Hyperconnectivity of neuronal circuits due to increased synaptic protein synthesis is postulated to cause Autism Spectrum Disorders (ASD). The mammalian target of rapamycin (mTOR) is strongly implicated in ASD via upstream signaling. However, downstream regulatory mechanisms are ill-defined. We show that knockout (KO) of the eukaryotic translation Initiation Factor 4E-Binding Protein 2 (4E-BP2), an eIF4E-repressor downstream of mTOR, or eIF4E overexpression lead to increased translation of neuroligins, which are post-synaptic proteins that are causally linked to ASD. 4E-BP2-KO mice exhibit an increased ratio of excitatory to inhibitory synaptic inputs and autistic-like behaviors: social interaction deficits, altered communication and repetitive/stereotyped behaviors. Pharmacological inhibition of eIF4E activity or normalization of neuroligin 1, but not neuroligin 2 protein amounts, restore the normal excitation/inhibition ratio and rectify the social behavior deficits. Thus, translational control by eIF4E regulates the synthesis of neuroligins, maintaining the excitation to inhibition balance, and its dysregulation engenders ASD-like phenotypes.

In Aplysia californica, the serotonin-mediated translocation of protein kinase C (PKC) Apl II to neuronal membranes is important for synaptic plasticity. The orthologue of PKC Apl II, PKC, has been reported to require phosphatidic acid (PA) in conjunction with diacylglycerol (DAG) for translocation. We find that PKC Apl II can be synergistically translocated to membranes by the combination of DAG and PA. We identify a mutation in the C1b domain (arginine 273 to histidine; PKC Apl II-R273H) that removes the effects of exogenous PA. In Aplysia neurons, the inhibition of endogenous PA production by 1-butanol inhibited the physiological translocation of PKC Apl II by serotonin in the cell body and at the synapse but not the translocation of PKC Apl II-R273H. The translocation of PKC Apl II-R273H in the absence of PA was explained by two additional effects of this mutation: (i) the mutation removed C2 domain-mediated inhibition, and (ii) the mutation decreased the concentration of DAG required for PKC Apl II translocation. We present a model in which, under physiological conditions, PA is important to activate the novel PKC Apl II both by synergizing with DAG and removing C2 domain-mediated inhibition.Protein kinase Cs (PKCs) are a family of lipid-activated kinases that mediate a wide variety of cellular processes, including the regulation of synaptic strength in the nervous system (23,42,48). In Aplysia californica, behavioral sensitization is mediated in part by an increase in the strength of the connections between mechanoreceptor sensory neurons and motor neurons (19). This increase, called synaptic facilitation, is mediated by the neurotransmitter serotonin (5HT), which induces facilitation in isolated ganglia as well as in cocultures of sensory neurons and motor neurons (5, 6). Sensitizing stimulation causes the translocation of PKC to neuronal membranes (39, 53). In the Aplysia nervous system, there are two phorbol ester-regulated PKCs: PKC Apl I, which is homologous to the Ca 2ϩ -activated PKC family in vertebrates (␣, ␤1, ␤2, and ␥) that are called conventional or classical PKCs (cPKCs), and PKC Apl II, which is homologous to the Ca 2ϩ -independent epsilon family of PKC in vertebrates (ε and ) that are called novel PKCs (nPKCs) (21,42,43). PKC Apl I and PKC Apl II translocate under different conditions to mediate distinct types of synaptic facilitation (53). PKC Apl II, but not PKC Apl I, is translocated by the application of 5HT to sensory neurons and is required for 5HT-mediated facilitation at synapses that previously have been depressed (24). In contrast, combining 5HT and the firing of the sensory neuron leads to the additional translocation of PKC Apl I, and PKC Apl I is required for the intermediate-term facilitation induced by the combination of sensory neuron firing and 5HT (53).Both cPKCs and nPKCs contain two C1 domains and one C2 domain. However, the C2 domain of nPKCs is located N terminal to the C1 domains and lacks critical aspartic acid residues involved in coordinating Ca 2ϩ ions in cPKCs (2...

Learning is highly regulated by the pattern of training. In Aplysia, an important organism for the development of cellular and molecular models of learning, spaced versus massed application of the same stimulus leads to different forms of memory. A critical molecular step underlying memory is the serotonin (5HT)-mediated activation of the novel PKC Apl II. Here, we demonstrate that activation of PKC Apl II is highly sensitive to the pattern of 5HT application. Spaced applications downregulate PKC translocation through PKA signaling, whereas massed applications lead to persistent translocation of PKC. Differential regulation of PKC translocation is mediated by competing feedback mechanisms that act through protein synthesis. These studies elucidate a fundamental molecular difference between spaced and massed training protocols.

SUMMARY1. In dogs anaesthetized with chloralose, distension of small balloons in the pulmonary vein-atrial junctions and left atrial appendage, to stimulate left atrial receptors, caused a reduction in activity in efferent renal nerves. This response was maintained during distension of the balloons for 30 min periods.2. In a second group of dogs, cooling the cervical vagi in steps reduced the magnitude of the response in renal nerves. In seven dogs, the response in fourteen preparations of renal nerves was slightly reduced with the vagi at 18 00 and markedly reduced or abolished at 12 'C. The effect of cooling the vagi was the same as the previously shown effect of cooling on the increase in activity in myelinated afferent vagal fibres during similar stimulation of atrial receptors.3. In a third group of dogs, the cervical vagi were cooled to 9 0C. In six dogs, fifty-four preparations of renal nerves showed no significant response to distension of the balloons.4. In a fourth group of dogs, both vagi were sectioned in the neck. In three dogs, twenty-four preparations of renal nerves then showed no response to distension of the balloons.5. It is concluded that the reduction in activity in efferent renal nerves during distension of small balloons in the pulmonary vein-atrial junctions and left atrial appendage involves only atrial receptors discharging into myelinated vagal fibres.