High-fat/high-sucrose diet worsens metabolic outcomes and widespread hypersensitivity following early-life stress exposure in female mice.

Exposure to stress early in life has been associated with adult-onset comorbidities such as chronic pain, metabolic dysregulation, obesity, and inactivity. We have established an early-life stress model using neonatal maternal separation (NMS) in mice, which displays evidence of increased body weight and adiposity, widespread mechanical allodynia, and hypothalamic-pituitary-adrenal axis dysregulation in male mice. Early-life stress and consumption of a Western-style diet contribute to the development of obesity; however, relatively few preclinical studies have been performed in female rodents, which are known to be protected against diet-induced obesity and metabolic dysfunction. In this study, we gave naïve and NMS female mice access to a high-fat/high-sucrose (HFS) diet beginning at 4 wk of age. Robust increases in body weight and fat were observed in HFS-fed NMS mice during the first 10 wk on the diet, driven partly by increased food intake. Female NMS mice on an HFS diet showed widespread mechanical hypersensitivity compared with either naïve mice on an HFS diet or NMS mice on a control diet. HFS diet-fed NMS mice also had impaired glucose tolerance and fasting hyperinsulinemia. Strikingly, female NMS mice on an HFS diet showed evidence of hepatic steatosis with increased triglyceride levels and altered glucocorticoid receptor levels and phosphorylation state. They also exhibited increased energy expenditure as observed via indirect calorimetry and expression of proinflammatory markers in perigonadal adipose. Altogether, our data suggest that early-life stress exposure increased the susceptibility of female mice to develop diet-induced metabolic dysfunction and pain-like behaviors.

Spinal neuropeptide Y Y1 receptor-expressing neurons are a pharmacotherapeutic target for the alleviation of neuropathic pain.

Peripheral nerve injury sensitizes a complex network of spinal cord dorsal horn (DH) neurons to produce allodynia and neuropathic pain. The identification of a druggable target within this network has remained elusive, but a promising candidate is the neuropeptide Y (NPY) Y1 receptor-expressing interneuron (Y1-IN) population. We report that spared nerve injury (SNI) enhanced the excitability of Y1-INs and elicited allodynia (mechanical and cold hypersensitivity) and affective pain. Similarly, chemogenetic or optogenetic activation of Y1-INs in uninjured mice elicited behavioral signs of spontaneous, allodynic, and affective pain. SNI-induced allodynia was reduced by chemogenetic inhibition of Y1-INs, or intrathecal administration of a Y1-selective agonist. Conditional deletion of Npy1r in DH neurons, but not peripheral afferent neurons prevented the anti-hyperalgesic effects of the intrathecal Y1 agonist. We conclude that spinal Y1-INs are necessary and sufficient for the behavioral symptoms of neuropathic pain and represent a promising target for future pharmacotherapeutic development of Y1 agonists.

An Omega-3-rich Anti-inflammatory Diet Improved Widespread Allodynia and Worsened Metabolic Outcomes in Adult Mice Exposed to Neonatal Maternal Separation.

Inflammation plays a key role in the progression and maintenance of chronic pain, which impacts the lives of millions of Americans. Despite growing evidence that chronic pain can be improved by treating underlying inflammation, successful treatments are lacking and pharmaceutical interventions are limited due to drug side effects. Here we are testing whether a 'healthy human' diet (HHD), with or without anti-inflammatory components (HHAID), improves pain-like behaviors in a preclinical model of chronic widespread hypersensitivity induced by neonatal maternal separation (NMS). The HHD and HHAID are isocaloric and macronutrient-matched, have a low glycemic index, and fat content (35 kcal%) that is high in omega-3 fatty acids, while only the HHAID includes a combination of key anti-inflammatory compounds, at clinically relevant doses. Mice on these diets were compared to mice on a control diet with a macronutrient composition commonly used in rodents (20% protein, 70% carbohydrate, 10% fat). Our results demonstrate a benefit of the HHAID on pain-like behaviors in both male and female mice, despite increased caloric intake, adiposity, and weight gain. In female mice, HHAID specifically increased measures of metabolic syndrome and inflammation compared to the HHD and control diet groups. Male mice were susceptible to worsening metabolic measures on both the HHAID and HHD. This work highlights important sexual dimorphic outcomes related to early life stress exposure and dietary interventions, as well as a potential disconnect between improvements in pain-like behaviors and metabolic measures.

