Search results for "synapses"
showing 10 items of 183 documents
Presynaptic regulation of the electrically evoked release of endogenous dopamine from the isolated neurointermediate lobe or isolated neural lobe of …
1988
Isolated neurointermediate lobes (NILs) or isolated neural lobes (NLs) of the rat pituitary gland were incubated in Krebs-HEPES solution which contained pargyline and the dopamine uptake inhibitor GBR 12921. The release of endogenous dopamine was determined by HPLC with electrochemical detection. Electrical stimulation of the pituitary stalk induced a frequency-dependent release of dopamine. The release of dopamine from the combined NIL evoked by stimulation at 15 Hz was increased by 130% in the presence of the dopamine D2 receptor antagonist, (-)-sulpiride; the (+)-enantiomer of sulpiride had virtually no effect. When the stimulation frequency was 3 Hz (-)-sulpiride caused an increase in d…
Neuronal populations mediating the effects of endocannabinoids on stress and emotionality
2011
An adequate emotional response to stress is essential for survival and requires the fine-tuned regulation of several distinct neuronal circuits. Therefore, a precise control of these circuits is necessary to prevent behavioral imbalances. During the last decade, numerous investigations have evidenced that the endocannabinoid (eCB) system is able to crucially control stress coping. Its central component, the cannabinoid type 1 receptor (CB1 receptor), is located at the presynapse, where it is able to attenuate neurotransmitter release after its activation by postsynaptically produced and released eCBs. To date, the eCB system has been found to control the neurotransmitter release from severa…
Early histological maturation in the hippocampus of the guinea pig.
2000
The vesicular zinc-rich synaptic systems of the principal neurons of the hippocampus are well developed in newborn guinea pigs, a precocial species. In addition, alvear and fimbrial myelinated fibers as well as significant inhibitory interneurons (i.e. somatostatin, parvalbumin and opioid immunoreactive hippocampal interneurons) are also well developed. On the contrary, neither vesicular zinc synapses nor myelinated fibers nor the above mentioned immunoreactive interneurons are detectable in newborn specimens of other related altricial species such as rats or rabbits. These data suggest that early maturation of a highly integrative center related to cognitive map building such as the hippoc…
Oligodendrocyte precursor cells modulate the neuronal network by activity-dependent ectodomain cleavage of glial NG2.
2014
The role of glia in modulating neuronal network activity is an important question. Oligodendrocyte precursor cells (OPC) characteristically express the transmembrane proteoglycan nerve-glia antigen 2 (NG2) and are unique glial cells receiving synaptic input from neurons. The development of NG2+ OPC into myelinating oligodendrocytes has been well studied, yet the retention of a large population of synapse-bearing OPC in the adult brain poses the question as to additional functional roles of OPC in the neuronal network. Here we report that activity-dependent processing of NG2 by OPC-expressed secretases functionally regulates the neuronal network. NG2 cleavage by the α-secretase ADAM10 yields…
Gray Matter NG2 Cells Display Multiple Ca2+-Signaling Pathways and Highly Motile Processes
2011
NG2 cells, the fourth type of glia in the mammalian CNS, receive synaptic input from neurons. The function of this innervation is unknown yet. Postsynaptic changes in intracellular Ca(2+)-concentration ([Ca(2+)](i)) might be a possible consequence. We employed transgenic mice with fluorescently labeled NG2 cells to address this issue. To identify Ca(2+)-signaling pathways we combined patch-clamp recordings, Ca(2+)-imaging, mRNA-transcript analysis and focal pressure-application of various substances to identified NG2-cells in acute hippocampal slices. We show that activation of voltage-gated Ca(2+)-channels, Ca(2+)-permeable AMPA-receptors, and group I metabotropic glutamate-receptors provo…
Evidence for an involvement of NMDA and non-NMDA receptors in synaptic excitation of phrenic motoneurons in the rabbit
1991
Abstract The action of endogenous excitatory amino acids on phrenic motoneurons was studied in anesthetized, vagotomized, paralyzed and artificially ventilated rabbits. The NMDA receptor antagonists APV and ketamine, as well as the non-NMDA receptor antagonists GAMS and DNQX were administered by microinjection into the ventral horn of the spinal segments C3-C5. Injection of each antagonist resulted in a reversible reduction of the phrenic nerve activity. Results suggest an important function of endogenous excitatory amino acids in the excitation of phrenic motneurons. NMDA as well as non-NMDA receptors are involved. The functional role of both receptor types in bulbospinal neurotransmission…
Modulation of Neocortical Development by Early Neuronal Activity: Physiology and Pathophysiology.
2017
Animal and human studies revealed that patterned neuronal activity is an inherent feature of developing nervous systems. This review summarizes our current knowledge about the mechanisms generating early electrical activity patterns and their impact on structural and functional development of the cerebral cortex. All neocortical areas display distinct spontaneous and sensory-driven neuronal activity patterns already at early phases of development. At embryonic stages, intermittent spontaneous activity is synchronized within small neuronal networks, becoming more complex with further development. This transition is accompanied by a gradual shift from electrical to chemical synaptic transmiss…
Intrinsic volatility of synaptic connections — a challenge to the synaptic trace theory of memory
2017
According to the synaptic trace theory of memory, activity-induced changes in the pattern of synaptic connections underlie the storage of information for long periods. In this framework, the stability of memory critically depends on the stability of the underlying synaptic connections. Surprisingly however, synaptic connections in the living brain are highly volatile, which poses a fundamental challenge to the synaptic trace theory. Here we review recent experimental evidence that link the initial formation of a memory with changes in the pattern of connectivity, but also evidence that synaptic connections are considerably volatile even in the absence of learning. Then we consider different…
Brain choline has a typical precursor profile.
1998
Choline is product and precursor to both acetylcholine and membrane phospholipids, and, in the brain, is ultimately provided by the circulation. The brain is protected from excess choline and choline deprivation by a refined system of homeostatic mechanisms that maintain a level of extracellular choline that, for its role as precursor, meets saturation criteria under normal conditions. The kinetic and activity profiles of choline are typical for a biosynthetic precursor.
Hippocampal GABAergic Synapses Possess the Molecular Machinery for Retrograde Nitric Oxide Signaling
2007
Nitric oxide (NO) plays an important role in synaptic plasticity as a retrograde messenger at glutamatergic synapses. Here we describe that, in hippocampal pyramidal cells, neuronal nitric oxide synthase (nNOS) is also associated with the postsynaptic active zones of GABAergic symmetrical synapses terminating on their somata, dendrites, and axon initial segments in both mice and rats. The NO receptor nitric oxide-sensitive guanylyl cyclase (NOsGC) is present in the brain in two functional subunit compositions: α1β1and α2β1. The β1subunit is expressed in both pyramidal cells and interneurons in the hippocampus. Using immunohistochemistry andin situhybridization methods, we describe that the …