Age-related patterns of care: evidence against ageism in the treatment of early-stage breast cancer

PURPOSE

To assess whether the use of adjuvant systemic therapy in postmenopausal women with early-stage breast cancer is influenced by patient age.

METHODS

A retrospective cohort study based on data collected from medical records and from patients and their surgeons was performed among 746 postmenopausal patients diagnosed with early-stage breast cancer at 30 hospitals located throughout Minnesota. The adjusted odds of receiving hormonal therapy, chemotherapy, and both hormonal therapy and chemotherapy as a function of age was determined.

RESULTS

Among women with negative lymph nodes, 62% received some form of adjuvant drug therapy. For these women, the likelihood of receiving hormonal therapy or both hormonal therapy and chemotherapy did not vary with patient age and the likelihood of receiving chemotherapy declined with age. Among women with positive lymph nodes, 92% received some form of adjuvant therapy. For these women, the likelihood of receiving hormonal therapy increased with age and the likelihood of receiving chemotherapy declined with age, as did the likelihood of receiving both hormonal therapy and chemotherapy.

CONCLUSION

The observed associations between age and the use of adjuvant systemic therapy appear to reflect, in general, available information about treatment efficacy and do not suggest underuse among elderly women with early-stage breast cancer. The use of adjuvant therapy depends on clinical factors that predict the increased risk of metastases or the increased likelihood of response to treatment, rather than other sociodemographic factors. Our results also suggest that younger postmenopausal women with positive lymph nodes compared with older women may be undertreated with respect to tamoxifen because of the substitution of chemotherapy for hormonal therapy.

Neural correlates of habituation of the proleg withdrawal reflex in larvae of the hawk moth, Manduca sexta

The larval proleg withdrawal reflex of the hawk moth, Manduca sexta, exhibits robust habituation. This reflex is evoked by deflecting one or more mechanosensory planta hairs on a proleg tip. We examined neural correlates of habituation in an isolated proleg preparation consisting of one proleg and its segmental ganglion. Repeated deflection of a single planta hair caused a significant decrease in the number of action potentials evoked in the proleg motor nerve (which carries the axons of proleg retractor motor neurons). Significant response decrement was seen for interstimulus intervals of 10 s, 60 s and 5 min. Response decrement failed to occur in the absence of repetitive stimulation, the decremented response recovered spontaneously following a rest, and electrical stimulation of a body wall nerve facilitated the decremented response (a neural correlate of dishabituation). Adaptation of sensory neuron responses occurred during repeated hair deflections. However, when adaptation was eliminated by direct electrical stimulation of sensory neurons, the response in the proleg motor nerve still decreased significantly. Muscle recordings indicated that the response of an identified proleg retractor motor neuron decreased significantly during habituation training. Thus, habituation of the proleg withdrawal reflex includes a central component that is apparent at the level of a single motor neuron.

Decision analysis--effects of prophylactic mastectomy and oophorectomy on life expectancy among women with BRCA1 or BRCA2 mutations

BACKGROUND

Women with BRCA1 or BRCA2 mutations have an increased risk of breast cancer and ovarian cancer. Prophylactic mastectomy and oophorectomy are often considered as ways of reducing these risks, but the effect of the procedures on life expectancy has not been established.

METHODS

In a decision analysis, we compared prophylactic mastectomy and prophylactic oophorectomy with no prophylactic surgery among women who carry mutations in the BRCA1 or BRCA2 gene. We used available data about the incidence of cancer, the prognosis for women with cancer, and the efficacy of prophylactic mastectomy and oophorectomy in preventing breast and ovarian cancer to estimate the effects of these interventions on life expectancy among women with different levels of risk of cancer.

RESULTS

We calculated that, on average, 30-year-old women who carry BRCA1 or BRCA2 mutations gain from 2.9 to 5.3 years of life expectancy from prophylactic mastectomy and from 0.3 to 1.7 years of life expectancy from prophylactic oophorectomy, depending on their cumulative risk of cancer. Gains in life expectancy decline with age at the time of prophylactic surgery and are minimal for 60-year-old women. Among 30-year-old women, oophorectomy may be delayed 10 years with little loss of life expectancy.

CONCLUSIONS

On the basis of a range of estimates of the incidence of cancer, prognosis, and efficacy of prophylactic surgery, our model suggests that prophylactic mastectomy provides substantial gains in life expectancy and prophylactic oophorectomy more limited gains for young women with BRCA1 or BRCA2 mutations.

Steroid hormones act directly to trigger segment-specific programmed cell death of identified motoneurons in vitro

In larvae of the hawkmoth, Manduca sexta, accessory planta retractor (APR) motoneurons undergo a segment-specific pattern of programmed cell death at pupation. APR death is triggered hormonally by the prepupal peak of the ecdysteroid, 20-hydroxyecdysone (20-HE). Previous studies found no evidence that cellular interactions regulate the segmental pattern of APR death in vivo. To test the hypothesis that 20-HE acts directly on APRs to trigger a cell-autonomous, segment-specific pattern of death, APRs were labeled with the fluorescent dyes DiI or DiA, removed from the nervous system before the prepupal peak, and placed in low-density cell culture. Physiological levels of 20-HE triggered the same segment-specific pattern of APR death in vitro as seen in vivo, both in cultures containing a single APR and in cultures containing two APRs removed from the same donor animal. The presence or absence of contact with other cells did not influence the APRs' responses to 20-HE. The death of APRs in culture was characterized by fragmentation or rounding up of the cell body and fragmentation of the neurites. These findings suggest that intrinsic segmental identity regulates whether these motoneurons live or die when exposed to a steroid hormone during development.

Patient preferences concerning the trade-off between the risks and benefits of routine radiation therapy after conservative surgery for early-stage breast cancer

PURPOSE

To assess patients' preferences regarding the trade-off between risks and benefits of radiation therapy after conservative surgery for early-stage breast cancer.

PATIENTS AND METHODS

Utilities (measures of preference) of 97 early-stage breast cancer patients treated with conservative surgery and radiation therapy and 20 medical oncology nurses were assessed for five health states using standard gambles.

RESULTS

Patients had the highest mean utility for treatment with conservative surgery and radiation therapy without a local recurrence (0.92), intermediate utilities for treatment with conservative surgery alone followed either by no local recurrence or by a local recurrence salvaged by conservative surgery and radiation therapy (0.88 and 0.87, respectively), and the lowest utilities for treatment with or without radiation therapy followed by a local recurrence salvaged by mastectomy and reconstructive surgery (0.82 and 0.81, respectively). All differences between health states' utilities were significant (P < .0001), except between the two intermediate and two lowest rated health states. None of the clinical or sociodemographic factors examined explained more than 5% of the variability in the patients' utilities or their differences. Nurses' utilities were similar to those of the patients.

