ABSTRACT
Damage to the adult motor cortex leads to severe and frequently irreversible deficits in motor function. Transplantation of embryonic cortical neurons into the damaged adult motor cortex was previously shown to induce partial recovery, but reports on graft efferents have varied from no efferent projections to sparse innervation. Here, we grafted embryonic cortical tissue from transgenic mice overexpressing a green fluorescent protein into the damaged motor cortex of adult mice. Grafted neurons developed efferent projections to appropriate cortical and subcortical host targets, including the thalamus and spinal cord. These projections were not a result of cell fusion between the transplant and the host neurons. Host and transplanted neurons formed synaptic contacts and numerous graft efferents were myelinated. These findings demonstrate that there is substantial anatomical reestablishment of cortical circuitry following embryonic cortex grafting into the adult brain. They suggest that there is an unsuspected potential for neural cell transplantation to promote reconstruction after brain injury.
Subject(s)
Brain Injuries , Motor Cortex/cytology , Motor Cortex/surgery , Nerve Regeneration/physiology , Neurons/transplantation , Animals , Brain Injuries/pathology , Brain Injuries/physiopathology , Brain Injuries/surgery , Brain Tissue Transplantation/methods , Doublecortin Domain Proteins , Embryo, Mammalian , Green Fluorescent Proteins/genetics , In Situ Hybridization, Fluorescence/methods , Mice , Mice, Inbred C57BL , Mice, Transgenic , Microscopy, Immunoelectron/methods , Microtubule-Associated Proteins/metabolism , Neural Pathways/physiology , Neurons/metabolism , Neurons/ultrastructure , Neuropeptides/metabolismABSTRACT
Dopaminergic receptors of the D1 type are highly expressed in the dorsal striatum and nucleus accumbens. In the dorsal striatum, they are rarely observed on presynaptic terminals. However, their subcellular localization in the nucleus accumbens core and shell had not been compared to that of dorsal striatum. Here we investigated the subcellular localization of D1 receptors in these three brain regions using immunogold labeling and electron microscopy. We showed that, among all presynaptic terminals forming asymmetric contact with dendritic processes, the percentage of D1R immunoreactive terminals was low in the dorsal striatum (8.2%), but reached in the nucleus accumbens core and shell 25.5 and 29%, respectively. These observations are consistent with electrophysiological studies, which showed that D1 stimulation inhibits the response of target neurons to glutamatergic input via presynaptic mechanisms in the nucleus accumbens but not in the dorsal striatum.
Subject(s)
Corpus Striatum/ultrastructure , Nucleus Accumbens/ultrastructure , Receptors, Dopamine D1/ultrastructure , Animals , Immunohistochemistry , Male , Microscopy, Electron, Transmission , Presynaptic Terminals/ultrastructure , Rats , Rats, Sprague-DawleyABSTRACT
We have studied "in vivo" neurochemically identified striatal neurons to analyze the localisation and the trafficking of dopamine and acetylcholine G protein coupled receptors (GPCR) (D1R, D2R, m2R and m4R) under the influence of neurotransmitter environment. We have identified receptors in tissue sections through immunohistochemical detection at the light and electron microscopic level. We have identified receptors in normal animals and after acute and chronic stimulations. We have quantified receptors through image analysis at the electron microscopic level in relation to various subcellular compartments. Our results demonstrate that, in normal conditions, GPCRs are mostly associated with plasma membrane of the striatal neurons, mostly at extra-synaptic sites. In certain instances (m4R; D2R), receptors have prominent localisation inside the rough endoplasmic reticulum. Our results also show that two distinct receptors for a same neurotransmitter may have distinct subcellular localisation in a same neuronal population (m2R versus m4R) and that the same neurotransmitter receptor (m4R) can have distinct localisation in distinct neuronal populations (cytoplasm versus cell surface). After acute stimulation, cell surface receptors undergo dramatic subcellular changes that involve plasma membrane depletion, internalisation in endosomes and in multivesicular bodies. Such changes are reversible after the end of the stimulation and are blocked by antagonist action. Chronic stimulation also provokes changes in subcellular localisation with specific pattern: plasma membrane depletion, and exaggerated storage of receptors in rough endoplasmic reticulum and eventually Golgi complex (D1R; m2R and m4R). Decreasing chronic receptor stimulation reverses such changes. These results demonstrate that, "in vivo", in the striatum, GPCRs undergo complex intraneuronal trafficking under the influence of neurochemical environment in conditions that dramatically modulate the number of cell surface receptors available for interaction with neurotransmitters or drugs. This confirms that "in vivo", the trafficking and the subcellular compartmentalization of GPCRs may contribute to regulate neuronal sensitivity and neuronal interactions in physiological, experimental and pathological conditions, including in therapeutic conditions.
