Biomedical subjects

S L Hooper

Publications and source records attributed to S L Hooper.

29 records · Page 2Linked to original sources

PubMed1993

Physiology and biochemistry of peptidergic cotransmission in Aplysia.

The marine mollusc Aplysia, whose simple nervous system facilitates study of the neural basis of behavior, was used to investigate the role of peptidergic cotransmission in feeding behavior. Several novel modulatory neuropeptides were purified and localized to identified cholinergic motoneurons. Physiological and biochemical studies demonstrated that these peptides are released when the motoneurons fire at frequencies that occur during normal behavior, and that the peptides modify the relationship between muscle contraction amplitude and relaxation rate so as to maintain optimal motor output when the intensity and frequency of feeding behavior change.

Amino Acid Sequence↗

PubMed1993

Hormonal responses of elite swimmers to overtraining.

Fourteen elite swimmers had measurements of stress hormones taken at five points during a 6-month season: early-, mid- and late-season, during tapering for National Trials, and 1-3 d after the Trials. Training details and subjective ratings of fatigue were recorded daily in log books. Plasma norepinephrine and epinephrine concentrations were significantly correlated with swim training volume (r = 0.37 and 0.33, respectively, P < 0.05 for each). No significant differences were seen in norepinephrine or cortisol concentrations at the five sampling times. Epinephrine levels were significantly lower (P < 0.05) after competition compared with values early in the season and shortly before competition. Symptoms of the overtraining syndrome were identified in three of the swimmers, based on performance decrements and high, prolonged levels of fatigue. In these three swimmers, norepinephrine levels tended to be higher than those of the other swimmers from mid-season onward and were significantly higher (P < 0.01) during tapering. If these findings can be confirmed in larger numbers and different types of athletes, norepinephrine level may provide a useful marker of the overtraining syndrome.

Adolescent↗

PubMed1992

Peptidergic co-transmission in Aplysia: functional implications for rhythmic behaviors.

Despite their ubiquitous presence in the central and peripheral nervous systems, the behavioral functions of peptide co-transmitters remain to be elucidated. The marine mollusc Aplysia, whose simple nervous system facilitates the study of the neural basis of behavior, was used to investigate the role of peptidergic co-transmission in feeding behavior. Several novel modulatory neuropeptides were purified, and localized to identified cholinergic motorneurons. Physiological and biochemical studies demonstrated that these peptides are released when the motorneurons fire at frequencies that occur during normal behavior, and that the peptides modify the relationship between muscle contraction amplitude and relaxation rate so as to maintain optimal motor output when the intensity and frequency of feeding behavior change.

Amino Acid Sequence↗

PubMed1990

Sensory input induces long-lasting changes in the output of the lobster pyloric network.

1. A long-lasting restructuring of the pyloric neural network of the lobster stomatogastric nervous system (STS) by a multisynaptic sensory afferent is described. This restructuring can be obtained either by mechanical stimulation of the pyloric region of the stomach or by brief high-frequency electrical stimulation of a nerve that innervates this region, the lateral posterolateral nerve (lpln). Electron microscopy shows that this nerve contains several thousand very small fibers (approximately 0.3 microns diam), the activation of some subset of which is responsible for the effects of lpln stimulation. 2. These stimulation paradigms result in both short-duration changes in pyloric activity and modulatory effects long outlasting the stimulus end. The long-lasting changes include the cessation of rhythmic ventricular dilator (VD) and lateral pyloric (LP) neuron activity, and thus result in a reduced pyloric pattern in which only the pyloric dilator (PD), inferior cardiac (IC), anterior burster (AB), and pyloric (PY) neurons are active. 3. Tonic low-frequency lpln stimulation, alternatively, results in the VD neuron rhythmically firing long spike bursts with a cycle frequency much slower than that of the pyloric network while an otherwise complete pyloric pattern continues. In this new bursting pattern the VD neuron fires exclusively with another STS neural network, the cardiac sac (CS) network, and thus functionally "switches" from the pyloric to the CS network. This switch of the VD neuron from the pyloric to the CS network also occurs when the CS network is spontaneously active. 4. Our results thus demonstrate that sensory input can provoke a long-lasting modification of the functional configuration of a rhythmic neural network. They further extend the concept of flexibility in nervous systems by showing that individual neurons can belong to more than one neural network, "switching" from one to another in response to sensory input or spontaneous central nervous activity.

