Proceedings of The Physiological Society
University College London (2003) J Physiol 547P, PC2
NOS in the cephalopod 'cerebellum'
Anna Di Cosmo*, Carlo Di Cristo* and John B. Messenger
*Department of Biological and Environmental Sciences, University of Sannio, Benevento, Italy and Department of Zoology, University of Cambridge, Cambridge, UK
The brain of Sepia is essentially organized hierarchically: motor programmes, usually originating in the optic lobes, are executed via higher motor centres, where specific motor commands are generated and directed to the appropriate sets of motoneurons in the lower centres (Messenger, 1983).
Nitric oxide synthase (NOS) has been shown by immunohistochemistry to be present in specific regions of the central nervous system (CNS) of the cephalopod mollusc Sepia officinalis (cuttlefish). NOS activity is Ca2+/calmodulin-dependent and the purified NOS from brain and optic lobes exhibited on SDS-PAGE a band at 150 kDa (Palumbo et al. 1999; Di Cosmo et al. 2000).
Our finding, that in Sepia NOS occurs in higher motor centres, in particular in the spines of the anterior basal and peduncle lobes, is most arresting. In both these lobes (studies performed on five animals) there are immunopositive cells of varying sizes, but more importantly there are positively stained fibres in the neuropil. In the posterior anterior basal lobe, the spine region contains numerous immunopositive small cells and strongly staining fine parallel fibres. The fibres run laterally for varying distances along the spine, giving off collateral branches. They presumably serve to carry signals for shorter and longer distances across the lobe. Other immunopositive fibres are seen dorsal and ventral to the immunopositive spine region. Presumably these come from the peduncle lobe. In these areas there are no immunopositive cells. In the peduncle lobe there are a few weakly staining cell bodies. They are seen only in the spine region, lying next to the well-defined boundary of the spine; they are more obvious in the median bank. They are about 10 µm in diameter and sometimes their immunopositive axons are seen entering the spine neuropil. From the peduncle lobe, some immunopositive tracts reach the anterior basal lobe.
In this our findings agree completely with those of Chichery & Chichery (1994), who stained sections of cuttlefish brains for NADPH-diaphorase. Like us they report very strong staining in the posterior anterior basal lobe spine and some staining in the peduncle lobe spine.
These two regions of the brain are thought to constitute cerebellar analogues (Messenger, 1967a,b; Hobbs & Young, 1973; Messenger, 1979; Camm et al. 1985; Gleadall, 1990). Each spine region is characterized by an array of fine parallel fibres intrinsic to the lobe, giving it the appearance of a single folium of a vertebrate cerebellum. In Octopus removal of the peduncle lobes does not abolish locomotion, but it does lead to motor dysfunction: movements are imprecise and jerky (Messenger, 1967b). Input to these lobes derives from the statocysts, the optic lobes and receptors in the arms and mantle; the output is to lower and intermediate motor centers and to the optic lobes. In short, these lobes are strikingly similar in their function, cyto-architecture and connectivity to the vertebrate cerebellum and, like the cerebellum, which contains the highest level of NOS in the mammalian brain (Rodrigo et al. 1994), they are now shown to contain high levels of NOS.
Where applicable, experiments conform with Society ethical requirements