Beneficial effect of the nonselective opiate antagonist naloxone hydrochloride and the thyrotropin-releasing hormone (TRH) analog YM-14673 on long-term neurobehavioral outcome following experimental brain injury in the rat

Endogenous Opioid Dynorphin Is a Potential Link between Traumatic Brain Injury, Chronic Pain, and Substance Use Disorder

Traumatic brain injury (TBI) is a serious public health problem associated with numerous physical and neuropsychiatric comorbidities. Chronic pain is prevalent and interferes with post-injury functioning and quality of life, whereas substance use disorder (SUD) is the third most common neuropsychiatric diagnosis after TBI. Neither of these conditions has a clear mechanistic explanation based on the known pathophysiology of TBI. Dynorphin is an endogenous opioid neuropeptide that is significantly dysregulated after TBI. Both dynorphin and its primary receptor, the ĸ-opioid receptor (KOR), are implicated in the neuropathology of chronic pain and SUD. Here, we review the known roles of dynorphin and KORs in chronic pain and SUDs. We synthesize this information with our current understanding of TBI and highlight potential mechanistic parallels between and across conditions that suggest a role for dynorphin in long-term sequelae after TBI. In pain studies, dynorphin/KOR activation has either antinociceptive or pro-nociceptive effects, and there are similarities between the signaling pathways influenced by dynorphin and those underlying development of chronic pain. Moreover, the dynorphin/KOR system is considered a key regulator of the negative affective state that characterizes drug withdrawal and protracted abstinence in SUD, and molecular and neurochemical changes observed during the development of SUD are mirrored by the pathophysiology of TBI. We conclude by proposing hypotheses and directions for future research aimed at elucidating the potential role of dynorphin/KOR in chronic pain and/or SUD after TBI.

Do Toxic Synergies of Underlying Etiologies Predispose the Positive Association Between Traumatic Brain Injury and ADHD?

Objective: In their meta-analysis, Adeyemo et al. reported a strong association between mild traumatic brain injury (mTBI) and ADHD. However, less is understood about why such an association exists. Method: This commentary focuses on the underlying etiologies of both conditions to reveal potential toxic synergisms that could explain this association. Results: Alcohol and substance abuse are recognized comorbidities in both conditions. The author of this commentary has recently been the first to propose that chronic exposure to nitrous oxide (N₂O), an increasing environmental air pollutant and greenhouse gas, may contribute to the cognitive impairment seen in conditions such as ADHD and autism. The toxic synergisms from combined GABA-mimetics, such as ethanol, and nontoxic N₂O exposure have been previously elucidated and are further contextualized here. Conclusion: The conclusion of this commentary is that the toxicological interdependence of the underlying etiologies for mTBI and ADHD may help to explain their association as found in the meta-analysis conducted by Adeyemo et al. This commentary explores this dynamic further and, in so doing, underscores the need for additional research to validate these important conclusions.

Therapeutic approaches of trophic factors in animal models and in patients with spinal cord injury

Trophic factors are naturally produced by different tissues that participate in several functions such as the intercellular communication, in the development, stability, differentiation and regeneration at the cellular level. Specifically, in the case of spinal injuries, these factors can stimulate neuronal recovery. They are applied both in experimental models and in clinical trials in patients. The trophic factors analysed in this review include gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), growth hormone (GH), melatonin, oestrogens, the family of fibroblast growth factors (FGFs), the family of neurotrophins and the glial cell-derived neurotrophic factor (GDNF). There are some trophic (neurotrophic) factors that already been tested in patients with spinal cord injury (SCI), but only shown partial recovery effect. It is possible that, the administration of these trophic factors together with physical rehabilitation, act synergistically and, therefore, significantly improve the quality of life of patients with SCI.

Neurobiology of Opioid Use Disorder and Comorbid Traumatic Brain Injury

IMPORTANCE

Treating patients with opioid use disorder (OUD) and traumatic brain injury illustrates 6 neurobiological principles about the actions of 2 contrasting opioid analgesics, morphine and fentanyl, as well as pharmacotherapies for OUD, methadone, naltrexone, and buprenorphine.

OBSERVATIONS

This literature review focused on a patient with traumatic brain injury who developed OUD from chronic morphine analgesia. His treatment is described in a neurobiological framework of 6 opioid action principles.

CONCLUSIONS AND RELEVANCE

The 6 principles are (1) coactivation of neuronal and inflammatory immune receptors (Toll-like receptor 4), (2) 1 receptor activating cyclic adenosine monophosphate and β-arrestin second messenger systems, (3) convergence of opioid and adrenergic receptor types on 1 second messenger, (4) antagonist (eg, naltrexone)-induced receptor trafficking, (5) genetic μ-opioid receptor variants influencing analgesia and tolerance, and (6) cross-tolerance vs receptor antagonism as the basis of OUD pharmacotherapy with methadone or buprenorphine vs naltrexone.