CONCLUSIONS

These results strongly suggest that fear of a local recurrence and an actual local recurrence leading to mastectomy have such a negative impact on quality of life that patients are willing to accept the risks and inconvenience of radiation therapy to avoid them. There is also considerable interpatient variability that was not explained by the clinical or sociodemographic factors examined.

Neural mechanisms of behavioral plasticity: metamorphosis and learning in Manduca sexta

This review summarizes our current understanding of the neural circuit underlying the larval proleg withdrawal reflex (PWR) of Manduca sexta and describes how PWR function changes in two contexts: metamorphosis and learning. The first form of PWR plasticity occurs during the larval-pupal transformation, when the reflex is lost. One mechanism that contributes to this loss is the weakening of monosynaptic excitatory connection from proleg sensory neurons to proleg retractor motor neurons. This change is associated with the hormonally-mediated regression of proleg motor neuron dendrites, which may break synaptic contacts between the sensory and motor neurons. After pupation, some of the proleg motor neurons die in a segment-specific pattern that persists even after individual motor neurons are isolated from the nervous system and exposed to hormones in vitro. The second form of PWR plasticity involves short-term, activity-dependent changes in neural function during the larval stage. The nicotinic cholinergic connections from proleg sensory neurons to motor neurons exhibit several forms of plasticity including facilitation, depression, post-tetanic potentiation and two types of muscarinic modulation. Larval PWR behavior exhibits two simple forms of learning-habituation and dishabituation-which involve alterations in the central PWR circuit. These studies of a simple circuit illustrate neural mechanisms by which behaviors undergo both short- and long-term modifications.

Target muscles and sensory afferents do not influence steroid-regulated, segment-specific death of identified motoneurons in Manduca sexta

Programmed cell death plays a critical role in sculpting the nervous system during embryonic development. In holometabolous insects, cell death also plays an important role in the reorganization of the nervous system during metamorphosis. In Manduca sexta, cell death and the factors that regulate it can be studied at the level of individually identified neurons. The accessory planta retractor (APR) motoneurons undergo segment-specific death during the larval-pupal transformation. APRs in abdominal segments 1, 5, and 6 die at pupation; those in abdominal segments 2, 3, and 4 survive until adulthood. Juvenile hormone and ecdysteroids regulate the metamorphic restructuring of the nervous system, but the factors that determine which APRs will live and which will die are not known. The present study assessed the possible importance of cell-cell interactions in determining APR survival at pupation by removing APR's target muscle or mechanosensory input early in the final larval instar, prior to the hormonal cues that trigger the larval-pupal transformation. The motoneurons showed their normal, segment-specific pattern of death in nearly all cases. These results suggest that target muscles and sensory input play little or no role in determining the segment-specific pattern of APR survival at pupation.

Habituation and dishabituation of the proleg withdrawal reflex in larvae of the sphinx hawk, Manduca sexta

The neural circuit for the proleg withdrawal reflex (PWR) of Manduca sexta larvae exhibits activity-dependent plasticity. This study demonstrates habituation and dishabituation of PWR behavior. Repeated deflection of 1 or 5 mechanosensory hairs on a proleg at a 60-s interstimulus interval (ISI) for 20 trials produced a significant decrease in evoked force of proleg withdrawal. Habituation was similar with 30-s and 60-s ISIs and nonsignificant with a 5-min ISI or without repeated stimulation. Habituated responses recovered after cessation of stimulation or pinch of the body wall (dishabituation). The role of intersegmental influences was tested by severing connectives to leave different numbers of ganglia connected to the test segment. Habituation was robust even in test segments that were disconnected from the rest of the central nervous system. The PWR of Manduca is appropriate for further analysis of cellular mechanisms underlying learning.

Use of hematopoietic colony-stimulating factors: the American Society of Clinical Oncology survey. The Health Services Research Committee of the American Society of Clinical Oncology

PURPOSE

Dissemination of use of the hematopoietic colony-stimulating factors (CSFs) is unprecedented in oncology, with almost all physicians having experience with granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF) shortly after the drugs received Food and Drug Administration (FDA) approval in 1991. The American Society of Clinical Oncology (ASCO) Health Services Research Committee sought to assess patterns of use of CSFs before dissemination of its first-ever publication of ASCO guidelines.

METHODS

A questionnaire describing clinical scenarios was mailed to American oncologists and hematologists who practice medical oncology. In each scenario, the physician was asked whether he would prefer to use a CSF to prevent or treat neutropenia.

RESULTS

The response rate to the mailed survey was 49% (N = 475). Most physicians preferred to use CSFs for secondary prophylaxis in patients receiving chemotherapy at rates of 44% to 85%, rather than reduce doses. Patterns of use did not differ for palliative, curative, or adjuvant chemotherapy. While the majority of CSF patterns of care were similar to those recommended in the ASCO guidelines, more than half of the physicians chose to use CSFs in the treatment of febrile neutropenia, an area not supported in the subsequent guidelines. In general, physicians at academic medical centers and in Health Maintenance Organization (HMO) practices were more likely to prefer dose-reduction strategies over addition of CSFs, while fee-for-service physicians preferred the opposite strategies.

CONCLUSION

Variations in CSF preferences for use were related to differences in clinical characteristics (history of afebrile v febrile neutropenia), drug characteristics (G-CSF or GM-CSF), and physician practice characteristics (HMO or fee-for-service setting). However, before dissemination of the guidelines, the majority of American oncologists preferred strategies that were subsequently included in the ASCO CSF guidelines. CSF guidelines would be most likely to reduce CSF use for treatment of afebrile and uncomplicated febrile neutropenia.

