Adrenal medullary transplants reduce formalin-evoked c-fos expression in the rat spinal cord

Effects of scopolamine treatment and consequent convulsion development in c‑fos expression in fed, fasted, and refed mice

Fasting, anticholinergics, and seizures affect c‑fos activation in the brain. Additionally, antimuscarinic treated fasted animals develop convulsion soon after re‑feeding. Therefore, we assessed whether c‑fos expression changes in fed, fasting, and refed animals and how scopolamine treatment affects these changes. We further assessed whether there is a change in c‑fos expression after convulsions. For this purpose, BALB/c mice fasted for 1, 3, 6, 12, 24 and 48 h periods were used. The animals were treated with saline or scopolamine. Half\r\nof the animals treated with saline or scopolamine were given food 20 min after injection. All animals were observed for development of convulsions for 30 min. At the end of this period, the brains of all animals were removed, and the percentage of c‑fos active cells in the hypothalamus was determined immunohistochemically. Convulsions occurred within 1‑48 h of fasting, after scopolamine treatment and re‑feeding. Compared to fed animals, c‑fos expression was not significantly changed in those undergoing different fasting periods, but significantly decreased after 12 h fasting. After animals were allowed to eat, c‑fos activation significantly increased in the 1, 3, 6 and 12 refed‑saline groups and decreased in the 48 refed‑saline group. Scopolamine treatment in 1‑24 h fasted animals increased c‑fos expression, but decreased in 48 h fasted animals. Whereas convulsion development in scopolamine‑treated 3, 6, 12 and 24 h refed animals suppressed c‑fos expression. These results demonstrate that re‑feeding and scopolamine treatment induces neuronal activity in the hypothalamus, while scopolamine induced convulsions after food intake suppressed the c‑fos activity.

Review of the history and current status of cell-transplant approaches for the management of neuropathic pain

Treatment of sensory neuropathies, whether inherited or caused by trauma, the progress of diabetes, or other disease states, are among the most difficult problems in modern clinical practice. Cell therapy to release antinociceptive agents near the injured spinal cord would be the logical next step in the development of treatment modalities. But few clinical trials, especially for chronic pain, have tested the transplant of cells or a cell line to treat human disease. The history of the research and development of useful cell-transplant-based approaches offers an understanding of the advantages and problems associated with these technologies, but as an adjuvant or replacement for current pharmacological treatments, cell therapy is a likely near future clinical tool for improved health care.

Expansion of formalin-evoked Fos-immunoreactivity in rats with a spinal cord injury

Peripheral tissue injury as well as spinal cord injury (SCI) may lead to sensitization of dorsal horn neurons and alterations in nociceptive processing. Thus, peripheral injuries experienced by SCI patients, even if not initially perceived, could result in a persistent and widespread activation of dorsal horn neurons and emerge as chronic pain with interventive repair or modest recovery from SCI. To visualize the spinal neuron response to peripheral tissue injury following complete SCI in rats, the neural transcription factor Fos was quantitated in the spinal cord. Two weeks following either a complete transection of the spinal cord at the level of T8 or a sham surgery (laminectomy), rats were injected with formalin into the left hind paw. Sham-operated rats demonstrated biphasic hind paw pain-related behavior following formalin injection, but transected rats displayed fewer behaviors in the second (tonic) phase. Stereological analysis of the sham group revealed that the extent of formalin-induced Fos expression was within the lumbar dorsal horn, with numerous Fos-like immunoreactive profiles in the ipsilateral dorsal horn and some contralateral immunoreactive profiles. In contrast, the level of Fos-like immunoreactivity in the transected group was significantly elevated and expanded in range compared to the sham group, with increases observed in the normal laminar distribution regions, as well as multi-segmentally through sacral levels and increases in the contralateral dorsal horn segments. The data demonstrate that widespread activation of spinal, especially dorsal horn, neurons following peripheral insult can occur in the injured spinal cord, despite reduced pain responsiveness, and suggests that exaggerated pain may emerge as spinal recovery or repair progresses.