Transcription factor REST negatively influences the protein kinase C-dependent up-regulation of human mu-opioid receptor gene transcription

Mu-opioid receptor expression increases during neurogenesis, regulates the survival of maturing neurons and is implicated in ischemia-induced neuronal death. The repressor element 1 silencing transcription factor (REST), a regulator of a subset of genes in differentiating and post-mitotic neurons, is involved in its transcriptional repression. Extracellular signaling molecules and mechanisms that control the human mu-opioid receptor (hMOR) gene transcription are not clearly understood. We examined the role of protein kinase C (PKC) on hMOR transcription in a model of neuronal cells and in the context of the potential influence of REST. In native SH-SY5Y neuroblastoma cells, PKC activation with phorbol 12-myristate 13-acetate (PMA, 16 nM, 24h) down-regulated hMOR transcription and concomitantly elevated the REST binding activity to repressor element 1 of the hMOR promoter. In contrast, PMA activated hMOR gene transcription when REST expression was knocked down by an antisense strategy or by retinoic acid-induced cell differentiation. PMA acts through a PKC-dependent pathway requiring downstream MAP kinases and the transcription factor AP-1. In a series of hMOR-luciferase promoter/reporter constructs transfected into SH-SY5Y cells and PC12 cells, PMA up-regulated hMOR transcription in PC12 cells lacking REST, and in SH-SY5Y cells either transfected with constructs deficient in the REST DNA binding element or when REST was down-regulated in retinoic acid-differentiated cells. These findings help explain how hMOR transcription is regulated and may clarify its contribution to epigenetic modifications and reprogramming of differentiated neuronal cells exposed to PKC-activating agents.

Endomorphins and morphine limit anoxia-reoxygenation-induced brain mitochondrial dysfunction in the mouse

The protection of brain mitochondria from oxidative stress is an important therapeutic strategy against ischemia-reperfusion injury and neurodegenerative disorders. Isolated brain mitochondria subjected to a 5 min period of anoxia followed by 5 min reoxygenation mirrored the effect of oxidative stress in the brain. The present study attempts to evaluate the protective effects of endomorphin 1 (EM1), endomorphin 2 (EM2), and morphine (Mor) in an in vitro mouse brain mitochondria anoxia-reoxygenation model. Endomorphins (EM1/2) and Mor were added to mitochondria prior to anoxia or reoxygenation. EM1/2 and Mor markedly improved mitochondrial respiratory activity with a decrease in state 4 and increases in state 3, respiratory control ratio (RCR) and the oxidative phosphorylation efficiency (ADP/O ratio), suggesting that they may play a protective role in mitochondria. These drugs inhibited alterations in mitochondrial membrane fluidity, lipoperoxidation, and cardiolipin (CL) release, which indicates protection of the mitochondrial membranes from oxidative damage. The protective effects of these drugs were concentration-dependent. Furthermore, these drugs blocked the enhanced release of cytochrome c (Cyt c), and consequently inhibited the cell apoptosis induced by the release of Cyt c. Our results suggest that EM1/2 and Mor effectively protect brain mitochondria against oxidative stresses induced by in vitro anoxia-reoxygenation and may play an important role in the prevention of deleterious effects during brain ischemia-reperfusion and neurodegenerative diseases.

Ischemic insults promote epigenetic reprogramming of mu opioid receptor expression in hippocampal neurons

Transient global ischemia is a neuronal insult that induces delayed, selective death of hippocampal CA1 pyramidal neurons. A mechanism underlying ischemia-induced cell death is activation of the gene silencing transcription factor REST (repressor element-1 silencing transcription factor)/NRSF (neuron-restrictive silencing factor) and REST-dependent suppression of the AMPA receptor subunit GluR2 in CA1 neurons destined to die. Here we show that REST regulates an additional gene target, OPRM1 (mu opioid receptor 1 or MOR-1). MORs are abundantly expressed by basket cells and other inhibitory interneurons of CA1. Global ischemia induces a marked decrease in MOR-1 mRNA and protein expression that is specific to the selectively vulnerable area CA1, as assessed by quantitative real-time RT-PCR, Western blotting, and ChIP. We further show that OPRM1 gene silencing is REST-dependent and occurs via epigenetic modifications. Ischemia promotes deacetylation of core histone proteins H3 and H4 and dimethylation of histone H3 at lysine-9 (H3-K9) over the MOR-1 promoter, an signature of epigenetic gene silencing. Acute knockdown of MOR-1 gene expression by administration of antisense oligodeoxynucleotides to hippocampal slices in vitro or injection of the MOR antagonist naloxone to rats in vivo affords protection against ischemia-induced death of CA1 pyramidal neurons. These findings implicate MORs in ischemia-induced death of CA1 pyramidal neurons and document epigenetic remodeling of expression of OPRM1 in CA1 inhibitory interneurons.

Experimental models of traumatic brain injury: do we really need to build a better mousetrap?

Approximately 4000 human beings experience a traumatic brain injury each day in the United States ranging in severity from mild to fatal. Improvements in initial management, surgical treatment, and neurointensive care have resulted in a better prognosis for traumatic brain injury patients but, to date, there is no available pharmaceutical treatment with proven efficacy, and prevention is the major protective strategy. Many patients are left with disabling changes in cognition, motor function, and personality. Over the past two decades, a number of experimental laboratories have attempted to develop novel and innovative ways to replicate, in animal models, the different aspects of this heterogenous clinical paradigm to better understand and treat patients after traumatic brain injury. Although several clinically-relevant but different experimental models have been developed to reproduce specific characteristics of human traumatic brain injury, its heterogeneity does not allow one single model to reproduce the entire spectrum of events that may occur. The use of these models has resulted in an increased understanding of the pathophysiology of traumatic brain injury, including changes in molecular and cellular pathways and neurobehavioral outcomes. This review provides an up-to-date and critical analysis of the existing models of traumatic brain injury with a view toward guiding and improving future research endeavors.

