Showing papers by "University of Puerto Rico, Medical Sciences Campus published in 1998"

Effect of a serotonergic extrinsic modulatory neuron (MCC) on radula mechanoafferent function in Aplysia.

Abstract: The serotonergic metacerebral cells (MCCs) and homologous neurons in related mollusks have been extensively investigated within the context of feeding. Although previous work has indicated that the MCCs exert widespread actions, MCC modulation of sensory neurons has not been identified. We characterized interactions between the MCCs and a cell that is part of a recently described group of buccal radula mechanoafferents. The cell, B21, has a peripheral process in the tissue underlying the chitinous radula [the subradula tissue (SRT)]. Previous studies have shown that B21 can fire phasically during ingestive motor programs and provide excitatory drive to the circuitry active during radula closing/retraction. We now show that activity of B21 can be modulated by serotonin (5-HT) and the MCCs. Centrally, although a slow depolarization is typically recorded in B21 as a result of MCC stimulation, this depolarization does not cause B21 to spike. It can, however, increase B21 excitability enabling a pulse that was previously subthreshold to elicit an action potential in B21. B21 is in fact rhythmically depolarized during the radula closing/retraction phase of ingestive motor programs. Thus central effects of the MCCs on radula mechanoafferent activity are only likely to be apparent while B21 is receiving input from the feeding central pattern generator. Peripherally, radula mechanoafferent neurons can be activated 1) when a mechanical stimulus is applied to the biting surface of the SRT and 2) when the SRT contracts. MCC stimulation and 5-HT modulate B21 responses to both types of stimuli. For example, MCC stimulation and low concentrations of 5-HT cause subthreshold mechanical stimuli applied to the SRT to become suprathreshold. 5-HT and MCC stimulation also enhance SRT contractility. Peripheral effects of MCC activity are also likely to be phase dependent. For example, MCC stimulation does not cause B21 to respond to peripheral stimuli with an afterdischarge. Consequently, radula mechanoafferents are likely to be activated when food is present between the radula halves during radula closing/retraction but are not likely to continue to fire as opening/protraction is initiated. In a similar vein, MCC effects on the contractility of the SRT will only be apparent when contractions are elicited by motor neuron activity. SRT motor neurons are rhythmically activated during ingestive motor programs. Thus we have shown that radula mechanoafferent activity can be modulated by the MCCs and that this modulation is likely to occur in a phase-dependent manner.

The ecology of the introduced patas monkey (Erythrocebus patas) population of southwestern Puerto Rico.

Abstract: This paper presents the results of a study on the introduced, free-ranging patas monkey population of Southwestern Puerto Rico (SWPR). It describes information on the population size, social group composition, diet, daily ranging patterns, and patas home range during a 3 year period. The patas monkey population in the study area consisted of approximately 120 individuals in four heterosexual groups and several all-male bands. Within their home ranges (26.8 km2), the population density was 4.47 individuals/km2. Home range size among the population's four heterosexual groups varied from 3.72 km2 to 15.39 km2, and minimum daily distance traveled ranged from 0.8-2.0 km. In general, the social structure and mating system of this population parallels what has been described for African populations. However, habitat use, ranging behavior, and the quality of intergroup interactions suggests that patas of this population exhibit territorial behavior.

Elevated expression of chitinase 1 and chitin synthesis in myosin II-deficient Saccharomyces cerevisiae.

Abstract: To determine if the attached cells formed in Myosin II-deficient Saccharomyces cerevisiae result from deficient chitinase 1 (CTS1) expression, the activity of chitinase 1 was assayed. Secretion of this enzyme was not prevented by a MYO1 gene deficiency, and soluble and cell wall-associated Cts1p activity were increased approximately 5-fold and 20-fold, respectively, in these cells. The increase in soluble activity was correlated with an increase in enzyme levels. Likewise, intracellular chitinase activity was increased approximately 22-fold, and the chitin content of cell walls was elevated 2-fold. These data suggest that the origin of myo1-associated phenotypes is not due to deficient chitinase expression and may instead be due to a deregulation of cell wall metabolism in these cells.

Indirect synaptic inputs from filiform hair sensory neurons contribute to the receptive fields of giant interneurons in the first-instar cockroach.

Abstract: The first-instar cockroach, Periplaneta americana, detects air movements using four filiform hair sensilla, which make synaptic connections to seven pairs of giant interneurons (GIs) in the terminal abdominal ganglion. The directional sensitivities of some of the GIs, predicted from their patterns of monosynaptic inputs, may not be the same as in the second instar or adult. Intracellular recordings were made to determine the contribution of polysynaptic inputs to the receptive fields of first-instar GIs. The ventral GI1, and the dorsal GI5, GI6, and GI7 were all found to have indirect synaptic inputs from filiform afferents. The indirect inputs were excitatory to GI1, GI5, and GI7, and inhibitory to GI6 and GI7. The indirect excitatory input to GI1 was predicted to alter qualitatively its receptive field, allowing it to respond to wind from the side of the animal, as in the adult. Inhibition was predicted to sharpen the receptive fields of GI6 and GI7. The inhibitory postsynaptic potentials reversed 6–8 mV below resting potential and were blocked by picrotoxin, indicating that they are GABAergic. Indirect excitation also altered the predicted receptive field of GI7, one of the inputs being an unusual “off-response” to movement of a filiform hair in its inhibitory direction.