Expression and transport function of the glutamate transporter EAAC1 inXenopus oocytes is regulated by syntaxin 1A

The function of several membrane proteins is regulated by interaction with the SNARE protein syntaxin 1A; this includes regulation of GAT1, the transporter for the dominating inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Here we demonstrate that also EAAC1, the transporter for the dominating excitatory neurotransmitter, is down-regulated by interaction with syntaxin 1A. This is shown by coexpression of EAAC1 and syntaxin 1A in Xenopus oocytes. Total EAAC1 expression is not significantly affected by the coexpression of syntaxin 1A, but more proteins become targeted to the membrane as demonstrated by biotinylation. Colocalization by coimmunoprecipitation suggests direct interaction between the two proteins. In contrast to the number of transporters, the glutamate transport activity becomes reduced, and even stronger inhibition is observed for the EAAC1-mediated conductance uncoupled from glutamate translocation. We conclude that the interaction of syntaxin 1A with EAAC1 particularly disrupts the structure of the conductance pathway of EAAC1.

Mechanisms underlying anorexia after microinjection of bombesin into the lateral cerebroventricle

Intracerebroventricular (i.c.v.) injections of bombesin (BN) and gastrin-releasing peptide (GRP) dose-dependently decreased food intake in male Wistar rats fasted for 17 h. Neuromedin B (NMB) did not show any effect on food intake. After BN administration, locomotor activity did not significantly change, compared with a vehicle-injected group. The anorexia induced by BN (0.3 microg) was perfectly inhibited by pretreatment with a GRP-receptor antagonist, [D-Tyr(6)]BN(6-13) methyl ester (10 microg), an NO synthase inhibitor, L-nitro-arginine (30 microg), and a PKG inhibitor, H-9 (2 microg). The cGMP concentration in the hypothalamus increased 1 h after administration when compared with the vehicle-injected group. On the other hand, an NMB-receptor antagonist, BIM23127 (10 microg), and the protein kinase (PK) C inhibitors, chelerythrine (2 microg) and Go6983 (2 microg), inhibited only the late phase of the anorexia. A PKC activator, phorbol 12, 13-dibutyrate (3 microg), injected into the ventricle decreased food intake. These findings suggest that BN suppresses food intake mainly mediated through the GRP receptor and NO-cGMP-PKG pathway, and NMB receptor and PKC is partly involved in the late phase of the anorexia.

Pharmacology of GABAC receptors: responses to agonists and antagonists distinguish A- and B-subtypes of homomeric rho receptors expressed in Xenopus oocytes

GABA(C) receptors, expressed predominantly in vertebrate retina, are thought to be formed mainly by GABA rho subunits. Five GABA rho subunits have been cloned from white perch retina, four of which form functional homooligomeric receptors when expressed in Xenopus oocytes. These rho subtypes, classified as rho1A, rho1B, rho2A and rho2B receptors based on amino acid sequence alignment, exhibit distinct temporal and pharmacological properties. To examine further the pharmacological properties associated with the various rho receptor subtypes, we investigated the effects of a selective GABA(C) receptor antagonist, TPMPA, on the GABA-mediated activity of receptors formed in Xenopus oocytes by the four GABA rho subunits. In addition, we recorded the activation profiles of beta-alanine, taurine, and glycine, three amino acids that modulate neuronal activity in various parts of the CNS and are purported to be rho receptor agonists. TPMPA effectively inhibited GABA-elicited responses on A-type receptors, whereas B-type receptors exhibited a relatively low sensitivity to the drug. A-type and B-type receptors also displayed distinctly different reactions to agonists. Both taurine and glycine-activated the B-type receptors, whereas these agents had no detectable effect on A-type receptors. Similarly, beta-alanine evoked large responses from B-type receptors, but was far less effective on A-type receptors. These results indicate that, in addition to the characteristic response properties identified previously, there is a pattern of pharmacological reactions that further distinguishes the A- and B-subtypes of GABA rho receptor.

Galanin Microinjection in the Third Ventricle Increases Voluntary Ethanol Intake

BACKGROUND

The neuropeptide galanin increases food intake. Chronic ethanol (EtOH) increases the expression of galanin in the hypothalamus. The research presented here examines the effects of microinjection of galanin in the third ventricle on voluntary alcohol intake.