Animals↗

PubMed1990

Cellular and synaptic mechanisms responsible for a long-lasting restructuring of the lobster pyloric network.

1. In the lobster Palinurus vulgaris a sensory input in the lateral posterolateral nerve (lpln) of the stomatogastric nervous system (STS) is able to turn on the cardiac sac (CS) network and to induce dramatic long-lasting alterations in the output of the pyloric network. This long-lasting alteration of pyloric network output consists primarily of changes in the activity of the two neurons that innervate the muscles of the cardiopyloric valve of the stomach, with the dilator neuron (the ventricular dilator, VD) transferring from the pyloric network to the CS network and the constrictor neuron (the inferior cardiac, IC) shifting to fire earlier in the pyloric pattern. 2. The inferior ventricular (IV) neurons of the CS network make complex multiaction synaptic connections onto several pyloric neurons in a related species, Panulirus interruptus. We show that many of the short-term alterations in pyloric activity observed during CS network bursts in Palinurus are due to similar IV neuron synaptic connections. However, the long-lasting effects of lpln stimulation on pyloric output are not due to this synaptic input, because 1) direct activation of the IV neurons does not induce long-lasting changes in pyloric activity and 2) pharmacologic disconnection of this synaptic input does not abolish lpln stimulation's long-lasting effects. Lpln stimulation therefore activates two different neuronal inputs to the pyloric network. 3. The transfer of the VD neuron from the pyloric to the CS network is the result of the concerted actions of these two inputs. Lpln stimulation turns on the CS network, and the IV neurons of the CS network excite the VD neuron and ensure it fires with the CS network. The second neuronal input (that not involving known CS network neurons) abolishes in a long-lasting fashion the VD neuron regenerative (plateau) properties, and thus suppresses the ability of the VD neuron to participate in the pyloric rhythmic pattern between CS network bursts. 4. Experimental manipulation of VD neuron activity can both mimic and reverse the effects of lpln stimulation on the IC neuron. The changes in IC neuron activity are therefore not due to direct lpln-activated synaptic input onto the IC neuron, but instead are indirect "network" effects arising from the changes in VD neuron activity.

Animals↗

PubMed1989

Switching of a neuron from one network to another by sensory-induced changes in membrane properties.

A neuron that is an integral member of the pyloric neural network of the lobster stomatogastric nervous system leaves this network and instead fires exclusively with another stomatogastric nervous system network, the cardiac sac network, whenever the cardiac sac network is active. This switch is associated with the neuron losing, in a long-lasting fashion, regenerative oscillatory membrane properties that underlie its participation in the pyloric network. Functional membership of neurons in central networks is thus not fixed, and long-lasting neuromodulatory influences, controlled at least in part by sensory inputs, can switch neurons from one network to another.

Action Potentials↗

PubMed1987

Modulation of the lobster pyloric rhythm by the peptide proctolin.

The modulation of the pyloric network of the stomatogastric ganglion (STG) of the lobster Panulirus interruptus by the neuropeptide proctolin is described. First, the effects of proctolin on the pyloric motor patterns were characterized in terms of frequency and phase relations. Pyloric cycle frequency and lateral pyloric (LP) neuron activity increased and ventricular dilator (VD) neuron activity decreased with increasing concentrations (10(-9)-10(-6) M) of applied proctolin. Next, the effects of proctolin on the individual neurons that constitute the pyloric network were determined. Identified neurons were isolated from chemical and electrical presynaptic inputs by using pharmacological agents (Marder and Eisen, 1984a) and/or photoinactivation following Lucifer yellow injection (Miller and Selverston, 1979). Proctolin increased the amplitude and frequency of bursts produced by isolated pacemaker anterior burster (AB) neurons. Isolated LP and pyloric (PY) neurons responded to proctolin with increases in activity only when they were at or above threshold. All other pyloric neurons were unaffected. To determine how the direct effects of proctolin on isolated neurons resulted in the observed changes in frequency and phase relations in the motor pattern of the intact pyloric circuit seen in proctolin, individual neurons were deleted from the circuit. A comparison of proctolin's effects on isolated neurons with those on the intact network shows that the synaptic connectivity among neurons directly affected by proctolin and those unaffected by it shapes the network's response to proctolin.

