Injection of solutions into cerebral tissue: Relation between volume and diffusion

Retrieval of contextual memory can be predicted by CA3 remapping and is differentially influenced by NMDAR activity in rat hippocampus subregions

Episodic memory is essential to navigate in a changing environment by recalling past events, creating new memories, and updating stored information from experience. Although the mechanisms for acquisition and consolidation have been profoundly studied, much less is known about memory retrieval. Hippocampal spatial representations are key for retrieval of contextually guided episodic memories. Indeed, hippocampal place cells exhibit stable location-specific activity which is thought to support contextual memory, but can also undergo remapping in response to environmental changes. It is unclear if remapping is directly related to the expression of different episodic memories. Here, using an incidental memory recognition task in rats, we showed that retrieval of a contextually guided memory is reflected by the levels of CA3 remapping, demonstrating a clear link between external cues, hippocampal remapping, and episodic memory retrieval that guides behavior. Furthermore, we describe NMDARs as key players in regulating the balance between retrieval and memory differentiation processes by controlling the reactivation of specific memory traces. While an increase in CA3 NMDAR activity boosts memory retrieval, dentate gyrus NMDAR activity enhances memory differentiation. Our results contribute to understanding how the hippocampal circuit sustains a flexible balance between memory formation and retrieval depending on the environmental cues and the internal representations of the individual. They also provide new insights into the molecular mechanisms underlying the contributions of hippocampal subregions to generate this balance.

Leptin excites basolateral amygdala principal neurons and reduces food intake by LepRb-JAK2-PI3K-dependent depression of GIRK channels

Leptin is an adipocyte-derived hormone that modulates food intake, energy balance, neuroendocrine status, thermogenesis, and cognition. Whereas a high density of leptin receptors has been detected in the basolateral amygdala (BLA) neurons, the physiological functions of leptin in the BLA have not been determined yet. We found that application of leptin excited BLA principal neurons by activation of the long form leptin receptor, LepRb. The LepRb-elicited excitation of BLA neurons was mediated by depression of the G protein-activated inwardly rectifying potassium (GIRK) channels. Janus Kinase 2 (JAK2) and phosphoinositide 3-kinase (PI3K) were required for leptin-induced excitation of BLA neurons and depression of GIRK channels. Microinjection of leptin into the BLA reduced food intake via activation of LepRb, JAK2, and PI3K. Our results may provide a cellular and molecular mechanism to explain the physiological roles of leptin in vivo.

Arduino based intra-cerebral microinjector device for neuroscience research

Stereotaxic surgery is a less invasive form of surgery that uses a three-dimensional coordinate system to place instruments at a specific location in the brain. Through this type of surgery, one can place needles among other tools within the structures of the brain. Therefore, injections can be given in order to deliver substances that cannot cross the blood-brain barrier. The two most important parameters of the microinjection to control are volume and speed. The volume should not be so large that it displaces the brain tissue and tears it. The injection speed must also be slow so that the liquid that comes out of the syringe can diffuse into the tissue without displacing it and damaging it. Thus, the objectives of the present work are: 1) To develop not a 3D printed prototype but an end-user device. 2) The device must be for animal research only. 3) It must have the same precision in volume and speed as commercial devices. 4) It must be adjustable for microsyringes from 0.5 µl to 1 ml. 5) It must be possible to place it directly on the stereotaxic surgery apparatus and to use it separately. 6) The price must be substantially lower than that of the commercial devices.

Prepulse inhibition of the acoustic startle reflex impairment by 5-HT2A receptor activation in the inferior colliculusis prevented by GABAA receptor blockade in the pedunculopontine tegmental nucleus

The relationship between serotonin dysfunction and schizophrenia commenced with the discovery of the effects of lysergic acid diethylamide (LSD) that has high affinity for 5-HT_2A receptors. Activation of these receptors produces perceptual and behavioural changes such as illusions, visual hallucinations and locomotor hyperactivity. Using prepulse inhibition (PPI) of the acoustic startle, which is impaired in schizophrenia,we aimed to investigate:i) the existence of a direct and potentially inhibitory neural pathway between the inferior colliculus (IC) and the pedunculopontine tegmental nucleus (PPTg) involved in the mediation of PPI responses by a neural tract tracing procedure;ii) if the microinjection of the 5-HT_2A receptors agonist DOI in IC would activate neurons in this structure and in the PPTg by a c-Fos protein immunohistochemistry study;iii) whether the deficits in PPI responses, observed after the administration of DOI in the IC, could be prevented by the concomitant microinjection of the GABA_A receptor antagonist bicuculline in the PPTg.Male Wistar rats were used in this study. An IC-PPTg reciprocated neuronal pathway was identified by neurotracing. The number of c-Fos labelled cells was lower in the DOI group in IC and PPTg, suggesting that this decrease could be due to the high levels of GABA in both structures. The concomitant microinjections of bicuculline in PPTg and DOI in IC prevented the PPI deficit observed after the IC microinjection of DOI. Ourfindings suggest that IC 5-HT_2A receptors may be at least partially involved in the regulation of inhibitory pathways mediating PPI response in IC and PPTg structures.

Reduced mechanical hypersensitivity by inhibition of the amygdala in experimental neuropathy: Sexually dimorphic contribution of spinal neurotransmitter receptors

Here we studied spinal neurotransmitter mechanisms involved in the reduction of mechanical hypersensitivity by inhibition of the amygdaloid central nucleus (CeA) in male and female rats with spared nerve injury (SNI) model of neuropathy. SNI induced mechanical hypersensitivity that was stronger in females. Reversible blocking of the CeA with muscimol (GABAA receptor agonist) induced a reduction of mechanical hypersensitivity that did not differ between males and females. Following spinal co-administration of atipamezole (α2-adrenoceptor antagonist), the reduction of mechanical hypersensitivity by CeA muscimol was attenuated more in males than females. In contrast, following spinal co-administration of raclopride (dopamine D2 receptor antagonist) the reduction of hypersensitivity by CeA muscimol was attenuated more in females than males. The reduction of mechanical hypersensitivity by CeA muscimol was equally attenuated in males and females by spinal co-administration of WAY-100635 (5-HT1A receptor antagonist) or bicuculline (GABAA receptor antagonist). The CeA muscimol induced attenuation of ongoing pain-like behavior (conditioned place preference test) that was reversed by spinal co-administration of atipamezole in both sexes. The results support the hypothesis that CeA contributes to mechanical hypersensitivity and ongoing pain-like behavior in SNI males and females. Disinhibition of descending controls acting on spinal α2-adrenoceptors, 5-HT1A, dopamine D2 and GABAA receptors provides a plausible explanation for the reduction of mechanical hypersensitivity by CeA block in SNI. The involvement of spinal dopamine D2 receptors and α2-adrenoceptors in the CeA muscimol-induced reduction of mechanical hypersensitivity is sexually dimorphic, unlike that of spinal α2-adrenoceptors in the reduction of ongoing neuropathic pain.