METHODS

Male Sprague Dawley rats with a cannula in the third ventricle were given access to increasing concentrations of EtOH for 12 hr/day until all acquired a preference for 7% EtOH over water in a two-bottle choice. Rats then received a microinjection of galanin (0, 1, and 3 nmol) alone or in combination with the galanin antagonist M40 (1 nmol) and with M40 alone to determine the effects on EtOH and water intake. Tests were conducted during both the light and dark periods of a 12:12-hr light-dark cycle with food available ad libitum. As a control for galanin-induced calorie intake, both EtOH and food were measured in a subset of rats during the dark.

RESULTS

Microinjections of galanin (1.0 and 3.0 nmol) increased EtOH consumption during both periods of the light-dark cycle. Galanin's effect on ethanol intake during the light was large relative to the very low intake of food and water during this period. Rats increased their intake of EtOH but not food. Receptor specificity for galanin (3 nmol) was shown by the galanin antagonist M40, which blocked the increase in EtOH intake. M40 alone decreased EtOH intake slightly.

CONCLUSIONS

These data show that galanin injected in the third ventricle increases EtOH consumption and that the effect can occur during both the light and the dark periods of the diurnal cycle in the presence of food and water. This suggests that galanin may play a role in augmenting voluntary alcohol intake and perhaps the development of alcohol dependence.

The amygdala is critical for opioid-mediated binge eating of fat

Endogenous opioid peptides within the nucleus accumbens are thought to mediate the hedonic aspects of food intake, particularly foods such as fat and sugar. In view of evidence that the amygdala also regulates positive affect, we hypothesized this brain region participates in the control of opioid-mediated food intake. The robust increase in the intake of fat following intra-accumbens administration of the mu-opioid agonist D-Ala2,Nme-Phe4,Glyol5-enkephalin (DAMGO) was completely blocked by concurrent temporary inactivation (muscimol, GABA(A) agonist) of either the basolateral or central nucleus of the amygdala. In summary, we demonstrate that amygdala inactivation prevents the intra-accumbens opioid induced "binge" eating of fat, possibly through reducing the hedonic properties of high-fat palatable food.

Differential sensitivities of pyrogenic chemokine fevers to CC chemokine receptor 5 antibodies

Macrophage inflammatory protein (MIP)-1beta and RANTES (regulated on activation, normal T-cells expressed and secreted) are members of the CC-family of chemokines. Although these two peptides are structurally and functionally related to one another, each exhibits distinct features, which allows it to independently regulate specific aspects of the host inflammatory response. They evoked intense and functionally different febrile responses when applied directly on pyrogen-sensitive cells located in the in the preoptic area of the anterior hypothalamus (POA). The present experiments were carried out to test the central role of CCR5, a functional receptor for MIP-1beta and RANTES, in the febrile responses induced by these chemokines when injected directly into the POA. The microinjection of an equimolecular dose (50 pg) of either MIP-1beta or RANTES into the POA induced a rapid onset; monophasic fever in rats that persisted for a long period. The microinjection of 2.0 microg specific neutralizing antibodies against CCR5 (anti-CCR5) into the POA fails to affect the effects on body temperature induced by MIP-1beta. However, pretreatment with the same dose of anti-CCR5 suppressed the febrile response induced by RANTES given at the same site. The microinjection of control IgG or anti-CCR5 does not affect basal temperature, when administered alone at the same hypothalamic site. The present experiments show that hypothalamic CCR5 are functionally involved in the febrile response induced by RANTES, but not by MIP-1beta. They also suggest the existence of functionally different components in the presumptive primary locus of the thermoregulatory controller, in which both chemotactic cytokines, together other mediators, could play a relevant role in the complex process of fever pathogenesis.

A method to record changes in local neuronal discharge in response to infusion of small drug quantities in awake monkeys

A newly designed combination microelectrode-injection system is described which can be used to record electrophysiological responses of individual neurons in the primate brain to local administration of small quantities of drugs or other compounds. The assembly of the system is simple, and the materials used are inexpensive. The system consists of a standard tungsten microelectrode alongside fused silica tubing within a polyimide sleeve. The major advantage of this device is the ability to record with excellent quality, changes in the activity of single cells in vivo within 50-100 microm of the location of drug injections.