Current status of clinical trials for acute spinal cord injury

Acute spinal cord injury (ASCI) occurs as a result of physical disruption of spinal cord axons through the epicenter of injury leading to deficits in motor, sensory, and autonomic function. This is a debilitating neurological disorder common in young adults that often requires life-long therapy and rehabilitative care, placing a significant burden on our healthcare system. While no cure exists, research has identified various pharmacological compounds that specifically antagonize primary and secondary mechanisms contributing to the etiology of ASCI. Several compounds including methylprednisolone (MPSS), GM-1 ganglio-side, thyrotropin releasing hormone (TRH), nimodipine, and gacyclidine have been tested in prospective randomized clinical trials of ASCI. MPSS and GM-1 ganglioside have shown evidence of modest benefits. Clearly trials of improved neuroprotective agents are required. Promising potential therapies for ASCI include riluzole, minocycline, erythropoietin, and the fusogen polyethylene glycol, as well as mild hypothermia.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

Central nervous system effects of thyrotropin-releasing hormone and its analogues: opportunities and perspectives for drug discovery and development

Besides its well-known endocrine role in the thyroid system, thyrotropin-releasing hormone (L-pyroglutamyl-L-histidyl-L-prolinamide) has been long recognized as a modulatory neuropeptide. After a brief overview of the extrahypothalamic and receptor distribution, and of the neurophysiological, neuropharmacological and neurochemical effects of this tripeptide, this review discusses efforts devoted to enhance therapeutically beneficial central nervous system effects via structural modifications of the endogenous peptide. An enormous array of maladies affecting the brain and the spinal cord has been a potential target for therapeutic interventions involving agents derived from thyrotropin-releasing hormone as a molecular lead. Successful development of several centrally active analogues and recent accounts of efforts aimed at improving metabolic stability, selectivity and bioavailability are highlighted.

New treatments for concussion: the next millennium beckons

As increased understanding of the pathophysiology of mild traumatic brain injury and concussion develops, so the scientific rationale for interventional pharmacological therapy becomes paramount. A number of agents have been postulated or have been the subject of anecdotal noncontrolled trials. This paper reviews the published evidence in this regard. To date no effective pharmacological therapy exists that satisfies Class I evidence-based medicine criteria.

Role of altered cyclooxygenase metabolism in impaired cerebrovasodilation to nociceptin/orphanin FQ following brain injury

This study was designed to determine the role of altered cyclooxygenase metabolism in impaired pial artery dilation to the newly described opioid, nociceptin orphanin FQ (NOC/oFQ), following fluid percussion brain injury (FPI) in newborn pigs equipped with a closed cranial window. Recent studies show that NOC/oFQ contributes to oxygen free radical generation observed post FPI in a cyclooxygenase dependent manner. FPI was produced by using a pendulum to strike a piston on a saline filled cylinder that was fluid coupled to the brain via a hollow screw inserted through the cranium. NOC/oFQ (10(-8), 10(-6) M) modestly increased cerebrospinal fluid (CSF) 6-keto-PGF(1alpha), and thromboxane B(2) (TXB(2)), the stable breakdown products of PGI(2) and TXA(2), in sham animals (1148 +/- 83 to 1681 +/- 114 and 308 +/- 16 to 424 +/- 21 pg/ml for control and 10(-6) M NOC/oFQ 6-keto-PGF(1alpha), and TXB(2), respectively). In 1-h post FPI animals, basal levels of 6-keto-PGF(1alpha), and TXB(2) were elevated. NOC/oFQ stimulated release of 6-keto-PGF(1alpha), was blocked while such release of TXB(2) was enhanced (720 +/- 63 to 1446 +/- 117 pg/ml for control and 10(-6) M NOC/oFQ CSF TXB(2)). NOC/oFQ (10(-8), 10(-6) M) induced pial artery dilation that was reversed to vasoconstriction by FPI while the cyclooxygenase inhibitor indomethacin (5 mg/kg, intravenous) partially restored such vascular responses (8 +/- 1 and 15 +/- 1 vs. -7 +/- 1 and -12 +/- 1 vs. 7 +/- 1 and 12 +/- 1% for 10(-8), 10(-6) M NOC/oFQ in sham, FPI and FPI-Indo pretreated animals). Similar observations were made in FPI animals pretreated with the thromboxane receptor antagonist SQ 29,548 or the free radical scavenger polyethylene glycol superoxide dismutase and catalase. These data indicate that altered NOC/oFQ induced cyclooxygenase metabolism contributes to impairment of dilation to this opioid following FPI.

Role of nociceptin/orphanin FQ in age-dependent cerebral hemodynamic effects of brain injury

This study was designed to compare the role of the newly described endogenous opioid nociceptin/orphanin FQ (NOC/oFQ) in the reductions of cerebral blood flow (CBF) and pial artery diameter observed following fluid percussion brain injury (FPI) in chloralose anesthetized newborn and juvenile pigs as a function of time postinsult. FPI elevated CSF NOC/oFQ concentration from 70 +/- 3 to 444 +/- 51 within 1 h and to 1,931 +/- 112 pg/mL (n = 7) within 8 h, whereas concentrations returned to control value within 168 h in the newborn. In contrast, FPI elevated CSF NOC/oFQ from 77 +/- 4 to 202 +/- 16 pg/mL (n = 7) within 1 h, while values returned to control value within 8 h in the juvenile. Topical NOC/oFQ (10(-8), 10(-6) M) induced vasodilation was reversed to vasoconstriction by FPI in the newborn while such responses were only attenuated in the juvenile at 1 h post insult (control, 9 +/- 1 and 16 +/- 1%; FPI newborn, -8 +/- 1 and -14 +/- 1%; FPI juvenile, 2 +/- 1 and 5 +/- 1%, n = 7). Such altered dilation returned to control value within 168 h in newborns and 8 h in juveniles. Blood flow in the cerebrum was reduced from 57 +/- 4 to 23 +/- 3 mL x min(-1) x 100 g(-1) (n = 7) within 1 h and returned to control value with 168 h post FPI in newborns. In animals pretreated with [F/G] NOC/oFQ (1-13) NH2 (1 mg/kg, i.v.), a NOC/oFQ antagonist, however, CBF only fell to 39 +/- 4 mL x min(-1) x 100 g(-1) (n = 7) at 1 h post insult in newborns. In contrast, CBF was only reduced from 57 +/- 6 to 32 +/- 2 in untreated and to 39 +/- 3 mL/min(-1) x 100 g(-1) (n = 7) in treated juveniles within 1 h post FPI. Similar observations for reductions in pial artery diameter were made in untreated and treated newborns and juveniles. These data suggest that an elevated CSF NOC/oFQ concentration and altered vascular responsiveness to this opioid contribute to reductions in CBF and pial artery diameter observed following FPI. Because such NOC/oFQ changes were greater in newborns versus juveniles, these data further suggest that NOC/oFQ contributes to age-related cerebral hemodynamic differences in the effects of FPI.

