Immunocytochemical localization of a methionine-enkephalin-resembling neuropeptide in the central nervous system of the American cockroach, Periplaneta americana L

Analgesia in amphibians: preclinical studies and clinical applications

Preclinical studies of analgesia in amphibians or recommendations for clinical use of analgesics in amphibian species are extremely limited. This article briefly reviews the issues surrounding the use of analgesics in amphibians, starting with common definitions of pain and analgesia when applied to nonhuman animals. Nociceptive and endogenous opioid systems in amphibians are reviewed, and results of preclinical research on opioid and nonopioid analgesics summarized. Recommended opioid and nonopioid analgesics are summarized, and practical recommendations made for their clinical use.

The opiate system in invertebrates

The presence in diverse species of a similar mode of communication, that of a soluble messenger binding to a receptor, raises the question as to whether the specific components of this system are equally widespread. Do invertebrates use the same hormones and receptors as vertebrates do? Invertebrates ranging from unicellular organisms to insects have been shown to contain opiate-like peptides and binding sites, and they exhibit biological responses to opiates. However, critical genetic data are lacking. It is not known how signal systems arise phylogenetically, but it is conceivable that signal molecules that are already present cause the formation of their own receptors from membrane proteins.

Effects of FMRFamide-related peptides and morphine on the isolated foregut of the locust schistocerca gregaria

1. Morphine and YAGFMamide were the most effective potentiators of 5-hydroxytryptamine (5-HT)-induced relaxation of the isolated foregut. 2. Morphine had no effect on proctolin-induced tissue contraction which was inhibited by YGGFMamide and YFMRFamide. 3. The differing potency of FaRPs and morphine to potentiate 5-HT effects and reduce proctolin responses suggests that there are two separate FaRP receptor sub types. 4. This proposal is supported by the observation that, while naloxone (10(-5) M) is a relatively potent antagonist of FaRP induced inhibition of proctolin contraction, it has less effect on FaRP-induced potentiation of 5-HT-induced relaxation.

Opiate effect on the threat display in the crab Carcinus mediterraneus

The well-known defense response of a crab (laterus merus display, LMD) was easily evoked in Carcinus mediterraneus by striking the cephalothoraxic protogastric region between the eyestalks. Following a program aimed at investigating the regulatory action of diverse neuromodulators on the LMD of this crab, a study on the role of opioids was started by testing the effect of morphine administration. Injection of morphine HC1 (MP) (40, 50, 60, 70, or 100 micrograms/g) produced a dose-dependent reduction of the LMD so elicited that dissipated with the postinjection time. Only MP doses higher than 50 micrograms/g were effective 30 min after drug administration. The MP-induced inhibition of LMD was blocked by a 4.8-micrograms naloxone HC1/g dose injected 10 min before MP. These results and those previously obtained as the action of GABA on the LMD of this crab are discussed in connection with results reporting a similar effect of these drugs on another agonistic item of behavior in the crab Chasmagnatus granulatus. The possibility of demonstrating habituation of the LMD to an iterated stimulation in C. mediterraneus and of using such a process to elucidate the acting paths of the drugs is discussed.

Immunocytochemical localization of leucomyosuppressin-like peptides in the CNS of the cockroach, Leucophaea maderae

Immunocytochemistry was used to determine sites of synthesis and pathways for the transport of the neuropeptide, Leucomyosuppressin (pQDVDHVFLRFamide) in the cockroach, Leucophaea maderae. This study led to identification of neurons in the brain and thoracic ganglia reactive to polyclonal antibodies raised against this peptide. No immunoreactive cells were found in the subesophageal or abdominal ganglia. Although the corpus cardiacum contained no intrinsic cells immunoreactive to LMS antibodies, the periphery of this organ and that of the nervi corporis allati contain an abundance of LMS-reactive terminals.