The initiation of pre-ecdysis and ecdysis behaviors in larval Manduca sexta: the roles of the brain, terminal ganglion and eclosion hormone

Each larval molt of Manduca sexta culminates in the sequential performance of pre-ecdysis (cuticle loosening) and ecdysis (cuticle shedding) behaviors. Both behaviors are thought to be triggered by the release of a peptide, eclosion hormone (EH), from brain neurons whose axons extend the length of the nervous system. EH bioactivity appears in the hemolymph at the onset of pre-ecdysis behavior, and EH injection can trigger pre-ecdysis and ecdysis behaviors prematurely. The present study examined the effects of removing or disconnecting portions of the central nervous system prior to the time of EH release on the initiation of pre-ecdysis and ecdysis behaviors at the final larval molt. We found that the initiation of pre-ecdysis abdominal compressions at the appropriate time required the terminal abdominal ganglion (AT) but not the brain; the initiation of pre-ecdysis proleg retractions at the appropriate time required neither the AT nor the brain; the initiation of ecdysis at the appropriate time usually required the brain but did not require the AT; and premature pre-ecdysis (but not ecdysis) could be elicited in isolated abdomens by injection of EH. Finally, pre-ecdysis behavior performed by brainless larvae was not associated with the normal elevation of EH bioactivity in the hemolymph or the normal loss of EH immunoreactivity from peripheral neurohemal release sites.

Novel dual innervation of a larval proleg muscle by two similar motoneurons in the tobacco hornworm Manduca sexta

In Manduca sexta, the accessory planta retractor muscle (APRM), which retracts the larval proleg, is innervated by two excitatory motoneurons, the accessory planta retractor motoneurons (APRs). These muscles and motoneurons have been the focus of a number of developmental and behavioral studies. The present study investigated properties of the pair of APRs that innervate each APRM and determined their pattern of innervation of APRM fibers. Members of APR pairs could not be distinguished by their anatomical or electrical properties (resting membrane potential, input resistance and spike threshold). Spontaneous synaptic inputs to members of APR pairs were highly correlated, whereas spontaneous synaptic inputs to APRs and functionally dissimilar motoneurons were not well correlated. Synaptic inputs from identified mechanosensory neurons and interneurons to the two APRs were qualitatively similar, but the magnitude of the response to sensory stimulation sometimes differed within a pair. Both APRs produced large, rapidly rising excitatory junction potentials in APRM fibers. Within the APRM, some fibers were singly innervated by one or the other APR while the remaining fibers were dually innervated by both APRs. In dually innervated fibers, the motor terminals of the two APRs were spatially segregated. This innervation pattern appears to be unique among insects and shares some properties with the innervation of vertebrate muscle.

Cell culture approaches to understanding the actions of steroid hormones on the insect nervous system

During metamorphosis of the hawkmoth, Manduca sexta, ecdysteroids regulate the dendritic remodeling and programmed death of identified motoneurons. These changes contribute to the dramatic reorganization of behavior that accompanies metamorphosis. As a step toward elucidating cellular and molecular mechanisms by which ecdysteroids affect neuronal phenotype, we have investigated the responses of Manduca motoneurons to ecdysteroids in vitro. Following dendritic regression at the end of larval life, thoracic leg motoneurons placed in culture respond to ecdysteroids by an increase in branching complexity, similar to events in vivo. Growth cone structure is affected markedly by ecdysteroids. At pupation, a rise in ecdysteroids triggers the segment-specific death of proleg motoneurons: the same segmental pattern of death is observed when motoneurons from different segments are removed from the nervous system and exposed to ecdysteroids in vitro. These studies provide strong evidence that Manduca motoneurons are direct targets of steroid action and set the stage for further studies of the specific mechanisms involved.

Steroid hormone effects on neurons subserving behavior

Recent advances in understanding effects of steroid hormones at the level of individual neurons have been achieved using model systems. Steroid hormone effects on dendritic morphology, synaptic function and ionic conductances have been implicated in the regulation of behavior in both vertebrates and invertebrates. Particularly exciting are studies demonstrating steroid hormone effects on specific synaptic connections and ionic currents. There also has been important progress in understanding the diversity of sites and mechanisms of hormone action, encompassing both genomic and non-genomic effects of steroids on neuronal properties.

Comparison of time-tradeoff utilities and rating scale values of cancer patients and their relatives: evidence for a possible plateau relationship

Because they are easy to administer, rating scales are often used as proxies for utility measures. The authors investigated the relationship between time-tradeoff utilities and rating scale values in two populations: 124 cancer patients asked to evaluate their current states of health and 102 relatives and close friends of cancer patients asked to evaluate health-state scenarios. None of the models tested effectively described the relationship between individual patients' rating scale values and time-tradeoff utilities for their current states of health. In contrast, both a plateau and a power-function model explained the variability in the responses of the relatives reasonably well (R2 = 0.56 and R2 = 0.58, respectively). Given that many respondents who were unwilling to trade off any time assigned rating scale values of well below 100, a plateau model may represent the best approach to adjusting rating scale values for health-state scenarios when it is not feasible to elicit time-tradeoff utilities.

Decreased monosynaptic sensory input to an identified motoneuron is associated with steroid-mediated dendritic regression during metamorphosis in Manduca sexta

The proleg withdrawal reflex of Manduca sexta larvae is mediated by mono- and polysynaptic connections from afferents innervating mechanosensory planta hairs (PHs) to ipsilateral proleg retractor motoneurons. During the larval-pupal transformation, a rise in ecdysteroids causes the dendrites of proleg motoneurons to regress and, concurrently, the proleg withdrawal reflex is lost. The objective of this study was to identify synaptic correlates of dendritic regression that contributed to this behavioral change. The accessory planta retractor (APR) motoneuron regresses during the larval-pupal transformation and dies in a segment-specific pattern after pupation. The compound excitatory postsynaptic potential (cEPSP) evoked in APR by electrically stimulating the proleg sensory nerve decreased in amplitude during the larval-pupal transformation. The developmental decrease in cEPSP amplitude, the extent of APR's regression, and several of APR's intrinsic electrical properties were similar in segments in which the motoneuron was fated to live or die. In heterochronic mosaic pupae bearing retained larval PH afferents, APR's dendritic regression was associated with decreases in both the mean amplitude of monosynaptic EPSPs produced by PH afferents and the proportion of PH afferents that produced detectable EPSPs. These changes appeared due to a developmental decrease in the size of the synaptic currents produced by PH afferents. Evidence was also obtained suggesting that PH afferents do not regress at pupation. These findings support the hypothesis that the ecdysteroid-mediated regression of proleg motoneuron dendrites disconnects them from sensory inputs and, thereby, contributes to the elimination of the proleg withdrawal reflex.

Using a pen-based computer to collect health-related quality of life and utilities information

We have developed a system that uses the Newton MessagePad technology as part of a client-client-server paradigm to collect health-related quality of life information from breast cancer patients attending an outpatient clinic at the Dana-Farber Cancer Institute. Patients are asked to fill out an electronic questionnaire on the Newton, which then uploads the information into the institution's Oracle database. The program consists of a separate questionnaire engine and question base, facilitating questionnaire design and allowing us to give different questionnaires to different patients dynamically. The results of a preliminary trial show excellent user-acceptance of the device. Finally, we present a general framework for such systems and discuss issues that developers must consider when implementing a pen-based computer project.

