Catecholaminergic neurons in the nucleus tractus solitarii which send their axons to the midbrain periaqueductal gray express Fos protein after noxious stimulation of the stomach: a triple labeling study in the rat

Neuromodulation with percutaneous electrical nerve field stimulation is associated with reduction in signs and symptoms of opioid withdrawal: a multisite, retrospective assessment

BACKGROUND

Finding an effective, non-pharmacological approach to treat opioid withdrawal could remove some of the barriers associated with pharmacotherapy. The BRIDGE® is a noninvasive, percutaneous electrical nerve field stimulator developed to target pain.

OBJECTIVES

This pilot study aimed to determine (1) the effects of the BRIDGE on withdrawal scores during the induction phase of opioid withdrawal therapy, (2) the percentage of subjects who successfully transitioned to medication assisted therapy (MAT).

METHODS

Adult patients treated with the BRIDGE during medically supervised withdrawal were included in this open label, uncontrolled, and retrospective study. The clinical opioid withdrawal scale (COWS) scores were prospectively recorded at different intervals (20, 30, and 60 min) and analyzed retrospectively. A subset of patients had scores recorded 5-days post-BRIDGE. Those who returned to the clinic and received their first dose of maintenance medication were considered to be successfully transitioned.

RESULTS

In this cohort (n=73), 65% were male. The mean COWS score prior to BRIDGE placement was 20.1 (±6.1). Twenty minutes after BRIDGE placement, the mean score was reduced to 7.5 (±5.9) (62.7% reduction, p<0.001). The scores further decreased after 30 minutes 4.0 (±4.4) and 60 minutes 3.1 (±3.4) (84.6% reduction, p<0.001). No rescue medications were administered during this period. The mean withdrawal score on day 5 was 0.6 (97.1% reduction, p<0.001) (n=33). Overall, 64/73 patients (88.8%) successfully transitioned to MAT.

CONCLUSIONS

Neurostimulation with the BRIDGE is associated with a reduction in opioid withdrawal scores. This effect persisted during the induction period and allowed for effective transition to MAT.

Catecholaminergic neurons in medullary nuclei are among the post-synaptic targets of descending projections from infralimbic area 25 of the rat medial prefrontal cortex

The infralimbic (IL) 'visceromotor' area of the rat medial prefrontal cortex projects to strategic subcortical nuclei involved in autonomic functions. Central among these targets are the nucleus tractus solitarius (NTS) and the rostral ventrolateral medulla (rVLM). By combining tract-tracing using the anterograde tracer biotinylated dextran amine (BDA) with immunolabeling for tyrosine hydroxylase (TH; an enzyme marker of catecholaminergic neurons), a limited proportion of BDA-labeled IL axonal boutons in the NTS and rVLM was found to be closely associated with TH immunopositive (+) target structures. Such structural appositions were mainly located proximally over the labeled dendritic arbors of identified TH+ neurons. Quantitative ultrastructural examination revealed that in NTS, TH+ dendritic shafts comprised 7.0% of the overall post-synaptic target population innervated by BDA-labeled IL boutons, whereas TH+ dendritic spines represented 1.25% of targets. In rVLM, TH+ shafts represented 9.0% and TH+ spines 2.5% of IL targets. Labeled IL boutons established exclusively asymmetric Gray Type 1 (presumed excitatory) synaptic junctions. The results indicate that subpopulations of catecholaminergic neurons in the NTS and rVLM are among the spectrum of post-synaptic neurons monosynaptically innervated by descending 'excitatory' input from IL cortex. Such connectivity, albeit restricted, identifies the potential direct influence of IL cortex on the processing and distribution of cardiovascular, respiratory and related autonomic information by catecholaminergic neurons in the NTS and VLM of the rat.

