Handbook of psychopharmacology

Until recently, it has been impossible to approach learning with the techniques of cell biology. During the past several years, elementary forms of learning have been analyzed in higher invertebrates. Their nervous systems allow the experimental study of behavioral, neurophysiological, morphological, biochemical, and genetic components of the functional (plastic) changes underlying learning. In this review, we focus primarily on short-term sensitization of the gill and siphon reflex in the marine mollusk, Aplysia californica. Analyses of this form of learning provide direct evidence that protein phosphorylation dependent on cyclic adenosine monophosphate can modulate synaptic action. These studies also suggest how the molecular mechanisms for this short-term form of synaptic plasticity can be extended to explain both long-term memory and classical conditioning.

https://science.sciencemag.org/content/sci/218/4571/433.full.pdf

Molecular Biology of Learning: Modulation of Transmitter Release.

Cognitive Neuroscience and the Study of Memory

Recent studies of animals with complex nervous systems, including humans and other primates, have improved our understanding of how the brain accomplishes learning and memory. Major themes of recent work include the locus of memory storage, the taxonomy of memory, the distinction between declarative and procedural knowledge, and the question of how memory changes with time, that is, the concepts of forgetting and consolidation. An important recent advance is the development of an animal model of human amnesia in the monkey. The animal model, together with newly available neuropathological information from a well-studied human patient, has permitted the identification of brain structures and connections involved in memory functions.

Mechanisms of memory

In the search for principles of pattern generation in complex biological systems, an operational approach is presented that embraces both theory and experiment. The central mathematical concepts of self-organization in nonequilibrium systems (including order parameter dynamics, stability, fluctuations, and time scales) are used to show how a large number of empirically observed features of temporal patterns can be mapped onto simple low-dimensional (stochastic, nonlinear) dynamical laws that are derivable from lower levels of description. The theoretical framework provides a language and a strategy, accompanied by new observables, that may afford an understanding of dynamic patterns at several scales of analysis (including behavioral patterns, neural networks, and individual neurons) and the linkage among them.

https://science.sciencemag.org/content/sci/239/4847/1513.full.pdf

Dynamic pattern generation in behavioral and neural systems

1. A population of interneurons that control feeding behavior in the mollusk Pleurobranchaea has been analyzed by dye injection and intracellular stimulation/recording in whole animals and reduced preparations. The population consists of 12-16 somata distributed in two bilaterally symmetrical groups on the anterior edge of the cerebropleural ganglion (brain). On the basis of their position adjacent to the cerebral lobes, these cells have been named paracerebral neurons (PCNs). This study concerns pme subset pf [MCs. the large, phasic ones, which have the strongest effect on the feeding rhythm (21). 2. Each PCN sends a descending axon via the ipsilateral cerebrobuccal connective to the buccal ganglion. Axon branches have not been detected in other brain or buccal nerves and hence the PCNs appear to be interneurons. 3. In whole-animal preparations, tonic intracellular depolarization of the PNCs causes them to discharge cyclic bursts of action potentials interrupted by a characteristic hyperpolarization. In all specimens that exhibit feeding behavior, the interburst hyperpolarization is invariably accompanied by radula closure and the beginning of proboscis retraction (the "bite"). No other behavorial effect of PCN stimulation has been observed. 4. In whole-animal preparations, the PCNs are excited by food and tactile stimulation of the oral veil, rhinophores, and tentacles. When such stimuli induce feeding the PCNs discharge in the same bursting pattern seen during tonic PCN depolarization, with the cyclic interburst hyperpolarization phase locked to the bit. When specimens egest an unpalatable object by cyclic buccal movements, however, the PCNs are silent. The PCNs therefore exhibit properties expected of behaviorally specific "command" neurons for feeding. 5. Silencing one or two PCNs by hyperpolarization may weaken but does not prevent feeding induced by natural food stimuli. Single PCNs therefore can be sufficient but are not necessary to induction of feeding behavior. Instead the PCNs presumably operate as a population to control feeding. 6. In isolated nervous system preparations tonic extracellular stimulation of the stomatogastric nerve of the buccal ganglion elicits a cyclic motor rhythm that is similar in general features to the PNC-induced motor rhythm. Bursts of PCN action potentials intercalated at the normal phase position in this cycle intensify the buccal rhythm. Bursts of PCN impulses intercalated at abnormal phase positions reset the buccal rhythm. The PCNs, therefore, also exhibit properties expected of pattern-generator elements and/or coordinating neurons for the buccal rhythm. 7. The PCNs are recruited into activity when the buccal motor rhythm is elicited by stomatogastric nerve stimulation or stimulation of the reidentifiable ventral white cell. The functional synergy between the PCNs and the buccal rhythm is therefore reciprocal. 8...

Control of feeding motor output by paracerebral neurons in brain of Pleurobranchaea californica

Motor organization and generation of rhythmic feeding output in buccal ganglion of Pleurobranchaea.