Optomagnetic nanofluids for controlled brain hyperthermia: a critical study

Optomagnetic nanofluids (OMNFs) are colloidal dispersions of nanoparticles (NPs) with combined magnetic and optical properties. They are especially appealing in biomedicine since they can be used as minimally invasive platforms for controlled hyperthermia treatment of otherwise difficultly accessible tumors such as intracranial ones. On the one hand, magnetic NPs act as heating mediators when subjected to alternating magnetic fields or light irradiation. On the other hand, suitably tailored luminescent NPs can provide a precise and remote thermal readout in real time. The combination of heating and thermometric properties allows, in principle, to precisely monitor the increase in the temperature of brain tumors up to the therapeutic level, without causing undesired collateral damage. In this work we demonstrate that this view is an oversimplification since it ignores the presence of relevant interactions between magnetic (γ-Fe₂O₃ nanoflowers) and luminescent nanoparticles (Ag₂S NPs) that result in a detrimental alteration of their physicochemical properties. The magnitude of such interactions depends on the interparticle distance and on the surface properties of nanoparticles. Experiments performed in mouse brains (phantoms and ex vivo) revealed that OMNFs cannot induce relevant heating under alternating magnetic fields and fail to provide reliable temperature reading. In contrast, we demonstrate that the use of luminescent nanofluids (containing only Ag₂S NPs acting as both photothermal agents and nanothermometers) stands out as a better alternative for thermally monitored hyperthermia treatment of brain tumors in small animal models.

Pathway-specific inhibition of critical projections from the mediodorsal thalamus to the frontal cortex controls kindled seizures

There is a large unmet need for improved treatment for temporal lobe epilepsy (TLE); circuit-specific manipulation that disrupts the initiation and propagation of seizures is promising in this regard. The midline thalamus, including the mediodorsal nucleus (MD) is a critical distributor of seizure activity, but its afferent and efferent pathways that mediate seizure activity are unknown. Here, we used chemogenetics to silence input and output projections of the MD to discrete regions of the frontal cortex in the kindling model of TLE in rats. Chemogenetic inhibition of the projection from the amygdala to the MD abolished seizures, an effect that was replicated using optogenetic inhibition. Chemogenetic inhibition of projections from the MD to the prelimbic cortex likewise abolished seizures. By contrast, inhibition of projections from the MD to other frontal regions produced partial (orbitofrontal cortex, infralimbic cortex) or no (cingulate, insular cortex) attenuation of behavioral or electrographic seizure activity. These results highlight the particular importance of projections from MD to prelimbic cortex in the propagation of amygdala-kindled seizures.

Neuronal activity reorganization in motor cortex for successful locomotion after a lesion in the ventrolateral thalamus

Thalamic stroke leads to ataxia if the cerebellum-receiving ventrolateral thalamus (VL) is affected. The compensation mechanisms for this deficit are not well understood, particularly the roles that single neurons and specific neuronal subpopulations outside the thalamus play in recovery. The goal of this study was to clarify neuronal mechanisms of the motor cortex involved in mitigation of ataxia during locomotion when part of the VL is inactivated or lesioned. In freely ambulating cats, we recorded the activity of neurons in layer V of the motor cortex as the cats walked on a flat surface and horizontally placed ladder. We first reversibly inactivated ∼10% of the VL unilaterally using glutamatergic transmission antagonist CNQX and analyzed how the activity of motor cortex reorganized to support successful locomotion. We next lesioned 50%-75% of the VL bilaterally using kainic acid and analyzed how the activity of motor cortex reorganized when locomotion recovered. When a small part of the VL was inactivated, the discharge rates of motor cortex neurons decreased, but otherwise the activity was near normal, and the cats walked fairly well. Individual neurons retained their ability to respond to the demand for accuracy during ladder locomotion; however, most changed their response. When the VL was lesioned, the cat walked normally on the flat surface but was ataxic on the ladder for several days after lesion. When ladder locomotion normalized, neuronal discharge rates on the ladder were normal, and the shoulder-related group was preferentially active during the stride's swing phase.NEW & NOTEWORTHY This is the first analysis of reorganization of the activity of single neurons and subpopulations of neurons related to the shoulder, elbow, or wrist, as well as fast- and slow-conducting pyramidal tract neurons in the motor cortex of animals walking before and after inactivation or lesion in the thalamus. The results offer unique insights into the mechanisms of spontaneous recovery after thalamic stroke, potentially providing guidance for new strategies to alleviate locomotor deficits after stroke.

Elucidating the Pivotal Neuroimmunomodulation of Stem Cells in Spinal Cord Injury Repair

Spinal cord injury (SCI) is a distressing incident with abrupt onset of the motor as well as sensory dysfunction, and most often, the injury occurs as result of high-energy or velocity accidents as well as contact sports and falls in the elderly. The key challenges associated with nerve repair are the lack of self-repair as well as neurotrophic factors and primary and secondary neuronal apoptosis, as well as factors that prevent the regeneration of axons locally. Neurons that survive the initial traumatic damage may be lost due to pathogenic activities like neuroinflammation and apoptosis. Implanted stem cells are capable of differentiating into neural cells that replace injured cells as well as offer local neurotrophic factors that aid neuroprotection, immunomodulation, axonal sprouting, axonal regeneration, and remyelination. At the microenvironment of SCI, stem cells are capable of producing growth factors like brain-derived neurotrophic factor and nerve growth factor which triggers neuronal survival as well as axonal regrowth. Although stem cells have proven to be of therapeutic value in SCI, the major disadvantage of some of the cell types is the risk for tumorigenicity due to the contamination of undifferentiated cells prior to transplantation. Local administration of stem cells via either direct cellular injection into the spinal cord parenchyma or intrathecal administration into the subarachnoid space is currently the best transplantation modality for stem cells during SCI.

Gene delivery to neurons in the auditory brainstem of barn owls using standard recombinant adeno-associated virus vectors

Recombinant adeno-associated virus (rAAV) vectors are a commonly used tool for gene delivery. There is a large choice of different serotypes whose transduction efficiency varies for different animal species. In this study, three rAAV vectors were tested for transduction efficiency in the auditory brainstem of adult barn owls (Tyto alba) which are not standard laboratory animals. Injections with rAAV serotypes 2/1 and 2/5 resulted in reliable expression in various nuclei of the auditory brainstem of barn owls. Both vectors showed evidence of being spread by axonal transport. However, only rAAV2/5 also showed expression in regions far distant from the injection site, suggesting long-range axonal transport in connections along the auditory pathway. In contrast, injections with rAAV2/9 resulted in no expression. Our results demonstrate for the first time that commercially available rAAV vectors can be used for reliable gene expression in the barn owl auditory brainstem and pave the way toward optogenetic manipulation of neural activity in this important animal species in neuroethology and auditory physiology.

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Standard rAAV vectors effectively mediate gene expression in the barn-owl brain.

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rAAV2/1 was best suited for confined expression around the targeted injection site.

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Due to more axonal transport, rAAV2/5 resulted in wider spread of expressed genes.

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rAAV-mediated expression is expected to remain stable for an extended period of time.

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rAAV expression and stability are excellent prerequisites for optogenetic experiments.