Role of NOC/oFQ in impaired opioid-induced pial artery dilation following brain injury

Previous studies in piglets show that opioid-induced pial artery dilation was impaired following fluid percussion brain injury (FPI). This study was designed to determine the role of the newly described opioid nociceptin orphanin FQ (NOC/oFQ) in such impaired dilation to other opioids after FPI. CSF NOC/oFQ concentration was elevated from 70+/-6 to 444+/-56 pg/ml ( approximately 10(-10) M) within 1 h of FPI. Coadministration of NOC/oFQ (10(-10) M) with methionine enkephalin (10(-10), 10(-8), 10(-6) M) attenuated pial dilation induced by this opioid (7+/-1, 13+/-2, and 19+/-2 vs. 2+/-1, 6+/-1, and 7+/-2%) under non-brain injury conditions. Similar inhibition by NOC/oFQ was observed for leucine enkephalin and dynorphin. Methionine enkephalin (10(-10), 10(-8), 10(-6) M)-induced pial artery dilation was also inhibited within 1 h of FPI, but such responses were partially restored in animals pretreated with the NOC/oFQ receptor antagonist [F/G] NOC/oFQ (1-13) NH(2) (10(-6) M) (8+/-1, 14+/-1, and 21+/-1 vs. 1+/-1, 3+/-1, and 4+/-1 vs. 7+/-1, 11+/-1, and 17+/-1% for sham control, FPI and FPI pretreated with the NOC/oFQ receptor antagonist). Leucine enkephalin and dynorphin-induced pial artery dilation were similarly altered by FPI and partially restored by [F/G] NOC/oFQ (1-13) NH(2). These data indicate that the NOC/oFQ released by FPI contributes to impaired dilation to other opioids observed following this insult.

The rotating pole test: evaluation of its effectiveness in assessing functional motor deficits following experimental head injury in the rat

Neurological motor dysfunction is often an integral component of the neurological sequelae of traumatic brain injury (TBI). In experimental TBI, neurological motor testing is an outcome measure used to monitor severity of injury, and the response to treatment. This study evaluates the effectiveness and sensitivity of the rotating pole test (RP) to characterize and evaluate the temporal course of motor deficits after lateral fluid percussion (FP) injury to the rat brain. The results are compared with the previously characterized and widely used composite neuroscore of motor function (NS). The animals were required to walk across an elevated wooden pole that was either stationary or rotating to left or right directions at different speeds. Male Wistar rats underwent lateral FP injury of moderate severity (mean 2.4 atm, n = 9) or sham surgery (n = 9), and were tested at 48 h and 7 days post-injury using the NS and RP. The results of the NS directly correlated to the results of the RP, showing a significant injury effect at both 48 h and 7 days. This is the first study to show that the RP-test detects neurological motor deficits after lateral FP injury, and suggests that this technique is a reliable behavioral tool for evaluating neurological motor function in the acute period after experimental TBI.

Dynorphin A (1-13) neurotoxicity in vitro: opioid and non-opioid mechanisms in mouse spinal cord neurons

Dynorphin A is an endogenous opioid peptide that preferentially activates kappa-opioid receptors and is antinociceptive at physiological concentrations. Levels of dynorphin A and a major metabolite, dynorphin A (1-13), increase significantly following spinal cord trauma and reportedly contribute to neurodegeneration associated with secondary injury. Interestingly, both kappa-opioid and N-methyl-D-aspartate (NMDA) receptor antagonists can modulate dynorphin toxicity, suggesting that dynorphin is acting (directly or indirectly) through kappa-opioid and/or NMDA receptor types. Despite these findings, few studies have systematically explored dynorphin toxicity at the cellular level in defined populations of neurons coexpressing kappa-opioid and NMDA receptors. To address this question, we isolated populations of neurons enriched in both kappa-opioid and NMDA receptors from embryonic mouse spinal cord and examined the effects of dynorphin A (1-13) on intracellular calcium concentration ([Ca2+]i) and neuronal survival in vitro. Time-lapse photography was used to repeatedly follow the same neurons before and during experimental treatments. At micromolar concentrations, dynorphin A (1-13) elevated [Ca2+]i and caused a significant loss of neurons. The excitotoxic effects were prevented by MK-801 (Dizocilpine) (10 microM), 2-amino-5-phosphopentanoic acid (100 microM), or 7-chlorokynurenic acid (100 microM)--suggesting that dynorphin A (1-13) was acting (directly or indirectly) through NMDA receptors. In contrast, cotreatment with (-)-naloxone (3 microM), or the more selective kappa-opioid receptor antagonist nor-binaltorphimine (3 microM), exacerbated dynorphin A (1-13)-induced neuronal loss; however, cell losses were not enhanced by the inactive stereoisomer (+)-naloxone (3 microM). Neuronal losses were not seen with exposure to the opioid antagonists alone (10 microM). Thus, opioid receptor blockade significantly increased toxicity, but only in the presence of excitotoxic levels of dynorphin. This provided indirect evidence that dynorphin also stimulates kappa-opioid receptors and suggests that kappa receptor activation may be moderately neuroprotective in the presence of an excitotoxic insult. Our findings suggest that dynorphin A (1-13) can have paradoxical effects on neuronal viability through both opioid and non-opioid (glutamatergic) receptor-mediated actions. Therefore, dynorphin A potentially modulates secondary neurodegeneration in the spinal cord through complex interactions involving multiple receptors and signaling pathways.

