Ipsilateral Axons Research Articles

Developmental changes in the pattern of retinal projections in pigmented and albino rabbits

The distribution of retinal axons and/or terminals in the retino-recipient nuclei of pigmented and albino rabbits varying in age from the 24th postconceptional day (24PCD) to adulthood was examined following unilateral intraocular injections of the enzyme horseradish peroxidase. Both in pigmented and albino rabbits contralateral retinal axons and/or terminals in the dorsal and ventral lateral geniculate nuclei (DLG and VLG), superior colliculi (SC), pretecta (PT) and accessory optic tract nuclei (AON) were already present on 24PCD. In the period 26–30PCD the contralateral projection occupied the entire volume of the DLG, VLG and SC. Although 32PCD (the day of birth) the proportions of the volumes of DLG and VLG occupied by the contralateral projections were slightly reduced, their volume continued to increase in absolute terms up to adulthood. In pigmented rabbits the ipsilateral projections to all retino-recipient nuclei were most dense and extensive on 26PCD. From 26PCD, the relative extent of the ipsilateral projections was gradually reduced, but a reduction in their absolute extent did not become evident until 32PCD. By 32PCD the ipsilateral projection to the AON had disappeared completely. The distribution of ipsilateral axons and/or terminals and the relative proportion of the nuclei occupied by the ipsilateral projection in all other retino-recipient nuclei had become adult-like by 34PCD. In albino rabbits only a sparse ipsilateral projection to the presumptive superficial collicular layers was present on 24PCD. In the remaining retino-recipient nuclei an ipsilateral projection was present on 26PCD. From 26PCD the relative extent and from 30PCD the absolute extent of ipsilateral retinal axons and/or terminals was gradually reduced. The relative extent of the ipsilateral projection had become almost adult-like by 34PCD. Throughout development ipsilateral projections in albinos were consistently less dense and less extensive than those in pigmented rabbits, and unlike in pigmented rabbits, the ipsilateral projections to the VLG and PT were only transient. The differences betweent the two strains in the pattern of retinofugal projections were further enhanced during the period of segregation of the ipsilateral and contralateral projections. Considering the fact that in both strains there is a partial correspondence between the period in which the spatial extent of the ipsilateral projections is reduced and the period of retinal ganglion cell (RGC) death 79,80, it is likely that RGC death plays a role in the process of segregation of the retinal afferents into ocular domains. However, our data suggest that other mechanism(s) also play an important role in the process.

Terminal arbors of single ON‐center and OFF‐center X and Y retinal ganglion cell axons within the ferret's lateral geniculate nucleus

The lateral geniculate nucleus of the ferret contains not only eye-specific layers, but a further subdivision of layers A and A1 into inner and outer sublaminae that contain, respectively, ON-center and OFF-center cells (Stryker and Zahs, '83). To study how the arbors of single retinal ganglion cell axons correlate with these cellular divisions, we have examined the morphology of physiologically classified retinal axons in the ferret's lateral geniculate nucleus. As in cats, we could classify retinal axons as X or Y on the basis of a number of physiological criteria. X and Y axons have distinct patterns of termination in the lateral geniculate nucleus. Contralateral X axons innervate lamina A and ipsilateral axons lamina A1. X axons are further segregated in these laminae so that ON-center axons terminate in the inner sublamina, and OFF-center axons in the outer sublamina. We did not observe any branches of X axons innervating the medial interlaminar nucleus or the midbrain. Y axons have much larger terminal arbors and exhibit greater variation in their terminations. Generally, within layers A and A1, ON-center Y axons innervate the inner sublamina and OFF-center Y axons innervate the outer sublamina. However, they often innervate both sublaminae, and occasionally have a few boutons in the inappropriate lamina as well. Y axons also terminate in the dorsal C laminae, the interlaminar zones, and the media interlaminar nucleus; branches of these axons course toward the midbrain, presumably to innervate the superior colliculus. Thus, whereas the Y pathway in the ferret is one of high divergence, the X pathway appears to be the substrate for segregated ON and OFF channels through the lateral geniculate nucleus.

A population of ascending intersegmental interneurones in the locust with mechanosensory inputs from a hind leg.

