Opiates are utilized routinely and effectively as a short-term analgesic treatment for a variety of acute pain conditions such as occur following trauma, and for patients with painful terminal ...diseases such as cancer. Because opiate analgesics are highly addictive substances, their use in the treatment of chronic nonmalignant pain remains controversial.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
► We show that firms with higher quality boards borrow at lower rates. ► This relation exists after controls for ownership structure and CEO compensation. ► We also consider combined direct and ...indirect (covenant-related) loan costs. ► We find that such costs are lower if boards are large, experienced, and diverse. ► Overall, the evidence indicates that board quality impacts the cost of bank debt.
We analyze the relation between comprehensive measures of board quality and the cost as well as the non-price terms of bank loans. We show that firms that have higher quality boards with a greater advisory presence borrow at lower interest rates. This relation exists even after controlling for ownership structure, CEO compensation policy, and shareholder protection, as well as the size and financial characteristics of the borrower and of the loan. We also show evidence that board quality and other governance characteristics influence the likelihood that loans have covenant requirements, but the relations differ by covenant type. When we combine the direct and indirect costs of bank loans we find that firms with large, independent, experienced, and diverse boards and lower institutional ownership borrow more cheaply. Overall, the evidence indicates that board quality impacts the cost of bank debt.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The canonical two neuron model of opioid reward posits that mu opioid receptor (MOR) activation produces reward by disinhibiting midbrain ventral tegmental area (VTA) dopamine neurons through ...inhibition of local GABAergic interneurons. Although indirect evidence supports the neural circuit postulated by this model, its validity has been called into question by growing evidence for VTA neuronal heterogeneity and the recent demonstration that MOR agonists inhibit GABAergic terminals in the VTA arising from extrinsic neurons. In addition, VTA MOR reward can be dopamine-independent. To directly test the assumption that MOR activation directly inhibits local GABAergic neurons, we investigated the properties of rat VTA GABA neurons directly identified with either immunocytochemistry for GABA or GAD65/67, or in situ hybridization for GAD65/67 mRNA. Utilizing co-labeling with an antibody for the neural marker NeuN and in situ hybridization against GAD65/67, we found that 23±3% of VTA neurons are GAD65/67(+). In contrast to the assumptions of the two neuron model, VTA GABAergic neurons are heterogeneous, both physiologically and pharmacologically. Importantly, only 7/13 confirmed VTA GABA neurons were inhibited by the MOR selective agonist DAMGO. Interestingly, all confirmed VTA GABA neurons were insensitive to the GABA(B) receptor agonist baclofen (0/6 inhibited), while all confirmed dopamine neurons were inhibited (19/19). The heterogeneity of opioid responses we found in VTA GABAergic neurons, and the fact that GABA terminals arising from neurons outside the VTA are inhibited by MOR agonists, make further studies essential to determine the local circuit mechanisms underlying VTA MOR reward.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We compared brain activations in response to acute noxious thermal stimuli in controls and chronic back pain (CBP) patients. Pain perception and related cortical activation patterns were similar in ...the two groups. However, nucleus accumbens (NAc) activity differentiated the groups at a very high accuracy, exhibiting phasic and tonic responses with distinct properties. Positive phasic NAc activations at stimulus onset and offset tracked stimulus salience and, in normal subjects, predicted reward (pain relief) magnitude at stimulus offset. In CBP, NAc activity correlated with different cortical circuitry from that of normals and phasic activity at stimulus offset was negative in polarity, suggesting that the acute pain relieves the ongoing back pain. The relieving effect was confirmed in a separate psychophysical study in CBP. Therefore, in contrast to somatosensory pathways, which reflect sensory properties of acute noxious stimuli, NAc activity in humans encodes its predicted value and anticipates its analgesic potential on chronic pain.
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► NAc predicts the reward value for expected pain relief in healthy subjects ► NAc predicts the salience or arousal for imminent pain ► Pain relief causes distinct NAc activities in healthy versus chronic pain subjects
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Dopamine neurons in the ventral tegmental area (VTA) represent a critical site of synaptic plasticity induced by addictive drugs. Orexin/hypocretin-containing neurons in the lateral hypothalamus ...project to the VTA, and behavioral studies have suggested that orexin neurons play an important role in motivation, feeding, and adaptive behaviors. However, the role of orexin signaling in neural plasticity is poorly understood. The present study shows that in vitro application of orexin A induces potentiation of N-methyl-D-aspartate receptor (NMDAR)-mediated neurotransmission via a PLC/PKC-dependent insertion of NMDARs in VTA dopamine neuron synapses. Furthermore, in vivo administration of an orexin 1 receptor antagonist blocks locomotor sensitization to cocaine and occludes cocaine-induced potentiation of excitatory currents in VTA dopamine neurons. These results provide in vitro and in vivo evidence for a critical role of orexin signaling in the VTA in neural plasticity relevant to addiction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Neurologist S. Weir Mitchell first described “causalgia” following wartime nerve injury, with its persistent distal limb burning pain, swelling, and abnormal skin color, temperature, and sweating. ...Similar post‐traumatic symptoms were later identified in patients without overt nerve injuries after trauma. This was labeled reflex sympathetic dystrophy (RSD; now complex regional pain syndrome type I CRPS‐I). The pathophysiology