Assessing complex movement behaviors in rodent models of neurological disorders.

Behavioral phenotyping is a crucial step in validating animal models of human disease. Most traditional behavioral analyses rely on investigator observation of animal subjects, which can be confounded by inter-observer variability, scoring consistency, and the ability to observe extremely rapid, small, or repetitive movements. Force-Plate Actimeter (FPA)-based assessments can quantify locomotor activity and detailed motor activity with an incredibly rich data stream that can reveal details of movement unobservable by the naked eye. This report describes four specific examples of FPA analysis of behavior that have been useful in specific rat or mouse models of human neurological disease, which show how FPA analysis can be used to capture and quantify specific features of the complex behavioral phenotypes of these animal models. The first example quantifies nociceptive behavior of the rat following injection of formalin into the footpad as a common model of persistent inflammatory pain. The second uses actimetry to quantify intense, rapid circling behaviors in a transgenic mouse that overexpresses human laminin α5, a basement membrane protein. The third example assesses place preference behaviors in a rat model of migraine headache modeling phonophobia and photophobia. In the fourth example, FPA analysis revealed a unique movement signature emerged with age in a digenic mutant mouse model of Tourette Syndrome. Taken together, these approaches demonstrate the power and usefulness of the FPA in the examination and quantification of minute details of motor behaviors, greatly expanding the scope and detail of behavioral phenotyping of preclinical models of human disease.

Intrinsic Activity of C57BL/6 Substrains Associates with High-Fat Diet-Induced Mechanical Sensitivity in Mice.

Pain is significantly impacted by the increasing epidemic of obesity and the metabolic syndrome. Our understanding of how these features impact pain is only beginning to be developed. Herein, we have investigated how small genetic differences among C57BL/6 mice from 2 different commercial vendors lead to important differences in the development of high-fat diet-induced mechanical sensitivity. Two substrains of C57BL/6 mice from Jackson Laboratories (Bar Harbor, ME; C57BL/6J and C57BL/6NIH), as well as C57BL/6 from Charles Rivers Laboratories (Wilmington, MA; C57BL/6CR) were placed on high-fat diets and analyzed for changes in metabolic features influenced by high-fat diet and obesity, as well as measures of pain-related behaviors. All 3 substrains responded to the high-fat diet; however, C57BL/6CR mice had the highest weights, fat mass, and impaired glucose tolerance of the 3 substrains. In addition, the C57BL/6CR mice were the only strain to develop significant mechanical sensitivity over the course of 8 weeks. Importantly, the C57BL/6J mice were protected from mechanical sensitivity, which may be based on increased physical activity compared with the other 2 substrains. These findings suggest that activity may play a powerful role in protecting metabolic changes associated with a high-fat diet and that these may also be protective in pain-associated changes as a result of a high-fat diet. These findings also emphasize the importance of selection and transparency in choosing C57BL/6 substrains in pain-related research. PERSPECTIVE: Obesity and the metabolic syndrome play an important role in pain. This study identifies key differences in the response to a high-fat diet among substrains of C57BL/6 mice and differences in intrinsic physical activity that may influence pain sensitivity. The results emphasize physical activity as a powerful modulator of obesity-related pain sensitivity.

NCB5OR Deficiency in the Cerebellum and Midbrain Leads to Dehydration and Alterations in Thirst Response, Fasted Feeding Behavior, and Voluntary Exercise in Mice.

Cytosolic NADH-cytochrome-b5-oxidoreductase (NCB5OR) is ubiquitously expressed in animal tissues. We have previously reported that global ablation of NCB5OR in mice results in early-onset lean diabetes with decreased serum leptin levels and increased metabolic and feeding activities. The conditional deletion of NCB5OR in the mouse cerebellum and midbrain (conditional knock out, CKO mice) results in local iron dyshomeostasis and altered locomotor activity. It has been established that lesion to or removal of the cerebellum leads to changes in nutrient organization, visceral response, feeding behavior, and body weight. This study assessed whether loss of NCB5OR in the cerebellum and midbrain altered feeding or metabolic activity and had an effect on serum T3, cortisol, prolactin, and leptin levels. Metabolic cage data revealed that 16 week old male CKO mice had elevated respiratory quotients and decreased respiratory water expulsion, decreased voluntary exercise, and altered feeding and drinking behavior compared to wild-type littermate controls. Most notably, male CKO mice displayed higher consumption of food during refeeding after a 48-h fast. Echo MRI revealed normal body composition but decreased total water content and hydration ratios in CKO mice. Increased serum osmolality measurements confirmed the dehydration status of male CKO mice. Serum leptin levels were significantly elevated in male CKO mice while prolactin, T3, and cortisol levels remain unchanged relative to wild-type controls, consistent with elevated transcript levels for leptin receptors (short form) in the male CKO mouse cerebellum. Taken together, these findings suggest altered feeding response post starvation as a result of NCB5OR deficiency in the cerebellum.