A single pair of interneurons controls motor neuron activity during pre-ecdysis compression behavior in larval Manduca sexta

Manduca sexta molts several times as a larva (caterpillar) before becoming a pupa and then an adult moth. Each molt culminates in ecdysis behavior, during which the old cuticle is shed. Prior to each larval ecdysis, the old cuticle is loosened by pre-ecdysis behavior, which includes rhythmic, synchronous compressions of the abdomen. A previous study indicated that motor neuron activity during pre-ecdysis compression behavior is driven by an ascending neural pathway from the terminal abdominal ganglion. The present study describes a pair of interneurons, designated IN-402, that are located in the terminal ganglion and belong to the ascending pathway. Each IN-402 is synchronously active with pre-ecdysis compression motor bursts, and bilaterally excites compression motor neurons throughout the abdominal nerve cord via apparently monosynaptic connections. The pair of IN-402s appears to be the sole source of rhythmic synaptic drive to the motor neurons during the pre-ecdysis compression motor pattern. These interneurons play a key role in the production of larval pre-ecdysis behavior, and are candidates for contributing to the developmental weakening of pre-ecdysis behavior at pupation.

Oral care of people with disability: a qualitative exploration of the views of nursing staff

This study aimed to identify influences, attitudes and actions of nursing staff in relation to oral care for people with disabilities. Individual in-depth interviews of twenty two nursing staff were conducted. Enabling and inhibiting factors in the reported attitudes, approaches and practices were identified. The main enabling factors were that nursing staff saw mouth care as part of their role and took an empathic and caring approach to its delivery. They aimed to make the residents socially acceptable, improve their self-esteem and make their mouths clean and breath fresher. Inhibiting factors were: a lack of training, time constraints associated with workload, and poor understanding of the processes causing dental disease. The study concludes that improvements in oral care by nursing staff can be encouraged by working with nurses' attitudes, values and beliefs. Once the desired behaviour change has occurred then the lack of knowledge can be addressed.

Influence of interganglionic interactions on steroid-mediated dendritic reorganization and death of proleg motor neurons during metamorphosis in Manduca sexta

In Manduca sexta, the larval abdominal prolegs and their muscles degenerate at pupation. The proleg motor neurons undergo a period of dendritic regression, after which a specific subset of them dies. The surviving motor neurons undergo dendritic outgrowth during pupal-adult development, and most die after adult emergence. All of these events are regulated hormonally by ecdysteroids and juvenile hormone, but interactions of the motor neurons with other cells may potentially contribute as well. To investigate the possible influence of interganglionic neural interactions, we chronically isolated individual abdominal ganglia by severing the adjacent rostral and caudal connectives in the larval stage. Subsequent metamorphic changes in proleg motor neurons were examined in the isolated ganglia and ganglia adjacent to the isolated ganglia. Two abnormalities were observed: (1) some imprecision in the timing of motor neuron death, both at pupation and after adult emergence, and (2) the growth of ectopic neurites outside the neuropil boundaries during pupal-adult development (in ganglia with or without neuromas caused by connective transections). Other aspects of proleg motor neuron metamorphosis, including the segment-specific death of motor neurons at pupation, were the same as that in intact and sham-operated insects. Thus, interganglionic interactions appear to play a relatively minor role in the steroid-mediated metamorphic transformation of proleg motor neurons.

Organization of the larval pre-ecdysis motor pattern in the tobacco hornworm, Manduca sexta

The tobacco hornworm, Manduca sexta, undergoes several larval molts before transforming into a pupa and then an adult moth. Each molt culminates in ecdysis, when the old cuticle is shed. Prior to each larval ecdysis, the old cuticle is loosened by pre-ecdysis behavior, which consists of rhythmic compressions that are synchronous along the abdomen and on both body sides, and rhythmic retractions of the abdominal prolegs. Both pre-ecdysis and ecdysis behaviors are triggered by a peptide, eclosion hormone. The aim of the present study was to investigate the neural circuitry underlying larval pre-ecdysis behavior. The pre-ecdysis motor pattern was recorded in isolated nerve cords from eclosion hormone-treated larvae, and the effects of connective transections and ionic manipulations were tested. Our results suggest that the larval pre-ecdysis compression motor pattern is coordinated and maintained by interneurons in the terminal abdominal ganglion that ascend the nerve cord without chemical synaptic relays; these interneurons make bilateral, probably monosynaptic, excitatory connections with identified pre-ecdysis motor neurons throughout the abdominal nerve cord. This model of the organization of the larval pre-ecdysis motor pattern should facilitate identification of the relevant interneurons, allowing future investigation of the neural basis of the developmental weakening of the pre-ecdysis motor pattern that accompanies the larval-pupal transformation.

Muscarinic acetylcholine receptors modulate the excitability of an identified insect motoneuron

1. With the use of an isolated, perfused ganglion preparation from the tobacco hornworm, Manduca sexta, we have examined the responses of an identified proleg retractor motoneuron (designated PPR) to trains of stimuli delivered to sensory branches of the ventral nerve (VN). 2. Trains of stimuli (50 Hz, 100 ms to 5 s) delivered to the proleg sensory nerve, VNA, caused PPR to depolarize and initiate a bout of spiking activity that outlasted the stimulus. A fast component of this response was due to monosynaptic input from planta hair sensory neurons, acting on nicotinic acetylcholine receptors (nAChRs). The fast response to VNA stimulation was abolished when the ganglion was treated with the nicotinic antagonist, mecamylamine, leaving a slow, long-lasting depolarization of PPR, which we have called the slow excitatory postsynaptic potential (sEPSP). 3. A sEPSP could be evoked by stimulation of all the major subbranches of VNA ipsilateral to PPR's cell body. Small sEPSPs were also evoked by stimulation of all but one of the major contralateral subbranches of VNA. 4. During a sEPSP the spike threshold of PPR became more negative. This increase in excitability was not correlated with changes in membrane potential measured at the cell body, and there was no detectable change in input resistance. We conclude that the spike-threshold change reflects either a depolarization electrically remote from the cell body, or a change in PPR's spike initiation properties that are not reflected in the membrane potential. 5. Both the sEPSP and the associated change in PPR's spike threshold were blocked by several muscarinic antagonists. Scopolamine was effective at concentrations > 2 x 10(-7) M, atropine at concentrations > 1 x 10(-6) M, and pirenzepine at 5 x 10(-5) M. 4-Diphenylacetoxy-N-methylpiperidine (4-DAMP), methoctramine, hexahydrosiladifenidol, and AF-DX 116 were all poor antagonists. 6. Bath application of the muscarinic agonist oxotremorine-M (oxo-M) at concentrations > 3 x 10(-7) M increased the spontaneous spiking activity of PPR and other proleg motoneurons. In PPR, this increased activity was accompanied by a small depolarization and a more negative spike threshold, both of which were inhibited by 1 x 10(-7) M scopolamine. 7. At concentrations > 6 x 10(-8) M, bath-applied oxo-M depolarized PPR even when spike activity in the ganglion was blocked with tetrodotoxin. During such spike blockage, pressure ejection of brief puffs of oxo-M into the neuropil evoked a long-lasting depolarization of PPR that resembled the sEPSP.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of a protein synthesis inhibitor on the hormonally mediated regression and death of motoneurons in the tobacco hornworm, Manduca sexta

