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Biomedical subjects

J L Ram

Publications and source records attributed to J L Ram.

At least 55 records · Page 3Linked to original sources
PubMed1991

High levels of polysaccharides in Aplysia hepatopancreas and penis: differential effects of nutrition and development.

1. Carbohydrate levels in tissues of Aplysia californica were measured. In animals maintained in the laboratory without feeding for 1-2 weeks, the penis contained the highest concentration of glycogen. 2. Blood glucose ranged between 2.5 and 4.8 mg/dl and averaged 3.2 +/- 0.2 mg/dl. 3. Fed animals had significantly greater tissue glycogen levels than starved animals. The penis exhibited the smallest per cent increase in glycogen concentration in response to feeding. 4. In contrast, the hepatopancreas exhibited a large increase, attaining glycogen concentrations near that of the penis. 5. Most of the increase in total tissue glycogen in fed animals occurred in the hepatopancreas. 6. Starved and fed animals did not differ significantly in blood glucose concentration, thus indicating that blood glucose is regulated and excess glucose is stored. 7. The hepatopancreas is the major mobile glucose store. 8. The high concentrations of glycogen found in the penis were not affected by mating activity. 9. However, penis glycogen concentration increased greatly with reproductive maturation of Aplysia; in contrast, hepatopancreas glycogen concentration was relatively unaffected by development. 10. A structural role by carbohydrates in the penis is suggested.

Animal Nutritional Physiological Phenomena↗
PubMed1991

Insulin resistance, carbohydrate metabolism, and hypertension.

Hypertension and diabetes are common diseases in Westernized civilizations, and in the United States, the frequency of both diseases is increasing as the society ages. Factors contributing to the high prevalence and increasing frequency of these diseases include obesity, hyperinsulinemia and insulin resistance, genetic factors, and abnormal cellular handling of calcium and other cations. Obesity is a strong early predictor for the development of hypertension as a person progresses from childhood into adult life. Important factors contributing to obesity-related hypertension likely include enhanced sympathetic nervous system activity and insulin resistance and hyperinsulinemia. Recent evidence has also shown that many nonobese adults with untreated hypertension have insulin resistance and hyperinsulinemia. This observation strongly suggests that the disease called "hypertension" is characterized by fundamental metabolic abnormalities as well as by hemodynamic abnormalities. Recent observations have shown that impaired cellular responses to insulin are associated with increased vascular smooth muscle contraction. Insulin appears to attenuate the vascular response to both receptor-mediated and voltage-mediated calcium-induced contractions. Thus, insulin resistance, and the resultant reduction in the normal attenuating effect of insulin on vascular smooth muscle responses, appear to be associated with abnormal vascular smooth muscle handling of calcium and with exaggerated vascular contraction.

Animals↗
PubMed1991

Insulin attenuates vasopressin-induced calcium transients and a voltage-dependent calcium response in rat vascular smooth muscle cells.

Insulin attenuates the contractile responses of vascular smooth muscle (VSM) to various agonists. Insulinopenic and insulin-resistant rats lack this normal attenuation of vascular contractile responses. To study this attenuating mechanism, the effects of insulin on calcium (Ca2+) responses of cultured VSM cells (a7r5) to arginine vasopressin (AVP) and membrane potential were investigated. Insulin (1 and 100 mU/ml) shifted AVP dose-response curves to the right, reducing relative potency of AVP by 16-fold and 220-fold, respectively. Responses to AVP were significantly attenuated within 30 min of insulin application. The AVP-elicited rise in [Ca2+]i was partially dependent upon extracellular Ca2+. AVP-elicited inward current was reduced by 90 min of insulin treatment (100 mU/ml), from a peak current of -103 +/- 27 pA (normal) to -37 +/- 15 pA (insulin treated). Peak voltage-dependent Ca(2+)-dependent inward current was unaffected by insulin; however, the current-voltage curve was shifted 16 +/-3 mV to the right by insulin. Thus, insulin may reduce VSM contractile responses by attenuating agonist-mediated rises in [Ca2+]i mediated, in part, by reductions in Ca2+ influx through both receptor- and voltage-operated channels.

Animals↗
PubMed1990

Amiloride inhibits contraction and serotonin modulation of Aplysia muscle.

