Biomedical subjects

D W Morton

Publications and source records attributed to D W Morton.

6 recordsLinked to original sources

PubMed2001

Clinically relevant rat model for testing BOLD functional MR imaging techniques by using single-shot echo-planar imaging at 1.5 T.

By using a 1.5-T whole-body magnetic resonance (MR) imager, a high-spatial-resolution single-shot echo-planar technique was developed to perform blood oxygen level dependent functional MR imaging of rat sensory cortex during forepaw stimulation. This technique produced cubic 1-mm(3) voxels. Signal-to-noise ratio was 140-160 (43-44 dB). Optimal effective echo time was 50 msec. This system should prove useful for developing new functional MR imaging techniques with rapid adaptation to human use.

Animals↗

PubMed1996

Activity patterns of the B31/B32 pattern initiators innervating the I2 muscle of the buccal mass during normal feeding movements in Aplysia californica.

1. B31 and B32 are pattern-initiator neurons in the buccal ganglia of Aplysia. Along with the B61/B62 neurons, B31/B32 are also motor neurons that innervate the 12 buccal muscle via the I2 nerve. This research was aimed at determining the physiological functions of the B31/B32 and B61/B62 neurons, and of the I2 muscle. 2. Stimulating the I2 muscle in the radula rest position produces radula protraction. In addition, in behaving animals lesioning either the muscle or the I2 nerve greatly reduces radula protraction. 3. During buccal motor programs in reduced preparations, B31/B32 and B61/62 fire preceding activity in neuron B4, whose firing indicates the onset of radula retraction. In addition, during both ingestion-like and rejection-like patterns the activity in the I2 nerve is correlated with protraction. 4. B31/B32 fire at frequencies of 15-25 Hz. Neither B31/B32 nor B61/B62 elicit facilitating end-junction potentials (EJPs) and electromyograms (EMGs) in the I2 muscle. EMGs from B31/B32 are smaller than those from B61/B62. B31/B32 and B61/B62 innervate all areas of the muscle approximately uniformly. 5. In behaving animals, EMGs consistent with B31/B32 activity are seen in the I2 muscle during the protraction phase of biting, swallowing, and rejection movements. In addition, the I2 muscle receives inputs that cannot be attributed to either the B31/B32 or B61/B62 neurons, either because the potentials are too large, firing frequencies are too low, or a prominent facilitation is seen. Such potentials are associated with lip movements, and also with radula retraction. 6. EMGs were recorded from the I2 muscle during feeding behavior after a lesion of the I2 nerve. Animals that had severe deficits in protraction showed no activity consistent with B31/B32 or B61/B62, but did show activity during retraction. 7. Our data indicate that the I2 muscle and the B31/B32 motor neurons are essential constituents contributing to protraction movements. Activity in these neurons is associated with radula protraction, which occurs as a component of a number of different feeding movements. The I2 muscle may also contribute to retraction, via activation by other motor neurons.

Action Potentials↗

PubMed1994

Neural architectures for adaptive behavior.

How do animals use the same peripheral structures to generate different behavioral responses? Three different neuronal architectures have been proposed to mediate this task: dedicated circuitry; distributed circuitry; and reorganizing circuitry. This review will critically examine the evidence for these different architectures in invertebrate circuits, and then examine the evidence for them in more complex vertebrate circuits. The evidence suggests that these different architectures are unlikely to be found in pure form in most neural circuits, but are useful for guiding the experimental analysis of circuitry.

Adaptation, Psychological↗

PubMed1993

The timing of activity in motor neurons that produce radula movements distinguishes ingestion from rejection in Aplysia.

1. We have studied the neural circuitry mediating ingestion and rejection in Aplysia using a reduced preparation that produces ingestion-like and rejection-like motor patterns in response to physiological stimuli. 2. We have characterized 3 buccal ganglion motor neurons that produce specific movements of the radula and buccal mass. B8a and B8b act to close the radula. B10 acts to close the jaws and retract the radula. 3. The patterns of activity in these neurons can be used to distinguish the ingestion-like and rejection-like motor patterns. B8a, B8b and B10 are active together during the ingestion-like pattern. Activity in B8a and B8b ends prior to the onset of activity in B10 during the rejection-like pattern. 4. Our data suggest that these neurons undergo similar patterns of activity in vivo. During both feeding-like patterns, the activity and peripheral actions of B8a, B8b, and B10 are consistent with radula movements observed during ingestion and rejection. In addition, the extracellular activity produced by these neurons is consistent with neural activity observed in vivo during ingestion and rejection. 5. Our data suggest that the different activity patterns observed in these motor neurons contribute to the different radula movements that distinguish ingestion from rejection.

Animals↗

PubMed1993

In vivo buccal nerve activity that distinguishes ingestion from rejection can be used to predict behavioral transitions in Aplysia.

1. We are studying the neural basis of consummatory feeding behavior in Aplysia using intact, freely moving animals. 2. Video records show that the timing of radula closure during the radula protraction-retraction cycle constitutes a major difference between ingestion (biting or swallowing) and rejection. During ingestion, the radula is closed as it retracts. During rejection, the radula is closed as it protracts. 3. We observed two patterns of activity in nerves which are likely to mediate these radula movements. Patterns I and II are associated with ingestion and rejection, respectively, and are distinguished by the timing of radula nerve activity with respect to the onset of buccal nerve 2 activity. 4. The association of ingestion with pattern I is maintained when the animal feeds on a polyethylene tube, the same food substrate used to elicit rejection responses. Under these conditions, pattern I is associated with either swallowing or no net tube movement. 5. Most transitions from swallowing to rejection were preceded by one or more occurrences of pattern I in which there was no net tube movement, suggesting that these transitions can be predicted. 6. Our data suggest that these two patterns can be used to distinguish ingestion from rejection.

Animals↗

PubMed1991

Optical methods can be utilized to map the location and activity of putative motor neurons and interneurons during rhythmic patterns of activity in the buccal ganglion of Aplysia.

We sought to develop a map of the locations of neurons that are active during patterned activity in the buccal ganglion of Aplysia using optical techniques. Staining ganglia with a voltage-sensitive absorbance dye (JPW 1124) did not prevent them from generating patterned activity similar to that observed before staining, in response to shock of the esophageal nerve. Absorbance changes were monitored with a 124-element photodiode array, while extracellular electrodes monitored activity of the 6 buccal nerves. Optical and extracellular spikes were grouped with the aid of a template matching program; a total of 120 distinct units were detected in one 15 s recording. Optical signals (83 units) were found in the region of the ganglion containing mainly large neurons. Of these, 13 were detected on both optical and extracellular electrode recordings, suggesting that they might be motor neurons, while 25 of the optically detected neurons appeared not to be correlated with extracellular activity, suggesting that they might be interneurons. It was not possible to determine whether the remaining 45 optically identified units did or did not have correlated nerve activity. The ganglionic locations of putative motor neurons corresponded to the locations of large neurons identified by backfilling nerves of other buccal ganglia, and were consistent with the locations of putative motor neurons found in two other ganglia studied using optical methods. Thus, optical methods have generated a map of the locations and activity patterns of putative motor neurons and interneurons in the buccal ganglion that may be involved in the generation of rhythmic patterns.

Animals↗