Action Potentials↗

PubMed1986

Modulatory action and distribution of the neuropeptide proctolin in the crustacean stomatogastric nervous system.

Immunocytochemical methods were used to map the distribution of proctolinlike immunoreactivity in the stomatogastric nervous systems (stomatogastric ganglion (STG), paired commissural ganglia (CG), oesophageal ganglion (OG), and connecting nerves) of three crustacean species: Panulirus interruptus, Cancer borealis, and Homarus americanus. Although the patterns of proctolinlike staining were similar among the three species, some differences were also observed. Over 70% of the proctolinlike material in STGs, as measured by radioimmunoassay, was indistinguishable from authentic proctolin in reverse-phase high-performance liquid chromatography. Bath application of proctolin to STGs from Cancer and Panulirus induced characteristic and robust (though somewhat different) changes in their motor patterns. The threshold concentration was approximately 10(-9)M proctolin, and the effects were dose-dependent. These data suggest that the neuropeptide proctolin serves as a neuromodulator of the stomatogastric ganglion.

Animals↗

PubMed1986

The innervation of the pyloric region of the crab, Cancer borealis: homologous muscles in decapod species are differently innervated.

The muscles of the pyloric region of the stomach of the crab, Cancer borealis, are innervated by motorneurons found in the stomatogastric ganglion (STG). Electrophysiological recording and stimulating techniques were used to study the detailed pattern of innervation of the pyloric region muscles. Although there are two Pyloric Dilator (PD) motorneurons in lobsters, previous work reported four PD motorneurons in the crab STG (Dando et al. 1974; Hermann 1979a, b). We now find that only two of the crab PD neurons innervate muscles homologous to those innervated by the PD neurons in the lobster, Panulirus interruptus. The remaining two PD neurons innervate muscles that are innervated by pyloric (PY) neurons in P. interruptus. The innervation patterns of the Lateral Pyloric (LP), Ventricular Dilator (VD), Inferior Cardiac (IC), and PY neurons were also determined and compared with those previously reported in lobsters. Responses of the muscles of the pyloric region to the neurotransmitters, acetylcholine (ACh) and glutamate, were determined by application of exogenous cholinergic agonists and glutamate. The effect of the cholinergic antagonist, curare, on the amplitude of the excitatory junctional potentials (EJPs) evoked by stimulation of the pyloric motor nerves was measured. These experiments suggest that the differences in innervation pattern of the pyloric muscles seen in crab and lobsters are also associated with a change in the neurotransmitter active on these muscles. Possible implications of these findings for phylogenetic relations of decapod crustaceans and for the evolution of neural circuits are discussed.

Acetylcholine↗

PubMed1984

Modulation of a central pattern generator by two neuropeptides, proctolin and FMRFamide.

The neuropeptides, proctolin and FMRFamide, increase the frequency of, and modify the motor pattern produced by, the stomatogastric ganglion (STG) of the crab, Cancer irroratus. Both proctolin-like and FMRFamide-like immunoreactivities are present in fibers in the stomatogastric nerve which terminate in the neuropile of the STG. The neural output of the STG thus appears to be modulated by at least two different groups of peptidergic input fibers.

Animals↗

PubMed1984

Serotonergic innervation and modulation of the stomatogastric ganglion of three decapod crustaceans (Panulirus interruptus, Homarus americanus and Cancer irroratus).

The serotonergic innervation of the stomatogastric ganglion (STG) of three decapod crustacean species, Panulirus interruptus, Homarus americanus and Cancer irroratus, was studied. Immunohistochemical techniques were used to study the distribution of serotonin-like staining in regions of the stomatogastric system in the three species. In C. irroratus and H. americanus, but not in P. interruptus, serotonin-like staining was found in fibres in the stomatogastric nerve and in neuropil regions of the STG. High performance liquid chromatography confirmed the presence of serotonin in STG of C. irroratus and H. americanus, but serotonin was not found in STG of P. interruptus. Electrophysiological experiments showed that the pyloric motor output of the STG of all three species was influenced by bath applications of serotonin. The STG of P. interruptus responded to serotonin concentrations as low as 10-9M; however the STG of the other two species did not respond until serotonin concentrations in excess of 10-6M were applied. We conclude that serotonin may play a hormonal role in the control of the STG of P. interruptus, but is likely to be a neurotransmitter released by inputs to the STG of H. americanus and C. irroratus.

Animals↗