Increased accumbens Cdk5 expression in rats after short-access to self-administered cocaine, but not after long-access sessions

Upregulation of cyclin-dependent kinase 5 (Cdk5) after chronic cocaine administration has led to speculation that Cdk5 plays an important role in drug addiction. However, as Cdk5 involvement is implicated in a variety of neural events, including neuronal development, synaptic plasticity and learning, a specific role in drug abuse is yet to be determined. The present study utilized cocaine self-administration and food-reinforced operant procedures to assess possible relationships between cocaine intake, food-reinforced operant responding, behavioral activity, and Cdk5 levels in the nucleus accumbens (NAcc), ventral tegmental area (VTA), and prefrontal cortex (PFC) in rats. In Experiment 1, animals undergoing daily cocaine self-administration (1-h/30 days) or food-reinforced operant sessions (20-min/30 days) showed significant between-group differences in operant responding and behavioral activity, but no significant differences in NAcc, VTA or PFC Cdk5 levels compared to a Handled Control group. In Experiment 2, animals that had self-administered cocaine in 10 daily 1-h sessions (Short-Access Cocaine) showed significantly greater NAcc Cdk5 expression compared to an Unhandled Control group, and no evidence of cocaine-induced behavioral sensitization. Animals given 4-h daily access to cocaine over the same number of sessions (Long-Access Cocaine) showed significantly enhanced cocaine-reinforced responding and locomotor activation by the end of the sessions, but no significant differences in Cdk5 expression compared to Control animals. These findings suggest that overexpression of Cdk5 may be a transient adaptation to cocaine experience that subsides with increased cocaine exposure and does not correspond with measures of cocaine-induced behavioral sensitization.     

Identification of an immune-responsive mesolimbocortical serotonergic system: potential role in regulation of emotional behavior

Peripheral immune activation can have profound physiological and behavioral effects including induction of fever and sickness behavior. One mechanism through which immune activation or immunomodulation may affect physiology and behavior is via actions on brainstem neuromodulatory systems, such as serotonergic systems. We have found that peripheral immune activation with antigens derived from the nonpathogenic, saprophytic bacterium, Mycobacterium vaccae, activated a specific subset of serotonergic neurons in the interfascicular part of the dorsal raphe nucleus (DRI) of mice, as measured by quantification of c-Fos expression following intratracheal (12 h) or s.c. (6 h) administration of heat-killed, ultrasonically disrupted M. vaccae, or heat-killed, intact M. vaccae, respectively. These effects were apparent after immune activation by M. vaccae or its components but not by ovalbumin, which induces a qualitatively different immune response. The effects of immune activation were associated with increases in serotonin metabolism within the ventromedial prefrontal cortex, consistent with an effect of immune activation on mesolimbocortical serotonergic systems. The effects of M. vaccae administration on serotonergic systems were temporally associated with reductions in immobility in the forced swim test, consistent with the hypothesis that the stimulation of mesolimbocortical serotonergic systems by peripheral immune activation alters stress-related emotional behavior. These findings suggest that the immune-responsive subpopulation of serotonergic neurons in the DRI is likely to play an important role in the neural mechanisms underlying regulation of the physiological and pathophysiological responses to both acute and chronic immune activation, including regulation of mood during health and disease states. Together with previous studies, these findings also raise the possibility that immune stimulation activates a functionally and anatomically distinct subset of serotonergic neurons, different from the subset of serotonergic neurons activated by anxiogenic stimuli or uncontrollable stressors. Consequently, selective activation of specific subsets of serotonergic neurons may have distinct behavioral outcomes.     

Systematically generated antibodies against human gene products: high throughput screening on sections from the rat nervous system

