Cerebral parts of chemosensory systems of the snail: Structural bases of intersensory integration

Presented are data on distribution of afferent fibers from tentacular and labial nerves innervating chemosensory tentacular organs, lips, and mouth area in the cerebral ganglia of terrestrial pulmonary snails are in the article. By using Golgi impregnation and infusion of cobalt chloride and nickel, it has been shown that most terminal branches of afferent fibers of all chemosensory organs are located in several symmetric areas of both metacerebrums. A part of fibers both of tentacular and of labial nerves form peculiar tracts and terminate in the interior neuropil of procerebrums. In metacerebrums, various neurons providing connections with afferent fibers of chemosensory organs are revealed. Many of them also innervate interior neuropil and procerebrum cell bodies area. The data obtained allow considering procerebrums as higher integrative centers of chemosensory information.     

Localization of serotonin/tryptophan-hydroxylase-immunoreactive cells in the brain and suboesophageal ganglion of Drosophila melanogaster

We previously demonstrated that tryptophan hydroxylase (TPH), the rate-limiting enzyme of serotonin (5-HT) synthesis, was commonly present in the brains of some insects. The current study was aimed at determining the number of serotonergic neurons in the brain and suboesophageal ganglion of adult Drosophila melanogaster and to investigate further the differences in immunoreactivity between 5-HT and TPH. Brain sections of Drosophila were immunostaind with sheep anti-TPH polyclonal antibody and rabbit anti-5-HT antiserum. The 5-HT-like immunoreactive neurons were also immunoreactive for TPH and bilaterally symmetrical; 83 neurons were found in each hemisphere of the brain and suboesophageal ganglion of adult Drosophila. This technique of colocalizing 5-HT and TPH revealed a larger number of serotonergic neurons in the brain and suboesophageal ganglion than that previous reported, thus updating our knowledge of the 5-HT neuronal system of Drosophila.     

Serotonin-immunoreactive neurons in the median protocerebrum and suboesophageal ganglion of the sphinx moth Manduca sexta

Summary Serotonin-immunoreactive neurons in the median protocerebrum and suboesophageal ganglion of the sphinx moth Manduca sexta were individually reconstructed. Serotonin immunoreactivity was detected in 19–20 bilaterally symmetrical pairs of interneurons in the midbrain and 10 pairs in the suboesophageal ganglion. These neurons were also immunoreactive with antisera against DOPA decarboxylase. All major neuropil regions except the protocerebral bridge are innervated by these neurons. In addition, efferent cells are serotonin-immunoreactive in the frontal ganglion (5 neurons) and the suboesophageal ganglion (2 pairs of neurons). The latter cells probably give rise to an extensive network of immunoreactive terminals on the surface of the suboesophageal ganglion and suboesophageal nerves. Most of the serotonin-immunoreactive neurons show a gradient in the intensity of immunoreactive staining, suggesting low levels of serotonin in cell bodies and dendritic arbors and highest concentrations in axonal terminals. Serotonin-immunoreactive cells often occur in pairs with similar morphological features. With one exception, all serotonin-immunoreactive neurons have bilateral projections with at least some arborizations in identical neuropil areas in both hemispheres. The morphology of several neurons suggests that they are part of neuronal feedback circuits. The similarity in the arborization patterns of serotonin-immunoreactive neurons raises the possibility that their outgrowing neurites experienced similar forces during embryonic development. The morphological similarities further suggest that serotonin-immunoreactive interneurons in the midbrain and suboesophageal ganglion share physiological characteristics.Abbreviations CNS central nervous system - DDC DOPA decarboxylase - LAL lateral accessory lobe - SLI serotonin-like immunoreactivity - SOG suboesophageal ganglion - VLP ventro-lateral protocerebrum     

