Neuronal correlates of siphon withdrawal in freely behaving Aplysia

Abstract

1. Central neuronal mechanisms of siphon withdrawal in Aplysia were studied for the first time in intact, freely behaving animals by means of population recordings from implanted whole-nerve cuff electrodes. Intracellular follow-up studies were then conducted when the same animal was reduced to a semi-intact preparation. 2. Background spontaneous activity in the siphon nerve consisted of low-frequency firing of a population of efferent units containing identified siphon motoneurons. 3. Spontaneous patterned bursts of efferent activity occurred irregularly and were associated with all-or-nothing contractions of the parapodia, gill, and siphon. Spontaneous bursts were due to centrally generated activity in the interneuron II (INT II) network, an oscillatory network with endogenous pacemaker properties. 4. In intact animals, even weak tactile stimuli to the siphon typically triggered an INTII burst shortly after the stimulus-locked efferent activity. Thus, the stimulus can phase-advance the INT II oscillator. In semi-intact preparations, short-latency INT II bursts were triggered less less frequently and required more intense stimuli. 5. With weak to moderate-intensity stimuli in intact animals, the presence of short-latency triggered INT II bursts largely determined the duration of the siphon component and amplitude of the gill component of the withdrawal reflex. 6. When stimuli were repeated over a range of interstimulus intervals (from 60 to 1 min), the likelihood of triggering a short-latency INT II burst die not change systematically. Thus, the ability of the siphon stimulus to stably entrain the all-or-none INT II component over a wide range of intervals will interact behaviorally with the decrement of the monosynaptic component of the reflex with repetition.

Multiple Serotonergic Mechanisms Contributing to Sensitization in Aplysia: Evidence of Diverse Serotonin Receptor Subtypes

“…A tactile stimulus applied to the tail or siphon activates tail or siphon SNs, which excite MNs through monosynaptic (SN-MN synapses) and polysynaptic pathways (for a more detailed review, see Cleary et al 1995;Frost and Kandel 1995). More than 10 types of interneurons are known to participate in these polysynaptic pathways between SNs and MNs: (1) L25, R25, L26, and L33 are recruited during siphon withdrawal reflex and respiratory pumping (Kanz et al 1979;Byrne 1983;Eberly and Pinsker 1984;Frost and Kandel 1995), (2) L16, L29, L30, L33, and L34 mediate siphon withdrawal reflex only, and (3) Pl 4 and Pl 17 are involved in reflex tail withdrawal (Buonomano et al 1992;Cleary and Byrne 1993;Xu et al 1994). Moreover, Pl 17 is viewed as possibly providing a linkage between pleural and abdominal reflex circuits .…”

Role of interneurons in defensive withdrawal reflexes in Aplysia.

“…The first consists of four groups of neurons (L16, L29, L30, L34) that mediate reflex withdrawals only. The second subcircuit consists of interneurons (L25, R25, L26, L33) that are recruited during reflex withdrawals (Kanz et al 1979;Byrne 1983;Eberly and Pinsker 1984;Frost and Kandel 1995) but that also mediate the spontaneous withdrawal associated with respiratory pumping (Byrne and Koester 1978;Byrne 1983;Koester 1989).…”

Designing and Implementing Nervous System Simulations on LEGO Robots

“…However, the majority of nervous system research to date has relied on the use of isolated preparations or restrained subjects. While there have been many successful efforts to record neural activity from freely behaving animals [2][3][4][5] , the biorobotic approach provides a valuable tool to allow for nervous system manipulation in order to test systems level neuroscience hypotheses 6 . Simulated nervous systems operating on robots can be experimentally manipulated and allow for the extension of software modeling to the physical world.…”