Deafferentation Pain Resulting from Cervical Posterior Rhizotomy is Alleviated by Chromaffin Cell Transplants into the Rat Spinal Subarachnoid Space

OBJECTIVE

Deafferentation pain is common after posttraumatic brachial plexus avulsion in humans. Alleviation of such pain is poorly achieved by most therapeutic interventions; the only efficient neurosurgical procedure currently available is lesioning of the dorsal root entry zone. Previous work has demonstrated that adrenal medullary transplants into the lumbar spinal subarachnoid space can alleviate neuropathic pain behavior resulting from peripheral nerve or spinal cord injury. The purpose of this study was to evaluate the potential effects of adrenal medullary transplants on brachial plexus deafferentation pain.

METHODS

The cervical posterior rhizotomy model was selected as an upper segmental deafferentation model because it mimics the pathological situation after traumatic brachial plexus avulsion in humans. Animals underwent a right posterior cervical rhizotomy extending from C5 to T1 and received either adrenal medullary transplants or control striated muscle transplants into the cervical subarachnoid space. The clinical evolution was evaluated daily for self-directed behaviors indicative of ongoing pain, including onset, dermatomal extent, and severity.

RESULTS

In animals with muscle control transplants, self-directed behaviors appeared in 83.3% of the group, with a mean delay between rhizotomy and onset of self-directed behaviors of 8 days. In contrast, only 30.8% of the animals implanted with chromaffin cells exhibited any signs of self-directed behaviors, and these had a mean onset delay of 14 days.

CONCLUSION

The suppression of self-directed behaviors by adrenal medullary transplants is similar to that observed after dorsal root entry zone lesioning and suggests that this approach may offer a nonablative alternative in the management of deafferentation pain resulting from dorsal root avulsion.

Inhibition by the chromaffin cell-derived peptide serine-histogranin in the rat's dorsal horn

The heptadecapeptide histogranin, synthesized by adrenal chromaffin cells, is implicated in the analgesia produced by transplanting chromaffin cells into the spinal cord, including block of hyperalgesia mediated by NMDA-subtype glutamate receptors. To examine the neurophysiological basis for this analgesia, we applied the stable analog [Ser(1)]-histogranin (SHG) by iontophoresis near extracellularly recorded wide-dynamic range (WDR) neurons in anesthetized rats. When SHG was applied during peripheral electrical stimulation of A and C fibers at 0.1Hz, the C-fiber response was significantly inhibited but the A-fiber response was unaffected. SHG also opposed the NMDA-receptor-dependent post-tetanic facilitation (wind-up) of C-fiber responses produced by increasing the rate of peripheral afferent stimulation to 1Hz for 20s. To test whether block of NMDA-subtype receptors could be wholly or partially responsible for this suppression, SHG was applied during sequential pulsed iontophoresis of three agonists targeting distinct excitatory synaptic receptors: NMDA, kainate and substance P. All three excitatory effects were reversed by SHG; this reversal outlasted the 10-30min observation period when higher SHG doses were applied (>60nA). Histogranin therefore probably produces prolonged spinal analgesia by opposing the basal and potentiating synaptic effects of C-fibers on dorsal horn neurons. Actions besides or in addition to NMDA-receptor antagonism (e.g., agonism at inhibitory postsynaptic receptors or block of voltage-gated cation channels on C-fibers) are implied by the diversity of excitatory transmitters opposed by SHG.

Intrathecal grafting of porcine chromaffin cells reduces formalin-evoked c-Fos expression in the rat spinal cord

Chromaffin cells from the adrenal gland secrete a combination of neuroactive compounds including catecholamines, opioid peptides, and growth factors that have strong analgesic effects, especially when administered intrathecally. Preclinical studies of intrathecal implantation with xenogeneic bovine chromaffin cells in rats have provided conflicting data with regard to analgesic effects, and recent concern over risk of prion transmission has precluded their use in human clinical trials. We previously developed a new, safer source of adult adrenal chromaffin cells of porcine origin and demonstrated an in vivo antinociceptive effect in the formalin test, a rodent model of tonic pain. The goal of the present study was to confirm porcine chromaffin cell analgesic effects at the molecular level by evaluating neural activity as reflected by spinal cord c-Fos protein expression. To this end, the expression of c-Fos in response to intraplantar formalin injection was evaluated in animals following intrathecal grafting of 10(6) porcine or bovine chromaffin cells. For the two species, adrenal chromaffin cells significantly reduced the tonic phases of the formalin response. Similarly, c-Fos-like immunoreactive neurons were markedly reduced in the dorsal horns of animals that had received injections of xenogeneic chromaffin cells. This reduction was observed in both the superficial (I-II) and deep (V-VI) lamina of the dorsal horn. The present study demonstrates that both xenogeneic porcine and bovine chromaffin cells transplanted into the spinal subarachnoid space of the rat can suppress formalin-evoked c-Fos expression equally, in parallel with suppression of nociceptive behaviors in the tonic phase of the test. These findings confirm previous reports that adrenal chromaffin cells may produce antinociception by inhibiting activation of nociceptive neurons in the spinal dorsal horn. Taken together these results support the concept that porcine chromaffin cells may offer an alternative xenogeneic cell source for transplants delivering pain-reducing neuroactive substances.