Completion of the Human Genome Project and recent developments in proteomics make it possible to systematically generate affinity reagents to a large portion of the proteome. Recently an antibody-based human protein atlas covering many organs including four areas of the brain has been released (www.proteinatlas.org). Due to the heterogeneity, size, and availability of tissue a more thorough analysis of the human brain is associated with considerable difficulties. Here we applied 120 antibodies raised against 112 human gene products to the smaller rat brain, a rodent animal model, where a single section represents a 'superarray' including many brain areas, and consequently allowing analysis of a huge number of cell types and their neurochemicals. Immunoreactive structures were seen in the investigated brain tissue after incubation with 56 antibodies (46.6%), of which 25 (20.8%) showed a clearly discrete staining pattern that was limited to certain areas, or subsets of brain cells. Bioinformatics, pre-adsorption tests and Western blot analysis were applied to identify non-specific antibodies. Eleven antibodies, including such raised against four 'ambiguous' proteins, passed all validation criteria, and the expression pattern and subcellular distribution of these proteins were studied in detail. To further explore the potential of the systematically generated antibodies, all 11 antibodies that passed validation were used to analyze the spinal cord and lumbar dorsal root ganglia after unilateral transection of the sciatic nerve. Discrete staining patterns were observed for four of the proteins, and injury-induced regulation was found for one of them. In conclusion, the study presented here suggests that a significant portion (10%) of the antibodies generated to a human protein can be used to analyze orthologues present in the rodent brain and to produce a protein-based atlas of the rodent brain. It is hoped that this type of antibody-based, high throughput screening of brain tissue from various rodent disease models will provide new information on the brain chemical neuroanatomy and insights in processes underlying neurological pathologies.     

Electrophysiological estimates of the time course of semantic and metrical encoding in Chinese speech production

Previous research has shown that conceptual/semantic information precedes segmental information in stress language production (such as English or Dutch). The present study investigated the relative time course of semantic and metrical encoding during Chinese (a tone language) production. Participants were shown pictures and carried out a dual-choice go/nogo decision based on semantic information (whether the depicted item was of a living or non-living object) and metrical information (whether the tone of picture's name was one type, tone 1 or tone 2, or the other type, tone 3 or tone 4). The behavior data, the N200 (related to response inhibition) and the lateralized readiness potentials (LRP, related to response preparation) indicated that semantic encoding was prior to metrical encoding. It provided evidence for early semantic encoding and later metrical encoding of speech production, and supported the serial model or the cascading model, rather than the parallel model of language production. This conclusion relating to the time course of semantic versus segmental encoding in stress languages might be generalized to semantic versus metrical encoding in tone languages such as Chinese.     

Selective anterograde tracing of the individual serotonergic and nonserotonergic components of the dorsal raphe nucleus projection to the vestibular nuclei

It is well known that the dorsal raphe nucleus (DRN) sends serotonergic and nonserotonergic projections to target regions in the brain stem and forebrain, including the vestibular nuclei. Although retrograde tracing studies have reported consistently that there are differences in the relative innervation of different target regions by serotonergic and nonserotonergic DRN neurons, the relative termination patterns of these two projections have not been compared using anterograde tracing methods. The object of the present investigation was to trace anterogradely the individual serotonergic and nonserotonergic components of the projection from DRN to the vestibular nuclei in rats. To trace nonserotonergic DRN projections, animals were pretreated with the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), and then, after 7 days, the anterograde tracer biotinylated dextran amine (BDA) was iontophoretically injected into the DRN. In animals treated with 5,7-DHT, nonserotonergic BDA-labeled fibers were found to descend exclusively within the ventricular plexus and to terminate predominantly within the periventricular aspect of the vestibular nuclei. Serotonergic DRN projections were traced by injecting 5,7-DHT directly into DRN, and amino-cupric-silver staining was used to visualize the resulting pattern of terminal degeneration. Eighteen hours after microinjection of 5,7-DHT into the DRN, fine-caliber degenerating serotonergic terminals were found within the region of the medial vestibular nucleus (MVN) that borders the fourth ventricle, and a mixture of fine- and heavier-caliber degenerating serotonergic terminals was located further laterally within the vestibular nuclear complex. These findings indicate that fine-caliber projections from serotonergic and nonserotonergic DRN neurons primarily innervate the periventricular regions of MVN, whereas heavier-caliber projections from serotonergic DRN neurons innervate terminal fields located in more lateral regions of the vestibular nuclei. Thus, serotonergic and nonserotonergic DRN axons target distinct but partially overlapping terminal fields within the vestibular nuclear complex, raising the possibility that these two DRN projection systems are organized in a manner that permits regionally-specialized regulation of processing within the vestibular nuclei.     