Motor, Somatosensory, Viscerosensory and Metabolic Impairments in a Heterozygous Female Rat Model of Rett Syndrome.

Rett Syndrome (RTT), an autism-related disorder caused by mutation of the X-linked Methyl CpG-binding Protein 2 (MECP2) gene, is characterized by severe cognitive and intellectual deficits. While cognitive deficits are well-documented in humans and rodent models, impairments of sensory, motor and metabolic functions also occur but remain poorly understood. To better understand non-cognitive deficits in RTT, we studied female rats heterozygous for Mecp2 mutation (Mecp2-/x); unlike commonly used male Mecp2-/y rodent models, this more closely approximates human RTT where males rarely survive. Mecp2-/x rats showed rapid, progressive decline of motor coordination through six months of age as assessed by rotarod performance, accompanied by deficits in gait and posture. Mecp2-/x rats were hyper-responsive to noxious pressure and cold, but showed visceral hyposensitivity when tested by colorectal distension. Mecp2-/x rats ate less, drank more, and had more body fat resulting in increased weight gain. Our findings reveal an array of progressive non-cognitive deficits in this rat model that are likely to contribute to the compromised quality of life that characterizes RTT.

Rats bred for low and high running capacity display alterations in peripheral tissues and nerves relevant to neuropathy and pain.

INTRODUCTION: Diet and activity are recognized as modulators of nervous system disease, including pain. Studies of exercise consistently reveal a benefit on pain. This study focused on female rats to understand differences related to metabolic status and peripheral nerve function in females. METHODS: Here, we investigated parameters of peripheral nerve function relevant to pain in rats selectively bred for high (high-capacity runners; HCR) or low endurance exercise capacity (low-capacity runners; LCR) resulting in divergent intrinsic aerobic capacities and susceptibility for metabolic conditions. RESULTS: LCR female rats have reduced mechanical sensitivity, higher intraepidermal nerve fiber density and TrkA-positive epidermal axons, increased numbers of Langerhans and mast cells in cutaneous tissues, and a higher fat content despite similar overall body weights compared to female HCR rats. Sensory and motor nerve conduction velocities, thermal sensitivity, and mRNA expression of selected genes relevant to peripheral sensation were not different. CONCLUSIONS: These results suggest that aerobic capacity and metabolic status influence sensory sensitivity and aspects of inflammation in peripheral tissues that could lead to poor responses to tissue damage and painful stimuli. The LCR and HCR rats should prove useful as models to assess how the metabolic status impacts pain.

Neuronal cytoskeletal gene dysregulation and mechanical hypersensitivity in a rat model of Rett syndrome.

Children with Rett syndrome show abnormal cutaneous sensitivity. The precise nature of sensory abnormalities and underlying molecular mechanisms remain largely unknown. Rats with methyl-CpG binding protein 2 (MeCP2) mutation, characteristic of Rett syndrome, show hypersensitivity to pressure and cold, but hyposensitivity to heat. They also show cutaneous hyperinnervation by nonpeptidergic sensory axons, which include subpopulations encoding noxious mechanical and cold stimuli, whereas peptidergic thermosensory innervation is reduced. MeCP2 knockdown confined to dorsal root ganglion sensory neurons replicated this phenotype in vivo, and cultured MeCP2-deficient ganglion neurons showed augmented axonogenesis. Transcriptome analysis revealed dysregulation of genes associated with cytoskeletal dynamics, particularly those controlling actin polymerization and focal-adhesion formation necessary for axon growth and mechanosensory transduction. Down-regulation of these genes by topoisomerase inhibition prevented abnormal axon sprouting. We identified eight key affected genes controlling actin signaling and adhesion formation, including members of the Arhgap, Tiam, and cadherin families. Simultaneous virally mediated knockdown of these genes in Rett rats prevented sensory hyperinnervation and reversed mechanical hypersensitivity, indicating a causal role in abnormal outgrowth and sensitivity. Thus, MeCP2 regulates ganglion neuronal genes controlling cytoskeletal dynamics, which in turn determines axon outgrowth and mechanosensory function and may contribute to altered pain sensitivity in Rett syndrome.

