Vasco Galhardo

Forebrain pain mechanisms.

Emotional-affective and cognitive dimensions of pain are less well understood than nociceptive and nocifensive components, but the forebrain is believed to play an important role. Recent evidence suggests that subcortical and cortical brain areas outside the traditional pain processing network contribute critically to emotional-affective responses and cognitive deficits related to pain. These brain areas include different nuclei of the amygdala and certain prefrontal cortical areas. Their roles in various aspects of pain will be discussed. Biomarkers of cortical dysfunction are being identified that may evolve into therapeutic targets to modulate pain experience and improve pain-related cognitive impairment. Supporting data from preclinical studies in neuropathic pain models will be presented. Neuroimaging analysis provides evidence for plastic changes in the pain processing brain network. Results of clinical studies in neuropathic pain patients suggest that neuroimaging may help determine mechanisms of altered brain functions in pain as well as monitor the effects of pharmacologic interventions to optimize treatment in individual patients. Recent progress in the analysis of higher brain functions emphasizes the concept of pain as a multidimensional experience and the need for integrative approaches to determine the full spectrum of harmful or protective neurobiological changes in pain.

Cognitive impairment in pain through amygdala-driven prefrontal cortical deactivation.

Cognitive deficits such as impaired decision-making can be a consequence of persistent pain. Normal functions of the intact amygdala and prefrontal cortex are required for emotion-based decision-making that relies on the ability to assess risk, attribute value, and identify advantageous strategies. We tested the hypothesis that pain-related cognitive deficits result from amygdala-driven impairment of medial prefrontal cortical (mPFC) function. To do this, we used electrophysiological single-unit recordings in vivo, patch clamp in brain slices, and various behavioral assays to show that increased neuronal activity in the amygdala in an animal model of arthritis pain was accompanied by decreased mPFC activation and impaired decision-making. Furthermore, pharmacologic inhibition (with a corticotropin-releasing factor 1 receptor antagonist) of pain-related hyperactivity in the basolateral amygdala (BLA), but not central amygdala (CeA), reversed deactivation of mPFC pyramidal cells and improved decision-making deficits. Pain-related cortical deactivation resulted from a shift of balance between inhibitory and excitatory synaptic transmission. Direct excitatory transmission to mPFC pyramidal cells did not change in the pain model, whereas polysynaptic inhibitory transmission increased. GABAergic transmission was reduced by non-NMDA receptor antagonists, suggesting that synaptic inhibition was glutamate driven. The results are consistent with a model of BLA-driven feedforward inhibition of mPFC neurons. In contrast to the differential effects of BLA versus CeA hyperactivity on cortical-cognitive functions, both amygdala nuclei modulate emotional-affective pain behavior. Thus, this study shows that the amygdala contributes not only to emotional-affective but also cognitive effects of pain. The novel amygdalo-cortical pain mechanism has important implications for our understanding of amygdala functions and amygdalo-cortical interactions.

Rodent versions of the iowa gambling task: opportunities and challenges for the understanding of decision-making.

Impaired decision-making is a core problem in several psychiatric disorders including attention-deficit/hyperactivity disorder, schizophrenia, obsessive–compulsive disorder, mania, drug addiction, eating disorders, and substance abuse as well as in chronic pain. To ensure progress in the understanding of the neuropathophysiology of these disorders, animal models with good construct and predictive validity are indispensable. Many human studies aimed at measuring decision-making capacities use the Iowa gambling task (IGT), a task designed to model everyday life choices through a conflict between immediate gratification and long-term outcomes. Recently, new rodent models based on the same principle have been developed to investigate the neurobiological mechanisms underlying IGT-like decision-making on behavioral, neural, and pharmacological levels. The comparative strengths, as well as the similarities and differences between these paradigms are discussed. The contribution of these models to elucidate the neurobehavioral factors that lead to poor decision-making and to the development of better treatments for psychiatric illness is considered, along with important future directions and potential limitations.

Orbitofrontal cortex lesions disrupt risk assessment in a novel serial decision-making task for rats

Neurobiological mechanisms of decision-making have been shown to be modulated by a number of frontal brain regions. Among those areas, the orbitofrontal cortex (OFC) is thought to play an important role in the decision of behavioral actions when faced with alternative options of ambiguous outcome. Here we present a novel neurobehavioral task to study affective decision-making in the rat, based on evaluation of consecutive choices between two levers associated with rewards of different value and probability. Two groups of animals were studied; a sham control group (n=6) and an OFC-lesioned group (n=7). In the first 30 trials both groups had similar preference patterns but at the end of the 90 trials of the task both groups developed specific preferences. The control group systematically preferred the lever associated with smaller but more reliable rewards (low risk lever) while the OFC lesion group preferred the high risk lever (index of preference of 0.21+/-0.21 vs. -0.45+/-0.10; t-test, P<0.05). Analysis of choice persistence (i.e. choosing the same lever in consecutive trials) suggests that the OFC-lesioned group became less sensitive to risk, seeking large rewards irrespective of their success probability.

