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J M Ramirez

Publications and source records attributed to J M Ramirez.

At least 55 records · Page 3Linked to original sources
PubMed1993

Alteration of bursting properties in interneurons during locust flight.

1. The contribution of bursting properties to the generation of the flight motor pattern was examined for two identified interneurons (interneurons 566 and 567) in the flight system of the locust Locusta migratoria by means of intracellular recording and stimulation techniques. These interneurons are important elements in transmitting proprioceptive information from the hindwing tegula to wing elevator motoneurons. 2. Offset currents injected into these neurons revealed that bursts are triggered in the intact flying animal by synaptic input from tegula afferents (n = 10). These bursts lead to an amplification of proprioceptive input that is crucial for the generation of the intact flight motor pattern. In the absence of afferent input the activity of these neurons remained subthreshold for triggering a burst. This explains why these neurons exhibit only weak rhythmic oscillations in deafferented animals. 3. The property of interneuron 566 to burst was conditional, always being expressed during flight (n = 14) and occurring only occasionally in the quiescent animal. In the absence of flight, stimulation of tegula afferents never evoked bursts in interneuron 566 (n = 7) and depolarizing current pulses evoked weak bursts in only three of nine preparations. In 2 of 14 animals, bursting property of interneuron 566 was enhanced just after the termination of flight. 4. Variability in the bursting property was also found for interneuron 567. In the quiescent animal, tegula-evoked compound excitatory postsynaptic potentials were not sufficient to trigger bursts (n = 3) but depolarizing current pulses evoked always weak rhythmic bursting activity (n = 4). This bursting property was also variable and in one animal we found long-lasting plateau potentials that could be evoked by current injection after flight was elicited several times. 5. The data presented demonstrate that the capacity to burst is conditional in the interneurons 566 and 567. Bursting properties are always induced during flight and function to amplify proprioceptive pathways that are important for the generation of the intact flight motor pattern.

Afferent Pathways↗
PubMed1992

Reorganization of sensory regulation of locust flight after partial deafferentation.

Previous investigations have shown that the flight motor pattern of the mature locust (Locusta migratoria L.) relies heavily on the input of the hindwing tegulae. Removal of the hindwing tegulae results in an immediate change in the motor pattern: the wingbeat frequency (WBF) decreases and the interval between the activity of depressor and elevator muscles (D-E interval) increases. In contrast, removal of the forewing tegulae has little effect on the motor pattern. Here we report adaptive modifications in the flight system that occur after the removal of the hindwing tegulae. Over a period of about 2 weeks following hindwing tegula removal, the flight motor pattern progressively returned towards normal, and in about 80% of the animals recovery of the flight motor pattern was complete. We describe the changes in the activity pattern of flight muscles and in the patterns of depolarizations in flight motoneurons and flight interneurons associated with this recovery. In contrast to the situation in the intact animal, the activity of the forewing tegulae is necessary in recovered animals for the generation of the motor pattern. Removal of the forewing tegulae in recovered animals resulted in similar changes in the flight motor pattern as were observed in intact animals after the removal of the hindwing tegulae. Furthermore, electrical stimulation of forewing tegula afferents in recovered animals produced similar resetting effects on the motor pattern as electrical stimulation of the hindwing tegulae afferents in intact animals. From these observations we conclude that recovery is due to the functional replacement of the removed hindwing tegulae by input from the forewing tegulae.

Animals↗
PubMed1992

Connections of the forewing tegulae in the locust flight system and their modification following partial deafferentation.

The flight motor pattern of the adult locust (Locusta migratoria L.) is able to recover from the loss of the hindwing tegulae. This recovery is due to a functional substitution of the hindwing tegulae by the forewing tegulae (Büschges, Ramirez, and Pearson, 1992). To assess changes in the pathways from the forewing tegulae in the flight system, we investigated the pathways of the forewing tegula in intact locusts and in animals 2 weeks after hindwing tegula removal. The following physiological alterations in these pathways were found to be associated with the recovery: (1) In the intact locusts, the connections of forewing tegula afferents to flight interneurons are variable but this variability did not occur in recovered animals, and (2) larger numbers of forewing tegula afferents connect to interneurons that excite elevator motoneurons (interneurons 566 and 567) and to an interneuron that inhibits depressor motoneurons (interneuron 511). The size of unitary excitatory postsynaptic potentials (EPSPs) evoked by signal forewing tegula afferents was found not to be altered in recovered animals. The changes in connectivity of forewing tegula afferents are correlated with morphological alterations in the structure of the terminal processes of the afferents and with sprouting of some branches of interneurons receiving input from these afferents.