Involvement of cholecystokinin in the opioid tolerance induced by dipyrone (metamizol) microinjections into the periaqueductal gray matter of rats

The analgesic effect of non-steroidal anti-inflammatory drugs (NSAIDs) is partly due to an action upon the periaqueductal gray matter (PAG), which triggers the descending pain control system and thus inhibits nociceptive transmission. This action of NSAIDs engages endogenous opioids at the PAG, the nucleus raphe magnus and the spinal cord. Repeated administration of NSAIDs such as dipyrone (metamizol) and acetylsalicylate thus induces tolerance to these compounds and cross-tolerance to morphine. Since cholecystokinin plays a key role in opioid tolerance, the present study in rats investigated whether PAG cholecystokinin is also responsible for tolerance to PAG-microinjected dipyrone. Microinjection of cholecystokinin (1 ng/0.5 microl) into PAG blocked the antinociceptive effect of a subsequent microinjection of dipyrone (150 microg/0.5 microl) into the same site, as evaluated by the tail flick and hot plate tests. Microinjection of proglumide (0.4 microg/0.5 microl), a non-selective cholecystokinin antagonist, into PAG prevented the development of tolerance to subsequent microinjections of dipyrone, as well as cross-tolerance to microinjection of morphine (5 microg/0.5 microl) into the same site. In rats tolerant to PAG dipyrone, a PAG microinjection of proglumide restored the antinociceptive effect of a subsequent microinjection of dipyrone or morphine. These results suggest that PAG-microinjected dipyrone triggers and/or potentiates local opioidergic circuits leading to descending inhibition of nociception, on the one hand, and to a local antiopioid action by cholecystokinin, on the other. Reiteration of these events would then result in an enhancement of cholecystokinin's antiopioid action and thus tolerance to opioids and dipyrone in the PAG.

Cardiovascular responses to the injection of l-glutamate in the lateral hypothalamus of unanesthetized or anesthetized rats

The present experiment was designed to compare the cardiovascular effects of injections of 0.1 M L-glutamate (50, 100 or 500 nL) into the anterior (LHa), tuberal (LHt) or posterior (LHp) regions of the lateral hypothalamus (LH) of either unanesthetized or anesthetized male Wistar rats. In unanesthetized rats, L-glutamate caused significant depressor responses without significant heart rate (HR) effects. L-Glutamate caused similar depressor responses when injected into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. In urethane-anesthetized rats, L-glutamate caused either depressor responses or biphasic responses, characterized by a significant initial depressor component followed by a secondary pressor response which was significant only after the injection of L-glutamate in 500 nL. The depressor component was accompanied by significant bradycardia only when the LHa or LHt were stimulated. Similar depressor responses were observed after L-glutamate microinjection into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. The present results suggest that: 1) lateral hypothalamic L-glutamate-sensitive neurons are involved in cardiovascular control and may have a wide and homogeneous distribution throughout the LH; 2) these neurons are mainly associated to the expression of hypotensive responses in unanesthetized rats; and 3) bradycardiac responses are evidenced when L-glutamate is microinjected into the LHa and the LHt in urethane-anesthetized rats.

Pontine GABAergic pathways: role and plasticity in the hypoxic ventilatory response

The hypoxic ventilatory response (HVR) was compared before and after uni- and bi-lateral injections of bicuculline, a GABA(A) receptor antagonist, into the ventrolateral (vl) pons and before and after conditioning animals to chronic sustained hypoxia (CSH). The HVR was assessed by recording phrenic nerve activity (PNA) during and after brief exposures to hypoxia (8% O(2) and 92% N(2) for 45s). Inspiratory (T(I)) and expiratory (T(E)) durations were averaged before hypoxia, at the peak breathing frequency during hypoxia, before the end of hypoxia, immediately after hypoxia, and 60s after hypoxia. Blocking GABA(A) receptors in the vl pons prolonged T(E) during, but not after hypoxia. After CSH induced by 14 days in a hypobaric chamber (0.5atm), the HVR was attenuated compared to that in the naive animals. This plasticity of HVR was associated with selective induction of alpha6 and delta GABA(A) receptor subunit mRNAs specifically in the pons compared to the medulla. These physiological and molecular results illustrate the importance of pontine GABAergic pathways in shaping the response to hypoxia.