NMDA antagonist peptide supplementation enhances pain alleviation by adrenal medullary transplants

Spinal transplantation of adrenal medullary chromaffin cells has been shown to decrease pain responses in several animal models. Improved potency may be possible by engineering cells to produce greater levels of naturally derived analgesics. As an initial screen for potential candidates, adrenal medullary transplants were evaluated in combination with exogenously administered neuropeptides in rodent pain models. Histogranin is a 15-amino acid peptide that exhibits NMDA receptor antagonist activity. The stable derivative [Ser1]histogranin (SHG) can attenuate pain symptoms in some animal models. The formalin model for neurogenic inflammatory pain and the chronic constriction injury (CCI) model for neuropathic pain were used to evaluate the combined effects of chromaffin cell transplantation and intrathecal (IT) SHG injections. Animals were implanted with either adrenal medullary or control striated muscle tissue in the spinal subarachnoid space. For evaluation of formalin responses, animals were pretreated with SHG (0.5, 1.0, 3.0 microg) followed by an intraplantar injection of formalin, and flinching responses were quantified. Pretreatment with SHG had no significant effect on flinching behavior in control animals at lower doses, with incomplete attenuation only at the highest dose. In contrast, 0.5 microg SHG significantly reduced flinching responses in animals with adrenal medullary transplants, and 1.0 microg nearly completely eliminated flinching in these animals in the tonic phase. For evaluation of effects on neuropathic pain, animals received transplants 1 week following CCI, and were tested for thermal and mechanical hyperalgesia and cold allodynia before and following SHG treatment. The addition of low doses of SHG nearly completely eliminated neuropathic pain symptoms in adrenal medullary transplanted animals, while in control transplanted animals only thermal hyperalgesia was attenuated, at the highest dose of SHG. These results suggest that SHG can augment adrenal medullary transplants, and the combination may result in improved effectiveness and range in the treatment of chronic pain syndromes.

Immunoisolated chromaffin cells implanted into the subarachnoid space of rats reduce cold allodynia in a model of neuropathic pain: a novel application of microencapsulation technology

Intrathecal transplants of adrenal medullary chromaffin cells relieve chronic pain by secreting catecholamines, opioids, and other neuroactive substances. Recently, macrocapsules with semipermeable membranes were used to isolate immunologically xenogenic chromaffin cells, but the poor viability in vivo of the encapsulated chromaffin cells limited the usefulness of this method. In this study, we used a novel method of encapsulation to increase the viability of chromaffin cells. We found that microencapsulated chromaffin cells that were implanted into the subarachnoid space of rats relieved cold allodynia in a model of neuropathic pain. Furthermore, microencapsulated chromaffin cells were morphologically normal and retained their functionality. These findings suggest that the intrathecal placement of microencapsulated chromaffin cells might be a useful method for treating chronic pain.