Loss of NCB5OR in the cerebellum disturbs iron pathways, potentiates behavioral abnormalities, and exacerbates harmaline-induced tremor in mice.

Iron dyshomeostasis has been implicated in many diseases, including a number of neurological conditions. Cytosolic NADH cytochrome b5 oxidoreductase (NCB5OR) is ubiquitously expressed in animal tissues and is capable of reducing ferric iron in vitro. We previously reported that global gene ablation of NCB5OR resulted in early-onset diabetes and altered iron homeostasis in mice. To further investigate the specific effects of NCB5OR deficiency on neural tissue without contributions from known phenotypes, we generated a conditional knockout (CKO) mouse that lacks NCB5OR only in the cerebellum and midbrain. Assessment of molecular markers in the cerebellum of CKO mice revealed changes in pathways associated with cellular and mitochondrial iron homeostasis. (59)Fe pulse-feeding experiments revealed cerebellum-specific increased or decreased uptake of iron by 7 and 16 weeks of age, respectively. Additionally, we characterized behavioral changes associated with loss of NCB5OR in the cerebellum and midbrain in the context of dietary iron deprivation-evoked generalized iron deficiency. Locomotor activity was reduced and complex motor task execution was altered in CKO mice treated with an iron deficient diet. A sucrose preference test revealed that the reward response was intact in CKO mice, but that iron deficient diet consumption altered sucrose preference in all mice. Detailed gait analysis revealed locomotor changes in CKO mice associated with dysfunctional proprioception and locomotor activation independent of dietary iron deficiency. Finally, we demonstrate that loss of NCB5OR in the cerebellum and midbrain exacerbated harmaline-induced tremor activity. Our findings suggest an essential role for NCB5OR in maintaining both iron homeostasis and the proper functioning of various locomotor pathways in the mouse cerebellum and midbrain.

Output Properties of the Cortical Hindlimb Motor Area in Spinal Cord-Injured Rats.

The purpose of this study was to examine neuronal activity levels in the hindlimb area of motor cortex following spinal cord injury (SCI) in rats and compare the results with measurements in normal rats. Fifteen male Fischer-344 rats received a 200 Kdyn contusion injury in the thoracic cord at level T9-T10. After a minimum of 4 weeks following SCI, intracortical microstimulation (ICMS) and single-unit recording techniques were used in both the forelimb and hindlimb motor areas (FLA, HLA) under ketamine anesthesia. Although movements could be evoked using ICMS in the forelimb area with relatively low current levels, no movements or electromyographical responses could be evoked from ICMS in the HLA in any of the injured rats. During the same procedure, electrophysiological recordings were obtained with a single-shank, 16-channel Michigan probe (Neuronexus) to monitor activity. Neural spikes were discriminated using principle component analysis. Neural activity (action potentials) was collected and digitized for a duration of 5 min. Despite the inability to evoke movement from stimulation of cortex, robust single-unit activity could be recorded reliably from hindlimb motor cortex in SCI rats. Activity in the motor cortex of SCI rats was significantly higher compared with uninjured rats, and increased in hindlimb and forelimb motor cortex by similar amounts. These results demonstrate that in a rat model of thoracic SCI, an increase in single-unit cortical activity can be reliably recorded for several weeks post-injury.

Behavioral effects and mechanisms of migraine pathogenesis following estradiol exposure in a multibehavioral model of migraine in rat.