A population of some 35 intersegmental interneurones with somata in the metathoracic ganglion has been characterized by intracellular recording and staining. These interneurones integrate signals from extero- and proprioceptors on a hind leg. The somata are clustered in an anterior and lateral region of the dorsal cortex, and the axons project to more anterior ganglia in either the ipsilateral or contralateral connectives. Some of these interneurones are excited by afferents from a proprioceptor at the femorotibial joint, the femoral chordotonal organ. An afferent spike evokes a chemically mediated EPSP in an interneurone with a latency and consistency that suggest that the connection is direct. An individual interneurone codes particular features of the movement about the femorotibial joint, responding to flexion, extension, or both directions of movement with either phasic or tonic responses. These interneurones have an extensive field of fine branches ipsilateral to the hind leg from which they receive input. These branches are in lateral and intermediate regions of neuropil to which the afferents of the chordotonal organ also project. Axonal branches, from either an ipsilateral and contralateral axon, are sparse and varicose and occur in dorsal neuropil. Other interneurones are excited by afferents from exteroceptive hairs (trichoid sensilla). An individual interneurone is excited by a particular array of hairs on specific regions of a hind leg. The connections between the afferents and the interneurones appear direct. These interneurones have a dense and compact array of fine branches ipsilateral to the hind leg from which they receive input. These branches are in the most ventral region of neuropil, to which the hair afferents also project. Branches from the ipsilateral axons are sparse and varicose and occur in more dorsal neuropil. The interneurones can thus provide the more anterior ganglia with precise information about the movement of a joint in a hind leg and of the location of an exteroceptive stimulus. This information would be of importance in ensuring the correct co-ordination of the legs during walking.

The development of a population of spinal cord neurons and their axonal projections revealed by GABA immunocytochemistry in frog embryos.

The development of a population of cerebrospinal-fluid-contacting neurons in the spinal cord of the Xenopus embryo ('Kolmer-Agduhr' cells) has been followed by using an immunocytochemical procedure that identifies GABA in fixed nervous tissue. Stained Kolmer-Agduhr cells containing GABA first appeared at stage 25 and their numbers increased steadily with the developmental age of the embryo. The Kolmer-Agduhr neurons had ascending ipsilateral axons that often terminated in growth cones. These axons and growth cones could be stained by the GABA antiserum from the earliest stages of outgrowth from the Kolmer-Agduhr cell body. We measured the angle of the earliest axons' outgrowth relative to the rostrocaudal axis of the spinal cord. The initial outgrowth of axons was always rostral over a narrow range of angles. This observation is inconsistent with the hypothesis of random initial outgrowth followed by later selection of the correct orientation, which would predict that axons would initially grow out over a wide range of angles. Instead, it suggests that, even from the earliest moments, axon outgrowth from the Kolmer-Agduhr cells is directed rostrally in a specific stereotyped manner.

Excitation of upper cervical inspiratory neurons by inspiratory neurons of the nucleus retroambigualis in the cat

The experiments reported here examined inputs from inspiratory neurons of the nucleus retroambigualis to upper cervical inspiratory neurons. Antidromic mapping in contralateral C1 demonstrated the existence of axon collaterals for 9 of 19 nucleus retroambigualis axons tested (47%). Forty nucleus retroambigualis neurons were tested with antidromic mapping for a projection to ihe ipsilateral C1 segment; 9 40 (22%) had an ipsilateral axon (8 of these also projected contralaterally), and 2 40 (5%) had an axon collateral in ipsilateral C1. Cross-correlation histograms suggested monosynaptic excitation of an upper cervical inspiratory neuron by a contralateral nucleus retroambigualis neuron in 4 69 cases (6%) and common input to the pair in 2 69 cases (3%). Six of the 69 cross-correlograms were computed during antidromic activation of the nucleus retroambigualis neuron, and one of these six demonstrated direct excitation of the upper cervical inspiratory neuron by the retroambigualis neuron. We concluded that at least some upper cervical inspiratory neurons receive monosynaptic excitation from the contralateral, and possibly the ipsilateral, nucleus retroambigualis inspiratory neurons. These results, together with those published elsewhere for inputs from inspiratory neurons in the contralateral ventrolateral nucleus tractus solitarius, suggest that the rhythmic, inspiratory firing pattern of the upper cervical inspiratory neurons is due to excitatory fnputs from these two inspiratory bulbospinal neuron populations.

The early development of neurons with GABA immunoreactivity in the CNS of Xenopus laevis embryos.

