Date: Wed, 10 Jul 2002 15:17:14 -0700
To: "List for Toru Shimizu"
From: Georg Striedter
Subject: Whither HV?
A few days ago Erich asked me to summarize the evidence relating to the ventral hyperstriatum (HV) -- should it be grouped with HD, HI and HA? should it be grouped with the neostriatum? or should it be treated as a separate major telencephalic region (on a par with Wulst, neostriatal complex, archistriatum)? This issue is important for the nomenclature if we decide to rename HV (e.g. as ventral hypsopallium; as intermediate pallium, or as region HV).
I was not sure that I could (or should) do this by myself; so I asked Loreta and Luis for help and they have graciously given their advice. Still, as they so often say in prefaces, blame me not them if I've gotten something wrong. Also, I tried to think about making a table, as Erich asked, but my mind just doesn't seem to work well in "table format".... perhaps someone else can squeeze the following information into a table (if that is necessary).
- Classical Comparative Anatomy and Embryology:
- Ariens Kappers et al. considered HV to develop "both phylogenetically and ontogenetically" as "part of the general hyperstriatal mass". That's why they named it HV. however, they don't say a whole lot more about it than that.
- Durward and Haefelfinger, two classical comparative neuroembryologists, did not agree with this and suggested, instead, that HV develops in close association with the neostriatum. Haefelfinger therefore included HV in what he called the HV-neostriatal complex. What was their evidence? Hard to tell, actually, but it seems to have been mostly the fact that the boundary between HV and neostriatum develops relatively late (relative to other intratelencephalic boundaries).
- Radial Glia and Fate Mapping:
- According to Striedter and Beydler (1997), at least some radial glia extend from HV near the ventricular zone into the neostriatum, arguing that both HV and Neo are part of a single radial zone that gets subdivided relatively late in development.
- According to Striedter et al. (1998), at least some patches of the telencephalic ventricular zone give rise to cells that end up in both HV and Neo, indicating that the boundary between HV and Neo is not a lineage restriction boundary (at least at those early stages of development). These data corroborate the radial glia data and, collectively, support the hypothesis that HV develops as part of a general HV/neostriatal complex.
- Developmental Gene Markers:
- Puelles et al. (2000) report that the gene TBR1 in E10 chicks is expressed more strongly in Neo and HV than in the more dorsal regions. This supports the hypothesis that there is such a thing as a "HV/neostriatal complex".
- Puelles et al. (2000) also show a strong expression boundary for EMX1 at the boundary between HV and neostriatum, indicating that these two domains are molecularly distinct by E14. Dorsally, the extent of EMX1 expression varies with age: early on, it is expressed throughout the hyperstriatum; later it becomes relatively restricted to HV+HD.
These data support the hypothesis that HV is developmentally related to the other hyperstriatal areas, especially HD.
- Puelles an his collaborators also have some unpublished data on a gene that selectively labels the neostriatal complex (ventral pallium in their terminology) and not HV. These data provide support for the hypothesis that HV and Neo are molecularly distinct subdivisions. (I don't know what age these embryos are at.)
- Redies et al. (2001) have shown that cadherin-7 is expressed at high levels in HD, HI and HA, but at much lower levels in most of the neostriatum (except its caudolateral part). These data support the hypothesis that HV and HD/HA are molecularly distinct from one another. However, these cadherins have complex expression domains, being expressed in many places in various combinations.
- Adult Histochemistry:
- Brauth et al. (1986) found that neurotensin binding sites are densest in HV (but also quite dense in the surrounding areas, Neo and Wulst).
- Reiner et al. (1989) reported that kappa opioid receptors are elevated quite specifically in HV.
- Sun and Reiner (2000) showed that dopamine D1B receptor mRNA is expressed heavily in HV , much less so in Neo or HD.
- Connections and Physiology
- This subject remains quite shrouded in mystery, as far as I can tell, because very little work has been aimed directly at the functions or connections of HV. What follows are my impressions of the literature; this section would benefit greatly from input from Toru, Onur, or Martin....
- HD seems to be functionally part of the visual Wulst. It seems to have few connections with areas other than the Wulst.
- HV seems to be functionally related to either the neostriatum or HD, depending on what you look at. In my system (budgie vocal control system), the frontal part of HV seems to be closely interconnected with the frontal neostriatum. In the visual system, lateral HV reportedly gets inputs from part of the ectostriatum and projects to the Wulst. In the imprinting literature, IMHV gets some inputs from both the Wulst and the neostriatum, and has outputs to archistriatum and paleostriatum. In other words, we really can't (at this point) give a simple answer to the question "what does HV do?". Hopefully, as Dan pointed out, this nomenclature debate can serve to highlight pockets of ignorance.
- My take on all this:
I can see almost no evidence in support of grouping HV with HD, HI and HA (the EMX1 data is about it; see 3b).
My own glia and lineage data suggest that HV should be grouped with neostriatum. This seems to contradict the proposal by Puelles et al. that HV and Neo are molecularly distinct divisions. However, our data can be reconciled if we suppose that the HV/Neo complex becomes subdivided early on (between E10 and E14) by genes/proteins (e.g. EMX1) with expression boundaries that coincide with the HV/Neo boundary but not with any lineage restriction boundaries. Clearly, more work is needed to support this hypothesis. In the meantime, I think it is probably most sensible to give separate names to HV, neostriatum and Wulst.
As I said at the beginning. I've received some significant help in putting this together and I am sure that more help from others is needed. So, please let me know ....
Georg F. Striedter
Department of Neurobiology & Behavior
UC Irvine, 2205 Bio Sci II
Irvine, CA 92697-4550
office: (949) 824-5228