Synapse

The cloned 5‐HT₃ receptor from NCB‐20 neuroblastoma cells was expressed in Xenopus oocytes and the effect of the endogenous cannabinoid ligand, anandamide, was investigated on the function of this receptor. The oocytes expressing the cloned 5‐HT₃ receptors were voltage‐clamped at −70 mV. Anandamide, at the concentration range of 0.1–100 μM, reversibly inhibited 1 μM 5‐HT induced currents. The inhibition of 5‐HT induced currents by anandamide was concentration‐dependent with an EC₅₀ of 3.7 μM and slope value of 0.94. This inhibitory effect was not dependent on the membrane potential and anandamide did not have an effect on the reversal potential of 5‐HT‐induced currents. In the presence of 10 μM anandamide, the maximum 5‐HT‐induced response was also inhibited and the respective EC₅₀ values were 3.4 μM and 3.1 μM in the absence and presence of anandamide, indicating that anandamide acts as a noncompetitive antagonist on 5‐HT₃ receptors. CB₁ receptor antagonist SR‐141716A (1 μM) and pertussis toxin (5 μg/ml) did not cause a significant change on the inhibition of 5‐HT responses by anandamide. The effect of anandamide was not changed by preincubating the oocytes with 0.2 mM 8‐Br‐cAMP, a membrane‐permeable analog of cAMP, or Sp‐cAMPS (0.1 mM), a membrane‐permeable protein kinase A activator. These results suggest that the effect of anandamide is independent of the activation of cAMP pathway and not mediated by the activation of PTX sensitive G‐proteins. In conclusion, we demonstrated that the endogenous cannabinioid anandamide inhibits the function of 5‐HT₃ receptors expressed in Xenopus oocytes in a cannabinoid‐receptor independent and noncompetitive manner. Synapse 46:150–156, 2002. Published 2002 Wiley‐Liss, Inc.

The transcription factor ΔFosB accumulates and persists in brain in response to chronic stimulation. This accumulation after chronic exposure to drugs of abuse has been demonstrated previously by Western blot most dramatically in striatal regions, including dorsal striatum (caudate/putamen) and nucleus accumbens. In the present study, we used immunohistochemistry to define with greater anatomical precision the induction of ΔFosB throughout the rodent brain after chronic drug treatment. We also extended previous research involving cocaine, morphine, and nicotine to two additional drugs of abuse, ethanol and Δ⁹‐tetrahydrocannabinol (Δ⁹‐THC, the active ingredient in marijuana). We show here that chronic, but not acute, administration of each of four drugs of abuse, cocaine, morphine, ethanol, and Δ⁹‐THC, robustly induces ΔFosB in nucleus accumbens, although different patterns in the core vs. shell subregions of this nucleus were apparent for the different drugs. The drugs also differed in their degree of ΔFosB induction in dorsal striatum. In addition, all four drugs induced ΔFosB in prefrontal cortex, with the greatest effects observed with cocaine and ethanol, and all of the drugs induced ΔFosB to a small extent in amygdala. Furthermore, all drugs induced ΔFosB in the hippocampus, and, with the exception of ethanol, most of this induction was seen in the dentate. Lower levels of ΔFosB induction were seen in other brain areas in response to a particular drug treatment. These findings provide further evidence that induction of ΔFosB in nucleus accumbens is a common action of virtually all drugs of abuse and that, beyond nucleus accumbens, each drug induces ΔFosB in a region‐specific manner in brain. Synapse 358–369, 2008. © 2008 Wiley‐Liss, Inc.

The effects of cocaine on dopamine (DA) neurotransmission were evaluated by in vivo microdialysis in the striatum of halothane‐anesthetized rats. Intravenous cocaine produced a dose‐dependent, transient increase of the extracellular concentration of DA, with a peak response within 10 min and a return to control level by 30 min. The sharp DA response pattern was abolished in a calcium‐free environment, indicating that DA release enhanced by cocaine originates from a vesicular storage pool. Continuous administration of cocaine (via the perfusion medium) directly into the nigrostriatal terminal region also produced a dose‐dependent increase in DA release. Low concentrations (10⁻⁵ M and 10⁻⁶ M) of cocaine maintained DA at a constant stable level, consistent with the effects observed after potent DA uptake inhibitory agents (e.g., nomifensine and Lu19005). However, continuous exposure to high concentrations (< 10⁻⁴ M) induced a transient elevation of DA within 20 min, following which DA decreased to a stable but high level; this decrease might reflect tolerance to the effect of cocaine. Administration of cocaine (10⁻³ M) into the substantia nigra did not change striatal DA release. The local striatal action of cocaine was less potent than amphetamine in elevating DA overflow and in its effect on DA metabolism. These findings suggest that the fast transient enhancement of DA by intravenous cocaine is most likely a consequence of the transient presence of cocaine in the terminal region, correlating with the well‐known rapid pharmacokinetic and behavioral aspects of the drug.