Dopamine D4 receptor modulates inhibitory transmission in pallido-pallidal terminals and regulates motor behavior

Two major groups of terminals release GABA within the Globus pallidus; one group is constituted by projections from striatal neurons, while endings of the intranuclear collaterals form the other one. Each neurons' population expresses different subtypes of dopamine D2-like receptors: D₂ R subtype is expressed by encephalin-positive MSNs, while pallidal neurons express the D₄ R subtype. The D₂ R modulates the firing rate of striatal neurons and GABA release at their projection areas, while the D₄ R regulates Globus pallidus neurons excitability and GABA release at their projection areas. However, it is unknown if these receptors control GABA release at pallido-pallidal collaterals and regulate motor behavior. Here, we present neurochemical evidence of protein content and binding of D₄ R in pallidal synaptosomes, control of [³ H] GABA release in pallidal slices of rat, electrophysiological evidence of the presence of D₄ R on pallidal recurrent collaterals in mouse slices, and turning behavior induced by D₄ R antagonist microinjected in amphetamine challenged rats. As in projection areas of pallidal neurons, GABAergic transmission in pallido-pallidal recurrent synapses is under modulation of D₄ R, while the D₂ R subtype, as known, modulates striato-pallidal projections. Also, as in projection areas, D₄ R contributes to control the motor activity differently than D₂ R. This study could help to understand the organization of intra-pallidal circuitry.

The modulation of striatonigral and nigrotectal pathways by CB1 signalling in the substantia nigra pars reticulata regulates panic elicited in mice by urutu-cruzeiro lancehead pit vipers

Cannabinoid receptor type 1 (CB₁R) is widely distributed in the substantia nigra pars reticulata (SNpr). However, the role of CB₁R at the SNpr level in threatening situations is poorly understood. We investigated the role of CB₁R in the SNpr on the expression of fear responses in mice confronted with urutu-cruzeiro pit vipers. First, a bidirectional neurotracer was injected into the SNpr; then, immunostaining of the vesicular GABA transporter was conducted at the levels of the striatum (CPu) and deep layers of the superior colliculus (dlSC). In addition, CB₁R immunostaining and GABA labelling were performed in the SNpr. Using a prey-versus-snake paradigm, mice were pretreated with the CB₁R antagonist AM251 (100 pmol) and treated with the endocannabinoid anandamide (AEA, 5 pmol) in the SNpr, followed by bicuculline (40 ng) in the dlSC, and were then confronted with a snake. Bidirectional neural tract tracers associated with immunofluorescence showed the GABAergic striatonigral disinhibitory and nigrotectal inhibitory pathways. Furthermore, we showed that CB₁R labelling was restricted to axonal fibres surrounding SNpr GABAergic cells. We also demonstrated a decrease in the defensive behaviours of mice treated with AEA in the SNpr, but this effect was blocked by pre-treatment with AM251 in this structure. Taken together, our results show that the panicolytic consequences of the AEA enhancement in the SNpr are signalled by CB₁R, suggesting that CB₁R localised in axon terminals of CPu GABAergic neurons in the SNpr modulates the activity of the nigrotectal GABAergic pathway during the expression of defensive behaviours in threatening situations.

Contribution of the ventrolateral thalamus to the locomotion-related activity of motor cortex

The activity of motor cortex is necessary for accurate stepping on a complex terrain. How this activity is generated remains unclear. The goal of this study was to clarify the contribution of signals from the ventrolateral thalamus (VL) to formation of locomotion-related activity of motor cortex during vision-independent and vision-dependent locomotion. In two cats, we recorded the activity of neurons in layer V of motor cortex as cats walked on a flat surface and a horizontal ladder. We reversibly inactivated ~10% of the VL unilaterally with the glutamatergic transmission antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and analyzed how this affected the activity of motor cortex neurons. We examined neuronal subpopulations with somatosensory receptive fields on different segments of the forelimb and pyramidal tract projecting neurons (PTNs). We found that the VL contribution to the locomotion-related activity of motor cortex is very powerful and has both excitatory and inhibitory components. The magnitudes of both the excitatory and inhibitory contributions fluctuate over the step cycle and depend on locomotion task. On a flat surface, the VL contributes more excitation to the shoulder- and elbow-related neurons than the wrist/paw-related cells. The VL excites the shoulder-related group the most during the transition from stance to swing phase, while most intensively exciting the elbow-related group during the transition from swing to stance. The VL contributes more excitation for the fast- than slow-conducting PTNs. Upon transition to vision-dependent locomotion on the ladder, the VL contribution increases more for the wrist/paw-related neurons and slow-conducting PTNs.NEW & NOTEWORTHY How the activity of motor cortex is generated and the roles that different inputs to motor cortex play in formation of response properties of motor cortex neurons during movements remain unclear. This is the first study to characterize the contribution of the input from the ventrolateral thalamus (VL), the main subcortical input to motor cortex, to the activity of motor cortex neurons during vision-independent and vision-dependent locomotion.

Manipulating Neural Circuits in Anesthesia Research

The neural circuits underlying the distinct endpoints that define general anesthesia remain incompletely understood. It is becoming increasingly evident, however, that distinct pathways in the brain that mediate arousal and pain are involved in various endpoints of general anesthesia. To critically evaluate this growing body of literature, familiarity with modern tools and techniques used to study neural circuits is essential. This Readers' Toolbox article describes four such techniques: (1) electrical stimulation, (2) local pharmacology, (3) optogenetics, and (4) chemogenetics. Each technique is explained, including the advantages, disadvantages, and other issues that must be considered when interpreting experimental results. Examples are provided of studies that probe mechanisms of anesthesia using each technique. This information will aid researchers and clinicians alike in interpreting the literature and in evaluating the utility of these techniques in their own research programs.

Cannabidiol-induced panicolytic-like effects and fear-induced antinociception impairment: the role of the CB1 receptor in the ventromedial hypothalamus

RATIONALE

The behavioural effects elicited by chemical constituents of Cannabis sativa, such as cannabidiol (CBD), on the ventromedial hypothalamus (VMH) are not well understood. There is evidence that VMH neurons play a relevant role in the modulation of unconditioned fear-related defensive behavioural reactions displayed by laboratory animals.

OBJECTIVES

This study was designed to explore the specific pattern of distribution of the CB₁ receptors in the VMH and to investigate the role played by this cannabinoid receptor in the effect of CBD on the control of defensive behaviours and unconditioned fear-induced antinociception.

METHODS

A panic attack-like state was triggered in Wistar rats by intra-VMH microinjections of N-methyl-D-aspartate (NMDA). One of three different doses of CBD was microinjected into the VMH prior to local administration of NMDA. In addition, the most effective dose of CBD was used after pre-treatment with the CB₁ receptor selective antagonist AM251, followed by NMDA microinjections in the VMH.

RESULTS

The morphological procedures demonstrated distribution of labelled CB₁ receptors on neuronal perikarya situated in dorsomedial, central and ventrolateral divisions of the VMH. The neuropharmacological approaches showed that both panic attack-like behaviours and unconditioned fear-induced antinociception decreased after intra-hypothalamic microinjections of CBD at the highest dose (100 nmol). These effects, however, were blocked by the administration of the CB₁ receptor antagonist AM251 (100 pmol) in the VMH.

CONCLUSION

These findings suggest that CBD causes panicolytic-like effects and reduces unconditioned fear-induced antinociception when administered in the VMH, and these effects are mediated by the CB₁ receptor-endocannabinoid signalling mechanism in VMH.