两种软体动物神经系统一氧化氮合酶的组织化学定位

运用一氧化氮合酶(NOS)组织化学方法研究了软体动物门双壳纲种类中国蛤蜊和腹足纲种类嫁Qi神经系统中NOS阳性细胞以及阳性纤维的分布。结果表明：在蛤蜊脑神经节腹内侧,每侧约有10-15个细胞呈强NOS阳性反应,其突起也呈强阳性反应,并经脑足神经节进入足神经节的中央纤维网中;足神经节内只有2个细胞呈弱阳性反应,其突起较短,进入足神经节中央纤维网中,但足神经节中,来自脑神经节阳性细胞和外周神经系统的纤维大多呈NOS阳性反应;脏神经节的前内侧部和后外侧部各有一个阳性细胞团,其突起分别进入后闭壳肌水管后外套膜神经和脑脏神经索。脏神经节背侧小细胞层以及联系两侧小细胞层的纤维也呈NOS阳性反应。嫁Qi中枢神经系统各神经节中没有发现NOS阳性胞体存在;脑神经节、足神经节、侧神经节以及脑—侧、脑—足、侧—脏连索中均有反应程度不同的NOS阳性纤维,这些纤维均源于外周神经。与已研究的软体动物比较,嫁Qi和前鳃亚纲其它种类一样,神经系统中NO作为信息分子可能主要存在于感觉神经。而中国蛤蜊的神经系统中一氧化氮作为信息分子则可能参与更广泛的神经调节过程。     

Immunocytochemical and autoradiographic research on the growth of serotoninergic fibers to the cerebral ventricles in the perinatal period in rats

Anatomical relationships between serotoninergic (5-HT) fibers and cerebral ventricles were studied in rats from the 16th fetal day until the 9th postnatal day with immunocytochemistry and radioautography. In the latter case, 5-HT neuronal elements were detected according to their specific uptake of intraventricularly injected 3H-5-HT. On the 16th fetal day, occasional 5-HT fibers first spread from the main place of their origin in the raphe nuclei to the dorsocaudal portion of the 3rd ventricle and aqueduct. Two days later, a more extensive network of 5-HT fibers appeared around the dorsal portion of the 3rd ventricle, whereas fibers only rarely penetrated fibers became noticeable in the lateral and 3rd ventricles. The functional significance of hypothalamic and ventricular 5-HT is discussed from the standpoint of its being either a modulator of growth and differentiation of the developing brain, or a factor involved in some specific neuroendocrine functions.     

Fibers count in the anterior portion of the cord of the crayfish Astacus leptodactylis]

The number of fibers was analysed on cross section electron micrographs (x 1.000 and 4.500). About 300 axons of motoneurons leave the Ist thoracic ganglion. Approximately 180.000 sensory fibers enter the ganglion by lateral nerves. More than 90% of these fibers terminate on the ganglion neurons. The ganglion has descending connections with more caudally lying portions of the cord. The suboesophageal ganglion is closely associated with the 1st thoracic and other ganglia, and presumably contains a large vegetative center. The brain receives considerable information from the body via primary as well as secondary fibers, and controls the activity of the nerve cord through the system of various descending connective fibers.     

Neural control of olfaction and tentacle movements by serotonin and dopamine in terrestrial snail

We investigated the role of serotonin (5HT) and dopamine (DA) in the regulation of olfactory system function and odor-evoked tentacle movements in the snail Helix. Preparations of the posterior tentacle (including sensory pad, tentacular ganglion and olfactory nerve) or central ganglia with attached posterior tentacles were exposed to cineole odorant and the evoked responses were affected by prior application of 5HT or DA or their precursors 5-hydroxytryptophan (5HTP) and l-DOPA, respectively. 5HT applications decreased cineole-evoked responses recorded in the olfactory nerve and hyperpolarized the identified tentacle retractor muscle motoneuron MtC3, while DA applications led to the opposite changes. 5HTP and l-DOPA modified MtC3 activity comparable to 5HT and DA action. DA was also found to decrease the amplitude of spontaneous local field potential oscillations in the procerebrum, a central olfactory structure. In vivo studies demonstrated that injection of 5HTP in freely moving snails reduced the tentacle withdrawal response to aversive ethyl acetate odorant, whereas the injection of l-DOPA increased responses to “neutral” cineole and aversive ethyl acetate odorants. Our data suggest that 5HT and DA affect the peripheral (sensory epithelium and tentacular ganglion), the central (procerebrum), and the single motor neuron (withdrawal motoneuron MtC3) level of the snail’s nervous system.     