We have used an antibody to glutaraldehyde fixation complexes of gamma-amino butyric acid (GABA) to stain the developing central nervous system of Xenopus laevis embryos. Neuronal somata, growth cones, axons, and dendrites were found with GABA-like immunoreactivity. Transmission electron microscope (TEM) observations were made of axons and synapses. By observation of the earliest stages of differentiation of neurons, seven classes of putative GABAergic interneurons were discerned. 1) Ascending neurons are first stained in the hindbrain at stage 26 and later extend caudally in the spinal cord. They have ascending ipsilateral axons. 2) Midhindbrain reticulospinal neurons are first stained at stage 25 and develop as a compact group with descending ipsilateral and contralateral axons. 3) Vestibular complex commissural neurons are first stained at stage 29/30 in a dorsal position near the entry of the seventh and eighth cranial nerves. They have ventral commissural axons that descend contralaterally and their somata form a compact mass. 4) Rostral hindbrain commissural neurons are first stained at stage 33/34 just rostral to the entry of the trigeminal nerve. They each have a decussating projection. 5) Rostral midbrain neurons are first stained in the midbrain at stage 29/30 and are later associated with prominent dorsal and ventral commissures. 6) Optic tract and 7) rostral forebrain neurons are found in the forebrain associated with strongly stained axon tracts. The direction of axonal growth from its earliest stages was distinct for each class of hindbrain and spinal cord neuron.

Structural and functional characteristics of commissural neurons in the superior colliculus of the hamster.

Intracellular recording and horseradish peroxidase (HRP) injection techniques were employed to delineate the structural and functional properties of superior collicular (SC) neurons in the hamster that were antidromically activated by electrical stimulation of the contralateral tectum. A total of 39 such cells were completely characterized, injected, and recovered. In ten of these, the axonal filling allowed us to reconstruct at least a portion of the terminal arborization in the SC contralateral to the labelled cell. Two of the recovered neurons were located in the stratum griseum superficiale (SGS), three were in the stratum opticum (SO), ten were in the stratum griseum intermediale (SGI), 11 were in the stratum album intermedium (SAI), 11 were in the stratum griseum profundum (SGP) and two were located in the stratum album profundum (SAP). The recovered cells were highly varied in both their morphological and their physiological characteristics. Somal areas ranged between 74 microns2 and 364 microns2, and the sample of recovered neurons included horizontal cells, narrow field vertical cells, and a variety of other multipolar neurons. Over one-third (38.5%) of the recovered cells were unresponsive, 2.6% were exclusively visual, 33.3% responded only to innocuous cutaneous stimuli, 10.2% were bimodal, 7.7% were specifically nociceptive, and 7.7% had complex (Rhoades, Mooney, and Jacquin: J. Neurosci. 3:1342-1354, '83) somatosensory receptive fields. We observed no clear-cut correlations between the structural and functional characteristics of these neurons. The conduction latencies of the commissural SC neurons ranged between 0.8 and 14.0 ms. The most rapidly conducting cells were located in the SGP and SAP. Conduction latency had a significant negative correlation with soma area. Labelled axons, in many cases, had at least one terminal arbor in a portion of the SC that was mirror symmetric with the location of the cell from which it originated. In several cases, however, commissural axons gave off a number of collaterals across the mediolateral extent of the tectum. commissural axonal terminations were visible only in the laminae ventral to the SO. Several commissural SC neurons also had extensive ipsilateral axon collaterals. Both the ipsilateral and commissural axon branches of these cells gave off en passant and terminal swellings.

Evidence for differential effects of terminal and dendritic competition upon developmental neuronal death in the retina

Retinal ganglion cells with ipsilaterally projecting axons were labelled with horseradish peroxidase injected unilaterally along the optic pathway in adult rats. Unoperated controls were compared with three groups of animals operated at birth, given (a) contralateral enucleation, (b) contralateral lesion to the optic tract or (c) both lesions simultaneously. The numbers of ipsilaterally projecting cells were increased in all three operated groups, presumably because of a reduction in natural neuronal death following diminished terminal and dendritic competition. The pattern of increase of labelled cell density varied with the type of lesion: enucleation led to a major increase within lower temporal retina; optic tract lesion caused its major increase in upper temporal retina, centred at the location of the area centralis; and the double lesion combined both effects above. The distribution of cell-body sizes was differentially affected by the lesions: enucleation led to a shift in the distribution towards the small cell side of the spectrum, when compared with the controls; optic tract lesion shifted the distribution towards the large cell side of the spectrum, but only outside the temporal crescent; and the double lesion led to a shift towards small cells within the temporal crescent and towards large cells outside the crescent, again combining the effects of the single lesions. Large alpha-like neurones with ipsilateral axons were common in the nasal retina of both groups given optic tract lesions but they were rare in the nasal retina of unoperated and, especially, of enucleated rats. The limits of the temporal crescent were unchanged, notwithstanding the large numbers of cells outside the crescent in operated rats. It is suggested that postnatal competitive interactions at the level of terminals and of dendrites control natural neuronal death in the rat retina with different requirements regarding retinal topography and ganglion cell types. The postnatal regulation of neuronal numbers is not responsible for the generation of the nasotemporal division but may be involved in the development of differential distributions of specific ganglion cell types across the retina.

