Ken Lukowiak

Presynaptic action of neuropeptide Y in area CA1 of the rat hippocampal slice.

1. Neuropeptide tyrosine (neuropeptide Y, NPY), a recently isolated endogenous brain peptide, reduces the extracellular population spike evoked by stimulation of stratum radiatum in area CA1 of the in vitro rat hippocampal slice, without reducing the antidromically evoked population spike. To test the hypothesis that NPY acts presynaptically, intracellular recordings were made of pyramidal neurones of area CA1 in vitro. 2. Bath application of 10(‐6) M‐NPY causes a long‐lasting (1‐1.5 h), reversible reduction of the orthodromically evoked excitatory post‐synaptic potential (e.p.s.p.) recorded intracellularly from CA1 pyramidal neurones. This effect on the e.p.s.p. was dependent upon the concentration of NPY. 3. The resting membrane potential, slope input resistance, and action potential threshold, amplitude and duration of the CA1 pyramidal neurones were not affected by NPY. 4. The responses of CA1 pyramidal neurones to ionophoretic pulses of glutamate, applied to the dendrites during synaptic blockade, was also unaffected by NPY. 5. The evidence supports the hypothesis that NPY acts presynaptically in the CA1 region of hippocampus to reduce excitatory input to the pyramidal neurones.

Male-Female Conflict in a Simultaneous Hermaphrodite Resolved by Sperm Trading

On decrit le mode de copulation de Navanax inermis gastropode marin hermaphrodite et on le compare au systeme copulateur du poisson Hypoplectrus

Intermediate and long-term memories of associative learning are differentially affected by transcription Versus translation blockers in Lymnaea

SUMMARY Aerial respiratory behaviour in the pond snail, Lymnaea stagnalis, can be operantly conditioned. This associative learning then undergoes consolidation into a long-lasting memory which, depending on the training procedure used, causes intermediate-term memory (ITM; lasting 3 h) or long-term memory (LTM; lasting >6 h) to be formed. We determined the differential susceptibility of these two forms of memory to translation and transcription blockers. The injection of a translation blocker, Anisomycin, 2.5 h before training prevents the establishment of both ITM and LTM. On the other hand, injection of the transcription blocker Actinomycin D, 2.5 h before training, did not prevent the establishment of ITM, but did, however, prevent LTM formation. Thus in Lymnaea, following associative learning, both ITM and LTM are dependent on new protein synthesis. ITM appears to be dependent on protein synthesis from preexisting transcription factors, whilst LTM is dependent on protein synthesis from new transcription messages.

In Vitro Synaptogenesis between the Somata of Identified Lymnaea Neurons Requires Protein Synthesis But Not Extrinsic Growth Factors or Substrate Adhesion Molecules

Nerve growth factors, substrate and cell adhesion molecules, and protein synthesis are considered necessary for most developmental programs, including cell proliferation, migration, differentiation, axogenesis, pathfinding, and synaptic plasticity. Their direct involvement in synapse formation, however, has not yet been fully determined. The neurite outgrowth that precedes synaptogenesis is contingent on protein synthesis, the availability of externally supplied growth factors, and substrate adhesion molecules. It is therefore difficult to ascertain whether these factors are also needed for synapse formation. To examine this issue directly we reconstructed synapses between the cell somata of identified Lymnaeaneurons. We show that when paired in the presence of brain conditioned medium (CM), mutual inhibitory chemical synapses between neurons right pedal dorsal 1 (RPeD1) and visceral dorsal 4 (VD4) formed in a soma–soma configuration (86%; n = 50). These synapses were reliable and target cell specific and were similar to those seen in the intact brain. To test whether synapse formation between RPeD1 and VD4 required de novo protein synthesis, the cells were paired in the presence of anisomycin (a nonspecific protein synthesis blocker). Chronic anisomycin treatment (18 hr) after cell pairing completely blocked synaptogenesis between RPeD1 and VD4 (n = 24); however, it did not affect neuronal excitability or responsiveness to exogenously applied transmitters (n = 7), nor did chronic anisomycin treatment affect synaptic transmission between pairs of cells that had formed synapses (n = 5). To test the growth and substrate dependence of synapse formation, RPeD1 and VD4 were paired in the absence of CM [defined medium; (n = 22)] on either plain plastic culture dishes (n = 10) or glass coverslips (n = 10). Neither CM nor any exogenous substrate was required for synapse formation. In summary, our data provide direct evidence that synaptogenesis in this system requires specific, cell contact-induced, de novo protein synthesis but does not depend on extrinsic growth factors or substrate adhesion molecules.

Neuropeptide Y reduces orthodromically evoked population spike in rat hippocampal CA1 by a possibly presynaptic mechanism

Application of the brain neuropeptide Y (NPY) to rat hippocampus in vitro reversibly reduced the amplitude of the CA1 population spike evoked by stratum radiatum stimulation. Threshold for the effect was 10(-8) M. NPY had similar effects on single pulse- and paired pulse-evoked population spikes. Antidromic population spikes, evoked from the alveus, were unaffected by NPY. Thus, NPY appears to modulate excitatory transmission in the hippocampus by a presynaptic mechanism.