1. Serotonin (5-HT) potentiates acetylcholine (ACh)-elicited contractions of Aplysia buccal muscles. Serotonin potentiation was significantly reduced by 0.03 mM, 0.1 mM, and 0.3 mM amiloride. 2. Unpotentiated ACh-elicited contractions were significantly reduced by 0.1 mM and 0.3 mM amiloride. 3. Amiloride reduced ACh-elicited depolarization. The reduction in contraction caused by 0.3 mM amiloride (to 16% of control) was larger than could be explained by the reduction in depolarization (86% of control). 4. Amiloride had no effect on tension in skinned muscle fibers, indicating that amiloride probably did not have a direct effect on contractile mechanisms. 5. Potentiation of contraction produced by zero sodium (Tris substituted, 0 Na-Tris) medium could be abolished by 0.3 mM amiloride. 6. Zero Na-Tris increased 45Ca influx 2.7-fold. In the presence of 0.3 mM amiloride, 0 Na-Tris increased 45Ca influx only 1.4-fold. 7. Amiloride (0.3 mM) reduced the elevation of muscle cAMP caused by 10(-6) M 5-HT by 60%. Zero Na-Tris did not cause a change in muscle cAMP.

Acetylcholine↗
PubMed1989

Skinned muscle fibers of Aplysia: potentiation of contraction by "background" calcium and lack of effect of cyclic AMP.

1. Aplysia buccal muscle E1 can be skinned with saponin in a low ionic strength medium. Pulses of calcium, which were ineffective at causing contraction in intact fibers, elicited contraction in skinned fibers. 2. Tension in skinned fibers increased at [Ca2+] greater than 10(-7) M and was maximal at 6 x 10(-7) M. 10(-5) M [Ca2+] caused irreversible damage to the fibers. 3. Fibers did not exhibit "catch", i.e. they relaxed quickly upon removal of calcium. 4. Optimal pH for tension was 7.0. 5. Contractile responses to calcium pulses were increased by raising "background" [Ca2+] to 10(-7) M. 6. Cyclic AMP (10(-4) and 10(-3) M) had no effect on tension.

Animals↗
PubMed1989

Synthetic egg-laying hormone of Aplysia: quantitative studies of induction of egg laying in Stylocheilus and of the activation of Aplysia buccal neuron B16.

1. Synthetic Aplysia egg-laying hormone (ELH-lysine-amide) elicited egg laying in Stylocheilus at a threshold dose of 0.5 microgram per recipient, estimated to be a concentration in the circulation of Stylocheilus of approximately 70 nM. 2. Threshold level and size of egg mass produced by ELH-lysine-amide and bag cell extracts (containing biological ELH) were not significantly different. Latency to lay of recipients of 0.5-4.0 micrograms ELH-lysine-amide (30 +/- 1 min) was significantly longer (P less than 0.05) than for bag cell extract recipients (21 +/- 1 min). 3. ELH-lysine-amide depolarized and activated action potentials in Aplysia buccal neuron B16 in high magnesium, low calcium medium. 4. The lowest concentration of ELH-lysine-amide to activate a supra-threshold response of left and right B16 neurons ranged from 250 nM to 1 microM. 5. Threshold levels for responses to synthetic ELH-lysine-amide and to biological ELH were approximately the same in both egg-laying assay and electrophysiological assay, indicating the likely identity of synthetic and biological ELH. However, the shorter egg-laying latency with bag cell extract suggests that there may be additional factors in the extract that facilitate egg laying.

Animals↗
PubMed1988

Singleness of action in the interactions of feeding with other behaviors in Hermissenda crassicornis.

Singleness of action in the interactions of feeding behavior with other behaviors was studied in Hermissenda crassicornis. In Experiment 1 withdrawal of the oral veil from a tactile stimulus was inhibited during feeding elicited by application of a mussel homogenate to hungry animals. Rolling-over behavior was also inhibited during feeding. When animals were satiated, thereby abolishing the feeding response to mussel homogenate, withdrawal occurred in the presence of the food stimulus; however, rolling-over behavior was still inhibited. In Experiments 2 and 3 it was demonstrated that spontaneous locomotion was also inhibited in hungry animals by food stimuli; however, satiated animals ignored the food stimulus and continued to locomote. Both biting behavior and the suppressive effect of food stimuli on locomotion were also observed in dissected anterior ends of Hermissenda, suggesting that the mechanisms underlying the interaction of feeding with other behaviors may be accessible to study in the nervous system of reduced preparations.

Animals↗
PubMed1987

LY165163 and 8-OH-DPAT have agonist effects on a serotonin responsive muscle of Aplysia.

Serotonin enhances acetylcholine-elicited contractions of buccal muscle E1 of Aplysia. To characterize the serotonin receptor, actions of ligands of specific serotonin receptor subtypes were examined. Ketanserin, an antagonist at 5-HT2 receptors, had little effect. Two 5-HT1A ligands, LY165163 and 8-OH-DPAT, mimicked the effect of serotonin, although with slower kinetics. This suggests that the peripheral serotonin receptor in Aplysia more closely resembles 5-HT1 than 5-HT2 receptors.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1987

Inactivating and non-inactivating outward current channels in cell-attached patches of Helix neurons.

