Site-specific recombination and circular chromosome segregation

The Xer site-specific recombination system functions in Escherichia coli to ensure that circular plasmids and chromosomes are in the monomeric state prior to segregation at cell division. Two recombinases, XerC and XerD, bind cooperatively to a recombination site present in the E. coli chromosome and to sites present in natural multicopy plasmids. In addition, recombination at the natural plasmid site cer, present in ColEl, requires the function of two additional accessory proteins, ArgR and PepA. These accessory proteins, along with accessory DNA sequences present in the recombination sites of plasmids are used to ensure that recombination is exclusively intramolecular, converting circular multimers to monomers. Wild-type and mutant recombination proteins have been used to analyse the formation of recombinational synapses and the catalysis of strand exchange in vitro. These experiments demonstrate how the same two recombination proteins can act with different outcomes, depending on the organization of DNA sites at which they act. Moreover, insight into the separate roles of the two recombinases is emerging.

Regulation of riboflavin intestinal uptake by protein kinase A: studies with Caco-2 cells

Although the mechanism of riboflavin (RF) intestinal uptake has been the subject of many studies, virtually nothing is known about the cellular regulation of the uptake process. In the present study, we investigated the role of protein kinase A (PKA)- and C (PKC)-mediated pathways in the regulation of RF intestinal uptake using the confluent Caco-2 monolayers. Treatment of Caco-2 cells with 3-isobutyl-1-methylxanthine (IBMX), forskolin, cholera toxin, or dibutyryl adenosine 3',5'-cyclic monophosphate caused a significant inhibition in RF uptake. The inhibitory effect of IBMX was reversible and resulted from a significant decrease in the maximal velocity of the RF uptake process with no change in its apparent Michaelis constant. The IBMX-induced inhibition in RF uptake was not mediated via inhibition in the synthesis of the RF carrier protein or through inhibition in the recruitment of preexisting carrier protein into the plasma membrane. Calyculin A also inhibited RF uptake when added alone and further potentiated the inhibitory effect of IBMX when added together. Phorbol 12-myristate 13-acetate or chelerythrine, on the other hand, showed no significant effect on RF uptake. These results demonstrate for the first time that compounds that increase intracellular cAMP levels downregulate RF intestinal uptake and that this effect is mediated via a decrease in the activity of the RF uptake carrier. It is suggested that a PKA-mediated pathway(s) plays an important role in regulating RF intestinal uptake.

Evaluation of an antenatal HIV testing programme in an inner London health district

OBJECTIVE

To study an antenatal human immunodeficiency virus (HIV) testing programme in an inner London health district.

DESIGN

A standardised research interview was given to women in the first half of pregnancy and the findings were compared with those of the routine clinical interview. The observations were analysed in relation to the results of HIV antibody testing, either attributable by consent or anonymously, in these women.

SETTING

The Homerton Hospital, London.

SUBJECTS

Three thousand seven hundred and twenty-nine women, of whom 1696 (45.5%) consented to testing.

RESULTS

Four women who had consented to testing had a positive result. Amongst the 2,033 women (54.5%) who declined the test, four (or five) had a positive result. The number of risk factors ascertained by the research study interview was substantially greater than that elicited by the preceding routine interview. In addition, more information was obtained by a routine computer interview than by its unstructured equivalent. There was no obvious association between the presence of a risk factor and whether or not the women had consented to the test.

CONCLUSIONS

Our formal voluntary testing programme detected nearly 44% of HIV seropositive individuals. Thus, there were four known positives during the study period against a total of nine detected by anonymous testing. Since all the known positive results in the study were associated with recognised risk factors, there is some doubt as to the value of a universal testing programme. However, if testing is to be based upon the existence of a risk factor elicited at the booking history, then the deficiencies in this history revealed by the present study need to be corrected.