Influence of sex and estrous cycle on the effects of acute tryptophan depletion induced by a gelatin-based mixture in adult Wistar rats

Women are more vulnerable to develop depression and anxiety disorders than men. This may be related to higher serotonergic vulnerability in women. Serotonergic vulnerability entails that differences between people in the regulation of serotonin (5-HT) determine the vulnerability of an individual to develop depression or other 5-HT-related disorders. The aim of the present experiment was to evaluate whether male and female Wistar rats differ in serotonergic vulnerability. Here, a stronger behavioral response to acute tryptophan (TRP) depletion was assumed to reflect serotonergic vulnerability. Twenty-four male and 48 female rats were repeatedly subjected to treatment with a gelatin-based protein-carbohydrate mixture, either with or without L-tryptophan. Female estrous cycle phase was determined by means of vaginal smears and the females were divided into two groups based on their estrous cycle phase: pro-estrus/estrus and met-estrus/di-estrus. Blood samples showed stronger TRP depletion in males than females. There was no effect of estrous cycle on plasma TRP concentrations. In contrast, treatment effects on some brain TRP concentrations were influenced by estrous cycle phase, females in pro-estrus/estrus showed the strongest response to TRP depletion. In the open field test and home cage emergence test, females in pro-estrus/estrus also showed the strongest behavioral response to acute TRP depletion. In general, females showed more activity than males in anxiety-related situations and this effect appeared to be enhanced by TRP depletion. In the social interaction test, passive body contact in males and females in pro-estrus/estrus was decreased after TRP depletion whereas it was increased in females in the met-estrus/di-estrus phase. Acute TRP depletion affected object recognition, but did not affect behavior in the forced swimming test and a reaction time task. It is concluded that sex and estrous cycle phase can influence the behavioral response to TRP depletion, and that females in pro-estrus/estrus show the strongest behavioral response to acute TRP depletion.     

Morphology and physiology of lamina I neurons of the caudal part of the trigeminal nucleus

It has been suggested that in mammals, trigeminal lamina I neurons play a role in the processing and transmission of sensory information from the orofacial region. We investigated the physiological and morphological properties of trigeminal subnucleus caudalis (Sp5C) lamina I neurons in slices prepared from the medulla oblongata of 13- to 15-day-old postnatal rats using patch-clamp recordings and subsequent biocytin-streptavidin-Alexa labeling. Twenty-five neurons were recorded and immunohistochemically stained. The Sp5C lamina I consisted of several types of neurons which, on the basis of their responses to somatic current injection, can be classified into four groups: tonic neurons, which fired throughout the depolarizing pulse; phasic neurons, which expressed an initial burst of action potentials; delayed onset neurons, which showed a significant delay of the first action potential; and single spike neurons, characterized by only one to five action potentials at the very beginning of the depolarizing pulse even at high levels of stimulation intensity. Electrical stimulation of the spinal trigeminal tract evoked AMPA receptor-mediated excitatory postsynaptic currents (EPSC) exhibiting a strong polysynaptic component. AMPA receptor-mediated miniature excitatory postsynaptic currents (mEPSC) were characterized by a 10-90% rise time of 0.50+/-0.06 ms and a decay time constant of 2.5+/-0.5 ms. The kinetic properties of NMDA receptor-mediated EPSCs were measured at +40 mV. The 10-90% rise time was 8+/-2 ms and the deactivation time constants were 94+/-31 and 339+/-72 ms, respectively. Intracellular staining and morphological analysis revealed three groups of neurons: fusiform, pyramidal, and multipolar. Statistical analysis indicated that the electrophysiological properties and morphological characteristics are correlated. Tonic and phasic neurons were fusiform or pyramidal and delayed onset and single spike neurons were multipolar. Our results show that both the physiological and morphological properties of Sp5C lamina I neurons exhibit significant differences, indicating their specific integration in the processing and transmission of sensory information from the orofacial region.     