Most forms of neuronal plasticity are associated with induction of the transcription factor zif268 (egr1). Down‐regulation of cdc20 (p55^cdc)—a regulatory protein for the anaphase‐promoting complex, which controls access of specific substrates to the proteasome—was observed after transfection of a neuronal cell line with zif268. Treatment of cultured hippocampal neurones with NMDA, which elevates endogenous zif268 levels, also decreased cdc20 levels. Conversely, the levels of cdc20 were found to be increased in the cerebral cortex of mice with targeted deletion of the zif268 gene, when compared with wild‐type controls. Our findings indicate that expression of the cdc20 gene is down‐regulated by zif268 in neuronal cells, and provide new evidence that altered expression of proteasome‐regulatory genes following zif268 induction may be a key component of long‐lasting CNS plasticity. Synapse 61:463‐468, 2007. © 2007 Wiley‐Liss, Inc.

Agmatine, a metabolite of L‐arginine, is considered as a novel putative neurotransmitter. It has been detected in axon terminals that synapse with pyramidal cells in the hippocampus, a brain region that is critically involved in spatial learning and memory. However, the role of agmatine in learning and memory is poorly understood. Recently, we demonstrated water maze training‐induced increases in tissue levels of agmatine in the CA1 subregion of the hippocampus. This finding has raised an issue whether an endogenous agmatine could directly participate in learning and memory processes as a neurotransmitter. In the present study, quantitative immunogold‐labeling and electron‐microscopical techniques were used to analyze the levels of agmatine in CA1 stratum radiatum (SR) terminals (n = 600) of male Sprague–Dawley rats that had been trained to find a hidden escape platform in the water maze (WM) task or forced to swim (SW) in the pool with no platform presented. Agmatine levels were significantly increased by ∼85% in the synaptic terminals of SR of trained WM group compared with the SW control group (all P < 0.001). These results, for the first time, demonstrate spatial learning‐induced elevation in agmatine levels at synapses in the hippocampus and provide evidence of its participation in learning and memory processing as a novel neurotransmitter. Synapse, 2011. © 2010 Wiley‐Liss, Inc.

Phencyclidine exerts psychotomimetic effects in humans and is used as a pharmacological animal model for schizophrenia. We, and others, have demonstrated that phencyclidine induces cognitive deficits in rats that are associated with schizophrenia. These cognitive deficits can be normalized by inhibition of nitric oxide synthase. The development of selective microelectrochemical nitric oxide sensors may provide direct evidence for the involvement of nitric oxide in these effects. The aim of the present study was to use LIVE (long term in vivo electrochemistry) to investigate the effect of phencyclidine, alone or in combination with the nitric oxide synthase inhibitor L‐NAME, on nitric oxide levels in the medial prefrontal cortex of freely moving rats. Phencyclidine (2 mg kg⁻¹) produced an increase in cortical nitric oxide levels and this increase was ameliorated by L‐NAME (10 mg kg⁻¹). Tentatively, the results from the present study provide a biochemical rationale for the involvement of nitric oxide in the phencyclidine model of schizophrenia. Synapse 63:1083–1088, 2009. © 2009 Wiley‐Liss, Inc.

In general, it has been difficult to preserve electrophysiologically viable motoneurons in brain slices from adult mammals. The present study describes a new method for obtaining viable motoneurons in the facial nucleus of adult rat brain slices. The essence of the method was to use a modified artificial cerebrospinal fluid (ACSF) in which NaCl was replaced initially by sucrose; the modified ACSF was used during (1) slice preparation and (2) a 1 hr recovery period. The rationale for the modification is discussed in terms of the proposed acute neurotoxic effects of passive chloride entry and subsequent cell swelling and lysis. The actual recordings were made only after switching back to normal ACSF. Use of this method yielded large numbers of viable motoneurons that were suitable for intracellular recording; no motoneurons survived when normal ACSF (i.e., with NaCl) was used during slice preparation. A survey of some electrophysiological and pharmacological properties of facial motoneurons in this preparation, by means of current‐clamp and voltage‐clamp recording, revealed close similarities to the properties of adult motoneurons previously observed in vivo (e.g., time‐dependent inward rectification, apamin‐sensitive afterhyperpolarization, and serotonin‐induced slow depolarization).