Two species of inactivating outward current channels and a non-inactivating voltage-dependent current were seen in cell-attached patches of Helix neurons. Large, slowly inactivating channels had a slope conductance of 44 pS as measured with patch pipets containing the normal extracellular ion concentrations, including 4 mM potassium. Latency to maximal opening was 50-220 ms, and the inactivation time constant averaged 350 ms. Channel opening was decreased by preceding depolarization. The channels were selective for potassium and inhibited by 50 mM TEA. Small, quickly inactivating channels were 14 pS and had kinetics and voltage dependence similar to IA. Patch depolarization also activated a non-inactivating voltage-dependent outward current having channel conductance and/or kinetics such that individual channel openings and closings could not be distinguished. Such current was also seen in the presence of 50 mM TEA, but not in the presence of Co2+, characteristics which are similar to outward hydrogen ion currents, described by others in Helix neurons.

Calcium↗
PubMed1987

Caffeine effects on buccal muscles of Aplysia.

1. Caffeine (35-70 mM) elicited contractions of Aplysia buccal muscle El. In a Ca2+-free medium, in which ACh-elicited contractions rapidly fail, caffeine elicited contractions of approximately the same size as in normal medium. 2. 5-HT (10(-8) M and 10(-7) M) did not enhance caffeine-elicited contractions. 3. Lower concentrations (1-10 mM) of caffeine inhibited ACh-elicited contractions. Caffeine (7 mM) reduced the contraction by 80%. 4. Caffeine (7 mM) reduced ACh-elicited depolarization by 60%. 5. Caffeine (7 mM) increased 45Ca2+ influx into Aplysia buccal muscle I5. The stimulation of influx of 45Ca2+ by 10(-3) M ACh was non-additive with the stimulation caused by caffeine, and 7 mM caffeine reduced the influx caused by 10(-3) M ACh.

Acetylcholine↗
PubMed1986

Sensitivity of a peptide-activated neuron in Aplysia to serotonin and cyclic AMP-relevant agents.

Serotonin depolarized Aplysia buccal motoneuron B16. The response could be obtained in high-magnesium/low-calcium medium, indicating a direct effect on B16 and supporting a putative monosynaptic input to B16 from the serotonergic metacerebral neurons. Similar depolarizing effects in high-magnesium/low-calcium medium were obtained in response to 8-bromo cyclic AMP, isobutylmethylxanthine, theophylline and forskolin. Tolbutamide, a putative inhibitor of cyclic AMP-dependent protein kinase, blocked or reversed responses of B16 to egg-laying hormone containing extracts and to serotonin. Serotonin and forskolin significantly increased the cyclic AMP content of buccal ganglia, whereas egg-laying hormone-containing extracts did not.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1985

Regulation of calcium influx into buccal muscles of Aplysia by acetylcholine and serotonin.

Acetylcholine (ACh) causes contraction of Aplysia buccal muscles E1 and I5, and serotonin (5-hydroxytryptamine, 5-HT) enhances ACh-elicited contractions of these muscles. Possible roles of calcium influx in mediating these responses were examined by studying influx of 45Ca++. 5-HT increased calcium influx into both I5 and E1. Maximal influx occurred at 10(-6) M 5-HT and the increased influx could be sustained in the presence of 5-HT for at least 10 min. ACh also caused calcium influx, and calcium influx increased approximately in proportion to log[ACh] from 10(-5) M to 10(-3) M ACh. 5-HT and ACh probably bring about calcium influx by different mechanisms since the effect of ACh was additive to a maximal 5-HT response, and 10(-4) M hexamethonium bromide inhibited the increased influx caused by ACh but did not affect influx caused by 5-HT. Cyclic AMP analogues and forskolin neither caused an increase in calcium influx nor an increase in the influx caused by ACh. The data support a model in which ACh-elicited contractions of I5 and E1 are due primarily to calcium entry across the extracellular membrane, and 5-HT can "load" an intracellular site by a mechanism different from that activated by ACh. The data do not support a role for cyclic AMP in mediating the calcium influx response to 5-HT.

Acetylcholine↗
PubMed1984

Extracellular calcium dependence of contracture and modulation by serotonin in buccal muscle E1 of Aplysia.