Immunocytochemistry of GABA in the brain and suboesophageal ganglion ofManduca sexta

Summary We have used specific antisera against protein-conjugated-aminobutyric acid (GABA) in immunocytochemical preparations to investigate the distribution of putatively GABAergic neurons in the brain and suboesophageal ganglion of the sphinx mothManduca sexta. About 20000 neurons per brain hemisphere exhibit GABA-immunoreactivity. Most of these are optic-lobe interneurons, especially morphologically centrifugal neurons of the lamina and tangential neurons that innervate the medulla or the lobula complex. Many GABA-immunoreactive neurons, among them giant fibers of the lobula plate, project into the median protocerebrum. Among prominent GABA-immunoreactive neurons of the median protocerebrum are about 150 putatively negative-feedback fibers of the mushroom body, innervating both the calyces and lobes, and a group of large, fan-shaped neurons of the lower division of the central body. Several commissures in the supra- and suboesophageal ganglion exhibit GABA-immunoreactivity. In the suboesophageal ganglion, a group of contralaterally descending neurons shows GABA-like immunoreactivity. The frontal ganglion is innervated by immunoreactive processes from the tritocerebrum but does not contain GABA-immunoreactive somata. With few exceptions the brain nerves do not contain GABA-immunoreactive fibers.     

Immunocytochemical identification of serotoninergic neurons in planaria <Emphasis Type="Italic">Girardia tigrina</Emphasis>

Flatworms occupy an important position among simple organisms, which were first in the evolution having bilateral symmetry and centralized nervous system. This paper provides evidence of the presence of a biogenic amine serotonin in free-living flatworms planarians Girardia tigrina (Turbellaria, Platyhelminthes). Using immunohistochemical method, fluorescence and confocal laser scanning microscopy, we have identified serotonin neurons and their fibers using planarian whole-mount preparations and got important information about distribution of serotoninergic components in their body. Information on the number and size of serotonin-immunopositive neurons in the brain ganglion of G. tigrina and on the distribution density of serotoninergic neurons in the central nervous system of worms is presented for the first time. The published data concerning the serotoninergic signalization in flatworms are briefly overviewed.     

Anatomy of neurons crossing the tritocerebral commissures of the cockroach Periplaneta americana (Blattaria)

The neuronal connections of the tritocerebral commissures of Periplaneta americana were studied in the brain-suboesophageal ganglion complex and the stomatogastric nervous system by means of heavy metal iontophoresis through cut nerve ends followed by silver intensification. The tritocerebral commissure 1 (Tc1) contains mainly the processes of the subpharyngeal nerve (Spn) whose neurons are located in both tritocerebral lobes and in the frontal ganglion. Some neurons of the frontal ganglion project through the Tc1 to the contralateral tritocerebrum. A few fibers in this commissure were observed projecting to the protocerebrum and the suboesophageal ganglion. There are tritocerebral neurons which pass through the Tc1 or the tritocerebral commissure 2 (Tc2) and extend on into the stomatogastric nervous system. One axon of a descending gaint neuron appears in the Tc2. This neuron lies in the tritocerebrum and connects the brain to the contralateral side of the ventral nerve cord. In addition, sensory fibers of the labral nerve (Ln) traverse both commissures to the opposite tritocerebrum. The anatomical and physiological relevance of the identified neuronal pathways is discussed. © 1995 Wiley-Liss, Inc.     

Immunocytochemical studies on the central nervous system of the earthworm, Lumbricus terrestris

There are numerous aldehyde fuchsin (AF)-positive, neurosecretory cells of medium size (A cells) and a small number of large, AF-negative neurons (B cells) in the cortical layer of the cerebral ganglion. In the subesophageal ganglion, symmetrical groups of AF-positive cells lie ventrally. The peroxidase--antiperoxidase (PAP) method was used for the immunocytochemical study of substance P and ACTH in these ganglia. In addition, the presence of L-enkephalin and alpha endorphin could be confirmed. Using rabbit antibodies to substance P we found small immunoreactive neurons among negative A and B cells in the cerebral ganglion. The processes of these immunoreactive cells could be traced to the subcortical synaptic neuropil. With antibodies to ACTH, activity was visible in perikarya similar in size to A neurons. A part of the nerve terminals of the synaptic zone, some of the B neurons and further several nerve cells of the subesophageal ganglion reacted positively. Successive demonstration of substance P and ACTH on the same section showed that the two materials occurred in different cell types. Using antiopsin antibody in an indirect immunocytochemical test we observed strong reaction in numerous medium-sized perikarya and in nerve fibres of the synaptic zone of the cerebral ganglion, further in some neurons of the subesophageal and abdominal ganglia. In contrast to this result, the photoreceptor cells of the prostomium and cerebral ganglion were negative. Presumably, substance P is present in a perikaryon type hitherto unrecognized while ACTH and antiopsin reactions seem to be located first of all in A cells.     