Electroporation loading of calcium-sensitive dyes into the CNS

Calcium imaging of neural network function has been limited by the extent of tissue labeled or the time taken for labeling. We now describe the use of electroporation-an established technique for transfecting cells with genes-to load neurons with calcium-sensitive dyes in the isolated spinal cord of the neonatal mouse in vitro. The dyes were injected subdurally, intravascularly, or into the central canal. This technique results in rapid and extensive labeling of neurons and their processes at all depths of the spinal cord, over a rostrocaudal extent determined by the position and size of the electrodes. Our results suggest that vascular distribution of the dye is involved in all three types of injections. Electroporation disrupts local reflex and network function only transiently (approximately 1 h), after which time they recover. We describe applications of the method to image activity of neuronal populations and individual neurons during antidromic, reflex, and locomotor-like behaviors. We show that these different motor behaviors are characterized by distinct patterns of activation among the labeled populations of cells.

Prostaglandin E2 in the midbrain periaqueductal gray produces hyperalgesia and activates pain-modulating circuitry in the rostral ventromedial medulla

Recent years have seen significant advances in our understanding of the peripheral and spinal mechanisms through which prostaglandins contribute to nociceptive sensitization. By contrast, the possibility of a supraspinal contribution of these compounds to facilitated pain states has received relatively little attention. One possible mechanism through which prostaglandins could act supraspinally to facilitate nociception would be by recruitment of descending facilitation from brainstem pain-modulating systems. The rostral ventromedial medulla (RVM) is now known to contribute to enhanced responding in a variety of inflammatory and nerve injury models. Its major supraspinal input, the midbrain periaqueductal gray (PAG), expresses prostanoid receptors and synthetic enzymes. The aim of the present study was to determine whether direct application of prostaglandin E(2) (PGE(2)) within the ventrolateral PAG is sufficient to produce hyperalgesia, and whether any hyperalgesia could be mediated by recruiting nociceptive modulating neurons in the RVM. We determined the effects of focal application of PGE(2) in the PAG on paw withdrawal latency and activity of identified nociceptive modulating neurons in the RVM of lightly anesthetized rats. Microinjection of PGE(2) (50 fg in 200 nl) into the PAG produced a significant decrease in paw withdrawal latency. The PGE(2) microinjection activated on-cells, RVM neurons thought to facilitate nociception, and suppressed the firing of off-cells, RVM neurons believed to have an inhibitory effect on nociception. These data demonstrate a prostaglandin-sensitive descending facilitation from the PAG, and suggest that this is mediated by on- and off-cells in the RVM.

Activation of FAK and Src are receptor-proximal events required for netrin signaling

The axon guidance cue netrin is importantly involved in neuronal development. DCC (deleted in colorectal cancer) is a functional receptor for netrin and mediates axon outgrowth and the steering response. Here we show that different regions of the intracellular domain of DCC directly interacted with the tyrosine kinases Src and focal adhesion kinase (FAK). Netrin activated both FAK and Src and stimulated tyrosine phosphorylation of DCC. Inhibition of Src family kinases reduced DCC tyrosine phosphorylation and blocked both axon attraction and outgrowth of neurons in response to netrin. Mutation of the tyrosine phosphorylation residue in DCC abolished its function of mediating netrin-induced axon attraction. On the basis of our observations, we suggest a model in which DCC functions as a kinase-coupled receptor, and FAK and Src act immediately downstream of DCC in netrin signaling.

Nitric oxide pathway in the nucleus raphe magnus modulates hypoxic ventilatory response but not anapyrexia in rats

Nucleus raphe magnus (NRM) is one of the cellular groups of the brainstem that is involved in the physiologic responses to hypoxia and contains nitric oxide (NO) synthase. In the present study, we assessed the role of NO pathway in the NRM on the hypoxic ventilatory response (HVR) and anapyrexia (a regulated decrease in body temperature). To this end, pulmonary ventilation (VE) and body temperature (Tb) of male Wistar rats were measured before and after microinjection of N-monomethyl-L-arginine (L-NMMA, a nonselective nitric oxide synthase inhibitor, 12.5 microg/0.1 microl) into the NRM, followed by hypoxia. Control rats received microinjection of saline. Under resting conditions, L-NMMA treatment did not affect pulmonary VE or Tb. Typical hypoxia-induced hyperventilation and anapyrexia were observed after saline treatment. L-NMMA into the NRM reduced the HVR but did not affect hypoxia-induced anapyrexia. In conclusion, the present study indicates that NO in the NRM is involved in HVR, exerts an inhibitory modulation on the NRM neurons but does not mediate hypoxia-induced anapyrexia.