Metabolic clues regarding the enhanced performance of elite endurance athletes from orchiectomy-induced hormonal changes

This article examines the metabolic performance of an elite cyclist, Lance Armstrong, before and after his diagnosis with testicular cancer. Although a champion cyclist in 1-day events prior to his diagnosis of testicular cancer at age 25, he was not a contender in multi-day endurance cycle races such as the 3-week Tour de France. His genetic makeup and physiology (high VO2max, long femur, strong heavy build) coupled with his ambition and motivation enabled him at an early age to become one of the best 1-day cyclists in the world. Following his cancer diagnosis, he underwent a unilateral orchiectomy, brain surgery and four cycles of chemotherapy. After recovering, he returned to cycling and surprisingly excelled in the Tour de France, winning this hardest of endurance events 7 years running. This dramatic transformation from a 1-day to a 3-week endurance champion has led many to query how this is possible, and under the current climate, has led to suggestions of doping as to the answer to this metamorphosis. Physiological tests following his recovery indicated that physiological parameters such as VO2max were not affected by the unilateral orchiectomy and chemotherapy. We propose that his dramatic improvement in recovery between stages, the most important factor in winning multi-day stage races, is due to his unilateral orchiectomy, a procedure that results in permanent changes in serum hormones. These hormonal changes, specifically an increase in gonadotropins (and prolactin) required to maintain serum testosterone levels, alter fuel metabolism; increasing hormone sensitive lipase expression and activity, promoting increased free fatty acid (FFA) mobilization to, and utilization by, muscles, thereby decreasing the requirement to expend limiting glycogen stores before, during and after exercise. Such hormonal changes also have been associated with ketone body production, improvements in muscle repair and haematocrit levels and may facilitate the loss of body weight, thereby increasing power to weight ratio. Taken together, these hormonal changes act to limit glycogen utilization, delay fatigue and enhance recovery thereby allowing for optimal performances on a day-to-day basis. These insights provide the foundation for future studies on the endocrinology of exercise metabolism, and suggest that Lance Armstrong's athletic advantage was not due to drug use.     

Adenosine A2A receptors and brain injury: broad spectrum of neuroprotection, multifaceted actions and "fine tuning" modulation

This review summarizes recent developments that have contributed to understand how adenosine receptors, particularly A2A receptors, modulate brain injury in various animal models of neurological disorders, including Parkinson's disease (PD), stroke, Huntington's disease (HD), multiple sclerosis, Alzheimer's disease (AD) and HIV-associated dementia. It is clear that extracellular adenosine acting at adenosine receptors influences the functional outcome in a broad spectrum of brain injuries, indicating that A2A Rs may modulate some general cellular processes to affect neuronal cells death. Pharmacological, neurochemical and molecular/genetic approaches to the complex actions of A2A receptors in different cellular elements suggest that A2A receptor activation can be detrimental or protective after brain insults, depending on the nature of brain injury and associated pathological conditions. An interesting concept that emerges from these studies is A2A R's ability to fine tune neuronal and glial functions to produce neuroprotective effects. While the data presented here clearly highlight the complexity of using adenosinergic agents therapeutically in PD and other neurodegenerative disorders and point out many areas for further inquiry, they also confirm that adenosine receptor ligands, particularly A2A receptor ligands, have many promising characteristics that encourage the pursuit of their therapeutic potential.     

Modulators in concert for cognition: modulator interactions in the prefrontal cortex

Research on the regulation and function of ascending noradrenergic, dopaminergic, serotonergic, and cholinergic systems has focused on the organization and function of individual systems. In contrast, evidence describing co-activation and interactions between multiple neuromodulatory systems has remained scarce. However, commonalities in the anatomical organization of these systems and overlapping evidence concerning the post-synaptic effects of neuromodulators strongly suggest that these systems are recruited in concert; they influence each other and simultaneously modulate their target circuits. Therefore, evidence on the regulatory and functional interactions between these systems is considered essential for revealing the role of neuromodulators. This postulate extends to contemporary neurobiological hypotheses of major neuropsychiatric disorders. These hypotheses have focused largely on aberrations in the integrity or regulation of individual ascending modulatory systems, with little regard for the likely possibility that dysregulation in multiple ascending neuromodulatory systems and their interactions contribute essentially to the symptoms of these disorders. This review will paradigmatically focus on neuromodulator interactions in the PFC and be further constrained by an additional focus on their role in cognitive functions. Recent evidence indicates that individual neuromodulators, in addition to their general state-setting or gating functions, encode specific cognitive operations, further substantiating the importance of research concerning the parallel recruitment of neuromodulator systems and interactions between these systems.