The central projection of cephalic mechanosensory axons in the haematophagous bug Triatoma infestans

The projections of mechanosensory hairs located on the dorsal and lateral head of the adult haematophagous bug Triatoma infestans were analyzed by means of cobalt filling. Axons run into the anterior and posterior tegumentary nerve and project through the brain to the ventral nerve cord. The fibres are small in diameter and run as a fascicle. Some branches run into suboesophageal and prothoracic centres; others run as far as to the mesothoracic ganglion. These sensory projections resemble that of wind-sensitive head hairs of the locust. The functional role of this sensory system in this species is discussed.     

Antibodies as molecular probes in neurobiology

Immunocytochemical localization of 5-hydroxytryptamine (5-HT) in the nervous system and aggregate tissue cultures was performed employing an antibody to 6-OH-1,2,3,4-tetrahydro-beta-carboline. A number of immunochemical and biochemical tests with the antigen and the antibody and some procedural changes in the methodology applied for immunolocalization revealed the anti-5-HT-like affinity of the antibody, if applied in paraformaldehyde-fixed tissues. Studies in the hypothalamus, striatum, brainstem, spinal cord, and pineal gland show the complexities of the serotoninergic system. Ultrastructural immunocytochemistry with the preembedding technique reveals that 5-HT synapses are of the asymmetric type. The presynaptic element contains clear, round, small vesicles, with some large dense-core vesicles. The contacts are made with the somata and primary, secondary dendrites or with spines of non-5-HT neurons. Presynaptic dendrites are found in the n. raphe dorsalis, contacting non-5-HT dendrites. Double immunocytochemical methods demonstrated contacts of 5-HT fibers on enkephalin containing neurons of the spinal trigeminal nucleus and on somatostatin containing neurons of the medullary reticular formation. In vitro studies of cultured mesencephalic neurons were performed with the method of aggregating cultures. Such development of a miniature organized nerve tissue was followed up to 35 d in culture. Organization of the neuropil and synaptogenesis was studied using standard electron microscopy. The differentiation of neurons and astrocytes was studied using antibodies to 5-HT and GFAP. Serotonin immunoreactivity could be observed in neuronal bodies and processes at light microscope level as early as the fourth day of culture.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective uptake of noradrenaline,dopa, and 5-Hydroxytryptamine by the nervous system of Phocanema decipiens (Nematoda): A light autoradiographic and ultrastructural study

As determined by light microscopic autoradiography, parts of the nervous system of Phocanema decipiens have selective and high affinity mechanisms for the uptake of tritiated noradrenaline, dihydroxyphenylalanine (dopa) and 5-hydroxytryptamine. In the nervous system, noradrenaline is accumulated only by the four papillary nerves and two fibers in the nerve ring. The precursor dopa is also taken up by these neurons and, in addition, by the lateral nerves. 5-Hydroxytryptamine is accumulated by the three pharyngeal nerves, two cells in each lateral ganglion, and two other fibers in the nerve ring. With adjacent ultrathin sections, the labelled papillary nerve and lateral ganglion were examined ultrastructurally and found to contain various dense core vesicles which are similar to those in other aminergic neurons. The adjoining unlabelled cells of the same neurons are found, on the other hand, to contain dense agranular vesicles. With these results, the noradrenaline accumulating neurons are suggested to be noradrenergic and to contain the amine synthesizing enzymes. The lateral nerves are regarded, for the present, as dopaminergic neurons. These suggestions are in agreement with the previous demonstration of catecholaminergic neurons in this nematode. The 5-hydroxytryptamine accumulating neurons are tentatively identified as tryptaminergic.     