Cardiovascular responses to microinjection of l-glutamate into the NTS in AV3V-lesioned rats

The excitatory amino acid L-glutamate injected into the nucleus of the solitary tract (NTS) in unanesthetized rats similar to peripheral chemoreceptor activation increases mean arterial pressure (MAP) and reduces heart rate. In this study, we investigated the effects of acute (1 day) and chronic (15 days) electrolytic lesions of the preoptic-periventricular tissue surrounding the anteroventral third ventricle (AV3V region) on the pressor and bradycardic responses induced by injections of L-glutamate into the NTS or peripheral chemoreceptor activation in unanesthetized rats. Male Holtzman rats with sham or electrolytic AV3V lesions and a stainless steel cannula implanted into the NTS were used. Differently from the pressor responses (28+/-3 mm Hg) produced by injections into the NTS of sham-lesioned rats, L-glutamate (5 nmol/100 nl) injected into the NTS reduced MAP (-26+/-8 mm Hg) or produced no effect (2+/-7 mm Hg) in acute and chronic AV3V-lesioned rats, respectively. The bradycardia to l-glutamate into the NTS and the cardiovascular responses to chemoreflex activation with intravenous potassium cyanide or to baroreflex activation with intravenous phenylephrine or sodium nitroprusside were not modified by AV3V lesions. The results show that the integrity of the AV3V region is essential for the pressor responses to L-glutamate into the NTS but not for the pressor responses to chemoreflex activation, suggesting dissociation between the central mechanisms involved in these responses.

Further evidence on the anxiogenic-like effect of substance P evaluated in the elevated plus-maze in rats

Substance P (SP) and its preferred NK1 receptor are widely expressed throughout the fear-processing pathways of the brain and its role in the modulation of experimental anxiety has been demonstrated. SP, like other peptides, are cleaved by peptidases in two fragments: C-terminal (SP 6-11) and N-terminal (SP 1-7) that could be responsible for its anxiogenic-like response. In this study we investigate the effects of i.c.v. micro-injections of SP free acid (SPfa), which is resistant to enzymatic cleavage, the influence of the pretreatment with peptidase inhibitors (PIs), thiorphan and/or phosphoramidon, as well as the effects of SP 6-11 and SP 1-7 and the participation of NK1 and NK2 receptors on their behavioral effects. Adult male Wistar rats were treated with 10 pmol solutions of SP 6-11, SP 1-7 or 1 and 10 pmol of SPfa and evaluated in the elevated plus maze (EPM) test. Other experimental groups received thiorphan 0.2 pmol, phosphoramidon 2 pmol or both PIs 30 min prior SP 1-11, 10 pmol i.c.v. The C-terminal fragment (SP 6-11, 10 pmol) and SPfa (1 pmol) promoted an anxiogenic-like profile of action similar to 10 pmol of SP 1-11, i.e., a decrease of entries and time spent on the open arms, whereas the N-terminal fragment (SP 1-7) was inactive at the EPM. The effect of SP 6-11 was inhibited by pretreatment (100 pmol) with NK1 (FK 888) and NK2 (SR 48968) antagonists. Moreover, both PIs enhanced the SP effect when used alone, but their combination produced an apparent reversion of anxiogenic-like effect produced by SP. Altogether, our results give further support to the SP role in the modulation of experimental anxiety in rats.

Kappa opioids inhibit physiologically identified medullary pain modulating neurons and reduce morphine antinociception

Microinjection of kappa opioid receptor (KOR) agonists into the rostral ventromedial medulla (RVM) attenuates mu-opioid receptor mediated antinociception and stress-induced analgesia, yet is also reported to have an analgesic effect. To determine how KOR agonists produce both antinociceptive and antianalgesic actions within the RVM, the KOR agonist U69593 was microinjected directly into the RVM while concurrently monitoring tail flick latencies and RVM neuronal activity. Among RVM neurons recorded in vivo, two types show robust changes in activity just prior to the nocifensive tail flick reflex: ON cells burst just prior to a tail flick and their activity is pronociceptive, whereas OFF cells pause just prior to the tail flick and their activity is antinociceptive. Although RVM microinjection of U69593 did not affect tail flick latencies on its own, it did attenuate the on cell burst, an effect blocked by co-injection of the KOR antagonist, nor-binaltorphimine (nor-BNI). Furthermore, U69593 inhibited ongoing activity in subsets of OFF cells (4/11) and NEUTRAL cells (3/9). Microinjection of U69593 into the RVM also attenuated morphine antinociception and suppressed the excitation of off cells. Together with previous in vivo and in vitro studies, these results are consistent with the idea that KOR agonists can be either pronociceptive through direct inhibition of OFF cells, or antianalgesic through both postsynaptic inhibition and presynaptic inhibition of glutamate inputs to RVM OFF cells.