The role of motor command feedback in electrosensory processing

Sensory motor-coordination and the descending modulation of sensory perception can be particularly well studied in the mormyrid electrosensory lateral line lobe (ELL). In this first order sensory processing network, electroreceptive primary afferent input is integrated with a corollary discharge signal which modulates neuron excitability immediately after the generation of an electric organ discharge. Corollary discharge feedback to the electrosensory lobe allows the brain to distinguish between reafferent sensory input, generated by autostimulation of cutaneous electroreceptors (resulting from the fish's own electric discharge) and exafferent sensory input, evoked by stimulation of the same cutaneous electroreceptors by an external electric source. Mechanisms of this type define the context of incoming sensory information and are the first step in the dynamic regulation of perception. The corollary discharge pathway originates from a collateral branch of the electromotor command neuron axons. It is relayed via bulbar and mesencephalic command-associated nuclei and reaches the ELL by way of projections from the cerebellar posterior granular eminence to the superficial layer of the ELL, and from juxtalobar and juxtalemniscal nuclei to the deeper layers of ELL. ELL is a geometrically organized laminar structure containing a variety of cell types. A number of them combine a spiny dendritic tree in the superficial molecular layer with non-spiny basal dendrites in plexiform or deeper layers. Sensory input may reach the basal dendrites of these neurons either directly or indirectly, via granule cells in the deeper layers of ELL, on which the primary afferent fibers terminate. All neurons recorded intracellularly in the ELL show strong interaction between electrosensory and corollary discharge input. Corollary discharge gating of sensory processing is plastic and depends on dynamic sensory-motor association.

Follicular development from ovarian xenografts in SCID mice

Cortical slices of either cat or sheep ovaries were grafted under the renal capsules of ovariectomized SCID mice. The grafts became vascularized and were still surviving with large follicles present at autopsy up to nine months later. As developing follicles undergo atresia during the period of ischaemia after ovarian grafting, those found in long-term grafts at autopsy had presumably started to grow from the primordial stage after transplantation. Some follicles had reached a diameter of 3 mm with a normal antrum and appeared to be cytologically normal, but the latent period for the emergence of antral follicles was shorter in cat compared with sheep grafts. Oestradiol production from grafts, as indicated by vaginal cornification and plasma measurements collected at autopsy, was not constant and circulating concentrations varied among animals, and were sometimes far in excess of the normal physiological range of the host. The vaginal smears never presented cytological patterns like those of the normal mouse oestrous cycle, and ovulation had not occurred in any of the grafts. These results demonstrate that ovarian xenografts in SCID mice can serve as experimental models for investigating follicle development in species in which follicle growth in vitro and studies of the parent animal are impracticable.

Risk identification for HIV infection in an inner London antenatal population

This study was carried out to ascertain whether routine antenatal history taking is an effective means of identifying risk factors for HIV infection. Information about risk obtained at routine booking was compared with answers to selected questions obtained at a research interview. The study was conducted at St. Bartholomew's Hospital Homerton, and ran from February 1991 to March 1992. Of the 3729 women interviewed, 1671 had been hand booked (unstructured questionnaire) and 2058 had been computer booked (structured questionnaire). Hand booking failed to identify 77% of risk factors compared with 7% for computer booking. The findings highlight the underdetection of risk activity and confirm the need for intermittent, anonymous sampling to obtain background information against which a decision to implement universal testing may be made.

Comparative studies on vascular endothelium in vitro. I. Cytokine effects on the expression of adhesion molecules by human umbilical vein, saphenous vein and femoral artery endothelial cells

Endothelial cells (ECs) are very responsive to proinflammatory cytokines. ECs are stimulated by these substances to increase expression of cell surface adhesion molecules, leading to dramatically altered interactions with leukocytes. In these interactions, E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) are suggested to play the most important role. Recent evidence has suggested diversity in the responses of ECs from different regions of the vascular system. Human umbilical vein ECs (HUVECs) are the most often used EC culture model, although there are few studies comparing their response with other human EC types from the adult organism. In this study the expression of E-selectin, ICAM-1 and VCAM-1 on cultured human adult ECs from the saphenous vein (HSVECs) and from the femoral artery (HAFECs), as well as HUVECs was studied. Using a cell enzyme immunoassay as well as immunoelectron microscopical methods, we found that both HSVECs and HAFECs respond in a similar way to HUVECs to exogenous stimulation by IL-1 beta, TNF alpha or LPS. IL-1 beta and TNF alpha increased the expression of E-selectin on the cytoplasmic membranes of HUVECs, HSVECs and HAFECs and elicited even similar absolute quantities of this molecule, comparing the different cell types. ICAM-1 and VCAM-1 appeared to be regulated dose dependently by IL-1 beta, independent of the EC type. HUVECs as well as HSVECs and HAFECs gave a reproducible constitutive ICAM-1 expression, whereas E-selectin and VCAM-1 were absent on nonstimulated ECs.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultrasonic measurements of breathing rate in rats and computer assisted analysis