Animals↗
PubMed1992

Entrainment of the locomotor rhythm by group Ib afferents from ankle extensor muscles in spinal cats.

1. Previous studies have concluded that the timing of the locomotor rhythm can be strongly influenced by input from group Ib afferents from leg extensor muscles (Duysens and Pearson 1980; Conway et al. 1987). The main objective of the present study was to obtain additional evidence for this conclusion by examining the characteristics of entrainment of the locomotor rhythm by rhythmic stimulation of group I afferents and by rhythmic force pulses in the ankle extensor muscles. 2. A reduced, non-immobilized preparation was developed in spinal cats that allowed isometric contractions of ankle extensor muscles to be elicited by ventral root stimulation during the expression of locomotor activity. The same preparation was used to examine the influence of electrically stimulating group I afferents from the ankle extensors and the effect of rhythmically stretching these muscles. The locomotor rhythm was initiated by sustained mechanical stimulation of the perineum following the administration of Clonidine and, in some preparations, Naloxone. 3. The timing of the onset of flexor burst activity was examined during entrainment with saw-tooth and ramp-and-hold stretches of the ankle extensor muscles. Flexor bursts were initiated about 200 ms following the release from the stretch, and this latency was independent of the entrainment frequency. 4. The locomotor rhythm was readily entrained by rhythmic contractions of the ankle extensor muscles produced by ventral root stimulation provided the magnitude of the contractions was greater than about 10N. Repetitive stimulation of group I muscle afferents from the ankle extensors also entrained the locomotor rhythm, with the timing of motor activity being similar to that during entrainment with rhythmic muscle contractions. Burst activity in the ipsilateral extensors was coincident with the stimulus trains in both cases. This similarity argues for entrainment being produced mainly by input from group Ib afferents. 5. The functional implication of the results of this and previous studies is that input from group Ib afferents during the stance phase of walking acts to inhibit generation of flexor burst activity and to promote extensor activity. The proposal that a decline in Ib activity near the end of the stance phase is involved in regulating the stance to swing transition is discussed.

Afferent Pathways↗
PubMed1992

The use of naloxone to facilitate the generation of the locomotor rhythm in spinal cats.

The locomotor rhythm evoked by perineal stimulation in clonidine-treated acute and chronic spinal cats can be produced more easily when the opioid receptor antagonist naloxone is also administered. Naloxone increases the frequency of the locomotor rhythm and decreases the intensity of skin stimulation required for evoking the rhythm. A useful property of naloxone is that it can restore the locomotor rhythm when the rhythm wanes, thus prolonging the time period over which locomotor activity can be generated. Administration of naloxone without clonidine does not enable the locomotor rhythm to be generated by skin stimulation, but it does reduce the concentration of clonidine required for the expression of a robust rhythm and may increase the chance of a successful preparation. We conclude that naloxone is a useful pharmacological tool for studies on the locomotor pattern generator.

Animals↗
PubMed1991

Octopamine induces bursting and plateau potentials in insect neurones.

The membrane properties of some inter- and motoneurones in the respiratory and flight systems of the locust Locusta migratoria were characterized during octopamine perfusion by means of intracellular recording techniques. Octopamine induced active membrane properties in these neurones. Plateau-potentials were evoked by brief current pulses or synaptic input in 3 of the identified neurones and endogenous bursting was evoked by prolonged current pulses in one identified interneurone. Hyperpolarizing pulses injected into these neurones either prematurely terminated or suppressed these responses, indicating that these potentials are due to active membrane properties intrinsic to these neurones. Such intrinsic membrane properties have not been described in insects before. Further investigations are necessary to examine whether these properties may play an important role in the generation of rhythmic motor patterns as has previously been demonstrated in many other vertebrate and invertebrate motor systems.

Animals↗
PubMed1991

Dimeric carotenoid interaction in the light-harvesting antenna of purple phototrophic bacteria.