Impaired Spatial Memory Performance in a Rat Model of Neuropathic Pain Is Associated with Reduced Hippocampus–Prefrontal Cortex Connectivity

Chronic pain patients commonly complain of working memory deficits, but the mechanisms and brain areas underlying this cognitive impairment remain elusive. The neuronal populations of the mPFC and dorsal CA1 (dCA1) are well known to form an interconnected neural circuit that is crucial for correct performance in spatial memory-dependent tasks. In this study, we investigated whether the functional connectivity between these two areas is affected by the onset of an animal model of peripheral neuropathic pain. To address this issue, we implanted two multichannel arrays of electrodes in the mPFC and dCA1 of rats and recorded the neuronal activity during a food-reinforced spatial working memory task in a reward-based alternate trajectory maze. Recordings were performed for 3 weeks, before and after the establishment of the spared nerve injury model of neuropathy. Our results show that the nerve lesion caused an impairment of working memory performance that is temporally associated with changes in the mPFC populational firing activity patterns when the animals navigated between decision points—when memory retention was most needed. Moreover, the activity of both recorded neuronal populations after the nerve injury increased their phase locking with respect to hippocampal theta rhythm. Finally, our data revealed that chronic pain reduces the overall amount of information flowing in the fronto-hippocampal circuit and induces the emergence of different oscillation patterns that are well correlated with the correct/incorrect performance of the animal on a trial-by-trial basis. The present results demonstrate that functional disturbances in the fronto-hippocampal connectivity are a relevant cause for pain-related working memory deficits.

OpenControl : A free opensource software for video tracking and automated control of behavioral mazes

Operant animal behavioral tests require the interaction of the subject with sensors and actuators distributed in the experimental environment of the arena. In order to provide user independent reliable results and versatile control of these devices it is vital to use an automated control system. Commercial systems for control of animal mazes are usually based in software implementations that restrict their application to the proprietary hardware of the vendor. In this paper we present OpenControl: an opensource Visual Basic software that permits a Windows-based computer to function as a system to run fully automated behavioral experiments. OpenControl integrates video-tracking of the animal, definition of zones from the video signal for real-time assignment of animal position in the maze, control of the maze actuators from either hardware sensors or from the online video tracking, and recording of experimental data. Bidirectional communication with the maze hardware is achieved through the parallel-port interface, without the need for expensive AD-DA cards, while video tracking is attained using an inexpensive Firewire digital camera. OpenControl Visual Basic code is structurally general and versatile allowing it to be easily modified or extended to fulfill specific experimental protocols and custom hardware configurations. The Visual Basic environment was chosen in order to allow experimenters to easily adapt the code and expand it at their own needs.

Comparison of Anesthetic Depth Indexes Based on Thalamocortical Local Field Potentials in Rats

Background:Local field potentials may allow a more precise analysis of the brain electrical activity than the electroencephalogram. In this study, local field potentials were recorded in the thalamocortical axis of rats to (i) compare the performance of several indexes of anesthetic depth and (ii) investigate the existence of thalamocortical correlated or disrupted activity during isoflurane steady-state anesthesia. Methods:Five rats chronically implanted with microelectrodes were used to record local field potentials in the primary somatosensory cortex and ventroposterolateral thalamic nuclei at six periods: before induction of anesthesia; in the last 5 min of randomized 20-min steady-state end-tidal 0.8, 1.1, 1.4, and 1.7% isoflurane concentrations; and after recovery. The approximate entropy, the index of consciousness, the spectral edge frequency, and the permutation entropy were estimated using epochs of 8 s. A correction factor for burst suppression was applied to the spectral edge frequency and to the permutation entropy. The correlation between the derived indexes and the end-tidal isoflurane was calculated and compared for the two studied brain regions indexes. Coherence analysis was also performed. Results:The burst suppression–corrected permutation entropy showed the highest correlation with the end-tidal isoflurane concentration, and a high coherence was obtained between the two studied areas. Conclusions:The permutation entropy corrected with the classic burst suppression ratio is a promising alternative to other indexes of anesthetic depth. Furthermore, high coherence level of activity exists between the somatosensory cortical and thalamic regions, even at deep isoflurane stages.