Contrasting effects of dopamine and glutamate receptor antagonist injection in the nucleus accumbens suggest a neural mechanism underlying cue-evoked goal-directed behavior

Discriminative stimuli (DSs) inform animals that reward can be obtained contingent on the performance of a specific behavior. Such stimuli reinstate drug-seeking behavior, evoke dopamine release in the nucleus accumbens (NAc) and excite and inhibit specific subpopulations of NAc neurons. Here we show in rats that DSs can reinstate food-seeking behavior. In addition, we compare the effects of injecting dopamine receptor antagonists into the NAc with those of general NAc inactivation on the performance of a DS task. Selective antagonism of D1 receptors reduced responding to the DS and increased the latency to respond, whereas general inactivation of NAc neuronal activity increased the latency to respond to the DS and increased behaviors extraneous to the task, such as responding in the absence of cues and responding on the inactive lever. Based on these results and our previous findings that NAc neuronal responses to DSs are dependent on the ventral tegmental area, we propose a model for the functional role of NAc neurons in controlling behavioral responses to reward-predictive stimuli.

Possible involvement of the facial nucleus in regulation of respiration in rats

The facial nucleus (FN) has been known as a motor nucleus to control the activity of the facial skeletal muscles by its efferent somatic motoneurons. Much less, however, is known about the non-motor control functions of its interneurons. The present study was designed to investigate if the interneurons of the FN participate in controlling rhythmic respiration in the sodium thiopental-anesthetized and vagotomized Sprague-Dawley rats with facial motoneurons retrogradely degenerated with techniques of electrical and chemical stimulation of the FN and extracellular recording of discharge of neurons in the FN. Single pulse stimulation (75-100 microA, 0.2 ms) of the FN during inspiration caused a transient restrain in phrenic discharge. Short train stimulation (75-100 microA, 0.2 ms, 100 Hz, 3-5 pulses) delivered during the early- or mid-term of inspiration augmented the inspiratory duration, but switched the inspiration off when delivered during the later stage of inspiration. Short train stimulation delivered during expiration prolonged the expiratory duration. Continuous stimulation could inhibit the inspiration. Microinjection of kainic acid into the FN caused an augmentation in inspiratory duration and amplitude and in expiratory duration. These data indicate that the interneurons of the FN might participate in the modulation of respiration. Different discharge patterns of interneurons in the FN, interestingly some respiratory related patterns, were observed, which provide a possible structural basis for the role of the FN in respiratory regulation.

Microneedle Insertion Force Reduction Using Vibratory Actuation

The effect of vibratory actuation on microneedle insertion force was investigated. Hollow micro hypodermic injection needles were fabricated by a two-wafer polysilicon micromolding process. A vibratory actuator operating in the kHz range was coupled with the hypodermic microneedles. The force to insert microneedles into excized animal tissue was measured with a load cell. Results showed a greater than 70% reduction in microneedle insertion force by using vibratory actuation. The application of vibratory actuation provides a promising method to precisely control the microneedle insertion forces to overcome microneedle structural material limitations, minimize insertion pain, and enhance the efficiency of drug delivery.

Expression of G-protein signaling components in adult mammalian neurons by microinjection

Although methods for expressing foreign proteins in clonal cell lines are well established, mature neurons remain a difficult preparation for the introduction of foreign genes. Microinjection is a reliable method for producing robust targeted expression in neurons that has advantages over conventional transfection/infection methodologies. Here, I describe procedures for expressing signaling proteins in adult rat sympathetic neurons by direct microinjection of cRNA and cDNA into the cytoplasm and nucleus, respectively. The methods are applicable to a wide variety of peripheral and central neuron preparations, as well as clonal cell lines.