The carotenoid content of intracytoplasmic membrane vesicles isolated from purple phototrophic bacteria was reduced to a variable extent by mild extraction with light petroleum. Using preparations obtained from Rhodobacter capsulatus strains that contained the Light Harvesting System I (LHI) complex as the only major photosynthetic holochrome, it was shown that the visible circular dichroism of the carotenoids increased with the square of the membrane carotenoid content, as expected from being caused by dimeric exciton interaction. No chirality resulting from twists of the individual planar chromophore was detected. Therefore the contribution to carotenoid optical activity of non-degenerate interactions with bacteriochlorophyll or the apoprotein does not appear to be significant. The broadening of the absorption band of the bound pigment, caused by the splitting of the monomer transition, was demonstrated in membrane vesicles of both Rb, capsulatus and Rhodospirillum rubrum as a decrease of the fine structure of the band. Furthermore, the dimeric organization of the carotenoid pigments in the bacterial LHI complex accounted for the observed quantitative relationship between the fine structure of the band and the carotenoid content of the membrane.

Carotenoids↗
PubMed1991

Experimental glaucoma significantly decreases atrial natriuretic factor (ANF) receptors in the ciliary processes of the rabbit eye.

ANF binding sites were analysed in the ciliary processes of rabbits with unilateral experimental glaucoma which had been induced by injecting alpha-chymotrypsin into the posterior chamber of the right eyes. The intraocular pressure (IOP) of glaucomatous eyes was significantly greater (28.4 +/- 4 mmHg) than that of normotensive control eyes (13.1 +/- 1.4 mmHg, mean +/- S.E.M., n = 23, P less than 0.05). ANF concentrations in aqueous humour and the ciliary processes were significantly higher in glaucomatous eyes (91 +/- 2 pg ml-1 and 30.4 +/- 4.2 pg g-1 wet weight) than in normal eyes (3.1 +/- 2.2 pg ml-1 and 10.2 +/- 2.7 pg g-1 wet weight, respectively, n = 6, P less than 0.01). The number of ANF-binding sites (Bmax) in the ciliary processes of glaucomatous rabbit eyes was significantly decreased in comparison to the controls (24 +/- 4 vs. 13 +/- 3 fmol mg-1 protein, n = 10, P less than 0.05). These data suggest that ANF receptors in the ciliary processes are down-regulated and that ANF may play an important role in the pathophysiology of experimental glaucoma.

Animals↗
PubMed1991

Octopaminergic modulation of interneurons in the flight system of the locust.

1. Modulatory effects of octopamine perfusion on identified central neurons in the flight system of the locust Locusta migratoria were examined by means of intracellular recordings from the isolated metathoracic ganglion. 2. Octopamine increased the excitatory response of elevator motoneurons to electrical stimulation of the hindwing tegula and increased the probability of triggering rhythmic activity in the flight system by current injection into single interneurons. 3. These effects of octopamine on the flight system are due in part to octopamine inducing intrinsic bursting properties in flight interneurons. Plateau potentials were evoked in these interneurons by synaptic input from tegula or by the injection of depolarizing current pulses. These potentials were prematurely terminated by hyperpolarizing currents, and their generation was voltage sensitive in that they were suppressed with hyperpolarizing offset currents. 4. Longer depolarizing current pulses evoked endogenous bursting in a number of flight interneurons. This rhythmic bursting was reset by the injection of pulses of hyperpolarizing currents. The frequency of bursting was dependent on the injected current strength. 5. The injection of hyperpolarizing current into flight interneurons during octopamine-induced rhythmic activity lead to sudden decreases in the amplitude of the depolarizations thus indicating that plateau potentials contribute to the generation of the rhythmic depolarizations. 6. The shape of the depolarizations, the duration of the bursts (50-75 ms), and the frequency range of endogenous bursting (4-16 Hz) as seen in individual interneurons during octopamine perfusion were similar to the corresponding characteristics in the same neurons during wind-induced flight activity in deafferented locusts. This correspondence suggests that intrinsic bursting properties may play an important role in generating the normal motor pattern for flight.

Animals↗
PubMed1990

Phentolamine selectively affects the fast sodium component of sensory adaptation in an insect mechanoreceptor.

Phentolamine and related compounds have several different actions on nervous tissues in vertebrates and invertebrates, including a local anesthetic effect. However, recent work suggests that phentolamine can interfere with sensory transduction in insect mechanoreceptors at significantly lower concentrations than are required for conduction block. We tested the actions of phentolamine on sensory transduction and encoding in an insect mechanoreceptor, the cockroach tactile spine neuron and found that 500 microM phentolamine increased the action potential threshold by 50%. The passive membrane properties of the neuron were not affected, but one component of dynamic threshold change was strongly and selectively reduced. This component has previously been attributed to slowly inactivating sodium channels in the action potential initiating region, suggesting that these channels are the most phentolamine-sensitive sites.