Dorsal raphe nucleus 5-Hydroxytryptamine 2A receptors are critical for the organisation of panic attack-like defensive behaviour and unconditioned fear-induced antinociception elicited by the chemical stimulation of superior colliculus neurons

Microinjections of N-methyl-d-aspartic acid (NMDA) in the midbrain tectum structures produce panic attack-like defensive behaviours, followed by an antinociceptive response. It has been suggested that fear-related defensive responses organised by brainstem neurons can be modulated by 5-hydroxytryptamine (5-HT). However, there is a shortage of studies showing the role of dorsal raphe nucleus (DRN) 5-HT_2A receptors in the modulation of panic-like behaviour and fear-induced antinociception organised by the superior colliculus (SC). The purpose of this study was to investigate the participation of DRN 5-HT_2A receptors in the modulation of panic attack-like behaviour and antinociception evoked by intra-SC injections of NMDA. In experiment I, the animals received microinjections of physiological saline or NMDA (6, 9 and 12 nmol) in the deep layers of the SC (dlSC). In experiment II, the most effective dose of NMDA (12 nmol) or vehicle was preceded by microinjections of vehicle or the 5-HT_2A receptor selective antagonist R-96544 at different concentrations (0.5, 5 and 10 nM) in the DRN. Both proaversive and antinociceptive effects elicited by intra-dlSC injections of NMDA were attenuated by DRN pretreatment with R-96544. In addition, a morphological analysis showed that 5-HT_2A receptors are present in GABAergic interneurons in the DRN. Taken together, these findings suggest that DRN 5-HT_2A receptors are critical for the modulation of both panic attack-like defensive behaviour organised by SC neurons and unconditioned fear-induced antinociception. A possible interaction between serotonergic inputs, GABAergic interneurons and serotonergic outputs from the DRN was also considered.

Understanding the Effects of General Anesthetics on Cortical Network Activity Using Ex Vivo Preparations

General anesthetics have been used to ablate consciousness during surgery for more than 150 yr. Despite significant advances in our understanding of their molecular-level pharmacologic effects, comparatively little is known about how anesthetics alter brain dynamics to cause unconsciousness. Consequently, while anesthesia practice is now routine and safe, there are many vagaries that remain unexplained. In this paper, the authors review the evidence that cortical network activity is particularly sensitive to general anesthetics, and suggest that disruption to communication in, and/or among, cortical brain regions is a common mechanism of anesthesia that ultimately produces loss of consciousness. The authors review data from acute brain slices and organotypic cultures showing that anesthetics with differing molecular mechanisms of action share in common the ability to impair neurophysiologic communication. While many questions remain, together, ex vivo and in vivo investigations suggest that a unified understanding of both clinical anesthesia and the neural basis of consciousness is attainable.

Differential Anaesthetic Effects following Microinjection of Thiopentone and Propofol into the Pons of Adult Rats: A Pilot Study

Identifying the central nervous system sites of action of anaesthetics is important for understanding the link between their molecular actions and clinical effects. The aim of the present pilot study was to compare the anaesthetic effect of bilateral microinjections of propofol and thiopentone (both 200 μg/μl, in Intralipid and 0.9% saline respectively) into a recently discovered anaesthetic-sensitive region in the rat brainstem, the “mesopontine tegmental anaesthetic area” (MPTA). Microinjections (1 μl per side) were made into the MPTA of fifteen male Sprague-Dawley rats. The effect of each agent on spontaneous behaviour, postural control and nociceptive responsiveness was subjectively assessed according to established criteria. The main finding was that thiopentone induced an “anaesthesia-like” state, including complete atonia and loss of righting ability, in 20% of the subjects. Overall, thiopentone significantly reduced postural control and had a moderate antinociceptive effect compared to saline microinjections (P<0.01 and 0.05, respectively, Wilcoxon test). In contrast, propofol did not induce “anaesthesia” in any animal tested, although a similar antinociceptive effect to that of thiopentone was observed (P<0.05, Wilcoxon test). In summary, propofol and thiopentone have different effects when microinjected into the MPTA. While both agents reduced reflex withdrawal to a nociceptive stimulus, only thiopentone induced an “anaesthesia-like” state.

Infusions of scopolamine in dorsal hippocampus reduce anticipatory responding in an appetitive trace conditioning procedure

INTRODUCTION

Trace conditioning is impaired by lesions to dorsal hippocampus, as well as by treatment with the muscarinic acetylcholine antagonist scopolamine. However, the role of muscarinic receptors within hippocampus has received little attention.

METHODS

The present study examined the effects of intra-hippocampal infusion of scopolamine (30 µg/side) in an appetitive (2 vs. 10 s) trace conditioning procedure using sucrose pellets as the unconditioned stimulus (US). Locomotor activity (LMA) was examined in a different apparatus.

RESULTS

Intra-hippocampal scopolamine reduced responding to the 2 s trace conditioned stimulus (CS). Intra-hippocampal scopolamine similarly depressed responding within the inter-stimulus interval (ISI) at both 2 and 10 s trace intervals, but there was no such effect in the inter-trial interval. There was also some overall reduction in responding when the US was delivered; significant at the 10 s but not at the 2 s trace interval. A similar pattern of results to that seen in response to the CS during acquisition was shown drug-free (in the 5 s post-CS) in the extinction tests of conditioned responding. LMA was increased under scopolamine.

CONCLUSIONS

The results suggest that nonspecific changes in activity or motivation to respond for the US cannot explain the reduction in trace conditioning as measured by reduced CS responding and in the ISI. Rather, the findings of the present study point to the importance of associative aspects of the task in determining its sensitivity to the effects of scopolamine, suggesting that muscarinic receptors in the hippocampus are important modulators of short-term working memory.

Axons of Passage and Inputs to Superior Cervical Ganglion in Rat

Wheat germ agglutinin-horseradish peroxidase was injected into the entire (0.8 μL) or partial (rostral or caudal, 0.1-0.3 μL) superior cervical ganglion (SCG) of the rat (male Sprague-Dawley, N = 35) to examine the distribution of neurons in the middle (MCG) and inferior (ICG) cervical ganglion that send axons bypass the SCG. Whole-mounts of the SCG, cervical sympathetic trunk (CST), MCG, ICG, and sections of the brainstem and spinal cord were prepared. With entire SCG tracer injection, neurons were labeled evenly in the MCG (left: 258, right: 121), ICG (left: 848, right: 681), and CST (up to 770). Some neurons grouped in a single bulge just rostral to the MCG, which we termed as the "premiddle cervical ganglion" (pMCG). The left pMCG (120) is larger and has more neurons than the right pMCG (82). Centrally, neurons were labeled in lamina IX of cervical segments (C1: 18%, C2: 46%, C3: 33%, C4: 3%), intermediate zone of thoracic segments (T1: 31%, T2: 35%, T3: 27%, T4: 7%), and intermediate reticular nuclei (96%) and perifacial zone (4%) of brainstem. The rostral and caudal SCG injection selectively labeled neurons mainly in brainstem, C1-C2 and in T1-T2, respectively. Before projecting to their peripheral targets, many neurons in pMCG, MCG and ICG run rostrally within the CST rather than segmentally through the closest rami, from the level of SCG or above. Neurons in pMCG and MCG may have similar or complementary function and those in brainstem may be involved in the vestibulo-autonomic interaction. Anat Rec, 301:1906-1916, 2018. © 2018 Wiley Periodicals, Inc.