Migraine is one of the most common neurological disorders, leading to more than 1% of total disability reported and over 68 million visits to emergency rooms or physician's offices each year in the United States. Three times as many women as men have migraine, and while the mechanism behind this is not well understood, 17ß-estradiol (estradiol) has been implicated to play a role. Studies have demonstrated that exposure to estrogen can lead to activation of inflammatory pathways, changes in sodium gated channel activity, as well as enhanced vasodilation and allodynia. Estradiol receptors are found in trigeminal nociceptors, which are involved in signaling during a migraine attack. The purpose of this study was to investigate the role of estradiol in migraine pathogenesis utilizing a multibehavioral model of migraine in rat. Animals were surgically implanted with a cannula system to induce migraine and behavior was assessed following exposure to a proestrus level of estradiol for total locomotor activity, light and noise sensitivity, evoked grooming patterns, and enhanced acoustic startle response. Results demonstrated decreased locomotor activity, increased light and noise sensitivity, altered facial grooming indicative of allodynia and enhanced acoustic startle. Further examination of tissue samples revealed increased expression of genes associated with inflammation and vasodilation. Overall, this study demonstrates exacerbation of migraine-like behaviors following exposure to estradiol and helps further explain the underlying mechanisms behind sex differences found in this common neurological disorder.

Gait analysis at multiple speeds reveals differential functional and structural outcomes in response to graded spinal cord injury.

Open-field behavioral scoring is widely used to assess spinal cord injury (SCI) outcomes, but has limited usefulness in describing subtle changes important for posture and locomotion. Additional quantitative methods are needed to increase the resolution of locomotor outcome assessment. This study used gait analysis at multiple speeds (GAMS) across a range of mild-to-severe intensities of thoracic SCI in the rat. Overall, Basso, Beattie, and Bresnahan (BBB) scores and subscores were assessed, and detailed automated gait analysis was performed at three fixed walking speeds (3.5, 6.0, and 8.5 cm/sec). Variability in hindpaw brake, propel, and stance times were analyzed further by integrating across the stance phase of stepping cycles. Myelin staining of spinal cord sections was used to quantify white matter loss at the injury site. Varied SCI intensity produced graded deficits in BBB score, BBB subscores, and spinal cord white matter and total volume loss. GAMS measures of posture revealed decreased paw area, increased limb extension, altered stance width, and decreased values for integrated brake, propel, and stance. Measures of coordination revealed increased stride frequency concomitant with decreased stride length, resulting in deviation from consistent forelimb/hindlimb coordination. Alterations in posture and coordination were correlated to impact severity. GAMS results correlated highly with functional and histological measures and revealed differential relationships between sets of GAMS dynamics and cord total volume loss versus epicenter myelin loss. Automated gait analysis at multiple speeds is therefore a useful tool for quantifying nuanced changes in gait as an extension of histological and observational methods in assessing SCI outcomes.

Exposure to bisphenol A exacerbates migraine-like behaviors in a multibehavior model of rat migraine.

Migraine is a common and debilitating neurological disorder suffered worldwide. Women experience this condition 3 times more frequently than men, with estrogen strongly implicated to play a role. Bisphenol A (BPA), a highly prevalent xenoestrogen, is known to have estrogenic activity and may have an effect in migraine onset, intensity, and duration through estrogen receptor signaling. It was hypothesized that BPA exposure exacerbates migraine symptoms through estrogen signaling and downstream activation of nociception related pathways. Utilizing a multibehavior model of migraine in ovariectomized female rats, changes in locomotion, light and sound sensitivity, grooming, and acoustic startle were examined. Furthermore, changes in the expression of genes related to estrogen (ERα, GPR30), and nociception (extracellular signal regulated kinase, ERK, sodium gated channel, Nav1.8, and fatty acid amide hydrolase, FAAH) were studied following behavioral experiments. The following results were obtained: BPA treatment significantly exacerbated migraine-like behaviors in rats. Rats exposed to BPA demonstrated decreased locomotion, exacerbated light and sound aversion, altered grooming habits, and enhanced startle reflexes. Furthermore, BPA exposure increased mRNA expression of estrogen receptors, total ERK mRNA and ERK activation, as well as Nav1.8, and FAAH mRNA, indicative of altered estrogen signaling and altered nociception. These results show that BPA, an environmentally pervasive xenoestrogen, exacerbates migraine-like behavior in a rat model and alters expression of estrogen and nociception-related genes.

Vitamin D deficiency promotes skeletal muscle hypersensitivity and sensory hyperinnervation.