Cell therapy for neuropathic pain in spinal cord injuries

Cell therapy to treat neuropathic pain after spinal cord injury (SCI) is in its infancy. However, the development of cellular strategies that would replace or be used as an adjunct to existing pharmacological treatments for neuropathic pain have progressed tremendously over the past 20 years. The earliest cell therapy studies for pain relief tested adrenal chromaffin cells from rat or bovine sources, placed in the subarachnoid space, near the spinal cord pain- processing pathways. These grafts functioned as cellular minipumps, secreting a cocktail of antinociceptive agents around the spinal cord for peripheral nerve injury, inflammatory or arthritic pain. These initial animal, and later clinical, studies suggested that the spinal intrathecal space was a safe and accessible location for the placement of cell grafts. However, one major problem was the lack of a homogeneous, expandable cell source to supply the antinociceptive agents. Cell lines that can be reversibly immortalised are the next phase for the development of a practical, homogenous cell source. These technologies have been modelled with a variety of murine cell lines, derived from embryonic adrenal medulla or CNS brainstem, in which cells are transplanted, which downregulate their proliferative, oncogenic phenotype either before or after transplant. An alternative approach for existing human cell lines is the use of neural or adrenal precursors, in which the antinociceptive properties are induced by in vitro treatment with molecules that move the cells to an irreversible neural or chromaffin, and non-oncogenic, phenotype. Although such human cell lines are at an early stage of investigation, their clinical antinociceptive potential is significant given the daunting problem of difficult-to-treat neuropathic SCI pain.

Alterations of c-Fos mRNA expression in hypothalamic-pituitary-adrenal axis and various brain regions induced by intrathecal single and repeated substance P administrations in mice

The effect of substance P (Sub P) injected intrathecally (i.t.) on c-fos mRNA expression in various tissues was examined in the present study. We found that a single administration of Sub P (0.5 nM) caused an increase of the c-fos mRNA level in the hypothalamic-pituitary-adrenal (HPA) axis, hippocampus, and spinal cord. The time-course study showed that c-fos mRNA level was maximal at 10 min and began to decrease 30 min after the Sub P injection in all tissues, and the Sub P-induced increase of the c-fos mRNA level was returned to the control level 1 h after the injection. The kinetics of the c-fos mRNA expression in mice that were repeatedly injected with Sub P (every 30 min interval up to 4 times) were different in the HPA axis, hippocampus, and spinal cord. The increased c-fos mRNA level in the hypothalamus and the spinal cord induced by i.t. injected Sub P remained at a high level. In the pituitary gland, adrenal gland, and hippocampus, the increased level of c-fos mRNA expression gradually returned to the control level during the repeated substance P injections up to 4 times. Our results suggest that spinally injected Sub P-induced pain stress increases c-fos mRNA expression in the spinal cord, hippocampus, and HPA axis. In mice repeatedly injected with Sub P, the kinetics of c-fos mRNA appear to be different varied from tissue to tissue.

Grafts of immortalized chromaffin cells bio-engineered to improve met-enkephalin release also reduce formalin-evoked c-fos expression in rat spinal cord

Transplantation of adrenal medullary tissue for terminal cancer pain has been tested clinically, but this approach is not practical for routine use because of the shortage of organ donors and lack of tissue homogeneity. As a first alternative step, we have generated immortalized chromaffin cells over-expressing opioid peptides, namely met-enkephalin. Rat chromaffin cells have been genetically modified with vectors containing expression cassettes with either synthetic met-enkephalin or pro-enkephalin gene coding regions, fused with the nerve growth factor signal peptide for secretion. After stable transfection and differentiation in vitro, met-enkephalin and pro-enkephalin cells had higher met-enkephalin immunoreactivity and secreted met-enkephalin levels, compared to control cells containing the expression vector only. In the formalin hindpaw-injection model, 15 days after subarachnoid transplant of cells, grafts of met-enkephalin and pro-enkephalin cells significantly reduced the number of formalin-evoked c-fos immunoreactive spinal neurons in the spinal cord, compared to grafts of vector-alone chromaffin cells. The use of such expandable cell lines, for chronic spinal delivery of opiates, could offer an attractive and safe alternative strategy based on ex vivo gene therapy for the control of opioid-sensitive chronic pain.