As a prerequisite to pharmacological analysis of the excitatory effects of serotoinin (5‐HT) on piriform pyramidal cells and interneurons, this study first examined the physiological characteristics of these two cell types. Intracellular recordings confirmed that the subpopulation of 5‐HT‐activated cells located at the border of layers II and III and indeed interneurons. Voltage clamp recordings in pyramidal cells showed that the increase in excitability produced by 5‐HT in these cells was the result of voltage‐ and Ca²⁺‐dependent outward currents with the characteristics of I_M and I_AHP.

Pharmacological studies were designed to discriminate 5‐HT₂ from 5‐HT_1C responses in interneurons and pyramidal cells of piriform cortex. The 5‐HT antagonist spiperone, which has a much higher affinity for 5‐HT₂ receptors than for 5‐HT_1C receptors, blocked the excitatory effect of 5‐HT at lower concentrations in interneurons (IC₅₀ = 31 nM) than in pyramidal cells (IC₅₀ = 2.1 μM). Similarly, ritanserin, a drug which also has a higher affinity for 5‐HT₂ than 5‐HT_1C receptors, blocked the effect of 5‐HT at lower concentrations in interneurons (IC₅₀ = 400 nM) than in pyramidal cells (IC₅₀ = 8.1 μM). In contrast, LY 53857, an antagonist with higher affinity for 5‐HT_1C than for 5‐HT₂ receptors, blocked the effect of 5‐HT at lower concentrations in pyramidal cells (IC₅₀ = 26 nM) than in interneurons (IC₅₀ = 364 nM). The 5‐HT_1C partial agonist/5‐HT₂ antagonist mCPP produced agonist‐like effects in only 66% of pyramidal cells tested indicating that not all pyramidal cells may express 5‐HT_1C receptors.

In that both spiperone and ritanserin have higher affinity for 5‐HT₂ receptors than for 5‐HT_1C receptors and LY 53857 has a higher affinity for 5‐HT_1C receptors than for 5‐HT₂ receptors, these data suggest that in piriform cortex excitatory effects of 5‐HT are mediated by 5‐HT_1C receptors in pyramidal cells and by 5‐HT₂ receptors in interneurons.

Fatty acid amide hydrolase (FAAH) regulates tissue concentrations of N‐acylethanolamines (NAEs), including the endocannabinoid, N‐arachidonylethanolamide (anandamide, AEA). FAAH activity and NAEs are widely distributed throughout the brain and FAAH activity regulates an array of processes including emotion, cognition, inflammation, and feeding. However, there is relatively little research describing how this system develops throughout adolescence, particularly within limbic circuits regulating stress and reward processing. Thus, this study characterized temporal changes in NAE content (AEA, oleoylethanolamine [OEA], and palmitoylethanolamide [PEA]) and FAAH activity across the peri‐adolescent period, in four corticolimbic structures (amygdala, hippocampus, prefrontal cortex, and hypothalamus). Brain tissue of male Sprague–Dawley rats was collected on postnatal days (PND) 25, 35, 45, and 70, representing pre‐adolescence, early‐ to mid‐adolescence, late adolescence, and adulthood, respectively. Tissue was analyzed for AEA, OEA, and PEA content as well as FAAH activity at each time point. AEA, OEA, and PEA exhibited a similar temporal pattern in all four brain regions. NAE concentrations were lowest at PND 25 and highest at PND 35. NAE concentrations decreased between PNDs 35 and 45 and increased between PNDs 45 and 70. FAAH activity mirrored the pattern of NAE content in which it decreased between PNDs 25 and 35, increased between PNDs 35 and 45, and decreased between PNDs 45 and 70. These age‐dependent patterns of NAE content and FAAH activity demonstrate temporal specificity to the development of this system and could contribute to alterations in stress sensitivity, emotionality, and executive function which also fluctuate during this developmental period. Synapse, 2013. © 2012 Wiley Periodicals, Inc.