Lamprey Striatum

Cross references:   Striatum    Basal Ganglia     Nucleus Accumbens Septi   
Lamprey Nucleus Accumbens    Lamprey Nervous System   

Organization of the lamprey striatum – transmitters and projections   
Only abstract available online for free. 
    The purpose of the present study is to characterize the striatum of the lamprey by immunohistochemical and tracing techniques.  
    Cells immunoreactive for GABA and substance P (SP), and positive for acetylcholinesterase, are present in the lamprey striatum. Immunoreactive (ir) fibers were detected by antisera raised against SP, dopamine, enkephalin and serotonin. These immunoreactive fibers were mainly located in the periventricular neuropil that borders the striatum and in which GABAergic striatal neurons distributed their dendritic arbors.  
    Putative connections between the striatum, the ventral part of the lateral pallium, and the diencephalic motor centers involved in the control of locomotion were studied by using fluorescein-coupled dextran amines (FDA) as a tracer. The striatum projects to the ventral part of the lateral pallium (lpv), where GABA-ir cells and SP-ir fibers were also present. The lpv in turn projects to the ventral thalamus, which has descending connections to the reticulospinal cells involved in the control of locomotion.  
    These results, together with previous findings of histaminergic and neurotensin projections, suggest that the lamprey striatum and its inputs with regard to neurotransmitters/modulators are very similar to those of modern amniotes, including primates, and are thus conserved to a high degree."  

Afferents of the lamprey striatum with special reference to the dopaminergic system: a combined tracing and immunohistochemical study.  
The origin of afferents to the striatum in lamprey (Lampetra fluviatilis) was studied by using fluorescein-coupled dextran-amines (FDA). Injection of FDA into the striatum retrogradely labeled several cell populations in the forebrain and the rostral rhombencephalon. No retrograde labeled cells were seen in the mesencephalon.  
    A dopamine-specific antiserum was used to determined the distribution of dopaminergic perikarya and fibers. Many dopamine-immunoreactive (DA-ir) fibers were present throughout the brain, but the highest density of labeled fibers was in the mediobasal prosencephalon, especially in the striatum, the lateral hypothalamic area, and the neurohypophysis.  
    Most DA-ir cells were located in the mediobasal diencephalon (preoptic region, nucleus commissurae postopticae, hypothalamus, and nucleus tuberculi posterioris). In the mesencephalon, only a few immunopositive cells were observed in the tectum opticum. In the rhombencephalon, DA-ir cells were observed in the isthmic region, dorsally to the descending trigeminal tract, and caudally to the posterior rhombencephalic reticular nucleus.  
    The rostralmost spinal cord received many descending DA-ir fibers from the brainstem.
    Along the spinal cord, DA-ir neurons were also found, some of which projected to the medioventral surface, forming a prominent plexus.  
    On the basis of double-labeling experiments, it is shown that the dopaminergic input to the striatum originates from the nucleus tuberculi posterioris. Thus, the striatum receives inputs from different structures, including a strong dopaminergic innervation from the diencephalon. Much of the dopaminergic system in Lampetra fluviatilis is basically similar to that seen in some teleosts, but it presents differences with other anamniote (elasmobranch) as well as amniote groups." 

The dopamine D2 receptor gene in lamprey,  Its Expression in the Striatum and Cellular Effects of D2 Receptor Activation  (PubMed)   
    Full length article available online for free.  Many active links.     
Abstract: HTML: From the abstract
    "All basal ganglia subnuclei have recently been identified in lampreys, the phylogenetically oldest group of vertebrates. Furthermore, the interconnectivity of these nuclei is similar to mammals and tyrosine hydroxylase-positive (dopaminergic) fibers have been detected within the input layer, the striatum.  
    Striatal processing is critically dependent on the interplay with the dopamine system, and we explore here whether D2 receptors are expressed in the lamprey striatum and their potential role.  
    We have identified a cDNA encoding the dopamine D2 receptor from the lamprey brain and the deduced protein sequence showed close phylogenetic relationship with other vertebrate D2 receptors, and an almost 100% identity within the transmembrane domains containing the amino acids essential for dopamine binding.  
    There was a strong and distinct expression of D2 receptor mRNA in a subpopulation of striatal neurons, and in the same region tyrosine hydroxylase-immunoreactive synaptic terminals were identified at the ultrastructural level. The synaptic incidence of tyrosine hydroxylase-immunoreactive boutons was highest in a region ventrolateral to the compact layer of striatal neurons, a region where most striatal dendrites arborise.   Application of a D2 receptor agonist modulates striatal neurons by causing a reduced spike discharge and a diminished post-inhibitory rebound.  
    We conclude that the D2 receptor gene had already evolved in the earliest group of vertebrates, cyclostomes, when they diverged from the main vertebrate line of evolution (560 mya), and that it is expressed in striatum where it exerts similar cellular effects to that in other vertebrates. These results together with our previous published data (Stephenson-Jones et al. 2011, 2012) further emphasize the high degree of conservation of the basal ganglia, also with regard to the indirect loop, and its role as a basic mechanism for action selection in all vertebrates."      
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Dopamine differentially modulates the excitability of striatal neurons of the direct and indirect pathways in lamprey.   (PubMed) 
    Full length HTML available online for free.  Many diagrams and active links.   
from the abstract
    "The functions of the basal ganglia are critically dependent on dopamine. In mammals, dopamine differentially modulates the excitability of the direct and indirect striatal projection neurons, and these populations selectively express dopamine D1 and D2 receptors, respectively.  
    Although the detailed organization of the basal ganglia is conserved throughout the vertebrate phylum, it was unknown whether the differential dopamine modulation of the direct and indirect pathways is present in non-mammalian species. We aim here to determine whether the receptor expression and opposing dopaminergic modulation of the direct and indirect pathways is present in one of the phylogenetically oldest vertebrates, the river lamprey.  
    Using in situ hybridization and patch-clamp recordings, we show that D1 receptors are almost exclusively expressed in the striatal neurons projecting directly to the homolog of the substantia nigra pars reticulata.  
    In addition, the majority of striatal neurons projecting to the homolog of the globus pallidus interna/globus pallidus externa express D1 or D2 receptors.  
    As in mammals, application of dopamine receptor agonists differentially modulates the excitability of these neurons, increasing the excitability of the D1-expressing neurons and decreasing the excitability of D2-expressing neurons. Our results suggest that the segregated expression of the D1 and D2 receptors in the direct and indirect striatal projection neurons has been conserved across the vertebrate phylum. Because dopamine receptor agonists differentially modulate these pathways, increasing the excitability of the direct pathway and decreasing the excitability of the indirect pathway, this organization may be conserved as a mechanism that biases the networks toward action selection."