Reciprocal inhibitory interneurones in the Xenopus embryo spinal cord.

The mechanism of reciprocal inhibition between antagonistic motor centres during swimming in the paralysed Xenopus embryo has been investigated further. Paired intracellular recordings have been made from interneurones and motoneurones in an attempt to identify neurones which make direct inhibitory synapses onto motoneurones on the opposite side of the spinal cord. A physiological class of inhibitory interneurones is described which, when stimulated by intracellular current passage, evoke short-latency, probably monosynaptic, strychnine-sensitive inhibitory potentials in contralateral motoneurones. These inhibitory interneurones fire once per swimming cycle in phase with the ipsilateral motor root discharge. They therefore have a pattern of activity which would cause them to inhibit motoneurones of the antagonistic motor centre at an appropriate part of the swimming cycle. The intracellular injection of horseradish peroxidase (HRP) has allowed the morphology of these inhibitory interneurones to be characterized. They have unipolar cell bodies with a thick proximal process with short dendrites which crosses the spinal cord ventrally and then bifurcates with one axonal branch ascending into the hind brain and the other descending the spinal cord. These anatomical features are typical of the 'commissural interneurones' first described by Roberts & Clarke (1982). There are also some inhibitory interneurones which can inhibit motoneurones on the same side of the spinal cord. At least some of these interneurones may be commissural interneurones with ipsilateral axons and they may play a role in the generation of the swimming rhythm.

Postnatal development of primary visual projections in the tammar wallaby (Macropus eugenii).

The time course and pattern of retinal innervation of primary visual areas was traced in pouch-young wallabies. Tritiated proline was injected into one eye of animals ranging in age from 1 to 72 days after birth. These results are compared to the 11 primary visual areas found in the adult wallaby, seven of which receive binocular input while four are monocular. At birth retinal ganglion cell axons have not reached any visual areas. Two to 4 days after birth, all of the axons are crossing to the contralateral optic tract. Nine to 12 days after birth axons begin to invade the contralateral lateral geniculate nucleus, the superior colliculus, and the medial terminal nucleus. Twenty to 21 days after birth, ipsilateral axons invade the lateral geniculate nucleus and superior colliculus. The contralateral projection precedes the ipsilateral projection in all binocular visual areas. By 25 days, ipsilateral and contralateral afferents share common territory in the lateral geniculate nucleus; however, afferents from each eye are initially concentrated in appropriate areas. Between 52 and 72 days, afferents to the dorsal lateral geniculate nucleus are gradually segregated into nine terminal bands. Four are contralateral while five are ipsilateral. By 72 days, the ipsilateral component to the superior colliculus is clustered beneath the contralateral projection a deeper layer. Projections to four monocular visual areas--lateral posterior nucleus, dorsal terminal nucleus, lateral terminal nucleus, and nucleus of the optic tract--are established later than binocular visual areas, except the suprachiasmatic nucleus. The suprachiasmatic nucleus is the last to be bilaterally innervated even though it is situated closest to the optic chiasm. At the light microscope level a mature pattern of visual development is emerging by 72 days, although the eyes do not open until 140 days.

The normal and abnormal postnatal development of retinogeniculate projections in golden hamsters: An anterograde horseradish peroxidase tracing study