1.

Complex behavior in the carnivorous marine gastropod Pleurobranchaea californica is described (Figs. 1–6).




2.

Situations requiring behavioral choice can be created by simultaneously delivering the stimuli for two different behavior patterns. In such situations feeding is elicited in preference to other behaviors, including sexual activity and righting responses.




3.

Two behaviors have been examined in detail, the withdrawal response to light and feeding. The withdrawal response habituates; correlated studies on the nervous system showed that the habituation has two causes, adaptation of the visual response (Figs. 8, 9) and habituation of the participating central pathways (Figs. 10–12). The central habituation is specific to pathways involving the visual input. Neuromuscular adaptation is not involved in the behavioral habituation.




4.

The sequence of muscular activity causing the rhythmic feeding movements was determined by cinematography (Fig. 14) as well as anatomical (Fig. 15) and electromyographic (Figs. 16, 17) methods. Central nerve cells were located which either excite or inhibit efferent outflow to the feeding apparatus (Figs. 21, 22).

Behavioral choice and habituation in the marine mollusk Pleurobranchaea californica MacFarland (Gastropoda, Opisthobranchia)

Of the many important concepts that have stemmed from the prolific research of Professor C. A. G. Wiersma, perhaps the one that has had the greatest impact on comparative neurobiology is that of the “command” neuron. The term has a long history of application in the invertebrates (for recent reviews, see Bowerman and Larimer, 1976a; Davis, 1976; Kennedy and Davis, 1977) and has recently found its way into the mammalian literature (Grillner, 1975). As evidenced at this symposium, however, the concept has also stirred considerable debate. Given the importance of the topic and the incompleteness of existing data on such neurons, this debate is both inevitable and desirable. As I hope to show in this chapter, such debate can help to clarify our thinking on the subject of the command neuron and can also illuminate fruitful areas for future research.

The Command Neuron

1

Sensory reception in the molluscPleurobranchaea californica was studied in whole animals and surgically reduced preparations by delivering chemical and mechanical stimuli while observing behavior or recording extracellularly the responses of the corresponding nerves Sensory structures studied included the rhinophores, tentacles and oral veil




2

Specimens reliably (50% or more) exhibited feeding responses to 10 of 18 amino acids tested (Table 1), including alanine and glycine In 14 electrophysiological experiments on the rhinophore, medium to high centripetal responses to alanine and/or glycine were obtained in 7 preparations (Fig 2), while little or no response was obtained in 7 preparations Responses to different amino acids were sometimes mediated by the same centripetal unit (Fig 2)




3

The rhinophore nerves showed vigorous excitatory responses to variations in the salt concentration (Figs 3, 4), osmolarity (Figs 5, 6), and pH (Figs 7, 8) of sea water solutions directed onto the rhinophore sensory epithelium The rhinophore and tentacle nerves showed strong excitatory responses to various salt solutions directed onto the corresponding sensory structure, including 1 osmolar NaCl, NaBr, NaI, Na2SO4 and KCl, but not LiCl (Table 2) Curves relating extracellular discharge to stimulus strength typically showed a minimum in the physiological range and increases to either side of this range (Figs 4, 8)




4

All nerves studied showed excitatory responses to stimulation with mechanical stimuli (Figs 9–11) Maps of receptive fields of different nerves (Fig 10) delineated areas of functional innervation for each nerve and showed little overlap The same centripetal unit(s) typically responded to mechanostimulation of a wide peripheral area (Fig 11)




5

All nerves studied showed excitatory responses to application of liquefied food substances to the sensory structures (Figs 12–15) Dose response curves for different food stimuli (Fig 13) were similar except at higher stimulus strengths, where mean discharge rates were significantly different for different foods These and other data furnish neurophysiological evidence for discrimination between different food stimuli, as suggested also by earlier behavioral studies (Davis et al 1980)




6

For all stimuli, severing the afferent nerves leading from the peripheral sensory epithelium abolished electrophysiological responses Therefore the responses observed were mediated by the sensory epithelium rather than by direct stimulation of peripheral ganglia or nerves




7

It is concluded that the rhinophores, tentacles and oral veil participate not only in food detection but also have the sensory capacity to detect changes in several other environmental parameters The data are consistent with the hypothesis that incoming afferent information is processed by peripheral ganglia before it is relayed centrally

William J. Davis

Papers

Control of feeding motor output by paracerebral neurons in brain of Pleurobranchaea californica

Motor organization and generation of rhythmic feeding output in buccal ganglion of Pleurobranchaea.

Behavioral choice and habituation in the marine mollusk Pleurobranchaea californica MacFarland (Gastropoda, Opisthobranchia)

The Command Neuron

Chemoreception and mechanoreception in the gastropod molluscPleurobranchaea californica