Serotonin [5-hydroxytryptamine (5-HT)] enhances acetyl choline (ACh)-elicited contractures of Aplysia buccal muscles E1 and I5 . The possible role of external calcium in regulating the magnitude of ACh contracture in the presence and absence of 5-HT was investigated. Superfusion of E1 with zero calcium medium caused ACh contractures to fail within one to two minutes. Recovery of ACh contracture upon restoring normal medium occurred within two to four minutes. In the absence of 5-HT, ACh contracture decreased proportionally to external [Ca++] in the concentration range of 0-10 mM; however, the amount of enhancement of ACh contracture following 5-HT treatment did not decrease with external [Ca++] as long as [Ca++] was above a threshold concentration that varied from preparation to preparation. For most preparations, the enhancement of ACh contracture by 5-HT was dependent on the presence of external calcium during 5-HT treatment. Calcium influx into muscles E1 and I5 increased approximately two and a half fold in the presence of 10(-6) M 5-HT. A model in which 5-HT brings about calcium "loading" of an ACh releasable intracellular storage site is discussed.

Acetylcholine↗
PubMed1984

Serotonin and forskolin enhance both magnitude of contraction and relaxation rate of Aplysia dorsal extrinsic muscle independently of acetylcholine receptor.

Hexamethonium bromide (Hex. Br.) blocks acetylcholine (ACh) elicited contractions but not electrically elicited contractions of isolated preparations of Aplysia californica dorsal extrinsic muscle. Serotonin (5-hydroxytryptamine, 5-HT) enhances both magnitude and relaxation rate of ACh and electrically elicited contractions. In the presence of Hex. Br., 5-HT still exhibits its modulatory effects on electrically elicited contractions. Forskolin enhances both magnitude and relaxation rate of ACh and electrically elicited contractions. Forskolin (10(-5) M) increases the cyclic AMP content of the accessory radula closer and dorsal extrinsic muscles.

Acetylcholine↗
PubMed1983

Neuropeptide activation of an identifiable buccal ganglion motoneuron in Aplysia.

Application of the neuropeptide egg-laying hormone (ELH) of Aplysia to buccal ganglia activates a cell which has an axon in buccal nerve B4(17). The ELH-activated axon innervates buccal mass muscle 15(12). Criteria to identify and to record intracellularly from the ELH-activated neuron prior to ELH application were developed, and properties of the intracellularly recorded response were observed. Of two major inputs into 15 activated by stimulation of nerve B4, the ELH-activated cell always corresponded to the one showing the lesser degree of facilitation at 1 Hz. ELH-containing extracts caused a slow smooth depolarization of this cell, leading to action potentials, which were not driven by discrete EPSPs. The response was not due to disinhibition, as IPSPs did not ordinarily occur prior to ELH application, although IPSPs sometimes occurred at high rates as ELH-containing extracts were washed off. ELH-containing Sephadex G-50 fractions activated the cell in both normal and high magnesium-low calcium media. On the basis of the location of its cell body and the amount and rate of decay of facilitation of its input into 15, the author suggests that the ELH-activated cell is the same as the previously identified 15 motoneuron, B16.

Action Potentials↗
PubMed1983

Serotonin-activated adenylate cyclase and the possible role of cyclic AMP in modulation of buccal muscle contraction in Aplysia.

The possible role of cyclic AMP in mediating opposite modulatory effects of serotonin (5-HT) on Aplysia buccal mass muscles E1 and E2 was examined. Serotonin enhances E1 contractions and inhibits E2 contractions. Adenylate cyclase in membranes of both E1 and E2 is stimulated approximately 180% by 10(-6) M 5-HT and 300% by 10(-3) M 5-HT. Dibutyryl cyclic AMP and 8-benzylthio cyclic AMP mimicked the effect of 5-HT on E1 but had no effect on E2. Theophylline (Th) and isobutylmethylxanthine (IBMX) mimicked the effect of 5-HT on E1 at high concentrations. Concentrations of Th and IBMX low enough not to have any direct effect on contraction increased both the magnitude and duration of the effect of 5-HT on E1 contraction. Neither Th nor IBMX had a direct effect on E2 contraction, although Th produced a small increase in the effect of 5-HT on E2. These data are consistent with the hypothesis that cyclic AMP mediates the enhancement effect of 5-HT on E1 contraction. Other mechanisms probably mediate the effect of 5-HT on E2 contraction.

Adenylyl Cyclases↗
PubMed1983

Forskolin activation of an identified peptide-sensitive motoneurone in Aplysia.

Activation of a physiological response by the adenylate cyclase activator, forskolin, has been suggested as a new criterion for testing the role of cyclic AMP. In Aplysia, motoneurone B16, which innervates muscle 15, is activated by the peptide egg-laying hormone (ELH). In high magnesium-low calcium medium, used to block synaptic activity, forskolin produced a similar response to ELH. Forskolin, at a concentration of 100 microM, consistently activated the ELH-sensitive neurone; vehicle produced no response while 30 microM forskolin usually produced lower levels of activity than 100 microM. The data are consistent with cyclic AMP mediation of the ELH response.

Animals↗