In adult hamsters, the dorsal lateral geniculate nucleus (LGd), which lacks a noticeable pattern of cellular lamination, receives fibers predominantly from the contralateral eye except for a medial segment which receives fibers from the ipsilateral eye. Using the method of anterograde transport of horseradish peroxidase (HRP), it is shown in this study that the contralateral and ipsilateral retinogeniculate fibers innervate the LGd by day 0 with the development of the contralateral fibers slightly ahead of the ipsilateral ones. The entire contralateral LGd is filled with retinal fibers by day 1. The ipsilateral LGd is almost completely covered with retinal fibers on day 2 but with the fiber density much higher in the dorsal half of the nucleus. Thus, fibers from both eyes overlap with each other completely beginning on day 2 in the LGd. The segregation of these fibers becomes obvious on day 6 as indicated by a decrease in the density of ipsilateral fibers in the ventral portion of the LGd while the ipsilateral projection continues to concentrate in the dorsal half of the nucleus. A low density area in the dorsomedial part of the contralateral LGd is observed on day 7. By day 8, the segregation of the contralateral and ipsilateral projections has achieved an adult-like pattern. Thus, there seems to be two phases for the normal development of the retinogeniculate fibers. In the first phase, axons from both eyes grow in and occupy the entire LGd. In the second phase, those axons occupying inappropriate areas of the LGd are eliminated to form the adult pattern. The effect of unilateral eye removal at birth on the development of the retinogeniculate projection from the remaining eye was also studied with the anterograde HRP method. The ipsilateral fibers in the experimental animals are distributed in the lateral portion of the nucleus in the first two postnatal days. The entire LGd is not filled with ipsilateral fibers until day 4. From day 6 onwards, the ipsilateral fibers are more extensive than those of the normal animals. In addition to a dense projection to the dorsal two-thirds of the LGd, moderate amount of ipsilateral axons can be detected in the remaining ventral portion of the nucleus in day 6 and older experimental animals. The development of the contralateral retinal fibers in the experimental animals is similar to that of the normal from day 1 to day 6, i.e. the entire LGd is densely filled with crossed optic axons. However, on day 7, there is no decrease in the density of the contralateral fibers in the medial sector of the LGd. The lack of restriction of retinal fibers is observed in all subsequent stages of development. These results suggest that axo-axonal interaction is important for the process of segregation of retinogeniculate projections observed in normal developing hamsters.

The development and restriction of the ipsilateral retinofugal projection in the chick

Although it is generally believed that the central projections of the retina in birds are entirely crossed, using wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) as an anterograde tracer, we have found that in normal posthatched chicks there is a small ipsilateral retinofugal projection to the diencephalon and midbrain. Most of the ipsilateral fibers appear to be directed to the lateral anterior and dorsolateral anterior nuclei of the thalamus, to the pretectal region, and to the ectomammillary nucleus and the adjoining nucleus externus. Even in the best preparations the numbers of ipsilateral fibers are so small that it is hardly surprising that they have been overlooked in previous axonal degeneration and autoradiographic experiments. A significantly larger ipsilateral retinal projection develops during the second week of incubation. The ipsilaterally directed fibers can be first seen on the fifth day of incubation and their numbers appear to increase until about embryonic day 12. At this stage the projection involves substantially more fibers than at hatching and is also more extensive in its distribution; in fact, in its general organization (but not its size) it closely parallels the normal crossed retinofugal system, contributing fibers to essentially all the primary visual relay nuclei in the diencephalon and midbrain and to much of the optic tectum, where the densest projection is to its caudomedial aspect. During the second week of incubation there is also a small number of retinal fibers, which after crossing in the optic chiasm, recross the midline in the posterior and tectal commissures (and also in the tectal roof plate), before ending in the pretectal region of the ipsilateral side. In addition, there is a markedly aberrant projection from the retina into the contralateral optic nerve. Most of the ipsilateral retinal fibers are eliminated between the twelfth and sixteenth days of incubation, and by day 17 the ipsilateral projection is reduced to its mature form. The progressive reduction in the ipsilateral projection occurs at a time when it is known (from other studies) that there is an appreciable loss of retinal ganglion cells; but whether the reduction is due to neuronal death or to the selective elimination of ipsilateral axon collaterals remains to be determined. The existence of a significant ipsilateral retinofugal component early in development, probably accounts, in part, for the distinctive and persistent ipsilateral projection that occurs if one eye is removed during the first few days of incubation.

The neuroanatomy of an amphibian embryo spinal cord

Horseradish peroxidase has been used to stain spinal cord neurons in late embryos of the clawed toad (Xenopus laevis). It has shown clearly the soma, dendrites and axonal projections of spinal sensory, motor and interneurons. On the basis of light microscopy we describe nine differentiated spinal cord neuron classes. These include the Rohon-Beard cells and extramedullary cells which are both primary sensory neurons, one class of motoneurons that innervate the segmental myotomes, two classes of interneurons with decussating axons, three classes of interneurons with ipsilateral axons and a previously undescribed class of ciliated ependymal cells with axons projecting ipsilaterally to the brain. We believe that all differentiated neuron classes are described and that this anatomical account is the most complete for any vertebrate spinal cord.

