The psychiatric disease risk factors DISC1 and TNIK interact to regulate synapse composition and function.

Disrupted in schizophrenia 1 (DISC1), a genetic risk factor for multiple serious psychiatric diseases including schizophrenia, bipolar disorder and autism, is a key regulator of multiple neuronal functions linked to both normal development and disease processes. As these diseases are thought to share a common deficit in synaptic function and architecture, we have analyzed the role of DISC1 using an approach that focuses on understanding the protein-protein interactions of DISC1 specifically at synapses. We identify the Traf2 and Nck-interacting kinase (TNIK), an emerging risk factor itself for disease, as a key synaptic partner for DISC1, and provide evidence that the DISC1-TNIK interaction regulates synaptic composition and activity by stabilizing the levels of key postsynaptic density proteins. Understanding the novel DISC1-TNIK interaction is likely to provide insights into the etiology and underlying synaptic deficits found in major psychiatric diseases.

Rab3A is required for brain-derived neurotrophic factor-induced synaptic plasticity: transcriptional analysis at the population and single-cell levels.

Brain-derived neurotrophic factor (BDNF) modulates synaptic strength in hippocampal neurons, in addition to promoting survival and differentiation. To identify genes involved in trophic regulation of synaptic plasticity, we have used a multidisciplinary approach of differential display and family-specific slot blots in combination with whole-cell patch-clamp recordings of dissociated hippocampal neurons. Three hour exposure to BDNF elicited a 2.6-fold increase in synaptic charge and a concomitant induction of 11 genes as revealed by differential display, including the small GTP-binding vesicular trafficking protein Rab3A and the enzyme guanylate cyclase (GC). Slot blot analysis on a population of neurons confirmed an average of 3.1-fold induction of these clones. In contrast, individual pyramidal-like neurons that were first characterized electrophysiologically in the presence of BDNF and subjected to transcriptional analysis displayed more robust increases (4.8-fold), emphasizing the neuronal heterogeneity. Transcriptional changes of Rab3A and GC were accompanied by translational regulation, shown by Western blot analysis. Furthermore, a number of GC-associated and Rab3A effector molecules were induced by BDNF at either the gene or protein levels. The functional role of Rab3A in BDNF-induced synaptic plasticity was assessed using cells derived from Rab3A knock-out mice. These neurons failed to show an increase in synaptic charge in response to BDNF at 10 min; however a late response to BDNF was detected at 20 min. This late response was similar in time course to that induced by postsynaptic activation of glutamate receptors. Our results demonstrate a requirement for Rab3A and may reveal a temporal distinction between presynaptic and postsynaptic mechanisms of BDNF-induced synaptic plasticity associated with learning and memory.

5-HT(7) receptors activate the mitogen activated protein kinase extracellular signal related kinase in cultured rat hippocampal neurons.

Medications that selectively increase 5-hydroxytryptamine are currently the most commonly prescribed antidepressants. However, it is not known which receptors for 5-hydroxytryptamine, nor which post-receptor cellular signals, mediate the antidepressant actions of 5-hydroxytryptamine. The hippocampus is highly innervated by serotonergic neurons and appears to be an ideal region of the brain for studying the antidepressant role of 5-hydroxytryptamine. Treatment with antidepressants has been shown to cause increased expression of proteins in the hippocampus that appear to be protective against stress-induced atrophy. This suggests a role for pathways, such as mitogen-activated protein kinase, that regulate protein synthesis. In the present study we found that 5-HT(7) receptors, expressed by cultured rat hippocampal neurons, couple to stimulation of the mitogen-activated protein kinase extracellular signal-regulated kinases ERK1 and ERK2. The 5-HT(1/7) receptor-selective agonist 5-carboxamidotryptamine maleate (5-CT) as well as the 5-HT(1A/7) receptor-selective agonists 8-hydroxy-N,N-dipropyl-aminotetralin (8-OH-DPAT) and N,N-dipropyl-5-carboxamidotryptamine maleate (dipropyl-5-CT) were found to activate extracellular signal-regulated kinase with equal efficacy to 5-HT. However, the EC(50) for 8-OH-DPAT was approximately 200-fold greater than that of 5-HT, a difference in potency consistent with the pharmacology of 5-HT(7), but not 5-HT(1A), receptors. Additionally, pretreatment with pertussis toxin, which would be expected to block the actions of 5-HT(1,) but not 5-HT(7,) receptors caused no inhibition. 4-Iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]N-2-pyridinyl-benzamide hydrochloride (p-MPPI) and N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-cyclohexanecarb oxamide maleate (WAY-100635), antagonists selective for 5-HT(1A) receptors, similarly caused no inhibition of the activity of 5-HT.In summary, these studies are the first to demonstrate that 5-hydroxytryptamine activates the mitogen-activated protein kinase ERK in primary neuronal cultures. That 5-HT(7) receptors couple to activation of extracellular signal-regulated kinase in hippocampal neurons suggests a possible role for 5-HT(7) receptors in mediating some of the actions of antidepressants that increase 5-hydroxytryptamine.

Blockade of NR2B-containing NMDA receptors prevents BDNF enhancement of glutamatergic transmission in hippocampal neurons.

Application of brain-derived neurotrophic factor (BDNF) to hippocampal neurons has profound effects on glutamatergic synaptic transmission. Both pre- and postsynaptic actions have been identified that depend on the age and type of preparation. To understand the nature of this diversity, we have begun to examine the mechanisms of BDNF action in cultured dissociated embryonic hippocampal neurons. Whole-cell patch-clamp recording during iontophoretic application of glutamate revealed that BDNF doubled the amplitude of induced inward current. Coexposure to BDNF and the NMDA receptor antagonist AP-5 markedly reduced, but did not entirely prevent, the increase in current. Coexposure to BDNF and ifenprodil, an NR2B subunit antagonist, reproduced the response observed with AP-5, suggesting BDNF primarily enhanced activity of NR2B-containing NMDA receptors with a lesser effect on non-NMDA receptors. Protein kinase involvement was confirmed with the broad spectrum inhibitor staurosporine, which prevented the response to BDNF. PKCI19-31 and H-89, selective antagonists of PKC and PKA, had no effect on the response to BDNF, whereas autocamtide-2-related inhibitory peptide, an antagonist of CaM kinase II, reduced response magnitude by 60%. These results demonstrate the predominant role of a specific NMDA receptor subtype in BDNF modulation of hippocampal synaptic transmission.

Brain-derived neurotrophic factor modulates hippocampal synaptic transmission by increasing N-methyl-D-aspartic acid receptor activity.

Neurotrophins (NTs) have recently been found to regulate synaptic transmission in the hippocampus. Whole-cell and single-channel recordings from cultured hippocampal neurons revealed a mechanism responsible for enhanced synaptic strength. Specifically, brain-derived neurotrophic factor augmented glutamate-evoked, but not acetylcholine-evoked, currents 3-fold and increased N-methyl-D-aspartic acid (NMDA) receptor open probability. Activation of trkB NT receptors was critical, as glutamate currents were not affected by nerve growth factor or NT-3, and increased open probability was prevented by the tyrosine kinase inhibitor K-252a. In addition, the NMDA receptor antagonist MK-801 blocked brain-derived neurotrophic factor enhancement of synaptic transmission, further suggesting that NTs modulate synaptic efficacy via changes in NMDA receptor function.