of symptoms is unknown and treatment options are limited. We propose that persistent RSD/CRPS‐I is a post‐traumatic neuralgia associated with distal degeneration of small‐diameter peripheral axons. Small‐fiber lesions are easily missed on examination and are undetected by standard electrophysiological testing. Most CRPS features—spreading pain and skin hypersensitivity, vasomotor instability, osteopenia, edema, and abnormal sweating—are explicable by small‐fiber dysfunction. Small fibers sense pain and temperature but also regulate tissue function through neuroeffector actions. Indeed, small‐fiber–predominant polyneuropathies cause CRPS‐like abnormalities, and pathological studies of nerves from chronic CRPS‐I patients confirm small‐fiber–predominant pathology. Small distal nerve injuries in rodents reproduce many CRPS features, further supporting this hypothesis. CRPS symptoms likely reflect combined effects of axonal degeneration and plasticity, inappropriate firing and neurosecretion by residual axons, and denervation supersensitivity. The resulting tissue edema, hypoxia, and secondary central nervous system changes can exacerbate symptoms and perpetuate pathology. Restoring the interest of neurologists in RSD/CRPS should improve patient care and broaden our knowledge of small‐fiber functions. Ann Neurol 2009;65:629–638
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Both the nucleus accumbens (NAc) and basolateral amygdala (BLA) contribute to learned behavioral choice. Neurons in both structures that encode reward-predictive cues may underlie the decision to ...respond to such cues, but the neural circuits by which the BLA influences reward-seeking behavior have not been established. Here, we test the hypothesis that the BLA drives NAc neuronal responses to reward-predictive cues. First, using a disconnection experiment, we show that the BLA and dopamine projections to the NAc interact to promote the reward-seeking behavioral response. Next, we demonstrate that BLA neuronal responses to cues precede those of NAc neurons and that cue-evoked excitation of NAc neurons depends on BLA input. These results indicate that BLA input is required for dopamine to enhance the cue-evoked firing of NAc neurons and that this enhanced firing promotes reward-seeking behavior.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The ventral tegmental area (VTA) has a central role in the neural processes that underlie motivation and behavioral reinforcement. Although thought to contain only dopamine and GABA neurons, the VTA ...also includes a recently discovered population of glutamate neurons identified through the expression of the vesicular glutamate transporter VGLUT2. A subset of VGLUT2(+) VTA neurons corelease dopamine with glutamate at terminals in the NAc, but others do not express dopaminergic markers and remain poorly characterized. Using transgenic mice that express fluorescent proteins in distinct cell populations, we now find that both dopamine and glutamate neurons in the medial VTA exhibit a smaller hyperpolarization-activated current (I(h)) than more lateral dopamine neurons and less consistent inhibition by dopamine D(2) receptor agonists. In addition, VGLUT2(+) VTA neurons project to the nucleus accumbens (NAc), lateral habenula, ventral pallidum (VP), and amygdala. Optical stimulation of VGLUT2(+) projections expressing channelrhodopsin-2 further reveals functional excitatory synapses in the VP as well as the NAc. Thus, glutamate neurons form a physiologically and anatomically distinct subpopulation of VTA projection neurons.
Pain is aversive, and its relief elicits reward mediated by dopaminergic signaling in the nucleus accumbens (NAc), a part of the mesolimbic reward motivation pathway. How the reward pathway is ...engaged by pain-relieving treatments is not known. Endogenous opioid signaling in the anterior cingulate cortex (ACC), an area encoding pain aversiveness, contributes to pain modulation. We examined whether endogenous ACC opioid neurotransmission is required for relief of pain and subsequent downstream activation of NAc dopamine signaling. Conditioned place preference (CPP) and in vivo microdialysis were used to assess negative reinforcement and NAc dopaminergic transmission. In rats with postsurgical or neuropathic pain, blockade of opioid signaling in the rostral ACC (rACC) inhibited CPP and NAc dopamine release resulting from non-opioid pain-relieving treatments, including peripheral nerve block or spinal clonidine, an α2-adrenergic agonist. Conversely, pharmacological activation of rACC opioid receptors of injured, but not pain-free, animals was sufficient to stimulate dopamine release in the NAc and produce CPP. In neuropathic, but not sham-operated, rats, systemic doses of morphine that did not affect withdrawal thresholds elicited CPP and NAc dopamine release, effects that were prevented by blockade of ACC opioid receptors. The data provide a neural explanation for the preferential effects of opioids on pain affect and demonstrate that engagement of NAc dopaminergic transmission by non-opioid pain-relieving treatments depends on upstream ACC opioid circuits. Endogenous opioid signaling in the ACC appears to be both necessary and sufficient for relief of pain aversiveness.
Increased activity of lateral habenula (LHb) neurons is correlated with aversive states including pain, opioid abstinence, rodent models of depression, and failure to receive a predicted reward. ...Agonists at the mu opioid receptor (MOR) are among the most powerful rewarding and pain relieving drugs. Injection of the MOR agonist morphine directly into the habenula produces analgesia, raising the possibility that MOR acts locally within the LHb. Consequently, we examined the synaptic actions of MOR agonists in the LHb using whole cell patch clamp recording. We found that the MOR selective agonist DAMGO inhibits a subset of LHb neurons both directly and by inhibiting glutamate release onto these cells. Paradoxically, DAMGO also presynaptically inhibited GABA release onto most LHb neurons. The behavioral effect of MOR activation will thus depend upon both the level of intrinsic neuronal activity in the LHb and the balance of activity in glutamate and GABA inputs to different LHb neuronal populations.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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