Properties of vestibular neurones projecting to neck segments of the cat spinal cord.

1. Vestibular neurones projecting to the upper cervical grey matter (vestibulocollic neurones) were identified by localized microstimulation in the C3 segment of the cat spinal cord.2. The neurones were found in the lateral (Deiters'), medial and descending nuclei bilaterally and projected to the spinal cord in the lateral and medial vestibulospinal tracts (LVST and MVST). Ipsilateral axons of Deiters' neurones were mostly in the LVST, axons of medial and descending neurones in the MVST; a few Deiters' neurones had axons in the MVST; some descending neurones had axons in the LVST. Most axons of contralateral neurones were in the MVST.3. The axons of 62% of ipsilateral vestibulocollic Deiters' neurones not only gave off a collateral to C3, but also extended as far as the cervical enlargement (;branching'); some of these neurones projected as far as the upper thoracic cord, almost none to the lumbar cord. Ipsilateral descending nucleus neurones branch in the same fashion, but there is no branching in the relatively small medial nucleus population.4. A large majority of vestibulocollic neurones receive monosynaptic excitation from the ipsilateral labyrinth and a number are inhibited by stimulation of the contralateral labyrinth (commissural inhibition). It is possible that commissural inhibition acts on a broad population of vestibular neurones involved in the control of eye, head and trunk movement.5. Vestibulocollic neurones do not make up a homogeneous population acting only on the neck. Instead it is likely that subpopulations, for example branching and non-branching neurones, have different functions.

Synaptic interactions of identified nerve cells in the spinal cord of the sea lamprey.

AbstractAs part of a continuing study on the organization of the lamprey nervous system, two additional groups of interneurons have been identified by physiological and morphological criteria in the isolated spinal cord of Petromyzon marinus. These and other identified nerve cells were tested for synaptic interactions using separate intracellular microelectrodes for stimulation and recording. Edge cells were identified by their unusual location in the lateral fiber tracts of the spinal cord. Their axons extended rostrally either on the ipsilateral or contralateral side of the cord. Some edge cells showed polysynaptic EPSP's and IPSP's after stimulation of sensory dorsal cells, but interactions with other identified neurons were rare. A single cell was excited by a giant interneuron. One edge cell produced IPSP's in a contralateral edge cell, and another produced IPSP's in lateral cells on the opposite side of the spinal cord. Thus, some edge cells have an inhibitory function. Lateral cells were distinguished from giant interneurons and edge cells by their cell bodies in the lateral grey of the spinal cord in the gill and trunk regions, their ipsilateral dendrites, and their long ipsilateral axons extending as far as the tail. Lateral cells were excited and inhibited polysynaptically by sensory dorsal cells and, in turn, produced weak IPSP's in unidentified neurons. Stimulation of lateral cells produced neither visible movements peripherally nor synaptic potentials in other lateral cells, in giant interneurons, or in edge cells. Giant interneurons were previously identified on the basis of their cell bodies in the caudal half of the spinal cord, their bilateral dendrites, and their long contralateral axons extending towards the brain. Giant interneurons exhibited unitary composite EPSP's when more caudal giant interneurons were stimulated. The two components of the EPSP were due to electrical and chemical transmission. Under the electron microscope a contact between a dendrite of one giant interneuron and the probable axon of another had separate junctions resembling chemical and electrical synapses. Intracellular stimulation of sensory dorsal cells produced both monosynaptic and polysynaptic EPSP's in giant interneurons. Some dorsal cells produced unitary composite EPSP's Giant interneurons are part of a convergent, multispecific sensory system extending towards the brain.

Zur Struktur und Entwicklung des Riesenfasersystems erster Ordnung von Sepia officinalis L. (Cephalopoda)

The differentiation and course of the first order giant nerve fibres in the medial and posterior suboesophageal lobes of the brain of Sepia officinalis is examined in different developmental stages. In earlier embryonic stages one pair of first order giant cells differentiates on each side. Later, as a normal phenomenon, one cell of each pair degenerates. The two remaining giant fibres cross in the palliovisceral lobe. On either side of the intersection one branch of the contralateral and one branch of the ipsilateral axon are connected with the second order giant fibres. This structure, which differs from that found in Loligo, apparently mediates the functional bilaterality of the giant fibre system.