Microdynamics of the piezo-driven pipettes in ICSI

Undesirably low success rates have been reported in the intracytoplasmic sperm injection procedure. Recently a method using piezo-driven pipettes with a very small mercury column contributed substantial improvements in this process. Despite the toxicity of mercury, this new procedure is commonly utilized in many laboratories. However, there is no study available to date on the micromechanics of this procedure. The underlying principles of piercing are not clear for both cases, with and without the mercury. Presently, the pressure burst, which is caused by the abrupt axial motion of the mercury column, is attributed to this effect. Here, we take the mercury-filled pipettes and try to understand the governing physics. The findings point out the occurrence of considerable lateral tip oscillations of the injection pipette as the piezoelectric pulse train is introduced. We claim that the lateral dynamics play an important role in the piercing and should be considered to enlighten the process and the effects of the mercury. These claims are analytically studied and experimentally verified.

A technique for long-term implantation of a microcatheter into the third ventricle of post-pubertal Chinese Meishan pigs based on ventriculography

The objectives of this study were to implant a microcatheter into the third ventricle of post-pubertal Chinese Meishan pigs, and to maintain the microcatheter for a long time without causing stress. Fourteen pigs (45-60 kg BW) were used. Each pig was anesthetized and the head was orientated on the stereotaxic apparatus. A radiopaque dye was placed into the ventricle via a guide cannula inserted 3.5 mm forward of the bregma. A microcatheter was inserted into the third ventricle using ventriculography, and fixed with dental cement to a metal-mesh protector and screw anchors embedded into the skull. The opposite end of the microcatheter was externalized from the dorsal neck so that corticotropin-releasing hormone (CRH) could be injected easily. Simultaneously, a catheter was fitted in the jugular vein, and the free end of the catheter was externalized from the dorsal neck. Microcatheter-implanted pigs showed a normal progesterone concentration profile, and a constant cortisol level during at least two estrous cycles. Furthermore, intracerebroventricular injections of CRH (25 microg/500 microl) resulted in an increased plasma cortisol concentration (P < 0.05). Thus, the technique developed in this study enables us to approach the third ventricle in post-pubertal freely-moving pigs effectively over a long time, without causing stress.

Genomic and nongenomic effects of intrahippocampal microinjection of testosterone on long-term memory in male adult rats

In addition to their well-known genomic effects via intracellular receptors, androgens rapidly alter neuronal excitability through a nongenomic pathway. The nongenomic effect of testosterone, as the main androgen, apart from its traditional effects, was assessed in one of the fundamental centers of learning and memory, the hippocampus, on long-term memory (LTM) in passive avoidance conditioning. Different doses of testosterone enanthate (T) or testosterone-BSA (T-BSA) bilaterally were injected into the CA1 region of the hippocampus 15 min before shock delivery (1 mA during 5 s) in a two-compartment passive avoidance apparatus. After 24 h, animals were tested for passive avoidance retrieval. Bilateral injection of 20 microg T or 55 microg T-BSA into the CA1 significantly decreases step-through latency. Therefore, it seems that testosterone can impair LTM in passive avoidance conditioning both via intracellular receptors and through nongenomic pathway.

Peripheral arousal-related hormones modulate norepinephrine release in the hippocampus via influences on brainstem nuclei

The peripheral hormone epinephrine (EPI) is known to modulate memory for arousing experiences. The mnemonic effects of EPI are attributed almost exclusively to actions on amygdala noradrenergic (NE) systems. EPI also increases neuronal activity in the locus coeruleus (LC), the primary source of NE to other limbic structures that process memory such as the hippocampus (HIPP). The actions of EPI on the LC suggest that its mnemonic properties may also be mediated by influencing NE output in the HIPP. To test this hypothesis, dialysate levels of NE were collected from the HIPP of male rats given an i.p. injection of saline that was followed 100 min later by i.p. EPI (0.3 mg/kg). NE levels sampled 20 min after EPI injection were significantly larger than baseline and continued to show significant peaks for 60 min. Experiment 2 examined whether peripheral signals initiated by EPI influence the HIPP via the nucleus of the solitary tract (NTS) by inactivating this nucleus with lidocaine prior to EPI injection. EPI injection did not increase NE levels sampled from the HIPP of rats given lidocaine into the NTS. EPI injection did produce significant elevations in HIPP NE levels in animals given a control solution into the NTS prior to the EPI injection. These findings indicate that the mnemonic effects of EPI reported in a wide range of learning conditions may not be mediated solely by NE release in the amygdala, but may also involve coactivation of the HIPP NE system.