Novel TRH analog improves motor and cognitive recovery after traumatic brain injury in rodents

Thyrotropin-releasing hormone (TRH) and certain TRH analogs show substantial neuroprotective effects in experimental brain or spinal cord trauma but also have other physiological actions (autonomic, analeptic, and endocrine) that may be undesirable for the treatment of neurotrauma in humans. We developed a novel TRH analog (2-ARA-53a), with substitutions at the NH(2)-terminus and imidazole ring, that preserves the neuroprotective action of TRH-like compounds while decreasing or eliminating their autonomic, analeptic, and endocrine effects. Rats administered 2-ARA-53a (1.0 mg/kg, n = 17) intravenously 30 min after lateral fluid percussion brain injury showed marked improvement in motor recovery compared with vehicle-treated controls (n = 14). Treatment of mice subjected to moderate controlled cortical impact brain injury, at the same dose and time after trauma (n = 8), improved both motor recovery and cognitive performance in a water maze place learning task compared with vehicle-treated controls (n = 8). In injured rats, no autonomic or analeptic effects were observed with this compound, and endocrine effects were significantly reduced with 2-ARA-53a, in contrast to those found with a typical NH(2)-terminal-substituted TRH analog (YM-14673). These findings demonstrate that the neuroprotective effects of TRH-related compounds can be dissociated from their other major physiological actions and suggest a potential role for dual-substituted TRH analogs in the treatment of clinical neurotrauma.

Cerebral hemodynamics after traumatic brain injury of immature brain

These studies were designed to characterize the cerebral hemodynamic effects of fluid percussion brain injury (FPI) in the newborn pig equipped with a closed cranial window. Reductions in cerebral blood flow, pial artery diameter, and cerebral oxygenation following FPI were greater in newborn (1-3 days old) vs. juvenile (3-4 weeks old) pigs, suggesting that newborns were exquisitely sensitive to brain injury. Additionally, in piglets, there was decremented dilation to nitric oxide, cGMP, and cAMP dependent stimuli following FPI. The membrane potential of vascular muscle is an important contributor to vascular tone and the activity of K+ channels is an important regulator of membrane potential. Recent studies indicate that altered dilator responsiveness and cerebral hemodynamic control following FPI results from impaired K+ ATP sensitive (KATP) and calcium sensitive (Kca+2) channel function. Impaired KATP channel function results, at least in part, from protein kinase C activation by the peptide endothelin-1. These observations indicate that the effects of brain injury on cerebral hemodynamics in the newborn are multifaceted and multifactorial.

Fentanyl infusion preserves cerebral blood flow during decreased arterial blood pressure after traumatic brain injury in cats

Hypotension after traumatic brain injury (TBI) has been associated with significant reductions in cerebral blood flow (CBF) in experimental animals. In humans, posttraumatic hypotension is associated with significantly worsened outcome, possibly because of cerebral hypoperfusion. The existence of opioid receptor-mediated cerebrovascular dilatory effects in humans has been theorized. We studied the systemic and cerebral vascular effects of fentanyl after fluid-percussion injury (FPI) TBI in isoflurane-anesthetized cats. In an approved protocol, 17 fasted cats were anesthetized, mechanically ventilated with 1-1.5% isoflurane in 70% N2O/30% O2, and prepared for FPI. Electroencephalogram (EEG) and intracranial pressure (ICP) were monitored. Cerebral blood flow and cardiac output were measured with radiolabelled microspheres. Animals received moderate FPI (2.2 atm) followed by 15 min of stabilization. Cats were then randomized to control (isoflurane anesthesia plus saline placebo) or fentanyl (isoflurane anesthesia plus fentanyl 50 microg x kg(-1) h(-1)) groups. CBF, EEG, and ICP were recorded at baseline (Baseline), 15 min post-FPI (post-FPI), and at 15, 75, and 135 min after beginning fentanyl or saline placebo infusions (INF 15, INF 75, INF 135). EEG, ICP, PaCO2, PaO2, pH, and temperature were similar between groups. Mean arterial pressure was significantly lower than in the control group after fentanyl administration, while total CBF was not significantly different from control values. In a previous study, decreasing MAP to 80 mm Hg after TBI in isoflurane-anesthetized cats resulted in a 30% decrease in CBF. In this study, fentanyl after TBI significantly decreased MAP but not CBF. Fentanyl administration was associated with preservation of CBF despite hypotension. Further research is necessary to evaluate the effects of fentanyl on cerebral autoregulation after TBI.

Altered release of prostaglandins by opioids contributes to impaired cerebral hemodynamics following brain injury

OBJECTIVES

After fluid percussion brain injury (FPI) in the newborn pig, pial arteries constrict and responses to dilator stimuli, including opioids, are blunted. This study was designed to determine if altered release of prostaglandins contributes to blunted opioid dilation of cerebral arteries in newborn piglets following brain injury.