Action Potentials↗
PubMed1990

Local anesthetic action of phentolamine on insect mechanoreceptors.

1. The effect of phentolamine on the response properties of insect mechanoreceptors and on the conduction in their axons was examined using electrophysiological techniques. 2. Phentolamine blocked conduction of action potentials along axons, an effect which exhibited 3 characteristics typical of local anesthetics: the effect was frequency-dependent, reversible and varied for nerves with different diameters. 3. The concentration of phentolamine required to block axonal conduction (1-2 x 10(-3) M) was significantly higher than that required to abolish the response of receptors to mechanical stimulation (3-5 x 10(-4) M). 4. All mechanoreceptors that were examined in Locusta migratoria and Periplaneta americana were inactivated by phentolamine (Table 1). The type I receptors (chordotonal, campaniform and hair sensilla) were inactivated within 5-15 min following phentolamine application. The only type II receptor examined (forewing stretch-receptor) underwent a phase of repetitive discharge before being inactivated. 5. Tolazoline and metoclopramide inactivated, like phentolamine, mechanoreceptors at lower concentrations than necessary to block axonal conduction. However, yohimbine and chlorpromazine inactivated mechanoreceptors and blocked axonal conduction at similar concentrations. 6. These findings suggest that phentolamine affects sense-organ specific ionic processes that are more sensitive to the drug than the ionic processes along the axons.

Action Potentials↗
PubMed1990

Chemical deafferentation of the locust flight system by phentolamine.

1. Phentolamine was injected into the haemolymph of locusts, Locusta migratoria, and its effects on the flight system were analyzed using electrophysiological techniques. 2. Doses of 150 microliters at 10(-2) M phentolamine inactivated the wing stretch-receptors and tegulae without influencing the central nervous system (CNS). The lack of effect on the CNS was demonstrated by the absence of any effect on the flight motor pattern in animals that had been mechanically deafferented prior to the administration of phentolamine. From these observations we conclude that phentolamine can be used to chemically deafferent the flight system of the locust. Consistent with this conclusion is that the administration of phentolamine in intact animals changed the flight motor pattern so that it resembled the pattern occurring in mechanically deafferented animals. 3. The two main advantages of deafferenting the flight system by injecting phentolamine were a) intracellular recordings from central neurons could be easily maintained during the process of deafferentation, and b) the contribution of different groups of proprioceptors to the generation of the motor pattern could be assessed since not all proprioceptors were inactivated simultaneously. 4. By intracellularly recording from elevator motoneurons and administering phentolamine we confirmed a number of previous results related to the function of the wing stretch-receptors and the tegulae.

Animals↗
PubMed1990

Immunoreactive atrial natriuretic factor in aqueous humor: its concentration is increased with high intraocular pressure in rabbit eyes.

Atrial natriuretic factor (ANF) concentration in the aqueous humor (AH) was studied in rabbits with experimental glaucoma induced by injecting alpha-chymotrypsin into the posterior chamber. In normal rabbit eyes, the ANF concentration in AH was 3.1 +/- 1.2 pg/ml (mean +/- SEM; n = 12), ranging from 0 to 5.8 pg/ml, whereas it was significantly higher in AH from glaucomatous rabbit eyes, being 81.0 +/- 9.8 pg/ml (n = 12). These findings were correlated with intraocular pressure (IOP), which was 13.0 +/- 2.4 mmHg (n = 12) in normal rabbit eyes and significantly greater in glaucomatous eyes: 24.4 +/- 3.0 mmHg (n = 12). Our data indicate that enhanced ANF release in AH during experimental glaucoma may play an important physiological role in modulating IOP.

Animals↗
PubMed1989

A subpopulation of dorsal unpaired median neurons in the blood-feeding insect Rhodnius prolixus displays serotonin-like immunoreactivity.