Decrease in NMDA receptor-signalling activity in the anterior cingulate cortex diminishes defensive behaviour and unconditioned fear-induced antinociception elicited by GABAergic tonic inhibition impairment in the posterior hypothalamus

Acute γ-aminobutyric acid (GABA) disinhibition in the posterior hypothalamus (PH) elicits defensive reactions that are considered anxiety- and panic attack-like behaviour, and these defensive reactions are followed by antinociception. Evidence indicates that the PH connects with the medial prefrontal cortex, particularly the anterior cingulate cortex (ACC), which seems to regulate these unconditioned fear-induced defensive responses. However, few studies have shown the participation of cortical regions in the control of behavioural and antinociceptive responses organised by diencephalic structures. It has been suggested that the glutamatergic system can mediate this cortical influence, as excitatory imbalance is believed to play a role in both defensive mechanisms. Thus, the aim of the present study was to investigate the involvement of ACC glutamatergic connections via blockade of local N-methyl-D-aspartate (NMDA) receptors to elaborate panic-like defensive behaviours and unconditioned fear-induced antinociception organised by PH neurons. Wistar rats were treated with microinjections of 0.9% NaCl or LY235959 (a selective NMDA receptor antagonist) in the ACC at different concentrations (2, 4 and 8 nmol/0.2μL), followed by GABA_A receptor blockade in the PH. Defensive reactions were analysed for 20min, and the nociceptive threshold was then measured at 10-min intervals for 60min. Pretreatment of the ACC with LY235959 reduced both panic-like defensive behaviour and fear-induced antinociception evoked by PH GABAergic disinhibition. Our findings suggest that ACC NMDA receptor-signalled glutamatergic inputs play a relevant role in the organisation of anxiety- and panic attack-like behaviours and in fear-induced antinociception.

Bi-Directional Theta Modulation between the Septo-Hippocampal System and the Mammillary Area in Free-Moving Rats

Hippocampal (HPC) theta oscillations have long been linked to various functions of the brain. Many cortical and subcortical areas that also exhibit theta oscillations have been linked to functional circuits with the hippocampus on the basis of coupled activities at theta frequencies. We examine, in freely moving rats, the characteristics of diencephalic theta local field potentials (LFPs) recorded in the supramammillary/mammillary (SuM/MM) areas that are bi-directionally connected to the HPC through the septal complex. Using partial directed coherence (PDC), we find support for previous suggestions that SuM modulates HPC theta at higher frequencies. We find weak separation of SuM and MM by dominant theta frequency recorded locally. Contrary to oscillatory cell activities under anesthesia where SuM is insensitive, but MM is sensitive to medial septal (MS) inactivation, theta LFPs persisted and became indistinguishable after MS-inactivation. However, MS-inactivation attenuated SuM/MM theta power, while increasing the frequency of SuM/MM theta. MS-inactivation also reduced root mean squared power in both HPC and SuM/MM equally, but reduced theta power differentially in the time domain. We provide converging evidence that SuM is preferentially involved in coding HPC theta at higher frequencies, and that the MS-HPC circuit normally imposes a frequency-limiting modulation over the SuM/MM area as suggested by cell-based recordings in anesthetized animals. In addition, we provide evidence that the postulated SuM-MS-HPC-MM circuit is under complex bi-directional control, rather than SuM and MM having roles as unidirectional relays in the network.

Translational considerations in injectable cell-based therapeutics for neurological applications: concepts, progress and challenges

Significant progress has been made during the past decade towards the clinical adoption of cell-based therapeutics. However, existing cell-delivery approaches have shown limited success, with numerous studies showing fewer than 5% of injected cells persisting at the site of injection within days of transplantation. Although consideration is being increasingly given to clinical trial design, little emphasis has been given to tools and protocols used to administer cells. The different behaviours of various cell types, dosing accuracy, precise delivery, and cell retention and viability post-injection are some of the obstacles facing clinical translation. For efficient injectable cell transplantation, accurate characterisation of cellular health post-injection and the development of standardised administration protocols are required. This review provides an overview of the challenges facing effective delivery of cell therapies, examines key studies that have been carried out to investigate injectable cell delivery, and outlines opportunities for translating these findings into more effective cell-therapy interventions.

The medullary dorsal reticular nucleus as a relay for descending pronociception induced by the mGluR5 in the rat infralimbic cortex

Metabotropic glutamate receptor 5 (mGluR5) activation in the infralimbic cortex (IL) induces pronociceptive behavior in healthy and monoarthritic rats. Here we studied whether the medullary dorsal reticular nucleus (DRt) and the spinal TRPV1 are mediating the IL/mGluR5-induced spinal pronociception and whether the facilitation of pain behavior is correlated with changes in spinal dorsal horn neuron activity. For drug administrations, all animals had a cannula in the IL as well as a cannula in the DRt or an intrathecal catheter. Heat-evoked paw withdrawal was used to assess pain behavior in awake animals. Spontaneous and heat-evoked discharge rates of single DRt neurons or spinal dorsal horn wide-dynamic range (WDR) and nociceptive-specific (NS) neurons were evaluated in lightly anesthetized animals. Activation of the IL/mGluR5 facilitated nociceptive behavior in both healthy and monoarthritic animals, and this effect was blocked by lidocaine or GABA receptor agonists in the DRt. IL/mGluR5 activation increased spontaneous and heat-evoked DRt discharge rates in healthy but not monoarthritic rats. In the spinal dorsal horn, IL/mGluR5 activation increased spontaneous activity of WDR neurons in healthy animals only, whereas heat-evoked responses of WDR and NS neurons were increased in both experimental groups. Intrathecally administered TRPV1 antagonist prevented the IL/mGluR5-induced pronociception in both healthy and monoarthritic rats. The results suggest that the DRt is involved in relaying the IL/mGluR5-induced spinal pronociception in healthy control but not monoarthritic animals. Spinally, the IL/mGluR5-induced behavioral heat hyperalgesia is mediated by TRPV1 and associated with facilitated heat-evoked responses of WDR and NS neurons.

Behavioral History of Withdrawal Influences Regulation of Cocaine Seeking by Glutamate Re-Uptake

Withdrawal from cocaine regulates expression of distinct glutamate re-uptake transporters in the nucleus accumbens (NAc). In this study, we examined the cumulative effect of glutamate re-uptake by multiple excitatory amino acid transporters (EAATs) on drug-seeking at two different stages of withdrawal from self-administered cocaine. Rats were trained on fixed ratio 1 (FR1), progressing to FR5 schedule of reinforcement. After one day of withdrawal, microinfusion of a broad non-transportable EAAT antagonist, DL-threo-beta-benzyloxyaspartate (DL-TBOA), into the NAc shell dose-dependently attenuated self-administration of cocaine. Sucrose self-administration was not affected by DL-TBOA, indicating an effect specific to reinforcing properties of cocaine. The attenuating effect on cocaine seeking was not due to suppression of locomotor response, as DL-TBOA was found to transiently increase spontaneous locomotor activity. Previous studies have established a role for EAAT2-mediated re-uptake on reinstatement of cocaine seeking following extended withdrawal and extinction training. We found that blockade of NAc shell EAATs did not affect cocaine-primed reinstatement of cocaine seeking. These results indicate that behavioral history of withdrawal influences the effect of re-uptake mediated glutamate clearance on cocaine seeking. Dynamic regulation of glutamate availability by re-uptake mechanisms may impact other glutamate signaling pathways to account for such differences.