DESIGN

Prospective, in vivo, cerebral hemodynamic animal study.

SETTING

University research laboratory.

SUBJECTS

Newborn (1- to 5-days old) piglets of either gender.

INTERVENTIONS

In anesthetized, newborn, 1- to 5-day-old pigs, a closed cranial window was used to measure pial artery diameter and to collect cortical periarachnoid cerebrospinal fluid (CSF) for determination of 6-keto-PGF1alpha, the stable metabolite of prostaglandin I2 (PGI2) and thromboxane B2 (TXB2), the stable metabolite of TXA2, via radioimmunoassay. FPI of moderate severity (1.9 to 2.3 atmospheres) was produced by using a pendulum to strike a piston on a saline-filled cylinder that was fluid coupled to the brain via a hollow screw inserted through the cranium.

MEASUREMENTS AND MAIN RESULTS

Methionine enkephalin (Met) vasodilation was blunted after FPI but was partially restored with indomethacin pretreatment (5 mg/kg i.v.) (8 +/- 1 [SEM] %, 13 +/- 1%, and 20 +/- 1% vs. 1 +/- 1%, 3 +/- 1%, and 5 +/- 1% vs. 7 +/- 1%, 10 +/- 1%, and 15 +/- 1%, respectively, for 10(-10), 10(-8), and 10(-6) M Met during control conditions, after FPI, and after FPI pretreated with indomethacin, n = 6). Similarly, restoration of Met dilation after FPI was observed with SQ 29,548, a TXA2 antagonist. Met-induced 6-keto-PGF1alpha release was blunted following FPI (889 +/- 20, 1130 +/- 33, and 1886 +/- 59 vs. 2630 +/- 36, 2775 +/- 30, and 2825 +/- 36 pg/mL for control, 10(-10), and 10(-6) M Met before and after FPI, respectively, n = 6). In contrast, Met-induced TXB2 release was enhanced after FPI (340 +/- 20, 423 +/- 25, and 473 +/- 30 pg/mL vs. 518 +/- 30, 726 +/- 90, and 901 +/- 35 pg/mL for control, 10(-10), and 10(-6) M Met before and after FPI, respectively, n = 6). Leucine enkephalin- and dynorphin-induced dilation and associated prostaglandin release were similarly altered following FPI. Beta endorphin-induced constriction was enhanced following FPI, and these potentiated responses were blunted after indomethacin or SQ 29,548 pretreatment.

CONCLUSIONS

These data show that FPI increases CSF 6-keto-PGF1alpha and TXB2 concentrations. These data suggest that altered release of prostaglandins by opioids contribute to impaired cerebral hemodynamics following FPI in piglets.

Effects of nalmefene, CG3703, tirilazad, or dopamine on cerebral blood flow, oxygen delivery, and electroencephalographic activity after traumatic brain injury and hemorrhage

Hemorrhage after traumatic brain injury (TBI) in cats produces significant decreases in cerebral oxygen delivery (DcereO2) and electroencephalographic (EEG) activity. To determine whether effective treatments for the separate insults of TBI and hemorrhagic shock would also prove effective after the clinically relevant combination of the two, we measured the effects of a kappa-opiate antagonist (nalmefene), an inhibitor of lipid peroxidation (tirilazad), a thyrotropin-releasing hormone analog (CG3703), a clinically useful pressor agent (dopamine) or a saline placebo on cerebral blood flow (CBF), and EEG activity after TBI and mild hemorrhagic hypotension. Cats (n = 40, 8 per group) were anesthetized with 1.6% isoflurane in N2O:O2 (70:30) and prepared for fluid-percussion TBI and microsphere measurements of CBF. Cats were randomized to receive nalmefene (1 mg/kg), tirilazad (5 mg/kg), CG3703 (2 mg/kg), dopamine (20 microg x kg(-1) x min[-1]) or a saline placebo (2 ml, 0.9% NaCl). Animals were injured (2.2 atm), hemorrhaged to 70% of preinjury blood volume, treated as just described and resuscitated with a volume of 10% hydroxyethyl starch equal to shed blood. CBF was determined and EEG activity recorded before injury, after hemorrhage, and 0, 60, and 120 min after resuscitation (R0, R60, and R120). CBF increased significantly after resuscitation (R0) in the nalmefene- and CG3703-treated groups. CBF did not differ significantly from baseline in any group at R60 or R120. DcereO2 was significantly less than baseline in the saline-, dopamine-, and tirilazad-treated groups at R60 and in the dopamine-, tirilazad-, and CG3703-treated groups at R120. EEG activity remained unchanged in the nalmefene-treated group but deteriorated significantly at R60 or R120 compared to baseline in the other groups. Nalmefene and CG3703 preserved the hyperemic response to hemodilution (otherwise antagonized by TBI), and nalmefene prevented the deterioration in DcereO2 and EEG activity that occurs after TBI and hemorrhage.

Endothelin production links superoxide generation to altered opioid-induced pial artery vasodilation after brain injury in pigs

BACKGROUND AND PURPOSE

Traumatic brain injury conveys significant morbidity and mortality to infants and children. In the newborn pig, opioids contribute to pial artery vasconstriction after fluid percussion injury (FPI). FPI attenuates vasodilation and cGMP production by methionine enkephalin (Met) and leucine enkephalin (Leu) and reverse dynorphin (Dyn) from a dilator to a constrictor. Superoxide anion (O2-) production contributes to altered cerebral hemodynamics after FPI, and O2- scavengers partially restore decreased dilator responses after FPI. Endothelin-1 (ET-1), a purported mediator of cerebral vasospasm, has been suggested to alter nitric oxide function and cGMP concentration. The present study was designed to determine the contribution of ET-1 to altered opioid-induced dilation after FPI and the role of O2- in such altered responses.