We describe, for the first time in insects, the presence of serotonin-like immunoreactive dorsal unpaired median (DUM) neurons. In unfed, untreated Rhodnius prolixus, the cell bodies of these DUM neurons displayed only faint serotonin-like immunofluorescence without any detectable fluorescence in the axons. There was, however, an extensive serotonin-like immunoreactive peripheral complex. We have enhanced the immunostaining of the cell bodies and axons of these DUM neurons by using 5,7-dihydroxytryptamine (5,7-DHT) and nerve transection, and have further defined their morphology with cobalt backfilling and Lucifer yellow injection. Injection of 5,7-DHT resulted in enhanced serotonin-like immunostaining, after 24 hours, of five DUM neurons in the mesothoracic ganglionic mass. Each DUM neuron possessed bifurcating serotonin-like immunoreactive axons projecting to the periphery via one of the five bilaterally paired abdominal nerves. Concomitant with the enhanced immunostaining in the cell body and axons of these DUM neurons was the depletion of a serotonin-like immunoreactive neurohaemal area lying on each of the abdominal nerves and the depletion of serotonin-like immunoreactive processes on the body wall. Enhancement of cell body and axon immunostaining was also observed in preparations in which the abdominal nerves had been transected 24 hours previously. The location and morphology of these DUM neurons were studied in further detail by using cobalt backfilling of the abdominal nerves and intracellular injection of Lucifer yellow followed by immunohistochemistry. The five serotonin-like immunoreactive DUM neurons were found to represent a subpopulation in a group of ten DUM neurons located in the mesothoracic ganglionic mass and associated with the abdominal nerves. Each abdominal nerve received projections from two DUM neurons, only one of which was serotonin-like immunoreactive. Electrophysiological recordings revealed that the serotonin-like immunoreactive DUM neurons of Rhodnius had similar properties to previously described octopaminergic DUM neurons of insects. The five DUM neurons in Rhodnius appear to represent a subpopulation of DUM neurons containing serotonin.

Action Potentials↗
PubMed1988

Generation of motor patterns for walking and flight in motoneurons supplying bifunctional muscles in the locust.

In the flight system of Locusta migratoria certain muscles move a wing and a leg (bifunctional muscles) and are active during the performance of walking and flight. A preparation that allowed intracellular recordings during these behaviors was developed to analyze the activity of motoneurons supplying these and other muscles. Motoneurons innervating bifunctional muscles were active during walking and flight, whereas motoneurons innervating unifunctional flight muscles were active only during flight. Both motor patterns, walking and flight, were sometimes generated simultaneously in our preparation. In bifunctional motoneurons the two patterns were superimposed, whereas in unifunctional motoneurons only the flight motor pattern was observed. All flight interneurons we examined were either inactive or tonically inhibited during walking. All interneurons that were strongly modulated during walking were either inactive, inhibited, or only weakly modulated during flight. Anatomical investigations showed that unifunctional flight motoneurons have their main processes in the extreme dorsal region of neuropil. With the exception of the second basalar motoneurons, all bifunctional motoneurons have their processes extending more ventrally in the neuropil. Flight interneurons have their processes restricted to the dorsal neuropil. Interneurons that were rhythmically active during walking had their processes distributed more ventrally. We conclude that motoneurons innervating bifunctional muscles are active during both motor patterns, walking and flight, and that these patterns are produced by two distinct interneuronal networks. The pattern-generating network for flight appears to be located in the extreme dorsal regions of the thoracic ganglia, and the network for walking is located more ventrally.

Animals↗
PubMed1988

A reexamination of the hypoglycemia-aggression hypothesis in laboratory mice.

The suggestion of a clinical link between hypoglycemia and aggression has been recently encouraged by the work of Virkkunen and others. Modern techniques have impressively established a correlation between reactive hypoglycemia (low blood sugar levels engendered by stimulation of endogenous insulin secretion) and hostility as expressed in a variety of situations. It is not surprising that blood sugar levels influence behavior, as the brain is entirely dependent on glucose reaching it via the vascular system. In spite of this impressive link, there are remarkably few successful studies involving the effects of manipulating glucose levels on fighting in infrahuman animals. As there have been several methodological developments in this area it was thought appropriate to reinvestigate such phenomena in mice. The effects of injected bovine insulin and glucose were assessed using an ethopharmacological methodology applied to social encounters by isolated male Swiss mice with docile anosmic opponents. Although manipulation of blood glucose levels did not consistently change attack or defensive behavior, these treatments did modify aspects of the interactions.

Aggression↗
PubMed1988

Offense and defense after lateral septal lesions in Columba livia.

It is generally agreed that there are several different types of animal aggression that may be distinguished in terms of their neural organization and that discrete lesions, in particular brain areas, may affect one but not other types of aggression. In this study the effects of electrolytic, bilateral lesions in lateral septum on offense and defense were examined in pigeons. Subjects were tested by introducing an adult conspecific stranger into their home cage. A postoperative increase in offensive patterns and a long-lasting drop in defense were observed in the lesioned birds. Its remarkable resemblance to the effects of antianxiety drugs, as well as the difference between the behavioral effects of medial septal damage are also discussed.

Aggression↗