Tyrosine hydroxylase is expressed in a subpopulation of small dorsal root ganglion neurons in the adult mouse

The expression of tyrosine hydroxylase (TH) was studied in adult mouse dorsal root ganglia (DRGs) and spinal cord by means of immunohistochemistry and in situ hybridization. TH immunoreactivity and TH mRNA were present in 10-15% of lumbar DRG neurons, in most cases being small/medium-sized. Only very few of these neurons coexpressed calcitonin gene-related peptide (CGRP), and only around 6% bound isolectin B4 (IB4). Dopamine beta-hydroxylase-positive(+) or aromatic amino acid decarboxylase (AADC)+ DRG neurons were rare and did not colocalize TH. No evidence for dopamine transporter expression was obtained. Axotomy of the sciatic nerve only showed a tendency towards reduction in the number of TH+ neurons. In the dorsal horn of the spinal cord, moderately dense and widespread TH+ nerve terminals were observed, mainly in the gray matter and they did not show a typical primary afferent pattern. Also, dorsal rhizotomy or peripheral axotomy had no apparent effect on TH-LI in the dorsal horn. In the skin, along with an abundant TH+ innervation of blood vessels and sweat gland acini, a number of fibers was observed in close relation to the skin surface, some even penetrating into the epithelium. These results demonstrate presence, in normal adult mouse DRGs, of a subpopulation of TH+, essentially CGRP- and IB4-negative small/medium-sized neurons. No evidence for transport of TH into central afferents was obtained, but the enzyme may be present in some sensory fibers in the skin. The fact that neither AADC nor the dopamine transporter could be visualized suggests of non-dopaminergic transmitter phenotype, but the levels of these two dopaminergic markers may be too low to be detected with the present methodology. A further alternative is that L-DOPA after release is extracellularly converted to dopamine.

Dorsal raphe nucleus and locus coeruleus neural networks and the elaboration of the sweet-substance-induced antinociception

In order to investigate the effects of monoaminergic neurons of the dorsal raphe nucleus (DRN) and locus coeruleus (LC) on the elaboration and control of sweet-substance-induced antinociception, male albino Wistar rats weighing 180-200 g received sucrose solution (250 g/L) for 7-14 days as their only source of liquid. After the chronic consumption of sucrose solution, each animal was pretreated with unilateral microinjection of ibotenic acid (1.0 microg/0.2 microL) in the DRN or in the LC. The tail withdrawal latencies of the rats in the tail-flick test were measured immediately before and 7 days after this treatment. The neurochemical lesion of locus coeruleus, but not of DRN neural networks with ibotenic acid, after the chronic intake of sweetened solution, decreased the sweet-substance-induced antinociception. These results indicate the involvement of noradrenaline-containing neurons of the LC in the sucrose-induced antinociception. We also consider the possibility of DRN serotonergic neurons exerting some inhibitory effect on the LC neural networks involved with the elaboration of the sweet-substance-induced antinociception.

Involvement of pre- and post-synaptic serotonergic receptors of dorsal raphe nucleus neural network in the control of the sweet-substance-induced analgesia in adult Rattus norvegicus (Rodentia, Muridae)

In order to investigate the effects of monoaminergic mechanisms of the dorsal raphe nucleus on the elaboration and control of sweet-substance-induced antinociception, male albino Wistar rats weighing 180-200 g received sucrose solution (250 g/L) for 14 days as their only source of liquid. After the chronic consumption of sucrose solution, each animal was pretreated with unilateral microinjection of methiothepin mesylate (5.0 microg/0.2 microL), or methysergide maleate (5.0 microg/0.2 microL) in the dorsal raphe nucleus. Each rat consumed an average of 15.6g sucrose/day. Their tail withdrawal latencies in the tail-flick test were measured immediately before and after this treatment. An analgesia index was calculated from the withdrawal latencies before and after the pharmacological treatment. The blockade of serotonergic receptor in the dorsal raphe nucleus with methysergide after the chronic intake of sucrose decreased the sweet-induced antinociception. However, microinjections of methiothepin in the dorsal raphe nucleus did not cause a similar effect on the tail-flick latencies after the chronic intake of sucrose solution, increasing the sweet-substance-induced analgesia. These results indicate the involvement of serotonin as a neurotransmitter in the sucrose-produced antinociception. Considering that the blockade of pre-synaptic serotonergic receptors of the neural networks of the dorsal raphe nucleus with methiothepin did not decrease the sweet-substance-induced antinociception, and the central blockade of post-synaptic serotonergic receptors decreased the sucrose-induced analgesia, the modulation of the release of serotonin in the neural substrate of the dorsal raphe nucleus seems to be crucial for the organization of this interesting antinociceptive process.

