[Physiological basis of functional MRI].

C Habas

Home/Archive/PubMed

PubMed · 12469010

[Physiological basis of functional MRI].

C Habas

View original source ↗Export metadata ↓

Abstract

Afferent neurotransmission of a given neuronal group and its subsequent dendritic activity are followed by a transient hemodynamic response such as an increase of the local blood flow and of the intravascular level of oxygen. This neurovascular regulation involves neurons, astrocytes, interneurons and various transmitter substances. The resulting changes in the magnetic susceptibility is then detected by the MRI machine which can specifically localize regional brain activity. Blood oxygenation level dependent contrast reflects afferent inputs and their post-synaptic (dendritic) processing, rather than the output from the concerned cerebral zone (spiking). In other words, this contrast depends on local informational treatment of an active zone without implying any effective influence upon its targets.

Explore related subjects

Afferent Pathways Astrocytes Brain Chemistry Cerebrovascular Circulation Dendrites Excitatory Postsynaptic Potentials Glucose Glycolysis Hemodynamics Homeostasis Humans Hypoxia, Brain Interneurons Magnetic Resonance Imaging Oxygen Consumption Synaptic Transmission English Abstract Journal Article Review

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

C Habas. 2002. [Physiological basis of functional MRI].. https://pubmed.ncbi.nlm.nih.gov/12469010/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2007

Descending GABAergic projections to the mesencephalic locomotor region in the lamprey Petromyzon marinus.

The mesencephalic locomotor region (MLR) plays a significant role in the control of locomotion in all vertebrate species investigated. Forebrain neurons are likely to modulate MLR activity, but little is known about their inputs. Descending GABAergic projections to the MLR were identified by double-labeling neurons using Neurobiotin injected into the MLR combined with immunofluorescence against GABA. Several GABAergic projections to the MLR were identified in the telencephalon and diencephalon. The most abundant GABAergic projection to the MLR came from the caudal portion of the medial pallium, a region that may have similarities with the amygdala of higher vertebrates. A small population of GABAergic cells projecting to the MLR was found in the striatum and the ventral portion of the lateral pallium, which could respectively correspond to the input and output components of the basal ganglia thought to be involved in the selection of motor programs. Other GABAergic projections were found to come from the thalamus and the hypothalamus, which could take part in the motivational aspect of motor behavior in lampreys. Electrophysiological experiments were also carried out to examine the effects of GABA agonists and antagonists injected into the MLR in a semi-intact lamprey preparation. The GABA agonist inhibited locomotion, whereas the GABA antagonist initiated it. These results suggest that the GABAergic projections to the MLR modulate the activity of MLR neurons, which would be inhibited by GABA at rest.

Afferent Pathways↗

PubMed2007

Anatomical organization of antennal lobe projection neurons in the moth Heliothis virescens.

A prerequisite for understanding how odor information is coded in the central nervous system is to know the morphology and spatial relationship of the principal neurons forming the olfactory pathways. The present account provides an anatomical description of the morphology of the neuronal connections between the antennal lobe and the protocerebrum in the moth Heliothis virescens, a species used for studies of olfactory processing and learning. Intracellular labeling and antennal lobe focal injections with dextran fluorescent markers were combined with neuropil immunostaining and three-dimensional reconstructions. The experiments revealed four antennocerebral tracts, the inner, middle, outer, and dorsomedial, and eight morphological types of projection neurons in addition to a neuron with an unpaired median soma in the subesophageal ganglion. Multiglomerular projection neurons, present in all but the dorsomedial antennocerebral tract, project in several olfactory foci of the protocerebral neuropil. With few exceptions, these neurons do not innervate the calyces of the mushroom body. Uniglomerular projection neurons appear most numerous in the inner antennocerebral tract but are also present in the outer and dorsomedial tracts. These neurons always ramify in the calyces of the mushroom body and in the lateral horn. The projection areas of the neurons following different tracts are largely separated in the secondary olfactory centers. This is most evident in the lateral horn, whereas, in the calyces, the axonal ramifications are more intermingled. The mushroom body architecture, revealed by neuropil immunolabeling, showed striking similarities to that of other lepidopteran species as well as insects of other taxa.

Afferent Pathways↗

PubMed2007

Vessicular glutamate transporters 1 and 2 are differentially associated with auditory nerve and spinal trigeminal inputs to the cochlear nucleus.

Projections of glutamatergic somatosensory and auditory fibers to the cochlear nucleus (CN) are mostly nonoverlapping: projections from the spinal trigeminal nucleus (Sp5) terminate primarily in the granule cell domains (GCD) of CN, whereas type I auditory nerve fibers (ANFs) project to the magnocellular areas of the VCN (VCNm) and deep layers of Dorsal CN (DCN). Vesicular glutamate transporters (VGLUTs), which selectively package glutamate into synaptic vesicles, have different isoforms associated with distinct subtypes of excitatory glutamatergic neurons. Here we examined the distributions of VGLUT1 and VGLU2 expression in the CN and their colocalization with Sp5 and ANF terminals following injections of anterograde tracers into Sp5 and the cochlea in the guinea pig. The CN regions that showed the most intense expression of VGLUT1 and VGLUT2 were largely nonoverlapping and were consistent with ANF and Sp5 projections, respectively: VGLUT1 was highly expressed in VCNm and the molecular layer of the DCN, whereas VGLUT2 was expressed predominantly in the GCD. Half (47% +/- 3%) of the Sp5 mossy fiber endings colabeled with VGLUT2, but few (2.5% +/- 1%) colabeled with VGLUT1. In contrast, ANFs colabeled predominantly with VGLUT1. The pathway-specific expression of VGLUT isoforms in the CN may be associated with the intrinsic synaptic properties that are unique to each sensory pathway.

Afferent Pathways↗