Distributions of gamma-aminobutyric acid immunoreactive and acetylcholinesterase-containing cells in the primary olfactory system in the terrestrial slug Limax marginatus

The tentacular ganglion, the primary olfactory system of terrestrial slugs, exhibits spontaneous oscillations with a spatial coherence. The digit-like extensions (digits) of the tentacular ganglion presumably house the cell bodies of the neurons underlying the oscillations. The present study was designed to identify the anatomical and physiological determinants of these oscillations with a special focus on whether the neurons located in the digits contribute to the coherent oscillations. We recorded field potentials from the spatially separated sites in the digits in the terrestrial slug Limax marginatus. We also simultaneously recorded tentacular nerve to monitor the coherent oscillations. The spatially separated regions in the digits oscillated at the same frequency as the tentacular nerve, indicating a single coherent activity. To study the neural networks underlying the coherent oscillations, we examined the distributions of acetylcholinesterase (AChE)-containing and gamma-aminobutyric acid immunoreactive (GABA-ir) neurons. AChE-containing and GABA-ir fibers were found to connect the neurons in a branch of the digits with those in other branches. We also used a vital staining technique with 1,1'-didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate to examine the projections of neurons in the digits. Large stained cells were detected in many branches of the digits after placing the dye on one of the cell masses located in right and left sides of the tentacular ganglion. They were detected in the cell masses and in many branches of the digits after placing the dye on a branch of the digits. Our results showed that the slug primary olfactory system has highly interconnected neural networks.     

Genetic dissection of trophic interactions in the larval optic neuropil of Drosophila melanogaster

The larval visual system of Drosophila melanogaster consists of two bilateral clusters of 12 photoreceptors, which express Rhodopsin 5 and 6 (Rh5 and Rh6) in a non-overlapping manner. These neurons send their axons in a fascicle, the larval optic nerve (LON), which terminates in the larval optic neuropil. The LON is required for the development of a serotonergic arborization originating in the central brain and for the development of the dendritic tree of the circadian pacemakers, the small ventral lateral neurons (LNv) [Malpel, S., Klarsfeld, A., Rouyer, F., 2002. Larval optic nerve and adult extra-retinal photoreceptors sequentially associate with clock neurons during Drosophila brain development. Development 129, 1443-1453; Mukhopadhyay, M., Campos, A.R., 1995. The larval optic nerve is required for the development of an identified serotonergic arborization in Drosophila melanogaster. Dev. Biol., 169, 629-643]. Here, we show that both Rh5- and Rh6-expressing fibers overlap equally with the 5-HT arborization and that it, in turn, also contacts the dendritic tree of the LNv. The experiments described here aimed at determining whether Rh5- or Rh6-expressing fibers, as well as the LNv, influence the development of this serotonergic arborization. We conclude that Rh6-expressing fibers play a unique role in providing a signal required for the outgrowth and branching of the serotonergic arborization. Moreover, the innervation of the larval optic neuropil by the 5-HT arborization depends on intact Rac function. A possible role for these serotonergic processes in modulating the larval circadian rhythmicity and photoreceptor function is discussed.     

The Larval Nervous System of Polygordius lacteus Scheinder, 1868 (Polygordiidae,Polychaeta): Immunocytochemical Data

The nervous system of the planktotrophic trochophore larva of Polygordius lacteus has been investigated using antibodies to serotonin (5-HT) and the neuropeptide FMRFamide. The apical ganglion contains three 5-HT-ir neurons, many FMRFamide-ir neurons and a tripartate 5-HT-ir and FMRFamide-ir neuropil. A lateral nerve extends from each side of the apical ganglion across the episphere and the ventral hyposphere, where the two nerves combine to form the paired ventral nerve cord. These nerves have both 5-HT-ir and FMRFamide-ir processes. Three circumferential nerves are associated with the ciliary bands: two prototroch and one metatroch nerve. All contain 5-HT-ir and FMRFamide-ir processes. An oral nerve plexus also contain both 5-HT-ir and FMRFamide-ir processes develops from the metatroch nerve, and an esophageal ring of FMRFamide-ir processes develops in later larval stages. In young stages the ventral ganglion contains two 5-HT-ir and two FMRFamide-ir perikarya; during development the ventral ganglion grows caudally and adds additional 5-HR-ir and FMRFamide-ir perikarya. These are the only perikarya that could be found along the lateral nerve and ventral nerve cord. The telotroch nerve develops from the ventral nerve cord. The 5-HT-ir and FMRFamide-ir part of the nervous system is strictly bilateral symmetric. and much of the system (i.e. apical ganglion, lateral nerves ventral nerve cord, dorsal nerve and oral plexus) is retained in the adult.     