Differential induction of c-fos expression in brain nuclei by noxious and non-noxious colonic distension: role of afferent C-fibers and 5-HT3 receptors

Experimental animal models have been established to gain insight into the pathogenesis and the mechanisms of visceral hyperalgesia in the irritable bowel syndrome (IBS). However, data about the mechanisms and pathways involved in the induction of neuronal activity in forebrain and midbrain structures by a physiological GI stimulus, like colonic distension (CD), in the range from non-noxious to noxious intensities are scarce. Thus, the effect of proximal CD with non-noxious (10 mmHg) and noxious (40 and 70 mmHg) stimulus intensities on neuronal activity in brain nuclei, as assessed by c-fos expression, was established. In additional studies, the role of vagal and non-vagal afferent sensory C-fibers and 5-HT(3) receptors in the mediation of visceral nociception was investigated in this experimental model at noxious colonic distension (70 mmHg). At CD, the number of c-Fos like immunoreactivity (c-FLI)-positive neurons increased pressure-dependently in the nucleus of the solitary tract (NTS), rostral ventrolateral medulla (RVLM), nucleus cuneiformis (NC), periaqueductal gray (PAG), and the amygdala (AM). In the dorsomedial (DMH) and ventromedial nucleus (VMH) of the hypothalamus, as well as in the thalamus (TH), neuronal activity was also increased after CD, but independently of stimulus intensities. A decrease of the CD-induced c-fos expression after sensory vagal denervation by perivagal capsaicin treatment was only observed in brainstem nuclei (NTS and RVLM). In all other activated brain nuclei examined, the CD-related induction of c-fos expression was diminished only after systemic neonatal capsaicin treatment. In the NTS and RVLM, a trend of decrease of c-fos expression was also observed after systemic neonatal capsaicin treatment. In order to assess the role of the 5-HT(3) receptor in CD-induced neuronal activation of brain nuclei, animals were pretreated with the 5-HT(3) receptor antagonist granisetron (1250 microg/kg, i.p. within 18 h before CD). Pretreatment with granisetron significantly reduced the number of c-FLI-positive cells/section in the NTS by 40%, but had no significant effect on the CD-induced c-fos expression in other brain areas. The data suggest that distinct afferent pathways and transmitters are involved in the transmission of nociceptive information from the colon to the brain nuclei activated by proximal colonic distension. Activation of NTS neurons at such a condition seems to be partially mediated via capsaicin-sensitive vagal afferents and 5-HT(3) receptors. In contrast, activation of brain nuclei in the di- and telencephalon by nociceptive mechanical stimulation of the proximal colon, as assessed by c-fos expression, is partially mediated by capsaicin-sensitive, non-vagal afferents, and independent of neurotransmission via 5-HT(3) receptors. The modulation of CD-induced c-fos expression exclusively in the NTS by granisetron points to a role of 5-HT(3) receptor antagonists in the modulation of vago-vagal sensomotoric reflexes rather than an influence on forebrain nuclei involved in nociception.

Extracellular signal-regulated kinases1/2 in neurons of the dorsal motor nucleus of the vagus nerve and nucleus of the solitary tract are activated by noxious visceral stimulus in mice

Phosphorylated extracellular signal-regulated kinases1/2 (pERK1/2) -like immunoreactivity (LI) was enhanced in the neurons of the nucleus of the solitary tract (NTS) and dorsal motor nucleus of the vagus nerve (DMV) 8 min after an intraperitoneal injection of acetic acid in the mouse; the enhancement in pERK1/2-LI was suppressed after vagotomy. With immunofluorescent double labeling technique, the co-localization of acetic acid-induced pERK1/2 and tyrosine hydroxylase-LIs was observed in some of the NTS and DMV neurons. These results suggest that ERK1/2 signal-transducting pathway is involved in neuronal activities in NTS and DMV which are induced by vagus-conveyed nociceptive visceral information, and that some of these pERK1/2- immunoreactive neurons in NTS and DMV are catecholaminergic.

