Neuregulin-1 (NRG-1) is genetically linked with schizophrenia, a neurodevelopmental cognitive disorder characterized by imbalances in glutamatergic and dopaminergic function. NRG-1 regulates numerous neurodevelopmental processes and, in the adult, suppresses or reverses long-term potentiation (LTP) at hippocampal glutamatergic synapses. Here we show that NRG-1 stimulates dopamine release in the hippocampus and reverses early-phase LTP via activation of D4 dopamine receptors (D4R). NRG-1 fails to depotentiate LTP in hippocampal slices treated with the antipsychotic clozapine and other more selective D4R antagonists. Moreover, LTP is not depotentiated in D4R null mice by either NRG-1 or theta-pulse stimuli. Conversely, direct D4R activation mimics NRG-1 and reduces AMPA receptor currents and surface expression. These findings demonstrate that NRG-1 mediates its unique role in counteracting LTP via dopamine signaling and opens future directions to study new aspects of NRG function. The novel functional link between NRG-1, dopamine, and glutamate has important implications for understanding how imbalances in Neuregulin-ErbB signaling can impinge on dopaminergic and glutamatergic function, neurotransmitter pathways associated with schizophrenia.depotentiation ͉ ErbB receptor ͉ plasticity ͉ schizophrenia ͉ clozapine T he trophic and differentiation factor NRG-1 and its receptors (ErbB2-4) are expressed in the developing nervous system and adult brain, including the hippocampus. NRG-1 is translated as a transmembrane protein and released in an activity-dependent manner (1). Initially, long-term NRG-1 signaling was shown to regulate neuronal expression of neurotransmitter receptor genes for glutamate, acetylcholine, and GABA (2-5). More recently, the tight association of the NRG-1 receptor ErbB4 with glutamate receptors at postsynaptic densities suggested that NRG-1 signaling could regulate synaptic function in a more acute fashion (6, 7). Consistent with this idea, we and others have shown that NRG-1␤ rapidly regulates glutamatergic (7-11) and cholinergic (12) synaptic function in the hippocampus and prefrontal cortex (PFC).Long term potentiation (LTP) and long term depression (LTD) at Schaeffer collateral-to-CA1 hippocampal synapses (SC-CA1) are believed to underlie complex cognitive processes such as learning and memory. At this synapse, postsynaptic NMDAR activation and increases in AMPAR excitatory postsynaptic currents (EPSCs) are necessary for LTP induction and expression, respectively. An additional mechanism that contributes to synaptic homeostasis at adult glutamatergic synapses is depotentiation (13,14). In acute hippocampal slices and in freely moving animals, LTP is reversed (depotentiated) by brief, subthreshold theta pulse stimulation (TPS) if delivered during a labile period shortly after LTP induction (14). In the amygdala, depotentiation correlates with fear extinction and requires AMPAR internalization (15). We recently reported that NRG-1␤ depotentiates early-phase LTP at hippocampal SC-CA1 synapses,...

Activation of endothelial nitric oxide synthase (eNOS) and subsequent nitric oxide production (NO) are events that mediate the effect of important angiogenic, vasopermeability, and vasorelaxation factors, including vascular endothelial growth factor (VEGF), bradykinin (BK), and acetylcholine (ACh). The N-terminal 16-kDa fragment of prolactin (16K-PRL) acts on endothelial cells to inhibit angiogenesis both in vivo and in vitro. Here, we show that 16K-PRL inhibits VEGF-induced eNOS activation in endothelial cells. Inhibition of eNOS activation may mediate the antiangiogenic properties of 16K-PRL, because the NO donor (Z)-1-[2-(2-aminoethyl)- N-(2-ammonio-ethyl)amino]diazen-1-ium-1,2-diolate (DETANONOate) prevented 16K-PRL from blocking the VEGF-induced proliferation of endothelial cells. In addition, 16K-PRL inhibited eNOS activation by BK and blocked the BK-evoked transient increase in intracellular Ca(2+) in endothelial cells. This finding suggests that 16K-PRL interferes with the mobilization of intracellular Ca(2+), thereby inhibiting the Ca(2+)-dependent activation of eNOS. Blockage of eNOS activation can lead to inhibition of vasodilation. Consistently, 16K-PRL inhibited BK-induced relaxation of coronary vessels in isolated perfused guinea pig hearts. Moreover, 16K-PRL inhibited eNOS activation induced by ACh, and this action resulted in the inhibition of both ACh-evoked relaxation of coronary vessels in isolated perfused rat hearts and ACh-induced, endothelium-dependent relaxation of rat aortic segments. In conclusion, 16K-PRL can block the Ca(2+)-mediated activation of eNOS by three different vasoactive substances, and this action results in the inhibition of both angiogenesis and vasorelaxation.

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The distribution of acetylcholine receptors (AChRs) within and around the neuromuscular junction changes dramatically during the first postnatal weeks, a period during which polyneuronal innervation is eliminated. We reported previously that protein kinase C (PKC) activation accelerates postnatal synapse loss. Because of the close relationship between axonal retraction and AChR cluster dispersal, we hypothesize that PKC can modulate morphological maturation changes of the AChR clusters in the postsynaptic membrane during neonatal axonal reduction. We applied substances affecting PKC activity to the neonatal rat levator auris longus muscle in vivo. Muscles were then stained immunohistochemically to detect both AChRs and axons. We found that, during the first postnatal days of normal development, substantial axonal loss preceded the formation of areas in synaptic sites that were free of AChRs, implying that axonal loss could occur independently of changes in AChR cluster organization. Nevertheless, there was a close relationship between axonal loss and AChR organization; PKC modulates both, although differently. Block of PKC activity with calphostin C prevented both AChR loss and axonal loss between postnatal days 4 and 6. PKC may act primarily to influence AChR clusters and not axons, insofar as phorbol ester activation of PKC accelerated changes in receptor aggregates but produced relatively little axon loss.