The larval-pupal transformation of Manduca sexta is accompanied by the loss of the abdominal prolegs. The proleg muscles degenerate, the dendritic arbors of proleg motoneurons regress, and a subset of the proleg motoneurons dies. The regression and death of proleg motoneurons are triggered by the prepupal peak of ecdysteroids in the hemolymph. To investigate the possible involvement of protein synthesis in these events, we gave insects repeated injections of the protein synthesis inhibitor, cycloheximide (CHX), during the prepupal peak. Examination of insects 3-5 days following CHX treatment showed that CHX inhibited the death of proleg motoneurons and the production of pupal cuticle in a dose-dependent fashion. When insects were allowed to survive for 10 days after the final CHX injection, motoneuron death and pupal cuticle production sometimes occurred belatedly, apparently in response to the ecdysteroid rise that normally triggers adult development. CHX treatments that inhibited motoneuron death were less effective in inhibiting dendritic regression in the same neurons. In another set of experiments, abdomens were isolated from the ecdysteroid-secreting glands prior to the prepupal peak, and infused with 20-hydroxyecdysone (20-HE). Single injections of CHX delivered just prior to the start of the 20-HE infusion inhibited motoneuron death and pupal cuticle production, but in the range of doses tested, did not prevent dendritic regression. Our findings suggest that protein synthesis is a required step in the steroid-mediated death of proleg motoneurons, and that dendritic regression is less susceptible to inhibition by CHX than is motoneuron death.

Hormonal regulation and segmental specificity of motoneuron phenotype during metamorphosis of the tobacco hornworm, Manduca sexta

The abdominal prolegs of Manduca sexta larvae are eliminated at the onset of metamorphosis. Previous work showed that the prepupal peak of ecdysteroids in the hemolymph causes the dendritic arbors of proleg motoneurons to regress and a stereotyped subset of the motoneurons to die. In the present study we investigated the parameters of ecdysteroid exposure that are important for eliciting these responses by directly infusing 20-hydroxyecdysone (20-HE) into the hemolymph of insects deprived of their own endocrine glands. Doses of 20-HE that were near threshold for evoking regression or death were consistently more effective when infused over a longer duration. Theoretical calculations of hemolymph hormone profiles produced by the infusions support a model of ecdysteroid action in which the hormone concentration must remain above a threshold level for a critical duration of time to be physiologically effective. We further found that segmental location can influence both the metamorphic fate and the hormonal sensitivity of Manduca motoneurons.

Cost effectiveness of prophylactic intravenous immune globulin in chronic lymphocytic leukemia

BACKGROUND

A recent randomized controlled trial of intravenous immune globulin in patients with chronic lymphocytic leukemia and hypogammaglobulinemia demonstrated a statistically significant reduction in the rate of bacterial infections among patients who received intravenous immune globulin. We used decision-analysis techniques to determine whether prophylactic intravenous immune globulin is likely to result in an overall clinical benefit to patients who receive this treatment and to examine its cost effectiveness.

METHODS

We constructed a model to compare two strategies: treatment with intravenous immune globulin at a dose of 400 mg per kilogram of body weight every three weeks and no immune globulin therapy. Baseline estimates of the efficacy of intravenous immune globulin were derived from the published results of the randomized trial. The costs of treatment, complications, and infections were estimated on the basis of component costs. Health outcomes were measured in terms of gains in quality-adjusted life expectancy.

RESULTS

Intravenous immune globulin therapy can result in a loss of quality-adjusted life expectancy when the inconvenience of treatment is taken into account. If the inconvenience of treatment is not considered, therapy results in a gain of 0.8 quality-adjusted days per patient per year of therapy at a cost of $6 million per quality-adjusted life-year gained.

CONCLUSIONS

Decision-analysis modeling may be applied to the results of randomized controlled trials to assess the potential clinical and financial effects of adopting the intervention in medical practice. In the case of intravenous immune globulin therapy in patients with chronic lymphocytic leukemia and hypogammaglobulinemia, this type of analysis suggests that treatment might not result in improved quality or length of life and that it is extraordinarily expensive in comparison with other treatments generally accepted as cost effective.

Value of follow-up procedures in patients with large-cell lymphoma who achieve a complete remission

Salvage therapy for relapsed large-cell lymphoma (LCL) is more effective in patients with minimal disease, suggesting that early detection of relapse might increase the chance of long-term survival. To determine whether current follow-up procedures are effective in identifying preclinical disease, we analyzed patterns of relapse in 139 LCL patients who achieved a complete remission (CR) with high/moderate-dose methotrexate with leucovorin, bleomycin, doxorubicin, cyclophosphamide, vincristine, and dexamethasone (M/m-BACOD). The timing and results of all posttreatment follow-up tests were examined in the 36 patients who relapsed from complete remission (CR) and 46 controls who remain in CR. Despite conscientious posttreatment follow-up, only two of the 36 relapses (6%) were detected before the development of symptoms. Sixty-seven percent of patients relapsed in new disease sites (42% in new and old sites, and 25% in new sites only). Consistent with this observation, the tests most sensitive to clinical relapse were those not targeted to specific sites of disease: gallium scan (sensitivity, 90%), physical examination (80%), and lactate dehydrogenase (LDH) (65%). Of screening tests performed, only LDH was successful in detecting preclinical relapse, with a sensitivity of 42% and specificity of 85% for impending symptomatic relapse. These results indicate that conventional screening was ineffective in detecting preclinical relapse in LCL patients. We recommend prospective evaluation of a strategy that (1) screens with a frequency appropriate to a patient's risk of relapse, (2) uses sensitive test(s) not targeted to specific sites, and (3) limits aggressive screening to those high-risk patients eligible for potentially curative salvage therapy.