Unilateral microinjection of acrolein into thoracic spinal cord produces acute and chronic injury and functional deficits

Although lipid peroxidation has long been associated with spinal cord injury (SCI), the specific role of lipid peroxidation-derived byproducts such as acrolein in mediating damage remains to be fully understood. Acrolein, an α-β unsaturated aldehyde, is highly reactive with proteins, DNA, and phospholipids and is considered as a second toxic messenger that disseminates and augments initial free radical events. Previously, we showed that acrolein increased following traumatic SCI and injection of acrolein induced tissue damage. Here, we demonstrate that microinjection of acrolein into the thoracic spinal cord of adult rats resulted in dose-dependent tissue damage and functional deficits. At 24h (acute) after the microinjection, tissue damage, motoneuron loss, and spinal cord swelling were observed on sections stained with Cresyl Violet. Luxol fast blue staining further showed that acrolein injection resulted in dose-dependent demyelination. At 8weeks (chronic) after the microinjection, cord shrinkage, astrocyte activation, and macrophage infiltration were observed along with tissue damage, neuron loss, and demyelination. These pathological changes resulted in behavioral impairments as measured by both the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and grid walking analysis. Electron microscopy further demonstrated that acrolein induced axonal degeneration, demyelination, and macrophage infiltration. These results, combined with our previous reports, strongly suggest that acrolein may play a critical causal role in the pathogenesis of SCI and that targeting acrolein could be an attractive strategy for repair after SCI.

The rostral ventromedial medulla control of cutaneous vasomotion of paws and tail in the rat: implication for pain studies

Thermal neutrality in rodents is achieved by large cyclic variations of the sympathetic drive of the vasomotion of the tail and paws, the most widely used target organs in current acute or chronic animal models of pain. Given the pivotal functional role of rostral ventromedial medulla (RVM) in nociception and rostral medullary raphe (rMR) in thermoregulation, two largely overlapping brain regions, we aimed at circumscribing the brainstem regions that are the source of premotor afferents to sympathetic preganglionic neurons that control the vasomotor tone of the tail and hind paws. A thermometric infrared camera recorded indirectly the vasomotor tone of the tail and hind paws. During the control period, the rat was maintained in vasoconstriction by preserving a stable, homogeneous, and constant surrounding temperature, slightly below the core temperature. The functional blockade of the RVM/rMR by the GABAA receptor agonist muscimol (0.5 nmol, 50 nl) elicited an extensive increase of the temperature of the paws and tail, associated with a slight decrease of blood pressure and heart rate. Both the increased heat loss through vasodilatation and the decrease heart-induced heat production elicited a remarkable reduction of the central temperature. The effective zones were circumscribed to the parts of the RVM/rMR facing the facial nucleus. They match very exactly the brain regions often described as specifically devoted to the control of nociception. Our data support and urge on the highest cautiousness regarding the interpretation of results aimed at studying the effects of any pharmacological manipulations of RVM/rMR with the usual tests of pain.

Galanin-Mediated Behavioural Hyperalgesia from the Dorsomedial Nucleus of the Hypothalamus Involves Two Independent Descending Pronociceptive Pathways

Activation of the dorsomedial nucleus of the hypothalamus (DMH) by galanin (GAL) induces behavioural hyperalgesia. Since DMH neurones do not project directly to the spinal cord, we hypothesized that the medullary dorsal reticular nucleus (DRt), a pronociceptive region projecting to the spinal dorsal horn (SDH) and/or the serotoninergic raphe-spinal pathway acting on the spinal 5-HT3 receptor (5HT3R) could relay descending nociceptive facilitation induced by GAL in the DMH. Heat-evoked paw-withdrawal latency (PWL) and activity of SDH neurones were assessed in monoarthritic (ARTH) and control (SHAM) animals after pharmacological manipulations of the DMH, DRt and spinal cord. The results showed that GAL in the DMH and glutamate in the DRt lead to behavioural hyperalgesia in both SHAM and ARTH animals, which is accompanied particularly by an increase in heat-evoked responses of wide-dynamic range neurons, a group of nociceptive SDH neurones. Facilitation of pain behaviour induced by GAL in the DMH was reversed by lidocaine in the DRt and by ondansetron, a 5HT3R antagonist, in the spinal cord. However, the hyperalgesia induced by glutamate in the DRt was not blocked by spinal ondansetron. In addition, in ARTH but not SHAM animals PWL was increased after lidocaine in the DRt and ondansetron in the spinal cord. Our data demonstrate that GAL in the DMH activates two independent descending facilitatory pathways: (i) one relays in the DRt and (ii) the other one involves 5-HT neurones acting on spinal 5HT3Rs. In experimental ARTH, the tonic pain-facilitatory action is increased in both of these descending pathways.

Metabotropic glutamate 5 receptor in the infralimbic cortex contributes to descending pain facilitation in healthy and arthritic animals

The involvement of the prefrontal cortex in pain processing has been recently addressed. We studied the role of the infralimbic cortex (IL) and group I metabotropic glutamate receptors (mGluRs) in descending modulation of nociception in control and monoarthritic (ARTH) conditions. Nociception was assessed using heat-induced paw withdrawal while drugs were microinjected in the IL of rats. Local anesthesia of the IL or the adjacent prelimbic cortex (PL) facilitated nociception, indicating that IL and PL are tonically promoting spinal antinociception. Phasic activation with glutamate (GLU) revealed opposing roles of the PL and IL; GLU in the PL had a fast antinociceptive action, while in the IL it had a slow onset pronociceptive action. IL administration of a local anesthetic or GLU produced identical results in ARTH and control animals. An mGluR5 agonist in the IL induced a pronociceptive effect in both groups, while mGluR5 antagonists had no effect in controls but induced antinociception in ARTH rats. Activation of the IL mGluR1 (through co-administration of mGluR1/5 agonist and mGluR5 antagonist) did not alter nociception in controls but induced antinociception in ARTH animals. IL administration of an mGluR1 antagonist failed to alter nociception in either experimental group. Finally, mGluR5 but not mGluR1 antagonists blocked the pronociceptive action of GLU in both groups. The results indicate that IL contributes to descending modulation of nociception. mGluR5 in the IL enhance nociception in healthy control and monoarthritic animals, an effect that is tonic in ARTH. Moreover, activation of IL mGluR1s attenuates nociception following the development of monoarthritis.

Ventral hippocampal histamine increases the frequency of evoked theta rhythm but produces anxiolytic-like effects in the elevated plus maze

The neurobiological underpinnings of anxiety are of paramount importance to the development of effective therapeutic treatments. To date, there is considerable pharmacological evidence suggesting that the suppression of hippocampal theta frequency is a robust and predictive assay of anxiolytic drug action. Recently, this idea has been challenged using histamine (2-(4-imidazolyl)ethanamine), an endogenous neurotransmitter involved in a number of brain and behavioral functions. Here, we systematically evaluate the effects of dorsal and ventral hippocampal histamine infusions on evoked theta frequency and behavioral anxiety. Given the complex pharmacological profile of histamine and its receptors in the hippocampus, we reasoned that local intra-hippocampal infusions would be a powerful test of the theta suppression model. While dorsal hippocampal infusions of histamine produced neither significant changes in anxious-like behavior in the elevated plus maze nor changes of evoked theta, ventral infusions of histamine produced potent behavioral anxiolysis which corresponded to an increase, and not a decrease, in evoked theta frequency. As a positive neurophysiological control, we demonstrated that diazepam, a proven anxiolytic drug, decreased the frequency of hippocampal theta following both dorsal and ventral hippocampal infusions. Our results further challenge the hippocampal theta frequency suppression model as a measure of anxiolytic drug action. This article is part of the Special Issue entitled 'Histamine Receptors'.

