The ultrastructure of a cerebellar analogue in octopus

Abstract

The peduncle lobe of Octopus, a centre concerned with regulating motor behaviour primarily on the basis of visual cues, though it also receives a "labyrinthine" or statocyst input, has been examined for the first time in the electron microsope. In the lower part of the lobe, the basal zone, there are large "motor" cells up to 20 p m across with a rounded, pale nucleus and a large perikaryon; there are also smaller cells, 4-10 p m in diameter with a dark irregularlyshaped nucleus. The latter receive synapses from afferent fibres to the lobe, and those from the principal afferent source, the ipsilateral optic lobe, have been characterised as large terminals with many small clear vesicles. Other optico-peduncular afferents and the small-cell fibres themselves run directly up to the second part of the lobe, the peduncle spine, which contains exclusively small granular cells about 5 p m in diameter. The fibres of these spine cells form a conspicuous and characteristic array of parallel fibres in the neuropil and they bear a striking resemblance to those of vertebrate cerebellar granule cells: serial synaptic relays are present along their length. These findings, together with earlier evidence about the effects on motor behaviour of lesions to the lobe, suggest a close functional and morphological analogy to a folium of the vertebrate cerebellum. The hypothesis is discussed that parallel fibres, with their narrow diameter and hence long conduction time, are an essential feature of fine motor control systems, and that their primary function is one of providing critical time delays in the millisecond range.Cephalopods are large, actively-moving molluscs with a well-developed brain that has proved to be very useful for studying a variety of neurological problems (e.g., Young, '66). The ultrastructure of the brain, however, is comparatively poorly known and the only detailed study to date is that of Gray ('70) on the vertical lobe, an area concerned with learning and memory. This paper presents the t s of an ultrastructural investigation into the peduncle lobe, a part of the visuo-motor system (Messenger, '67a,b).The behaviour of cephalopods is largely visual, and they possess well-developed eyes, associated with which are large optic lobes ( fig. 1). Complex analysis of visual information takes place in the outer layers or deep retina of the optic lobes (Young, '62, '74). Deeper in the medulla of the optic lobes are neurons that send commands to motor centres in the central brain (the supra-oesophageal basal lobes and the sub-oesophageal magnocellular lobe) and thence to the muscles of the mantle, funnel, fins and arms in what appears to be an essentially hierarchical fashion (Boycott, '61; but see Young, '76). This hierarchy is apparent from the motor behaviour under direct electrical stimulation of the various lobes.Many of the neurons that influence the motor system do so indirectly by pathways that involve the paired peduncle lobes that lie on the optic tracts ( fig. 1). Each receives a visual input from secon...

Nitric oxide synthase (NOS) in the brain of the cephalopod Sepia officinalis

“…These two regions of the brain are thought to constitute cerebellar analogues (Messenger, 1967a(Messenger, ,b, 1979Hobbs and Young, 1973;Budelmann and Young, 1984;Camm et al, 1985;Chichery and Chichery, 1987;Gleadall, 1990;Woodhams, 1977;Young, 1977). Each spine region is characterized by an array of fine parallel fibers intrinsic to the lobe, giving it the appearance of a single folium of a vertebrate cerebellum.…”

Quantitative differences among the brains of cephalopods

“…We also provide separate lists of the percentage volumes of the superior frontal, vertical and subfrontal lobes, since these are of special interest for their functions as memory systems (Tables The peduncle lobe and anterior basal lobe are considered together since both receive visual and static inputs and contain sets offine parallel fibres. Their outputs are to the motor centres, including the oculomotor centre, and they constitute higher motor controls, analogous to the vertebrate cerebellum (Hobbs & Young, 1973;Woodham, 1977;Messenger, 1979). We have emphasizcd this functional feature by calling them 'parallel-fibre' lobes.…”

Oxytocin/vasopressin and gonadotropin‐releasing hormone from cephalopods to vertebrates

“…There are neurons that send commands to motor centers in the central brain and hence to the muscles of the mantle, funnel, fins, and arms 37 . Many of the neurons indirectly influence the motor system by pathways that involve the peduncle lobe of the optic tract 66 (Fig. 3A).…”

“…3C). There are two types of cells in the basal zone cell layer: large motor cells and small cells 66 . Further experiments are necessary to confirm which type of cells express oct‐GnRH.…”

“…There are two types of cells in the basal zone cell layer: large motor cells and small cells. 66 Further experiments are necessary to confirm which type of cells express oct-GnRH. Transmitters involved in this system have not been clarified yet, but the presence of 5-HT 69 and GABA 70 has been reported.…”