PURPOSE

An ultrasound breathing rate measurement technique and a computer analysis algorithm have been developed to reduce the amount of time needed to collect and analyze animal breathing rate data, as well as to improve the testing environment. The system is not airtight, therefore, acclimatization and collection time is not limited, and the technique makes use of a top loading apparatus to facilitate animal entry.

METHODS AND MATERIALS

Breathing rate is measured using two ultrasound transducers housed directly above the rat thorax in the plexiglass jig. The breathing rate signal is stored and evaluated by computer. The ultrasound technique was tested using a loud speaker driven by a signal generator, over a range of 30 to 450 cycles/min. In addition, the ultrasonic breathing rate method was used to record the breathing rate response of Sprague Dawley rats, treated with graded single doses of radiation, over a period of 170 days.

RESULTS

For the loud speaker tests, the measured frequency agreed with that of the input signal with a maximum deviation of 1%. For the animal irradiations, all breathing rate data were analyzed by both user and computer selection of regular breathing. The techniques gave the same results at the 95% confidence limit. Using the computer program to assess the traces, 240 breathing rates can be determined per hour, from previously measured data.

CONCLUSION

A new technique for measuring breathing rate has been developed and enhances both the collection and analysis of data.

Storage of a sensory pattern by anti-Hebbian synaptic plasticity in an electric fish

Synaptic plasticity occurs in several regions of the vertebrate brain and is believed to mediate the storage of behaviorally significant information during learning. Synaptic plasticity is well demonstrated in most cases, but the behavioral meaning of the relevant neural signals and the behavioral role of the plasticity are uncertain. In this paper we describe a case of synaptic plasticity which involves identifiable sensory and motor signals and which appears to mediate the storage of an image of past sensory input. Corollary discharge signals associated with the motor command that drives the electric organ are prominent in the electrosensory lobe of mormyrid electric fish. Some of these corollary discharge signals elicit a negative image or representation of the electrosensory input pattern that has followed recent motor commands. When the temporal and spatial pattern of sensory input changes, the corollary discharge effect also changes in a corresponding manner. The cellular mechanisms by which the corollary discharge-evoked representation is stored were investigated by intracellular recording from cells of the electrosensory lobe and pairing intracellular current pulses with the corollary discharge signal. The results indicate that the representation of recent sensory input is stored by means of anti-Hebbian plasticity at the synapses between corollary discharge-conveying fibers and cells of the electrosensory lobe. The results also suggest that dendritic spikes and plasticity at inhibitory synapses are involved in the phenomenon.

Vasculitis with eosinophilia and digital gangrene in a patient with acquired immunodeficiency syndrome

Fewer than 40 cases of vasculitis have been described in the setting of human immunodeficiency virus infection. We describe a patient with the acquired immunodeficiency syndrome (AIDS), a heavy smoker, who developed a syndrome of constitutional symptoms, eosinophilia and digital gangrene. Vasculitis of the digital arteries was documented by angiography. He responded to high dose corticosteroid therapy with arrest of the ischemic process. After steroids were discontinued, he suffered a relapse of the vasculitis documented by skin biopsy. In patients with AIDS with this serious, potentially steroid responsive condition, steroid therapy should be considered in spite of the preexisting immunodeficiency state.