Musculoskeletal pain affects nearly half of all adults, most of whom are vitamin D deficient. Previous findings demonstrated that putative nociceptors ("pain-sensing" nerves) express vitamin D receptors (VDRs), suggesting responsiveness to 1,25-dihydroxyvitamin D. In the present study, rats receiving vitamin D-deficient diets for 2-4 weeks showed mechanical deep muscle hypersensitivity, but not cutaneous hypersensitivity. Muscle hypersensitivity was accompanied by balance deficits and occurred before onset of overt muscle or bone pathology. Hypersensitivity was not due to hypocalcemia and was actually accelerated by increased dietary calcium. Morphometry of skeletal muscle innervation showed increased numbers of presumptive nociceptor axons (peripherin-positive axons containing calcitonin gene-related peptide), without changes in sympathetic or skeletal muscle motor innervation. Similarly, there was no change in epidermal innervation. In culture, sensory neurons displayed enriched VDR expression in growth cones, and sprouting was regulated by VDR-mediated rapid response signaling pathways, while sympathetic outgrowth was not affected by different concentrations of 1,25-dihydroxyvitamin D. These findings indicate that vitamin D deficiency can lead to selective alterations in target innervation, resulting in presumptive nociceptor hyperinnervation of skeletal muscle, which in turn is likely to contribute to muscular hypersensitivity and pain.

Sex differences in behavior and expression of CGRP-related genes in a rodent model of chronic migraine.

OBJECTIVE: The objectives of this study were to develop a preclinical rodent model that produces migraine-like behaviors based on International Headache Society diagnostic criteria, to determine whether sex differences are present, and to determine whether expression of calcitonin gene-related peptide (CGRP) and the genes encoding its receptor in trigeminal ganglion or medulla correlates with those behaviors. BACKGROUND: Few animal studies of migraine have tested behaviors associated with migraine diagnostic criteria. In this study, changes in activity and in mechanical sensitivity of facial regions following application of inflammatory soup (IS) or vehicle (phosphate-buffered saline [PBS]) to the dura were measured to model changes in routine activity and allodynia. CGRP, an important mediator of migraine pathogenesis, and the 3 components of its receptor, calcitonin-like receptor (CLR), receptor activity-modifying protein 1 (RAMP1), and receptor component protein (RCP) mRNAs were quantified in the trigeminal ganglion and medulla to identify baseline sex differences and changes associated with application of IS or PBS to the dura. METHODS: Male and female Sprague-Dawley rats were implanted with a dural cannula. Groups of rats were treated with 10 or 20 µL volumes of IS or PBS. Baseline behavioral testing was conducted prior to surgery and again at 7 days postsurgery, and dural application of IS or PBS was performed repeatedly for a total of 8 applications. Locomotor activity was assessed using force plate actimetry during and following application to provide information on distance traveled, bouts of low mobility, spatial confinement, and focused energy. Periorbital and perimasseter sensory testing was performed 20 minutes post-application to measure allodynia. The rats were sacrificed 30 minutes following the final dural treatment, tissue was dissected and total RNAs were isolated from ipsilateral trigeminal ganglia and ipsilateral medulla. Quantitative real-time polymerase chain reactions were used to measure the expression of amplified constructs using gene-specific primers for CGRP, RAMP1, CLR, and RCP. RESULTS: Both males and females showed behavioral effects of IS application, but there were pronounced sex differences. Females showed effects at the lower dose, and activity changes were present for a longer duration, but males required fewer applications of IS to exhibit behavioral changes. Females showed increased withdrawal responses for periorbital and perimasseter mechanical testing (10 µL IS groups), and males showed increased perimasseter withdrawal responses (20 µL IS group). In the trigeminal ganglion, there were no baseline sex differences in CGRP-encoding mRNA, but females had lower baseline expression of RAMP1, CLR, and RCP-encoding mRNAs. In the medulla, females had higher baseline levels of CGRP-encoding mRNAs and lower baseline levels of RAMP1, CLR, and RCP-encoding mRNAs than males. Both IS and PBS increased expression of mRNAs encoding CGRP, RAMP1, RCP, and CLR in the trigeminal ganglion in males, but in females, only CLR and RCP were increased. In the medulla both IS and PBS increased expression of CGRP, CLR in males and CLR and RCP in females. Thus, expression of CGRP-related genes did not mirror the behavioral differences between IS and PBS groups. Instead, CGRP-related genes were upregulated by both IS and PBS applications. CONCLUSIONS: This study demonstrates significant changes in locomotor activity and facial allodynia associated with application of IS to the dura as well as significant sex differences, demonstrating that International Headache Society diagnostic criteria can be used to design a rodent behavioral model of migraine. In addition, there were prominent baseline sex differences in expression of CGRP and its receptor in both the trigeminal ganglion and medulla, but the majority of changes in expression of CGRP and its receptor were present in both the IS and PBS treated rats. This suggests that the CGRP pathway responds to changes in intracranial pressure or meningeal stretch, while migraine-like behaviors occur after meningeal inflammation.