Evaluation for roles of neurosteroids in modulating forebrain mechanisms controlling vasopressin secretion and related phenomena in conscious rats

Anteroventral third ventricular region (AV3V) that regulates autonomic functions through a GABAergic mechanism possesses neuroactive steroid (NS)-synthesizing ability. Although NS can exert effects by acting on a certain type of GABAA-receptor (R), it is not clear whether NS may operate to modulate AV3V GABAergic activity for controlling autonomic functions. This study aimed to investigate the issue. AV3V infusion with a GABAA antagonist bicuculline increased plasma vasopressin (AVP), glucose, blood pressure (BP), and heart rate in rats. These events were abolished by preinjecting its agonist muscimol, whereas the infusion with allopregnanolone, a NS capable of potentiating GABAA-R function, affected none of the variables in the absence or presence of such bicuculline actions. Similarly, AV3V infusion with pregnanolone sulfate, a NS capable of antagonizing GABAA-R, produced no effect on those variables. AV3V infusion with muscimol was effective in inhibiting the responses of plasma AVP or glucose, or BP to an osmotic loading or bleeding. However, AV3V infusion with aminoglutethimide, a NS synthesis inhibitor, did not affect any of the variables in the absence or presence of those stimuli. These results suggest that NS may not cause acute effects on the AV3V GABAergic mechanism involved in regulating AVP release and other autonomic function.

Bidirectional amygdaloid control of neuropathic hypersensitivity mediated by descending serotonergic pathways acting on spinal 5-HT3 and 5-HT1A receptors

Amygdala is involved in processing of primary emotions and particularly its central nucleus (CeA) also in pain control. Here we studied mechanisms mediating the descending control of mechanical hypersensitivity by the CeA in rats with a peripheral neuropathy in the left hind limb. For drug administrations, the animals had a guide cannula in the right CeA and an intrathecal catheter or another guide cannula in the medullary raphe. Hypersensitivity was tested with monofilaments. Glutamate administration in the CeA produced a bidirectional effect on hypersensitivity that varied from an increase at a low-dose (9μg) to a reduction at high doses (30-100μg). The increase but not the reduction of hypersensitivity was prevented by blocking the amygdaloid NMDA receptor with a dose of MK-801 that alone had no effects. The glutamate-induced increase in hypersensitivity was reversed by blocking the spinal 5-HT3 receptor with ondansetron, whereas the reduction in hypersensitivity was reversed by blocking the spinal 5-HT1A receptor with WAY-100635. Both the increase and decrease of hypersensitivity induced by amygdaloid glutamate treatment were reversed by medullary administration of a 5-HT1A agonist, 8-OH-DPAT, that presumably produced autoinhibition of serotonergic cell bodies in the medullary raphe. The results indicate that depending on the dose, glutamate in the CeA has a descending facilitatory or inhibitory effect on neuropathic pain hypersensitivity. Serotoninergic raphe neurons are involved in mediating both of these effects. Spinally, the 5-HT3 receptor contributes to the increase and the 5-HT1A receptor to the decrease of neuropathic hypersensitivity induced by amygdaloid glutamate.

Site selective activation of lateral hypothalamic mGluR1 and R5 receptors elicits feeding in rats

Recent findings from our lab indicate that metabotropic glutamate receptor (mGluR) activation elicits eating, and the goal of the current study was to specify whether the lateral hypothalamus (LH) is the actual brain site mediating this effect. To examine this issue we injected the selective mGluR group I agonist (S)-3,5-dihydroxyphenylglycine (DHPG) unilaterally into the LH and surrounding regions (n=5-8 subjects/brain site) of satiated adult male Sprague-Dawley rats and measured elicited feeding. We determined that 1.0 nmol elicited food intake only within the LH. Increasing the dose to 10 or 25 nmol produced a more sustained effect in the LH, and also elicited eating in several other brain sites. These results, demonstrating that the LH mediates the eating elicited by low doses of DHPG, suggest that the LH may contain mGluR whose activation can produce eating behavior.

A role of supraspinal galanin in behavioural hyperalgesia in the rat

INTRODUCTION

In chronic pain disorders, galanin (GAL) is able to either facilitate or inhibit nociception in the spinal cord but the contribution of supraspinal galanin to pain signalling is mostly unknown. The dorsomedial nucleus of the hypothalamus (DMH) is rich in galanin receptors (GALR) and is involved in behavioural hyperalgesia. In this study, we evaluated the contribution of supraspinal GAL to behavioural hyperalgesia in experimental monoarthritis.

METHODS

In Wistar-Han males with a four week kaolin/carrageenan-induced monoarthritis (ARTH), paw-withdrawal latency (PWL) was assessed before and after DMH administration of exogenous GAL, a non-specific GALR antagonist (M40), a specific GALR1 agonist (M617) and a specific GALR2 antagonist (M871). Additionally, the analysis of c-Fos expression after GAL injection in the DMH was used to investigate the potential involvement of brainstem pain control centres. Finally, electrophysiological recordings were performed to evaluate whether pronociceptive On- or antinociceptive Off-like cells in the rostral ventromedial medulla (RVM) relay the effect of GAL.

RESULTS

Exogenous GAL in the DMH decreased PWL in ARTH and SHAM animals, an effect that was mimicked by a GALR1 agonist (M617). In SHAM animals, an unselective GALR antagonist (M40) increased PWL, while a GALR2 antagonist (M871) decreased PWL. M40 or M871 failed to influence PWL in ARTH animals. Exogenous GAL increased c-Fos expression in the RVM and dorsal raphe nucleus (DRN), with effects being more prominent in SHAM than ARTH animals. Exogenous GAL failed to influence activity of RVM On- or Off-like cells of SHAM and ARTH animals.

CONCLUSIONS

Overall, exogenous GAL in the DMH had a pronociceptive effect that is mediated by GALR1 in healthy and arthritic animals and is associated with alterations of c-Fos expression in RVM and DRN that are serotonergic brainstem nuclei known to be involved in the regulation of pain.

Dopamine D2-like receptors modulate unconditioned fear: role of the inferior colliculus

Background

A reduction of dopamine release or D₂ receptor blockade in the terminal fields of the mesolimbic system clearly reduces conditioned fear. Injections of haloperidol, a preferential D₂ receptor antagonist, into the inferior colliculus (IC) enhance the processing of unconditioned aversive information. However, a clear characterization of the interplay of D₂ receptors in the mediation of unconditioned and conditioned fear is still lacking.

Methods

The present study investigated the effects of intra-IC injections of the D₂ receptor-selective antagonist sulpiride on behavior in the elevated plus maze (EPM), auditory-evoked potentials (AEPs) to loud sounds recorded from the IC, fear-potentiated startle (FPS), and conditioned freezing.

Results

Intra-IC injections of sulpiride caused clear proaversive effects in the EPM and enhanced AEPs induced by loud auditory stimuli. Intra-IC sulpiride administration did not affect FPS or conditioned freezing.

Conclusions

Dopamine D₂-like receptors of the inferior colliculus play a role in the modulation of unconditioned aversive information but not in the fear-potentiated startle response.