Immunofluorescent localization of dopamine-like and leucine-enkephalin-like neurons in the supraoesophageal ganglia of the American cockroach, Periplaneta americana

Leucine-enkephalin- and dopamine-like nerve cells and fibers were localized in the supraoesophageal ganglia (brain) of the American cockroach, Periplaneta americana, using immunofluorescence. The presence of leucine-enkephalin-like material was confirmed using immunoperoxidase staining. Several cells containing leucine-enkephalin-like material were found in the pars lateralis, and nerve fibers belonging to these cells were traced through the brain. Dopamine-like material was detected in deutocerebral neurons as well as the nerve processes arising from these cells which lead into the area of the deutocerebral glomeruli. Specific immunofluorescence was also obtained in the alpha and beta lobes of the corpora pedunculata with both the leucine-enkephalin and dopamine antibodies. However, the fluorescent banding pattern observed in both lobes was distinctly different with the two antibodies. No specific fluorescence was observed in the stalk or peduncle of the corpora pedunculata with either the leucine-enkephalin or the dopamine antibody. The findings suggest a possible interaction of leucine-enkephalinergic and dopaminergic nerve fibers in the alpha and beta lobes of the cockroach corpora pedunculata.

Effect of naloxone pretreatment on habituation in the crab Chasmagnathus granulatus

On sudden presentation of a passing shadow, the crab Chasmagnathus granulatus reacts with an escape response that habituates after repeating the same stimulus. In a first series of experiments, a range of naloxone (NX) doses (0.8, 2.4, 3.2, and 6.2 micrograms/g) was injected into crabs 15 min before one 15-trial habituation session. An enhancing effect of 3.2 micrograms NX/g on responsiveness appeared over trials, that cannot be explained either by a ceiling effect or by a delay in peak drug action. Two doses below 3.2 microgram/g and one dose above had no significant effect. Results from a second series of experiments showed that the 3.2 microgram NX/g effect vanishes after 15 trials (1 h after injection). The hypothesis that crab's habituation involves the action of an endogenous opioid mechanism is put forward to account for the naloxone pretreatment effect.

Opioid mechanisms in insects, with special attention to Leucophaea maderae

1. This review article provides information on the evolutionary history of neuroendocrine and related regulatory mechanisms. It focuses on the presence, diverse roles, and modes of operation of one class of neuropeptides, the endogenous opioids, in insects. 2. Opioid peptides, closely resembling those of vertebrates, have been identified in the brain and related neuroendocrine structures by means of immunocytochemistry and high-pressure liquid chromatography. 3. The demonstration of naloxone-sensitive, high-affinity binding sites for Met-enkephalin-like neuropeptides in the brain and digestive tract of Leucophaea deserves special attention because it provides new insights into the functional significance of opiate receptors paralleling those known in vertebrates. 4. Possible roles of receptor-mediated opioid systems in the insects discussed are regulation of the cyclicity of the female reproductive system, maintenance of normal midgut function mediated by the recurrent nerve, and locomotor activity.

Effect of morphine and naloxone on a defensive response of the crab Chasmagnathus granulatus

Male crabs (Chasmagnathus granulatus) exhibited a defensive response (DR) to an electric shock (8 V, 50 Hz, 1 sec). The DR so elicited was used as a model for studying the antinociceptive effect of morphine. Injections of morphine-HCl (MP) (25, 50, 100 and 150 micrograms/g) were administered and the DR was examined at 2, 7.5, 15, 30, 45 and 75 min post-injection. (a) MP produced a dose-dependent reduction of the crab's sensitivity to the nociceptive stimulus. (b) A 100 micrograms/g dose of MP caused a 50% response inhibition with an injection-shock interval of 30 minutes, but no inhibition occurred when the same dose was administered with 1.6 micrograms/g of naloxone-HCl, suggesting that MP acts through an opiate receptor. (c) The ED50 at 2 min post-injection was roughly 33 micrograms/g and the threshold dose was estimated to be 6.8 micrograms/g. These doses are lower than ED50 values reported for other arthropods (90 to 930 micrograms/g) and approach those of vertebrates. (d) The peak MP effect was reached quickly, within 2 min post-injection. The duration of the MP effect was calculated to be 45.0-75.0 min depending on the dose, and an indirect estimate of half-life elimination was 15.7 min. These values are remarkably lower than those reported for vertebrates. The shorter duration of the MP peak effect is attributable to a greater permeability of the arthropod blood-brain barrier as compared to that of vertebrates.