Nitric oxide synthase-immunoreactive cells in the CNS and periphery of Lymnaea

The presence and distribution of nitric oxide synthase (NOS) in the CNS and peripheral organs (buccal muscles, oesophagus, salivary glands, foot, mantle and pneumostome) of the pulmonate mollusc, Lymnaea stagnalis were studied using an antiserum developed against rat cerebellar NOS. NOS-immunopositive neurones in Lymnaea were localized predominantly in the buccal ganglia as well as in distinct areas of the cerebral and suboesophageal ganglia. NOS-immunoreactive terminals were also found on the somata of some central neurones. In the periphery, NOS-immunostaining was detected only in a few neurones in the pneumostome area and in the osphradial ganglion. In addition, approximately 100 NOS-immunopositive cells have been found in the salivary glands. Our data supports other recent reports indicating that NO may be a signal molecule in the CNS of molluscs.

9YExtinction: Does It or Doesn’t It? The Requirement of Altered Gene Activity and New Protein Synthesis

Many accounts of memory suggest that an initial learning experience initiates a cascade of cellular and molecular events that are required for the consolidation of memory from a labile into a more permanent state. Studies of memory in many species have routinely found that altered gene activity and new protein synthesis are the critical components of this memory consolidation process. During extinction, when organisms learn that previously established relations between stimuli have been severed, new memories are formed and consolidated. However, the nature of the learning that underlies extinction remains unclear and there are many processes that may contribute to the weakening of behavior that occurs during extinction. In this review, we suggest that the molecular mechanisms that underlie extinction may differ depending on the learning process that is engaged by extinction. We review evidence that extinction, like initial learning, requires transcription and translation, as well as evidence that extinction occurs when protein synthesis is inhibited. We suggest that extinction occurs through the interaction of multiple behavioral and molecular mechanisms.

Predator detection in Lymnaea stagnalis.

SUMMARY Laboratory-reared Lymnaea are capable of detecting and responding to the scent of a crayfish predator. The present investigation is a first attempt to characterize multiple stress-related behavioural responses resulting from predator detection and to depict the neurophysiological correlates of one of these illustrated behaviours. Snails respond to crayfish effluent (CE) by increasing the following behaviours: aerial respiration, exploratory/searching phase and sensitivity to the shadow-elicited full-body withdrawal response. In contrast, when snails detect CE they decrease both their righting response time when dislodged from the substratum and their basal cutaneous oxygen consumption. Interestingly, basal heart rate does not change in response to CE exposure. Finally, we directly measured the activity of the neuron that initiates aerial respiratory behaviour, RPeD1, in semi-intact preparations. Naïve snails exposed to CE prior to recording demonstrated both a significantly reduced spontaneous firing rate and fewer bouts of bursting activity compared with non-exposed snails. These data show that laboratory-reared Lymnaea that have never experienced a natural predator are still capable of detecting and responding to the presence of a historically sympatric predator. These data open a new avenue of research, which may allow a direct investigation from the behavioural to the neuronal level as to how an ecologically relevant stressful stimulus alters behaviour.

Impairing Forgetting by Preventing New Learning and Memory

Two causes of forgetting have been promulgated: memory trace decay and retroactive interference. The authors show that forgetting is an active process requiring both new learning and memory. In the present (1)Lymnaea model system, prevention of new learning of a conflicting association, inhibition of memory consolidation, or Right Pedal Dorsal 1 soma ablation, which blocks LTM formation, are all potent means to prevent forgetting. Thus procedures that alter the ability to learn or form memory of a new conflicting aerial respiratory association prevent forgetting of a learned associative behavior. These results are the 1st demonstration in any model system that forgetting requires the soma of a single neuron.

Electrophysiological and Behavioral Evidence Demonstrating That Predator Detection Alters Adaptive Behaviors in the Snail Lymnaea

Stress has been shown to both impair and enhance learning, long-term memory (LTM) formation, and/or its recall. The pond snail, Lymnaea stagnalis, both detects and responds to the scent of a crayfish predator with multiple stress-related behavioral responses. Using both behavioral and electrophysiological evidence, this investigation is a first attempt to characterize how an environmentally relevant stressor (scent of a predator) enhances LTM formation in Lymnaea. Using a training procedure that, in “standard” pond water (PW), results in an intermediate-term memory that persists for only 3 h, we found that training snails in “crayfish effluent” (CE) induces a memory that persists for 48 h (i.e., its now an LTM). In addition, if we use a training procedure that in PW produces an LTM that persists for 1 d, we find that snails trained in CE have an LTM that persists for at least 8 d. Furthermore, we describe how a single neuron (RPeD1), which has been shown to be a necessary site for LTM formation, reflects the behavioral changes in its firing properties that persist for the duration of the LTM. Finally, Lymnaea exhibit context-specific memory, that is, when a memory is formed in a specific context (food odorant), it is only recalled in that context. Here, we found that snails trained in CE demonstrate context generalization, that is, memory is recalled in multiple contexts. All data are consistent with the hypothesis that learning in a stressful, yet biologically relevant, environment enhances LTM and prolongs its retention.