Sensory processing and corollary discharge effects in mormyromast regions of mormyrid electrosensory lobe. II. Cell types and corollary discharge plasticity

1. This is the second of a series of papers on the electrosensory lobe and closely associated structures in electric fish of the family Mormyridae. The focus of the study is on the regions of the electrosensory lobe where primary afferent fibers from mormyromast electroreceptors terminate. 2. This second paper examines the responses of single cells in the mormyromast regions of the electrosensory lobe to electrosensory stimuli and to corollary discharge signals associated with the motor command that drives the electric organ to discharge. All recordings were extracellular. 3. Two major types of cells were identified: I cells, which were inhibited by electrosensory stimuli in the center of their receptive fields; and E cells, which were excited by such stimuli. 4. I cells and E cells shared a number of common features. Both types could have small receptive fields limited to only a few electroreceptors (3-5), and both types were markedly affected by the corollary discharge of the electric organ discharge (EOD) motor command. Cells of both types also showed clear plasticity in their responses to the corollary discharge or to the corollary discharge plus a stimulus. 5. I cells could be subdivided into three subtypes, I1, I2, and I3, on the basis of corollary discharge responses in the absence of sensory stimuli. I1 and I2 cells showed consistent corollary discharge bursts with little or no additional activity beyond the duration of the burst. The corollary discharge bursts of I1 cells were more stereotyped and of shorter latency than those of I2 cells. I3 cells had more spontaneous activity than I1 or I2 cells and minimal cells had more spontaneous activity than I1 or I2 cells and minimal corollary discharge responses in the absence of sensory stimuli. Field potentials indicated that all three subtypes of I cells were recorded in or near the ganglion layer of the electrosensory lobe. 6. Corollary discharge responses were plastic and depended on recent pairing of a sensory stimulus with the EOD motor command. Such plasticity was clearer in I2 and I3 cells than in I1 cells. Inhibitory sensory stimuli were paired with the EOD motor command for periods of a few seconds to several minutes. Such pairing resulted in a marked enhancement of the corollary discharge response in I2 cells, as shown by examining the effect of the motor command after turning off the stimulus. In I3 cells, such pairing resulted in a clear corollary burst to the command at the time of the previously paired inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Sensory processing and corollary discharge effects in the mormyromast regions of the mormyrid electrosensory lobe. I. Field potentials, cellular activity in associated structures

1. This is the first of a series of papers on the electrosensory lobe and closely associated structures in electric fish of the family Mormyridae. The study describes the neuronal responses to sensory stimuli and to corollary discharge signals associated with the motor command that drives the electric organ discharge (EOD). The study is focused on the regions of the electrosensory lobe where primary afferent fibers from mormyromast electroreceptors terminate. 2. This first paper of the series describes the field potentials in the caudal lobe of the cerebellum and in the electrosensory lobe. It also describes the different types of unit activity in the caudal lobe of the cerebellum. Granule cells of the caudal lobe of the cerebellum provide the parallel fibers for most of the molecular layer of the electrosensory lobe. Determination of the input and responses of these cells is therefore an important part of the effort to understand the electrosensory lobe. 3. Corollary discharge field potentials evoked by the EOD motor command are very prominent in the caudal lobe of the cerebellum and in the electrosensory lobe. The potentials indicate that corollary discharge excitation affects first the granule cells of the caudal lobe and then, a few milliseconds later, the deeper cellular layers of the electrosensory lobe. The prominence and complexity of the field potentials indicate that corollary discharge signals have an important and varied role in the processing of electrosensory information by the mormyrid electrosensory lobe. 4. The field potentials evoked by electrosensory stimuli suggest that direct primary afferent excitation is limited to the granule and intermediate layers of the electrosensory lobe, as is indicated also by anatomic studies. 5. Proprioceptive units are the most common type of unit recorded in the granule cell region of the caudal lobe of the cerebellum (eminentia granularis posterior). These units have a regular discharge rate that changes tonically in response to slight bending of the trunk, bending of the tail, or bending of individual fins. Proprioceptive input will have a strong effect on the molecular layer of the electrosensory lobe and will thus modulate the responses of electrosensory lobe cells to electrosensory stimuli. Such proprioceptive input to the electrosensory lobe would allow the expected effects of body position changes to be accounted for in the processing of electrosensory information. 6. Units with stereotyped, short-latency corollary discharge bursts to the EOD motor command were the next most common type of unit in the eminentia granularis posterior. These corollary discharge units were not affected by sensory stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Accidents in elderly care: a randomised controlled trial (part 3)