Habituation in the crab Chasmagnathus granulatus: effect of morphine and naloxone

The escape response decrement shown by the crab Chasmagnathus granulatus as a consequence of repeated shadow presentation, meets five of the seven tested parametric criteria of habituation. Results concerning stimulus generalization and dishabituation strongly suggest that neither motor fatigue nor sensory adaptation can account for the response waning. The effects of morphine and naloxone on performance were also studied. Neither 50 nor 5 micrograms morphine/g exerted any modulatory effect on memory retention. A dose of 50 micrograms morphine/g produced an anterograde detrimental effect on responsiveness but no long-term training effects could be detected after the drug's period of action. A dose of naloxone of 1.6 micrograms/g did not antagonize the effect of morphine. The potential value of the response habituation as a model for studying both habituation dynamics and the mechanisms that subserve it, and also for elucidating the effects of opiates on this memory process, is discussed.

Mapping of enkephalin-related peptides in the nervous system of the blowfly, Calliphora vomitoria, and their co-localization with cholecystokinin (CCK)- and pancreatic polypeptide (PP)-like peptides

The distribution of enkephalin-like immunoreactive material has been studied in the CNS of C. vomitoria. The presence of both Met- and Leu-enkephalin-related peptides is suggested by differential immunostaining with a variety of antisera. Comparisons made between certain of the enkephalin-immunoreactive perikarya, nerve fibres and terminals with cells in corresponding positions as evidenced in previously published neuroanatomical studies of the dipteran brain have suggested specific enkephalinergic pathways. As examples, one Met-enkephalin-immunoreactive neuron appears to link the lobula with the dorsal protocerebrum, and a group of Leu-enkephalin cells in the pars intercerebralis appear to have arborisations in both the central body (fan-shaped body) and the tritocerebral neuropil around the oesophageal foramen. Neuronal pathways of this type indicate that the enkephalin-like peptides of the fly brain are functioning as neurotransmitters and/or neuromodulators. In the thoracic ganglia, symmetrically arranged cells, immunoreactive to both Met- and Leu-enkephalin antisera, are positioned ventrally in pairs on either side of the mid-line in a sagittal plane. Very little immunoreactive material is observed in the neuropil, however, and the source of the accumulation of Leu-enkephalin-immunoreactivity in the dorsal neural sheath is not certain. It is suggested that this material, in contrast to that present in areas of the brain, acts as a neurohormone and that it may have a physiological role following its release into the haemolymph. The enkephalin-like immunoreactive material of certain neurons identified within the brain and thoracic ganglion shows a complex pattern of co-existence with pancreatic polypeptide- and gastrin/cholecystokinin-like peptides.

Methionine-enkephalin immunoreactivity in the gonads and nervous system of two insect species: Locusta migratoria and Sarcophaga bullata

Methionine(met)-enkephalin immunoreactivity as visualized by the peroxidase-antiperoxidase procedure, is present in spermatogonia, spermatocytes, spermatids, and young ovarian follicles of Locusta (panoistic type) and Sarcophaga (polytrophic type). Follicle cells and mature spermatozoa are always immunonegative as are locust vitellogenic follicles. In oocytes and in trophocytes, the met-enkephalin-like material first appears around the nucleus and is then dispersed throughout the cytoplasm. Later, it is present only in the periphery. In the ovary of both insects, no immunoreactivity is found with antisera against adrenocorticotrophic hormone, melanophore stimulating hormone, beta-endorphin, corticotropin releasing factor, or leucine-enkephalin. All these antisera yield a positive reaction when applied to the central nervous system as does the met-enkephalin antiserum. This study indicates that the met-enkephalin-like peptide may play a role in reproductive physiology.

Passive avoidance learning in the crab Chasmagnathus granulatus

Male crabs Chasmagnathus granulatus were trained by means of a method similar to the standard inhibitory avoidance technique widely used in vertebrates. Each crab was placed in the dark compartment (DC) of a double-chamber device, allowed to move towards the light compartment (LC) and latency to enter measured. Experimental crabs received a shock in LC, but controls were not punished. After 1 min, both experimental and control crabs were free to return to DC. On completion of 1, 2, 3 or 24 hr intertrial interval in DC a retention test was administered and latency to enter LC was measured. A single trial was proven enough to establish a LC-shock association that was detected up to 3 hr later, but no retention was proved after 24 hr. Memory was disrupted when crabs were removed from the apparatus during the 3 hr intertrial interval. Similarities and differences between the passive avoidance method used with crabs and that used with vertebrates are discussed.