Reidentification of larval interneurons in the pupal stage of the tobacco hornworm, Manduca sexta

The abdominal prolegs are the primary locomotory appendages of Manduca sexta larvae. After the prolegs are lost at pupation, some of the proleg motoneurons die while the survivors are respecified to carry out different functions in the adult moth. As a first step toward investigating the process of functional respecification at the synaptic level, we searched for larval interneurons that affected the activity of proleg motoneurons, and followed these interneurons into the pupal stage. Interneurons were judged to be individually identifiable based on their effects on proleg motoneuron activity and their anatomical features. Seven larval interneurons were identified and placed in five physiological classes based on their effects on proleg motoneurons: ipsilateral excitors, contralateral excitors, ipsilateral inhibitors, contralateral inhibitors, and bilateral inhibitor-excitors. Four of the larval interneurons produced apparently monosynaptic postsynaptic potentials in proleg motoneuron. Of the five larval interneurons that were reidentified in the early pupal stage, two showed minor but consistent structural modifications from the larval stage. Interneurons that produced unitary postsynaptic potentials in larval motoneurons continued to do so in pupal motoneurons. These studies demonstrate that individually identified interneurons can be followed through the larval-pupal transformation, during the initial stages of motoneuron respecification.

Developmental attenuation of the pre-ecdysis motor pattern in the tobacco hornworm, Manduca sexta

At the culmination of each molt, the larval tobacco hornworm exhibits a pre-ecdysis behavior prior to shedding its old cuticle at ecdysis. Both pre-ecdysis and ecdysis behaviors are triggered by the peptide, eclosion hormone (EH). Pre-ecdysis behavior consists of rhythmic abdominal compressions that loosen the old larval cuticle. This behavior is robust at larval molts, but at the larval-pupal molt the only comparable behavior consists of rhythmic dorso-ventral flexions of the anterior body. These flexions appear to be an attenuated version of the larval pre-ecdysis behavior because (1) they show the same EH dependence, and (2) the motor patterns recorded from EH treated, deafferented larval and pupal preparations are similar except that the pupal pattern is much weaker. Both patterns are characterized by rhythmic, synaptically-driven bursts of action potentials in motoneurons MN-2 and MN-3, which occur synchronously in all segments. However, the synaptic drive to the motoneurons and their resultant levels of activity are reduced during the pupal pre-ecdysis motor pattern, especially in posterior abdominal segments. Although the dendritic arbors of both motoneurons regress somewhat during the larval-pupal transformation, this does not appear to be the primary source of diminished synaptic drive because regression is greatest in the segments in which synaptic inputs remain the strongest. The developmental weakening of the pre-ecdysis motor pattern thus may be due to changes at the interneuronal level.

Activity-dependent induction of facilitation, depression, and post-tetanic potentiation at an insect central synapse

In Manduca sexta larvae, sensory neurons innervating planta hairs on the tips of the prolegs make monosynaptic excitatory connections with motoneurons innervating proleg retractor muscles. Tactile stimulation of the hairs evokes reflex retraction of the proleg. In this study we examined activity-dependent changes in the amplitude of the excitatory postsynaptic potentials (EPSPs) evoked in a proleg motoneuron by stimulation of individual planta hair sensory neurons. Deflection of a planta hair caused a phasic-tonic response in the sensory neuron, with a mean peak instantaneous firing frequency of greater than 300 Hz, and a tonic firing rate of 10-20 Hz. Direct electrical stimulation was used to activate individual sensory neurons to fire at a range of frequencies including those observed during natural stimulation of the hair. At relatively low firing rates (e.g., 1 Hz), EPSP amplitude was stable indefinitely. At higher instantaneous firing frequencies (greater than 10 Hz), EPSPs were initially facilitated, but continuous stimulation led rapidly to synaptic depression. High-frequency activation of a sensory neuron could also produce post-tetanic potentiation, in which EPSP amplitude remained elevated for several min following a stimulus train. Facilitation, depression, and post-tetanic potentiation all appeared to be presynaptic phenomena. These activity-dependent changes in sensory transmission may contribute to the behavioral plasticity of the proleg withdrawal reflex observed in intact insects.

Hormonally mediated changes in simple reflex circuits during metamorphosis in Manduca

During insect metamorphosis, the nervous system must be reorganized to allow the production of unique behaviors during each life stage. In the hawkmoth, Manduca sexta, it has been possible to follow this postembryonic phase of neuronal development at the level of identified neurons. Of particular interest in the present context are sensory neurons, motoneurons, and interneurons which persist through metamorphosis, but participate in different types of behavior at different stages of life. Many of these neurons undergo striking changes in their dendritic arborizations and axonal projection patterns, which can be correlated with changes in their synaptic interactions with other neurons. Manipulations of the ecdysteroid and juvenile hormone titers, both in vivo and in vitro, implicate these hormones in the regulation of metamorphic changes within the nervous system. Taking advantage of this endocrine control, it has been possible to create heterochronic mosaic animals that allow the relationship between specific cellular changes and behavioral alterations to be tested directly.

Postsynaptic changes at a sensory-to-motoneuron synapse contribute to the developmental loss of a reflex behavior during insect metamorphosis

The larval-pupal transformation of the tobacco hornworm, Manduca sexta, involves the loss of many larval-specific behaviors, including a simple withdrawal reflex of the abdominal prolegs. This reflex is mediated by monosynaptic excitatory connections between afferents that innervate mechanosensory hairs on the proleg [the planta hairs (PHs)] and motoneurons that innervate proleg retractor muscles. In response to hormonal cues during the final days of larval life, the dendritic arbors of proleg retractor motoneurons regress extensively. Intracellular recordings indicate that the synaptic depolarization evoked in proleg motoneurons by electrical stimulation of PH afferents decreases by 78% during the larval-pupal transformation, over the same time course that the motoneuron dendrites regress. During the same period the number of PH afferents and the extent of their central projections may decrease slightly. To test the relative contributions of developmental changes in the presynaptic afferents and postsynaptic motoneurons to the weakening of the reflex pathway, we generated heterochronic mosaic pupae that retained one larval proleg. The PH afferents on the retained proleg retained their larval characteristics while their postsynaptic targets, the proleg motoneurons, appeared to regress normally. In the mosaic hemisegments, electrical stimulation of PH afferents evoked only a small synaptic depolarization of the proleg motoneurons, similar in amplitude to that recorded in normally developing pupae; thus, the developmental status of the afferents was irrelevant to the loss of the reflex. These findings suggest that postsynaptic changes, e.g., structural regression of motoneuron dendrites, may cause the weakening of the reflex pathway. This is the first demonstrated correlation between the hormonally mediated regression of motoneuron dendrites and the loss of a specific behavior during metamorphosis.