The GABAβ receptor as a target for antidepressant drug action.

Preclinical and clinical data suggest that a modification in GABA(B) receptor expression and function may contribute to the symptoms of major depression and the response to antidepressants. This includes laboratory animal experiments demonstrating that antidepressants modify brain GABA(B) receptor expression and function and that GABA(B) receptor antagonists display antidepressant potential in animal models of this condition. Clinical and post-mortem studies reveal changes in GABAergic transmission associated with depression as well as depression-related changes in GABA(B) subunit expression that are localized to the cortical depression network. Detailed in this review are the preclinical and clinical data implicating a role for the GABA(B) receptor system in mediating symptoms of this disorder and its possible involvement in the response to antidepressants. Particular emphasis is placed on clinical and post-mortem studies, including previously unpublished work demonstrating regionally-selective modifications in GABA(B) receptor subunit expression in brain samples obtained from depressed subjects. Together with the earlier preclinical studies, these new data point to a role for the GABA(B) system in major depression and support the antidepressant potential of GABA(B) receptor antagonists.

Dopamine receptor alterations in female rats with diet-induced decreased brain docosahexaenoic acid (DHA): interactions with reproductive status.

Decreased tissue levels of n-3 (omega-3) fatty acids, particularly docosahexaenoic acid (DHA), are implicated in the etiologies of non-puerperal and postpartum depression. This study examined the effects of a diet-induced loss of brain DHA content and concurrent reproductive status on dopaminergic parameters in adult female Long-Evans rats. An alpha-linolenic acid-deficient diet and breeding protocols were used to produce virgin and parous female rats with cortical phospholipid DHA levels 20-22% lower than those fed a control diet containing adequate alpha-linolenic acid. Decreased brain DHA produced a significant main effect of decreased density of ventral striatal D(2)-like receptors. Virgin females with decreased DHA also exhibited higher density of D(1)-like receptors in the caudate nucleus than virgin females with normal DHA. These receptor alterations are similar to those found in several rodent models of depression, and are consistent with the proposed hypodopaminergic basis for anhedonia and motivational deficits in depression.

G-protein activation by neurokinin-1 receptors is dynamically regulated during persistent nociception.

Previous work has demonstrated that persistent nociception evokes increased neurokinin-1 receptor (NK-1) gene expression in the spinal cord dorsal horn of the rat within 2 h but has failed to elucidate the relationship between increased NK-1 gene expression at later time points and functional regulation of NK-1 receptor signaling. This study was undertaken to assess changes in NK-1 receptor mRNA levels in models of persistent inflammatory hyperalgesia and to relate them to changes in the functional coupling of NK-1 receptors to G-protein activity in the dorsal horn of the rat. Thus, unilateral intraplantar formalin or complete Freund's adjuvant was used to alter mechanical and thermal withdrawal thresholds in the inflamed paw. One to 96 h later, NK-1 receptor mRNA levels were quantified using solution hybridization-nuclease protection assays. Formalin-evoked inflammation produced a 2-fold unilateral increase in NK-1 receptor mRNA levels apparent from 2 to 96 h postinjection. Histological sections of the lumbar cord from similarly treated rats were used to generate concentration-response curves using GTPgammaS35 functional binding assays stimulated by an NK-1 selective agonist. Results showed that formalin evoked a transient, bilateral decrease in the maximal functional response to 35% of control in the treated side at 24 h postinjection and as much as a 10-fold leftward shift in the EC50 of the agonist at 12 to 96 h postinjection. These results provide novel evidence that peripheral nociceptive activation promotes a central mechanism of hyperalgesia through increased functional sensitivity of NK-1 receptors in the spinal cord dorsal horn.