METHODS

Injury of moderate severity (1.9 to 2.3 atm) was produced by the lateral FPI technique in anesthetized newborn pigs equipped with a closed cranial window. Superoxide dismutase (SOD)-inhibitable nitroblue tetrazolium (NBT) reduction was determined as an index of O2- generation.

RESULTS

FPI increased cerebrospinal fluid ET-1 from 20 +/- 2 to 93 +/- 6 pg/mL (approximately 10(-10) mol/L). Topical ET-1 (10(-10) mol/L) increased SOD-inhibitable NBT reduction from 1 +/- 1 to 16 +/- 3 pmol/mm2, similar to previously reported NBT reduction after FPI (14 +/- 2 pmol/mm2). BQ123 (10(-6) mol/L), an ET-1 antagonist, blunted the NBT reduction observed after FPI (4 +/- 1 pmol/mm2). Met produced pial vasodilation that was attenuated by FPI and partially restored by BQ123 pretreatment (7 +/- 1%, 11 +/- 1%, and 17 +/- 1% versus 3 +/- 1%, 6 +/- 1%, and 9 +/- 2% versus 5 +/- 1%, 9 +/- 1%, and 14 +/- 2% for 10(-10), 10(-8), and 10(-6) mol/L Met during control conditions, after FPI, and after FPI pretreated with BQ123, respectively). Met-induced dilation was associated with increased cerebrospinal fluid cGMP, and these biochemical changes were likewise blunted by FPI and partially restored by BQ123 (357 +/- 12, 455 +/- 15, 500 +/- 19, and 632 +/- 11 versus 264 +/- 4, 267 +/- 4, 295 +/- 12, and 305 +/- 15 versus 309 +/- 19, 432 +/- 11, 529 +/- 10, and 593 +/- 4 pg/mL for resting conditions, 10(-10), 10(-8), and 10(-6) mol/L Met during control conditions, after FPI, and after FPI pretreated with BQ123, respectively). Similar partial restoration of vascular and biochemical parameters was observed for Leu and Dyn.

CONCLUSIONS

These data show that ET-1, in concentrations similar to that present in cerebrospinal fluid after FPI, increases O2- production. These data also indicate the opioid-induced vasodilation and cGMP production are partially restored after FPI by ET-1 receptor blockade. These data suggest that ET-1 contributes to altered cerebral hemodynamics after FPI, at least in part, through elevated O2- production.

Role of vasopressin in altered pial artery responses to dynorphin and beta-endorphin following brain injury

Pial artery constriction following fluid percussion brain injury (FPI) is associated with elevated CSF dynorphin and beta-endorphin concentration in newborn pigs. Additionally, dynorphin is a dilator under control conditions and a vasoconstrictor under decreased cerebrovascular tone conditions. Vasopressin contributes to beta-endorphin-induced pial constriction and the constrictor potential for dynorphin. Recently, it has been observed that FPI reverses vasopressin from a dilator to a constrictor. The present study was designed to characterize the effect of FPI on beta-endorphin-induced constriction and the role of vasopressin in that constriction as well as in the reversal of dynorphin's vascular response following FPI. Brain injury of moderate severity (1.9 - 2.3 atm) was produced in anesthetized newborn pigs equipped with a closed cranial window. Dynorphin in physiologic and pharmacologic concentrations (10(-10), 10(-8), 10(-6) M) was reversed from a dilator to a constrictor following FPI (7 +/- 1, 11 +/- 1, and 16 +/- 1 vs -4 +/- 1, -7 +/- 1, and -11 +/- 1% before and after FPI, respectively). Dynorphin-induced vascular changes were accompanied by increased cortical periarachnoid CSF vasopressin and these biochemical changes were potentiated following FPI (24 +/- 4 vs 134 +/- 7 and 53 +/- 7 vs 222 +/- 14 pg/mliter for control and dynorphin (10(-6) M) before and after FPI, respectively). In contrast, in animals pretreated with the vasopressin receptor antagonist [1-(beta-mercapto-beta beta-cyclopentamethylene propionic acid) 2-(O-methyl)-Tyr-AVP] (MEAVP, 5 micrograms/kg iv), dynorphin-induced constriction following FPI was attenuated (6 +/- 1, 12 +/- 1, and 16 +/- 1, vs -2 +/- 1, -4 +/- 1, and -7 +/- 1% before and after FPI, respectively). Additionally, beta-endorphin-induced pial constriction was potentiated following FPI (-7 +/- 1, -10 +/- 1, -15 +/- 1 vs -10 +/- 1 -15 +/- 2, and -21 +/- 2% for beta-endorphin (10(-10), 10(-8), 10(-6) M) before and after FPI, respectively). beta-endorphin-induced CSF vasopressin release was similarly potentiated following FPI. Further, MEAVP blunted the augmented constrictor responses to beta-endorphin observed following FPI (-5 +/- 1, -9 +/- 1, -14 +/- 1 vs -2 +/- 1, -5 +/- 1, and -8 +/- 1% before and after FPI, respectively). These data indicate that FPI potentiates beta-endorphin-induced pial construction and reverses dynorphin from a dilator to a constrictor. Additionally, these data show that vasopressin contributes to augmented beta-endorphin pial constriction and the reversal of dynorphin's vascular effects following FPI. Further, since CSF dynorphin and beta-endorphin concentrations are increased following FPI, these data suggest that these two opioids contribute to pial artery constriction observed following FPI, at least, in part, via the release of vasopressin.