Respecification of larval proleg motoneurons during metamorphosis of the tobacco hornworm, Manduca sexta: segmental dependence and hormonal regulation

The principal locomotory appendages of the Manduca sexta caterpillar, the prolegs, are present on the third through sixth abdominal segments (anal prolegs located on the terminal segment were not included in this study). Previous studies have characterized some of the proleg retractor muscles and their motoneurons. In the present study we identified additional proleg motoneurons and their putative homologs in the non-proleg-bearing segments. One of the motoneurons present in the proleg-bearing segments is absent in the non-proleg-bearing segments. At pupation the prolegs are lost, their muscles degenerate, and some of their motoneurons regress structurally. Subsequently, subsets of the proleg motoneurons and their homologs in other segments die in a segment-specific pattern. This is the first report of segment-specific motoneurons, and of segment-specific death of identified motoneurons, in Manduca. During adult development the surviving proleg motoneurons innervate the tergosternal muscle (TSM) and grow bilateral dendritic arbors. Dendritic growth is completed by about the 12th of the 18 days of adult development. Following adult emergence all but one of the respecified proleg motoneurons dies. The hormonal dependence of dendritic outgrowth was tested by isolating abdomens to eliminate the ecdysteroid-secreting glands in the thorax. Between the second and fifth days after pupation the motoneurons became progressively more competent to undergo dendritic outgrowth following abdomen isolation. The extent of dendritic outgrowth paralleled the degree of morphological development attained by isolated abdomens. It is concluded that ecdysteroids are required for motoneuron outgrowth, but our findings suggest that, unless an abdominal source of ecdysteroids exists in pupae, a relatively small exposure may be sufficient.

Somatotopic mapping of sensory neurons innervating mechanosensory hairs on the larval prolegs of Manduca sexta

The abdominal prolegs are the principal locomotory appendages of the larval tobacco hornworm, Manduca sexta. The prolegs bear numerous mechanosensory bristle sensilla, each innervated by an afferent neuron that arborizes within the central nervous system (CNS). Based on their positions on the proleg, we have divided the sensilla into planta hairs (PHs), lateral hairs (LHs), and medial hairs (MHs). Previously, we found that PH afferents produce monosynaptic excitatory postsynaptic potentials (EPSPs) in proleg retractor muscle motoneurons, the size of which depends on the position of the hair in the PH array. In this paper we examined the central arbors of the proleg afferents to determine whether there was an anatomical correlate to the pattern of synaptic strengths. We found that the afferent arbors are arranged somatotopically within the CNS in a pattern similar to that for bristle afferents elsewhere on the abdomen; i.e., the anterior-posterior and medial-lateral position of a hair on the proleg was reflected in the location of the afferent arbor along the corresponding axes within sensory neuropil. All afferents terminated within a similar ventral region of neuropil. The arbors of PH, MH, and to a lesser extent, LH afferents, were enlarged as compared to afferents innervating hairs elsewhere on the abdomen. This feature, combined with the dense innervation of the proleg, causes the proleg region to be relatively overrepresented in sensory neuropil. We also examined the afferents innervating a pair of ventral midline hairs (VMHs) present in each abdominal segment, which, unlike the other afferents, showed segment-specific central arbors. We conclude that the somatotopic mapping of afferent arbors may contribute to the specificity of synaptic connections in this system.

Time course of hormonal independence for developmental events in neurons and other cell types during insect metamorphosis

The ecdysteroid dependence of developmental events during the larval-pupal transformation of the tobacco hornworm, Manduca sexta, was studied using the technique of abdomen ligation to eliminate the ecdysteroid-secreting prothoracic glands (PTG) in the thorax. The time at which a particular developmental event no longer required the presence of the PTG for its successful completion, i.e., when the event became ecdysteroid independent, was determined for the dendritic regression and death of proleg motor neuron PPR, the degeneration of its target muscle PPRM, and the secretion of pupal cuticle by the abdominal epidermis. Groups of abdomens were ligated from synchronously developing larvae at 12-hr intervals over the 4-day period preceding entry into the pupal stage. PPR's dendritic regression became ecdysteroid independent over the first 24 hr of this period. When abdomens were ligated midway through this period PPR became arrested in a partially regressed state. Twelve hours after PPR's regression became independent, the degeneration of PPRM and the secretion of pupal cuticle by the epidermis acquired independence. Another 12 hr elapsed before PPR's programmed death became independent. Thus, different developmental events acquired ecdysteroid independence in a stereotyped temporal sequence, and even different events within a single cell, i.e., PPR's regression and death, became independent at different times.

A reflex behavior mediated by monosynaptic connections between hair afferents and motoneurons in the larval tobacco hornworm, Manduca sexta

In the tobacco hornworm caterpillar, tactile stimulation of sensory hairs located on the tip of a proleg (the planta) evokes ipsilateral or bilateral retraction of the prolegs in that segment. We have used electrophysiological and anatomical methods to investigate the excitatory neural pathways linking the planta hair afferents and the proleg retractor motoneurons (MNs). An important technical innovation was the development of an isolated proleg and desheathed ganglion preparation that permits rapid and reversible ionic manipulations and drug applications. Action potentials (spikes) in individual planta hair afferents produce time-locked excitatory postsynaptic potentials (EPSPs) in ipsilateral proleg MNs which appear to be chemically-mediated and monosynaptic: the EPSPs have a short and constant latency, they follow afferent spikes without failure, they are reversibly abolished in elevated Mg++ saline, and they persist in saline with elevated Mg++ and Ca++ levels. Planta hair afferents also excite ipsilateral MNs by polysynaptic pathways, and their excitation of contralateral proleg MNs is exclusively polysynaptic. Cobalt-staining of the proleg MNs and planta hair afferents shows that the afferents terminate in ventral neuropil, and the proleg MNs have an unusual ventral projection into this region. The ventral projection is on the ipsilateral side, which is consistent with the electrophysiological finding that time-locked EPSPs are found only from ipsilateral hairs. Two factors that contribute to the strong monosynaptic excitation of proleg MNs by ipsilateral planta hairs are the convergence of many hair afferents onto each MN, and the facilitation shown at each afferent-MN synapse. At least 6 afferents converge on each MN, and at short interspike intervals the afferent-evoked EPSPs are enhanced by as much as 400% by homosynaptic facilitation. The EPSP is abolished reversibly by the cholinergic antagonists curare and atropine, suggesting that the neurotransmitter at the synapse is acetylcholine (ACh). This is of particular interest because the ACh receptors of tobacco-feeding Manduca larvae are reported to be less nicotine-sensitive than those of other insects.

