigger an escape behavior consisting of sequential C-shape body bending followed by corkscrew-like rolling, and finally an increase in forward locomotion (escape crawl). The downstream circuitry controlling the sequential coordination of escape responses is largely unknown. This work identifies a population of interneurons in the nerve cord, Down-and-Back (DnB) neurons, that are activated by noxious heat, promote nociceptive behavior, and are required for robust escape responses to noxious stimuli. Activation of DnB neurons can trigger both rolling, and the initial C-shape body bend independent of rolling, revealing modularity in the initial nociceptive responses. Electron microscopic circuit reconstruction shows that DnBs receive direct input from nociceptive and mechanosensory neurons, are presynaptic to pre-motor circuits, and link indirectly to a population of command-like neurons (Goro) that control rolling. DnB activation promotes activity in Goro neurons, and coincident inactivation of Goro neurons prevents the rolling sequence but leaves intact body bending motor responses. Thus, activity from nociceptors to DnB interneurons coordinates modular elements of nociceptive escape behavior. The impact of DnB neurons may not be restricted to synaptic partners, as DnB presynaptic sites accumulate dense-core vesicles, suggesting aminergic or peptidergic signaling. Anatomical analyses show that DnB neurons receive spatially segregated input from cIII mechanosensory and cIV nociceptive neurons. However, DnB neurons do not seem to promote or be required for gentle-touch responses, suggesting a modulatory role for cIII input. Behavioral experiments suggest that cIII input presented prior to cIV input can enhance nociceptive behavior. Moreover, weak co-activation of DnB and cIII neurons can also enhance nociceptive responses, particularly C-shape bending. These results indicate that timing and level of cIII activation might determine its modulatory role. Taken together, these studies describe a novel nociceptive circuit, which integrates nociceptive and mechanosensory inputs, and controls modular motor pathways to promote robust escape behavior. Future work on this circuit could reveal neural mechanisms for sequence transitions, peptidergic modulation of nociception, and developmental mechanisms that control convergence of sensory afferents onto common synaptic partners.

The possible involvement of spinal metabotropic glutamate receptors (mGluRs) were examined in animal models of persistent and chronic pain. In Study 1, it was shown that spinal administration of relatively selective group I mGluR antagonists, or a selective group III mGluR agonist, but not a non-selective mGluR antagonist, slightly, but significantly reduced nociceptive scores in the rat formalin test Also, spinal administration of a non-selective mGluR agonist, or a selective group I mGluR agonist, but not a relatively selective group II agonist, enhanced formalin-induced nociception. The pro-nociceptive effects of these agents were reversed by a non-selective mGluR antagonist or by an N-methyl-D-aspartate receptor (NMDAR) antagonist. In Study 2, it was shown that intrathecal administration of two non-selective mGluR agonists or a selective group I mGluR agonist, but not a selective group II or group III mGluR agonist, produced spontaneous nociceptive behaviours, (SNBs) in rats. Also, the SNBs induced by these agents were reduced by a non-selective mGluR antagonist or by an NMDAR antagonist. In Study 3, it was shown that intrathecal administration of a selective group I mGluR agonist produced persistent mechanical allodynia, mechanical hyperalgesia and heat hyperalgesia in rats. In Study 4, it was shown that early, but not late intrathecal administration of a relatively selective group I mGluR antagonist reduced nociceptive behaviours, in a model of neuropathic pain. In Study 5, it was shown that intrathecal administration of a selective group I mGluR antagonist reduced mechanical allodynia and cold hyperalgesia, while a selective group II mGluR agonist and a selective group III mGluR agonist only reduced mechanical allodynia and cold hyperalgesia, respectively, in the neuropathic pain model. Results from these studies first suggest that spinal group I mGluRs may be more critically involved in the development of chronic nociceptive behaviours, compared to persis

Thesis (Ph.D.)--University of California, San Francisco, 2004. / Includes bibliographical references. Also available online.

No description available.