Temporary inhibition of dorsal or ventral hippocampus by muscimol: distinct effects on measures of innate anxiety on the elevated plus maze, but similar disruption of contextual fear conditioning

Studies in rats, involving hippocampal lesions and hippocampal drug infusions, have implicated the hippocampus in the modulation of anxiety-related behaviors and conditioned fear. The ventral hippocampus is considered to be more important for anxiety- and fear-related behaviors than the dorsal hippocampus. In the present study, we compared the role of dorsal and ventral hippocampus in innate anxiety and classical fear conditioning in Wistar rats, examining the effects of temporary pharmacological inhibition by the GABA-A agonist muscimol (0.5 ug/0.5 ul/side) in the elevated plus maze and on fear conditioning to a tone and the conditioning context. In the elevated plus maze, dorsal and ventral hippocampal muscimol caused distinct behavioral changes. The effects of ventral hippocampal muscimol were consistent with suppression of locomotion, possibly accompanied by anxiolytic effects, whereas the pattern of changes caused by dorsal hippocampal muscimol was consistent with anxiogenic effects. In contrast, dorsal and ventral hippocampal muscimol caused similar effects in the fear conditioning experiments, disrupting contextual, but not tone, fear conditioning.

Pronociception from the dorsomedial nucleus of the hypothalamus is mediated by the rostral ventromedial medulla in healthy controls but is absent in arthritic animals

The dorsomedial nucleus of the hypothalamus (DMH) has been proposed to participate in stress-induced hyperalgesia through facilitation of pronociceptive cells in the rostroventromedial medulla (RVM). We hypothesized that the DMH participates in hyperalgesia induced by arthritis. The DMH was pharmacologically manipulated while assessing heat-evoked nociceptive behavior or the discharge rates of pronociceptive RVM ON- and antinociceptive RVM OFF-like cells in NAIVE, SHAM and monoarthritic (ARTH) animals. In NAIVE and SHAM animals, the changes in nociceptive behavior induced by activation of the DMH by glutamate and inhibition by lidocaine were in line with earlier evidence indicating that the DMH has a nociceptive facilitating role. However, in ARTH animals, neither activation nor inhibition of the DMH influenced pain-like behavior evoked by stimulation of an uninflamed skin region (paw and tail). In accordance with these behavioral results, activation or inhibition of the DMH induced pronociceptive changes in the discharge rates of RVM cells in NAIVE and SHAM animals, which suggests that the DMH has a pronociceptive role mediated by the RVM in normal animals. However, in ARTH animals, both glutamate and lidocaine in the DMH failed to influence either pain-like behavior or noxious stimulation-evoked responses of RVM cells, while blocking the DMH increased spontaneous activity in the pronociceptive RVM ON cells. Our data indicate that the DMH participates in descending facilitation of cutaneous nociception in healthy controls, but it is not engaged in the regulation of cutaneous nociception in monoarthritic animals, while a minor role in tonic suppression of nociception in arthritis cannot be discarded.

μ-opioid receptors in the stimulation of mesolimbic dopamine activity by ethanol and morphine in Long-Evans rats: a delayed effect of ethanol

RATIONALE

Naltrexone, a non-selective opioid antagonist, decreases the euphoria and positive subjective responses to alcohol in heavy drinkers. It has been proposed that the μ-opioid receptor plays a role in ethanol reinforcement through modulation of ethanol-stimulated mesolimbic dopamine release.

OBJECTIVES

To investigate the ability of naltrexone and β-funaltrexamine, an irreversible μ-opioid specific antagonist, to inhibit ethanol-stimulated and morphine-stimulated mesolimbic dopamine release, and to determine whether opioid receptors on mesolimbic neurons contribute to these mechanisms.

METHODS

Ethanol-naïve male Long Evans rats were given opioid receptor antagonists either intravenously, subcutaneously, or intracranially into the ventral tegmental area (VTA), followed by intravenous administration of ethanol or morphine. We measured extracellular dopamine in vivo using microdialysis probes inserted into the nucleus accumbens shell (n = 114).

RESULTS

Administration of naltrexone (intravenously) and β-funaltrexamine (subcutaneously), as well as intracranial injection of naltrexone into the VTA did not prevent the initiation of dopamine release by intravenous ethanol administration, but prevented it from being as prolonged. In contrast, morphine-stimulated mesolimbic dopamine release was effectively suppressed.

CONCLUSIONS

Our results provide novel evidence that there are two distinct mechanisms that mediate ethanol-stimulated mesolimbic dopamine release (an initial phase and a delayed phase), and that opioid receptor activation is required to maintain the delayed-phase dopamine release. Moreover, μ-opioid receptors account for this delayed-phase dopamine response, and the VTA is potentially the site of action of this mechanism. We conclude that μ-opioid receptors play different roles in the mechanisms of stimulation of mesolimbic dopamine activity by ethanol and morphine.

Tachycardic responses to stimulation of β-adrenoceptors in the brain parenchyma in conscious rats

This study aimed to investigate how stimulation of β-adrenoceptors in the anteroventral third ventricular region (AV3V; a pivotal forebrain area for autonomic functions) and other brain regions affects heart rate (HR) in conscious rats. Topical injections of the β-adrenergic agonist isoproterenol (Isop) into the AV3V caused dose-related and reversible increases in HR. Only its highest dose utilized significantly affected blood pressure (BP), inducing a decrease. The tachycardia due to AV3V Isop lasted significantly longer than that elicited by hypotension, and was inhibited by AV3V administration of the β-adrenergic antagonist propranolol or systemic infusion of a ganglion blocker hexamethonium. Plasma noradrenaline indicative of sympathetic nerve activity increased in parallel with rises in HR after the AV3V application of Isop. When Isop was locally injected into various brain regions other than the AV3V, region-related effectiveness in provoking tachycardia was observed that tended to be large in limbic structures and the hypothalamic paraventricular nucleus. No region responded to Isop applications with decreases in HR. These results suggest that β-adrenoceptors in the AV3V and other brain regions may be able to produce tachycardia by enhancing, at least in part, the efferent sympathetic nerve activity controlling cardiac function.

Neuroanatomical and neuropharmacological approaches to postictal antinociception-related prosencephalic neurons: the role of muscarinic and nicotinic cholinergic receptors

Several studies have suggested the involvement of the hippocampus in the elaboration of epilepsy. There is evidence that suggests the hippocampus plays an important role in the affective and motivational components of nociceptive perception. However, the exact nature of this involvement remains unclear. Therefore, the aim of this study was to determine the role of muscarinic and nicotinic cholinergic receptors in the dorsal hippocampus (dH) in the organization of postictal analgesia. In a neuroanatomical study, afferent connections were found from the somatosensory cortex, the medial septal area, the lateral septal area, the diagonal band of Broca, and the dentate gyrus to the dH; all these areas have been suggested to modulate convulsive activity. Outputs to the dH were also identified from the linear raphe nucleus, the median raphe nucleus (MdRN), the dorsal raphe nucleus, and the locus coeruleus. All these structures comprise the endogenous pain modulatory system and may be involved either in postictal pronociception or antinociception that is commonly reported by epileptic patients. dH-pretreatment with cobalt chloride (1.0 mmol/L CoCl2/0.2 μL) to transiently inhibit local synapses decreased postictal analgesia 10 min after the end of seizures. Pretreatment of the dH with either atropine or mecamylamine (1.0 μg/0.2 μL) attenuated the postictal antinociception 30 min after seizures, while the higher dose (5.0 μg/0.2 μL) decreased postictal analgesia immediately after the end of seizures. These findings suggest that the dH exerts a critical role in the organization of postictal analgesia and that muscarinic and nicotinic cholinergic receptor-mediated mechanisms in the dH are involved in the elaboration of antinociceptive processes induced by generalized tonic-clonic seizures.