Hormonally mediated reprogramming of muscles and motoneurones during the larval-pupal transformation of the tobacco hornworm, Manduca sexta

The larval-pupal transformation of Manduca sexta results from an exposure to ecdysteroids in the absence of juvenile hormone (the commitment pulse), followed by a larger exposure to ecdysteroids (the prepupal peak) with a reappearance of juvenile hormone (JH). The prepupal ecdysteroid peak triggers the degeneration of abdominal muscles, and the dendritic regression and death of identified motoneurones. The present experiments examined the role of the commitment pulse in the larval-pupal reprogramming of these cells. The commitment pulse did not overtly affect the muscles and motoneurones, but it switched their hormonal responsiveness; before the commitment pulse, exposure to ecdysteroids in the presence of JH had no effect on the larval cells, whereas after the commitment pulse the same treatment caused regression and death. Thus, JH lost its ability to prevent pupal development. Furthermore, treatment with ecdysteroids in the absence of JH before the commitment pulse promoted pupal development much less effectively than did the same treatment given after the commitment pulse, indicating that the commitment pulse facilitates the subsequent responsiveness to ecdysteroids. Thus, the commitment pulse covertly causes both qualitative and quantitative changes in the hormonal sensitivity of the larval muscles and motoneurones.

Steroid control of neuron and muscle development during the metamorphosis of an insect

Insect metamorphosis is controlled by a small ensemble of developmental hormones including a class of steroids--the ecdysteroids. In the tobacco hornworm, Manduca sexta, the progression from the larval to pupal to adult stages is controlled by the relative blood titers of ecdysteroids and juvenile hormone (JH). The cellular events in the nervous and muscular systems which accompany metamorphosis resemble those of embryonic development, but they occur in an animal which is larger and experimentally more tractable than an embryo. In this paper we review the role of ecdysteroids in directing the metamorphosis of the nervous and muscular systems in Manduca, and how JH modifies the cellular responses to the steroids. In particular, we describe how these hormones control muscle degeneration, changes in the structure and function of identified neurons, and programmed neuron death. One general finding is that interactions between cells (e.g., neurons and their target muscles) are not involved in their hormonal responses, but rather the hormones act independently and in parallel at the different sites. Another key finding is that the critical periods and hormonal requirements for the commitment to a particular differentiative pathway, and the phenotypic expression of that pathway, can differ, and are therefore experimentally separable. Finally, we find that the significance of a hormonal signal (e.g., a rise in blood ecdysteroids) is interpreted differently depending upon the previous history of hormone exposure of a neuron or muscle. This progressive change in the interpretation of hormonal signals is a major mechanism by which a limited number of hormones can orchestrate a complicated phenomenon such as metamorphosis.

Independent steroid control of the fates of motoneurons and their muscles during insect metamorphosis

The metamorphosis of insects is controlled by the blood titers of a small number of developmental hormones including a class of steroids, the ecdysteroids. We have studied the developmental fates of several muscles and their motoneurons during the larval-pupal transformation of the tobacco hornworm, Manduca sexta. The endocrine events which trigger pupal development are first, a fall in the blood titer of juvenile hormone, followed by two subsequent elevations of blood ecdysteroids. The small "commitment pulse" of ecdysteroids commits tissues to pupal development, whereas the sustained "prepupal peak" causes the new pupa to be formed (Riddiford, L. M. (1980) In Progress in Ecdysone Research, J.A. Hoffmann, ed., pp. 409-430, Elsevier/North-Holland Biomedical Press, Amsterdam). In the present experiments we were able to correlate specific aspects of the changing blood steroid titers with the degeneration of larval muscles, and with the dendritic regression and death of their motoneurons. The abdominal prolegs, which are the principal locomotory appendages of the caterpillar, are lost during the larval-pupal transformation. We have followed the fates of a proleg retractor muscle, PPRM, and its single motoneuron, PPR. Two other differently fated abdominal muscles not associated with the proleg were also studied. Surgical and endocrinological manipulations showed that PPRM degenerates in response to the rising phase of the prepupal ecdysteroid peak and that interactions with its motoneuron are not involved in the muscle's death. Motoneuron PPR responds to the rising prepupal peak by first reducing its dendritic arbor by 40% and then dying. Other proleg motoneurons regress but do not die, indicating that dendritic regression is programmed separately from neuronal death. Neither the dendritic reduction nor the death of PPR involves interactions with its target muscle. These results indicate that ecdysteroids have independent and parallel effects in the periphery, where they cause muscle degeneration, and in the central nervous system, where they cause dendritic regression and death of motoneurons.

Segmental specialization of a leech swim-initiating interneuron, cell 2051

The physiological and anatomical properties of an unpaired intersegmental interneuron designated cell 205 are described. Cell 205 is unusual among leech neurons in that it combines a variety of functional properties in a single cell. Constant current depolarization of cell 205 initiates and maintains swimming behavior in semi-intact leeches or the swim motor pattern in brainless, isolated nerve cords. During swim episodes elicited by other stimuli, cell 205 is rhythmically active. Current pulses passed into cell 205 during swimming reset the pattern, indicting that it has access to, or may be a member of, the swim central pattern generator (CPG). Cell 205 is the first interneuron in this system to exhibit both swim-initiating and CPG functions. Individual touch, pressure, and nociceptive primary mechanoreceptor neurons polysynaptically excite cell 205, which, in addition, is coupled electrically to the multimodal S interneuron. These inputs may contribute to the initiation and/or modulation of swimming in response to sensory stimuli. Cell 205 shares some common synaptic inputs and outputs with the only other known swim-initiating interneuron, cell 204, but the two cells differ fundamentally in that cell 204 exerts only a tonic effect on the CPG. No synaptic interactions were found between cells 204 and 205, but their excitatory effects on swimming summate. Unlike other swim neurons which are segmentally repeated, cell 205 generally is present only in segment 9, and numerous lines of evidence suggest that it is, in fact, a segmentally differentiated homolog of cell 204.