Immunocytochemical demonstration of proopiomelanocortin- and other opioid-related substances and a CRF-like peptide in the gut of the american cockroach, Periplaneta americana L

Using the peroxidase-antiperoxidase technique, we showed the presence of peptides which are immunologically resembling mammalian corticotropin releasing hormone (CRF)-, adrenocorticotropic hormone (ACTH)-, beta-endorphin (beta-END)-, alpha-melanocyte stimulating hormone (alpha-MSH)-, methionine-enkephalin (met-ENK)- and leucine enkephalin (leu-ENK)- like immunoreactivity in hundreds to thousands of endocrine cells and nerve fibers in the midgut of the American cockroach Periplaneta americana. In the cockroach hindgut no immunoreactive cell bodies could be observed, although nerve fibers were clearly noticed to be recognized by antisera to CRF, ACTH1-24, ACTH11-24 and beta-END. Nothing is exactly known as to the function(s) of the demonstrated materials, but one can speculate that these numerous immunoreactive cells, might have important paracrine and/or endocrine functions in the insect physiology.

Sex-related differences in the concentration of Met-enkephalin-like immunoreactivity in the nervous system of an insect, Schistocerca gregaria, revealed by radioimmunoassay

A radioimmunoassay has been used to measure Met-enkephalin-like immunoreactivity in tissue from male and female locusts, Schistocerca gregaria. The pattern of distribution within the two sexes was similar with about equal amounts present in the suboesophageal and 3 thoracic ganglia and a lower concentration in the cerebral ganglion. Female nervous tissue contained more than twice the amount of Met-enkephalin-like immunoreactivity than did that of males. No consistent immunoreactivity could be detected in the abdominal ganglia or non-neural tissues. The results are discussed in relation to recent evidence that peptides related or identical to enkephalins are present in invertebrates as well as higher organisms.

A new alternative for simultaneous immunohistochemical screening of 96 hybridoma clones for tissue-specific antibody productions selects a monoclonal antibody to insect corpus cardiacum

In the current search for the elucidation of the true structure of hitherto unidentified 'new' insect neuropeptides we designed a novel screening method to facilitate the primary detection of neurone-specific antibody secreting mouse-mouse hybridoma clones obtained after immunization with neuronal tissue homogenates. The present procedure is principally adapted from a conventional immunohistological test and enables one to rapidly screen 96 (and even more) clones at one time for potential secretion of specific antibodies to different tissue compounds, without the necessity of having a purified antigen. It has proved to be sensitive, rapid, practical and reproducible. As such it promises to be very useful to discriminate amongst the wide range of antibodies to various kinds of materials produced by hybridomas by detecting monoclonal antibodies directed against factors contained in well-defined tissues in which one is interested. This paper also reports the successful application of this method to a primary screening of clones producing murine monoclonal antibodies to substances of insect corpora cardiaca (CC), after immunization with crude antigen preparations.

Substance P-like immunoreactivity in the central nervous system of the blattarian insect Periplaneta americana L. revealed by a monoclonal antibody

Brains, retrocerebral complexes and frontal and suboesophageal ganglia of adult American cockroaches, Periplaneta americana, were immunohistochemically investigated with a specific monoclonal antibody (McAb) directed against a well characterized antigenic determinant, namely the COOH terminus of the endecapeptide substance P (SP). This resulted in the detection of several neurons and nerve fibres containing a substance antigenically closely related to this typically vertebrate neuropeptide. No difference in staining pattern could be observed between male and female insects. Related to the age of the adult specimens, however, a slight quantitative difference in SP immunoreactivity seems to occur, which probably might have functional implications. The SP-like peptide demonstrated in this study appears to be located in different neuronal structures than the ones that we earlier described as containing ACTH-, CRF-, OT-, AVP-, NP I-, NP II-, BPP-, FMRFamide-, AKH-, met-ENK-, FSH-, LH- and LHRF-like material (Verhaert et al. 1984a, b, 1985; Verhaert and De Loof 1985a, b).