Projection sites of superficial and deep spinal dorsal horn cells in the nucleus tractus solitarii of the rat

By using anterograde transport of biotin dextran amine injected into the cervical spinal dorsal horn, we have shown that fibres from superficial and deep dorsal horn project to the nucleus tractus solitarii via two distinct pathways. Afferent fibres from the superficial lamina (I-III) were found to course in the dorsal funiculus and terminate bilaterally in the caudal zone of the nucleus tractus solitarii (NTS), mainly within the commissural subnucleus. In contrast, afferents from the deeper dorsal horn laminae (IV-V) were found to course in the dorsolateral fasciculus and terminate ipsilaterally, mostly in the lateral areas of the caudal nucleus tractus solitarii. Similar, but more extensive patterns of labelled fibres were produced by injections into the white matter of the dorsal funiculus and dorsolateral fasciculus, respectively. These observations suggest that the caudal NTS not only serves as a location of visceral afferent convergence and integration, but may also be a receptive area for monosynaptic projections from dorsal horn neurons receiving sensory afferent inputs. Such projections may represent pathways through which NTS neurons are influenced by nociceptive and non-nociceptive information from the dorsal horn and thereby can co-ordinate the appropriate autonomic response, including adjustments in cardiorespiratory reflex output.

Parallel circuits mediating distinct emotional coping reactions to different types of stress

All animals, including humans, react with distinct emotional coping strategies to different types of stress. Active coping strategies (e.g. confrontation, fight, escape) are evoked if the stressor is controllable or escapable. Passive coping strategies (e.g. quiescence, immobility, decreased responsiveness to the environment) are usually elicited if the stressor is inescapable and help to facilitate recovery and healing. Neural substrates mediating active versus passive emotional coping have been identified within distinct, longitudinal neuronal columns of the midbrain periaqueductal gray (PAG) region. Active coping is evoked by activation of either the dorsolateral or lateral columns of the PAG; whereas passive coping is triggered by activation of the ventrolateral PAG. Recent anatomical studies indicate that each PAG column receives a distinctive set of ascending (spinal and medullary) and descending (prefrontal cortical and hypothalamic) afferents. Consistent with the anatomy, functional studies using immediate early gene expression (c-fos) as a marker of neuronal activation have revealed that the preferential activation of a specific PAG column reflects (i) the type of emotional coping reaction triggered, and (ii) whether a physical or psychological stressor was used.

Gastric acid-evoked c-fos messenger RNA expression in rat brainstem is signaled by capsaicin-resistant vagal afferents

BACKGROUND & AIMS

Gastric acid is known to contribute to ulcer pain, but the mechanisms of gastric chemonociception are poorly understood. This study set out to investigate the pathways and mechanisms by which gastric acid challenge is signaled to the brain.

METHODS

Neuronal excitation in the rat brainstem and spinal cord after intragastric administration of HCl (0.35-0.7 mol/L) was examined by in situ hybridization autoradiography for the immediate early gene c-fos.

RESULTS

Gastric acid challenge did not induce c-fos transcription in the spinal cord but caused many neurons in the nucleus tractus solitarii and area postrema to express c-fos messenger RNA (mRNA). The HCl concentration-dependent excitation of medullary neurons was in part associated with behavioral manifestations of pain but not directly related to the acid-induced injury and contraction of the stomach. Subdiaphragmatic vagotomy suppressed the c-fos mRNA response to intragastric acid, and morphine inhibited it in a naloxone-reversible manner, whereas pretreatment of rats with capsaicin was without effect.

CONCLUSIONS

Gastric acid challenge is signaled to the brainstem, but not the spinal cord, through vagal afferents that are sensitive to acid but resistant to capsaicin. It is hypothesized that the gastric acid-induced c-fos transcription in the brainstem is related to gastric chemonociception.

Fos expression in serotonergic midbrain neurons projecting to the paraventricular nucleus of hypothalamus after noxious stimulation of the stomach: a triple labeling study in the rat

Horseradish peroxidase (HRP) was stereotaxically injected into the paraventricular nucleus of the hypothalamus (PVH) and visceral noxious stimulation was given by an administration of formalin into the stomach. The brain sections were subjected to HRP histochemistry and immunostained with Fos and serotonin antibodies. The periaqueductal gray (PAG) and dorsal raphe nucleus (DR) contained single-labeled (Fos, 5HT, HRP), double-labeled (Fos/HRP, Fos/5HT, HRP/5HT) and triple-labeled (HRP/Fos/5HT) neurons. Triple-labeled neurons were mainly observed in the DR and in discrete areas of the PAG ipsilateral to side of the HRP injection. These findings suggest that a population of serotonergic midbrain neurons receive nociceptive visceral information and project to the PVH.