Distribution of FMRFamide-like immunoreactivity in the brain and suboesophageal ganglion of the sphinx mothManduca sexta and colocalization with SCPB-, BPP-, and GABA-like immunoreactivity

Summary Using an antiserum against the tetrapeptide FMRFamide, we have studied the distribution of FMRFamide-like substances in the brain and suboesophageal ganglion of the sphinx mothManduca sexta. More than 2000 neurons per hemisphere exhibit FMRFamide-like immunoreactivity. Most of these cells reside within the optic lobe. Particular types of FMRFamide-immunoreactive neurons can be identified. Among these are neurosecretory cells, putatively centrifugal neurons of the optic lobe, local interneurons of the antennal lobe, mushroom-body Kenyon cells, and small-field neurons of the central complex. In the suboesophageal ganglion, groups of ventral midline neurons exhibit FMRFamide-like immunoreactivity. Some of these cells have axons in the maxillary nerves and apparently give rise to FMRFamide-immunoreactive terminals in the sheath of the suboesophageal ganglion and the maxillary nerves. In local interneurons of the antennal lobe and a particular group of protocerebral neurons, FMRFamide-like immunoreactivity is colocalized with GABA-like immunoreactivity. This suggests that FMRFamide-like peptides may be cotransmitters of these putatively GABAergic interneurons. All FMRFamide-immunoreactive neurons are, furthermore, immunoreactive with an antiserum against bovine pancreatic polypeptide, and the vast majority is also immunoreactive with an antibody against the molluscan small cardioactive peptide SCP_B. Therefore, it is possible that more than one peptide is localized within many FMRFamide-immunoreactive neurons. The results suggest that FMRFamide-related peptides are widespread within the nervous system ofM. sexta and might function as neurohormones and neurotransmitters in a variety of neuronal cell types.Abbreviations AL antennal lobe - BPPLI bovine pancreatic polypeptide-like immunoreactivity - FLI FMRFamide-like immunoreactivity - GLI GABA-like immunoreactivity - NSC neurosecretory cell - SCP _B LI small cardioactive peptide_B-like immunoreactivity - SLI serotonin-like immunoreactivity - SOG suboesophageal ganglion     

The central morphology of the giant interneurons and their spatial relationship with the thoracic motorneurons in the cockroach, Periplaneta americana (Insecta)

Three groups of giant fibers are found in the cockroach ventral nerve cord. A latero-dorsal group (dorsal GIs), a latero-ventral group (ventral GIs) and a medio-ventral group. The morphology of all three groups of fibers within the thoracic ganglia is described. The morphology of the dorsal and ventral GI pathways in the abdominal and suboesophageal ganglia is also described. The projection patterns of the neurons in each ganglion are remarkably similar which suggests a common function. When motorneurons 5rl (depressor) and 6Br4 (levator) are stained simultaneously with the dorsal and ventral GI groups, some branches from both motor and giant neurons converge. The branching of the remaining medio-ventral group of fibers and their proximity to areas receiving motorneuronal input suggests that these are the small diameter axons described by Dagan and Parnas (1970).     

Serotonin-induced changes in the responses of the electroexcitable membrane of snail neurons

The effects of serotonin (5-HT) added to the washing solution on the plastic properties of the electroexcitable membrane of nonidentified neurons of the parietal ganglion and identified neurons RPa2 are studied on the isolated nervous system of the snail. The neurons of the first group, which became rapidly habituated to the intracellular stimulation, are shown to manifest the ability to restore action potential generation in the presence of 5-HT. In contrast, the neurons possessing endogenous rhythmic activity (RPa2) in the presence of 5-HT generate burst activity against the background of the development of slow waves of the membrane potential. A comparative analysis of the effect of 5-HT and compounds with a known effect on Ca²⁺ and the calcium-dependent potassium channels (quinine, CoCl₂ and CdCl₂) points to the existence of various mechanisms providing for the serotoninergic regulation of the plasticity of the electroexcitable neuron membrane. This difference stems from the processes of activation and blockade of the Ca-dependent mechanisms.A. I. Karaev Institute of Physiology Azerbaizhan Academy of Sciences, Baku. Translated from Neirofiziologiya, Vol. 24, No. 3, pp. 286–290, May–June, 1992.