Enhanced antinociception by nicotinic receptor agonist epibatidine and adrenal medullary transplants in the spinal subarachnoid space

Adrenal medullary transplants in the spinal subarachnoid space can reduce nociception, via the release of catecholamines and other analgesic substances, and this may be enhanced by stimulation of transplanted chromaffin cell surface nicotinic acetylcholine receptors (nAChRs). In addition, spinal nAChRs have been implicated in modulating nociception and can interact synergistically with alpha-adrenergic agents. Thus, enhanced antinociception by potent nAChR agonists such as frog skin derivative epibatidine in adrenal-transplanted animals could potentially occur via multiple mechanisms, including nicotinic-alpha-adrenergic synergy and stimulation of chromaffin cell nicotinic receptors. In order to test this, male Sprague-Dawley rats were implanted with intrathecal catheters and either adrenal medullary or control striated muscle transplants in the spinal subarachnoid space at the lumbar enlargement. Animals were tested for nociceptive responses before and after intrathecal injection of several doses of epibatidine using acute analgesiometric tests (tail flick, paw pressure) and the formalin test. After adrenal medullary, but not control, transplantation, nociceptive thresholds to acute noxious stimuli were slightly but consistently elevated, and phase 2 formalin responses decreased. Following intrathecal injection of epibatidine, acute nociceptive response latencies were modestly elevated and phase 2 formalin flinches modestly suppressed in control animals, but only at the highest dose test, with some attendant motor side-effects. In contrast, in adrenal medullary-transplanted animals, epibatidine elevated responses to acute noxious stimuli and markedly suppressed phase 2 formalin responses in a dose-related fashion. The enhanced antinociceptive effect following epibatidine was attenuated with either nAChR antagonist mecamylamine or alpha-adrenergic receptor antagonist phentolamine. The current results demonstrate that intrathecal injection of the nAChR ligand epibatidine can produce significant antinociception in adrenal-transplanted rats in both acute and tonic nociceptive tests and suggest that the use of nicotinic agents in combination with adrenal medullary transplantation could provide maximal therapeutic benefit by synergistically improving antinociception while avoiding the detrimental side-effects of these agents.

Comparison of c-Fos immunoreactivity in pancreatic beta cells and cells with neural crest, endoderm and mesoderm origin in rats

AIMS

Pancreatic beta cells are known to share many similarities with neuronal cells, but their origin remains controversial. It has been hypothesized that pancreatic beta cells are derived from neural crest cells. The aim of this study was to investigate the similarities between pancreatic beta cells and cells with neural crest, endoderm and mesoderm origin with respect to c-Fos immunoreactivity (c-Fos-ir), which has a role in important cellular processes including cellular proliferation, growth, differentiation and apoptosis.

METHODS

c-Fos-ir was analyzed by immunohistochemical methods in formaline-fixed, paraffin-embedded sections of rat pancreatic beta cells (BCs), in adrenal medullary chromaffin cells (CCs) that are derived from neural crest, in exocrine pancreatic acinar cells (ACs) that are derived from endoderm, and in adrenal cortex zona reticularis cells (RCs) that are derived from mesoderm.

RESULTS

The statistical comparisons revealed no significant differences between BCs and CCs with respect to c-Fos-ir (p>0.05). However, a highly significant difference (p<0.001) with respect to c-Fos-ir both between ACs and RCs, and between these two cell types and each of the two other cell types was noted.

CONCLUSIONS

As opposed to findings in cells without neural crest origin, the observed similarity between BCs and CCs with respect to c-Fos-ir, provides additional evidence for the similarity of these cells with cells derived from neural crest.

Comparison of c-Fos immunoreactivity in pancreatic beta cells and cells with neural crest origin in rats: an immunohistochemical study

Although a neural crest origin has been proposed for pancreatic beta cells, these cells are known to possess many similarities with neuronal cells. These similarities give rise to the hypothesis that undifferentiated neural crest cells can be transformed into beta cells. The objective of this study was to compare beta-cells and undifferentiated neural crest cells with respect to c-Fos immunoreactivity (c-Fos-IR), which plays a crucial role in certain cellular and biological processes and is used as a neuronal activity marker. For the purpose of the study, c-Fos-IR has been analysed by immunohistochemical methods in rat pancreatic beta cells, pulpal undifferentiated ectomesenchimal cells (PUECs) that are known to have a neural crest origin, and in small intestine fibroblasts which do not have a neural crest origin, in formaline-fixed, paraffin-embedded sections. There were no significant differences between beta-cells and PUECs in c-Fos-IR (p > 0.05) but there was a highly significant difference between fibroblasts and the other two type of cells ( p < 0.001). These results give rise to and support the suggestion that PUECs can be transformed into beta-cells.