Prefrontal cortex and mediodorsal thalamus reduced connectivity is associated with spatial working memory impairment in rats with inflammatory pain

Summary Multielectrode recordings in awake behaving rats show that inflammatory pain reduces working memory performance and disrupts the functional connectivity between the prefrontal cortex and the mediodorsal thalamus. Abstract The medial prefrontal cortex (mPFC) and the mediodorsal thalamus (MD) form interconnected neural circuits that are important for spatial cognition and memory, but it is not known whether the functional connectivity between these areas is affected by the onset of an animal model of inflammatory pain. To address this issue, we implanted 2 multichannel arrays of electrodes in the mPFC and MD of adult rats and recorded local field potential activity during a food‐reinforced spatial working memory task. Recordings were performed for 3 weeks, before and after the establishment of the pain model. Our results show that inflammatory pain caused an impairment of spatial working memory performance that is associated with changes in the activity of the mPFC–MD circuit; an analysis of partial directed coherence between the areas revealed a global decrease in the connectivity of the circuit. This decrease was observed over a wide frequency range in both the frontothalamic and thalamofrontal directions of the circuit, but was more evident from MD to mPFC. In addition, spectral analysis revealed significant oscillations of power across frequency bands, namely with a strong theta component that oscillated after the onset of the painful condition. Finally, our data revealed that chronic pain induces an increase in theta/gamma phase coherence and a higher level of mPFC–MD coherence, which is partially conserved across frequency bands. The present results demonstrate that functional disturbances in mPFC–MD connectivity are a relevant cause of deficits in pain‐related working memory.

Structural characterization of marginal (lamina I) spinal cord neurons in the cat: A golgi study

The neuronal population of the spinal cord lamina I (marginal zone) was structurally characterized, in the cat, by the use of the Golgi method complemented by multivariate analysis of morphometric data. Four cell types were identified, two of them including two subtypes. Fusiform cells accounted for 43% of impregnated cells and presented flame‐shaped rostrocaudally elongated perikarya and bipolar, either strictly longitudinal (fusiform A; 37%) or longitudinal and ventral (fusiform B; 6%) dendritic arbors with numerous short‐pedicled spines. Fusiform cells preferentially occupied the lateral one‐third of lamina I. Multipolar cells (22%) had ovoid perikarya with bulging surfaces and numerous primary dendritic trunks. Two subtypes could be distinguished: multipolar A cells (12%) with highly ramified dendrites covered with variably shaped spines and multipolar B cells (10%) with looser and less spiny dendritic arbors expanded for longer distances. Multipolar cells were more commonly found in the medial half of lamina I. Flattened cells (16%) possessed discoid perikarya flattened across the dorsoventral axis and aspiny, scarcely ramified dendritic arbors distributed horizontally within lamina I. They predominated in the intermediate one‐third of the lamina. Pyramidal cells had triangular prismatic perikarya partially encased in the white matter overlying lamina I. They represented 19% of the impregnated neurons and were located along the entire lateromedial extent of the lamina. Each neuronal type included a few cells with perikarya and dendritic arbors three times larger than the rest. These so‐called giant cells amounted to 6% of the entire lamina I neuronal population. According to the present data, the neuronal population of the spinal cord lamina I of the cat strongly resembles that of the rat (Lima and Coimbra, J. Comp. Neurol. 244:53–71, 1986), which strengthens the functional relevance of this structural classification. J. Comp. Neurol. 414:315–333, 1999.

Sustained attention deficits in rats with chronic inflammatory pain.

Attentional deficits are a common clinical manifestation in chronic pain patients. The causes for this impairment are not clear, and explanations range from distraction caused by painful feelings to pain-induced putative alterations of brain regions related to attention processing. However, none of these explanations have been experimentally tested and few studies have addressed this issue in animal models. In this study we compared sustained attention in the 5-choice serial reaction time task (5-CSRTT) in rats before and after chronic pain. Persistent pain was induced by intra-articular injection of Complete Freunds Adjuvant and the development of monoarthritis was accessed by sensitivity to von Frey filaments. Results showed that after the induction of persistent pain, animals presented more errors in accuracy and more omissions in the task trials. When the same animals were studied with two different doses of carprofen (5 and 10mg/kg), the performance was not altered, despite the analgesic effect of the drug. The persistence of attentional impairment during transient analgesia suggests that distraction due to painful stimuli is not the main cause for attentional deficits and that permanent alteration of neurobiological mechanisms of attention should follow chronic pain.