Relationship between opioids and activation of phospholipase C and protein kinase C in brain injury induced pial artery vasoconstriction

Previously, it has been observed that newborn pig pial artery constriction after fluid percussion brain injury was associated with elevated CSF dynorphin and beta endorphin concentration. Additionally, brain injury reversed dynorphin-induced pial artery vasodilation to vasoconstriction. The present study was designed to characterize the relationship between opioids and activation of phospholipase C (PLC) and protein kinase C (PKC) in brain injury-induced pial vasoconstriction. Anesthetized newborn pigs equipped with a closed cranial window were connected to a percussion device consisting of a saline-filled cylindrical reservoir with a metal pendulum. Brain injury of moderate severity (1.9-2.3 atm) was produced by allowing the pendulum to strike a piston on the cylinder. Brain injury decreased pial arteriolar diameter within 10 min of injury and continued to fall progressively for 3 h (130 +/- 5, 108 +/- 4 and 102 +/- 5 microns for 0, 10 and 180 min postinjury). In contrast, the PLC inhibitor, neomycin (10(-4) M), blunted brain injury-induced pial vasoconstriction (133 +/- 4, 129 +/- 4 and 135 +/- 5 microns for 0, 10 and 180 min postinjury, respectively). Similarly, staurosporine (10(-7) M), a PKC inhibitor, also blunted brain injury-induced vasoconstriction. beta endorphin (10(-8), 10(-6) M)-induced pial artery vasoconstriction was blunted by neomycin (12 +/- 1, 19 +/- 1 vs. 2 +/- 1, 4 +/- 2% constriction before and after neomycin, respectively). Staurosporine similarly blunted beta endorphin pial constriction (10 +/- 1, 15 +/- 1 vs. 1 +/- 1, 1 +/- 1% constriction before and after staurosporine, respectively). The constrictor potential for dynorphin was also inhibited by neomycin and staurosporine.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment with thyrotropin-releasing hormone (TRH) in patients with traumatic spinal cord injuries

Numerous preclinical studies have demonstrated that posttraumatic treatment of spinal cord injury (SCI) with thyrotropin-releasing hormone (TRH) or TRH analogs improves long-term behavioral recovery. The purpose of the present study is to provide preliminary data regarding the safety and potential efficacy of TRH in patients with acute SCI. A total of 20 patients with SCI were classified by clinical examination into complete and incomplete injury groups within 12 h of trauma and randomly assigned in double-blinded fashion to treatment with either TRH (0.2 mg/kg intravenous bolus followed by 0.2 mg/kg/h infusion over 6 h) or vehicle (equal volume physiological saline) placebo. A variety of physiological variables were followed during treatment. Clinical examination included motor and sensory testing, as well as assigning a Sunnybrook score based upon level of function. Patients were examined at 24 h, 72 h, 1 week, 1 month, 4 months, and 12 months after injury. TRH infusions were well tolerated. There appeared to be no discernible treatment effect in patients with complete injuries although data were available from only six such patients at 4 months. For the incomplete injury group, a total of 6 treated and 5 placebo patients had 4-month evaluations. TRH treatment was associated with significantly higher motor, sensory, and Sunnybrook scores than placebo treatment. Because of patients lost to subsequent follow-up, 12-month data were not highly informative. These observations must be interpreted with considerable caution because of the small patient numbers, but together with extensive animal studies they support the need for a larger multicenter clinical trial of TRH.

The role of opioids in newborn pig fluid percussion brain injury

The present study was designed to characterize the relationship between cerebral opioid concentration, cerebral hemodynamics, and cerebral oxygenation following percussion brain injury in neonatal pigs. Previous research found that opioids represent a significant vasoactive component in the regulation of the neonatal piglet cerebral circulation. Anesthetized newborn (1-5 days old) pigs equipped with a closed cranial window were connected to a percussion device consisting of a saline-filled cylindrical reservoir with a metal pendulum. Brain injury of moderate severity (1.9-2.3 atm.) was produced by allowing the pendulum to strike a piston on the cylinder. Fluid percussion brain injury decreased pial arteriolar diameter (132 +/- 5 to 110 +/- 5 microns within 10 min). Cerebral blood flow also fell within 10 min of injury and continued to fall progressively for 3 h, resulting in a 46 +/- 4% decrease. Within 30 s of brain injury, there was a transient increase in cerebral hemoglobin-O2 saturation that was reversed to a progressive profound decrease in cerebral hemoglobin-O2 saturation for the next 3 h, as measured by near infrared spectroscopy. CSF opioid concentrations were increased 10 min after brain injury; dynorphin showed the largest proportional increase (5.8 +/- 0.9 fold). The CSF concentration for other opioids continued to increase over 180 min while the dynorphin concentration progressively decreased with time. In naloxone (1 mg/kg i.v.) pretreated piglets, the brain injury induced decrease in arteriolar diameter was attenuated (129 +/- 5 to 121 +/- 5 microns within 10 min). Similarly, the decrease in regional cerebral blood flow and cerebral hemoglobin-O2 saturation observed following brain injury were also blunted by naloxone.(ABSTRACT TRUNCATED AT 250 WORDS)

Endogenous opiates: 1993

This paper is the sixteenth installment of our annual review of research concerning the opiate system. It is restricted to papers published during 1993 that concern the behavioral effects of the endogenous opiate peptides, and does not include papers dealing only with their analgesic properties. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; development; immunological responses; and other behaviors.