This paper reports the data on accidents from a randomised controlled trial evaluating health authority-funded nursing home and long stay care of the elderly ward care in one inner London health district. Respondents randomised to NHS nursing homes experienced a higher accident rate than respondents randomised to conventional long stay hospital wards for elderly people. Respondents in the homes also experienced an earlier decline in functional and mental ability than those in hospital. These disadvantages have to be balanced against the previously published observational data from the evaluation, which clearly indicated that quality of life in the homes was superior to that in the wards. The conclusion from this study is that earlier decline in functional and mental ability and increased accident risk in the more flexible environments of the nursing homes have to be balanced against an inferior quality of life in the large traditional hospital wards; such assessments are not easy to make on behalf of other people. This final part of the report details the authors' conclusions.

Accidents in elderly care: a randomised controlled trial (Part 2)

This paper reports the data on accidents from a randomised controlled trial evaluating health authority-funded nursing home and long stay care of the elderly ward care in one inner London health district. Respondents randomised to NHS nursing homes experienced a higher accident rate than respondents randomised to conventional long stay hospital wards for elderly people. Respondents in the homes also experienced an earlier decline in functional and mental ability than those in hospital. These disadvantages have to be balanced against the previously published observational data from the evaluation, which clearly indicated that quality of life in the homes was superior to that in the wards. The conclusion from this study is that earlier decline in functional and mental ability and increased accident risk in the more flexible environments of the nursing homes have to be balanced against an inferior quality of life in the large traditional hospital wards; such assessments are not easy to make on behalf of other people. The report is divided into three parts. This week, the results of the trial are presented.

Birth registry

Birth registries are among the most common type of registry found in hospitals. Brigham and Women's Hospital has a high number of births annually. The following represents a brief overview of the status of this type of registry in healthcare today.

A randomized controlled trial of nursing home and long-stay geriatric ward care for elderly people

This paper reports outcome data on mental and physical ability levels, mortality and accident rates, from a randomized controlled trial evaluating health authority funded nursing home and long-stay geriatric ward care in one inner London health district. There were no differences between settings in mortality rates, although respondents randomized to the nursing homes deteriorated more rapidly in overall, mental and functional ability levels. Previous analyses reported that they also experienced a higher accident rate than respondents in the wards. However, observational data from the evaluation clearly indicated that quality of life in the homes was superior to that in the wards. We conclude that the more rapid physical decline and greater risk of accident in the nursing homes have to be balanced against an inferior quality of life in the hospital, and that a judgement is not easy to make on behalf of other people.

Phase I study of monoclonal antibody-ricin A chain immunotoxin XomaZyme-791 in patients with metastatic colon cancer

Monoclonal antibody 791T/36, recognizing a Mr 72,000 antigen on the surface of colon carcinoma cells, has been used to construct an immunotoxin by conjugating to it the ribosomal inhibitor protein, ricin toxin A chain. The antibody 791T/36 has been shown to bind to membranes of freshly disaggregated tumor cells from human colon tumors, and to localize in tumors in vivo. Subacute toxicology testing in rats receiving immunotoxin i.v. showed, at highest doses, weight loss, decreased serum albumin, and hepatocyte vacuolization without elevation in liver function tests. A Phase I dose escalation study was carried out in which 17 patients with metastatic colorectal cancer were treated with doses of immunotoxin ranging from 0.02 to 0.2 mg/kg/day in 1-h i.v. infusions for a 5-day course. Side-effects included a composite of signs and symptoms thought to be generic to ricin A chain immunotoxins, including decreased serum albumin, mild fever, and flu-like symptoms, all being reversible. Two additional findings, reversible proteinuria and mental status changes, were also noted which may be characteristic of this immunotoxin. By 10-20 days after therapy, most patients developed IgM and IgG antibodies against both the ricin toxin A chain and the immunoglobulin portion of the immunotoxin, which were asymptomatic. A strong anticombining site antibody response was seen. Biological activity manifest as mixed tumor regression was seen in five patients.

Effect of thermal injury in the rat on transfer of IgA protein into bile

Severe thermal injury is associated with bacterial sepsis; the intestine is considered a likely source of invasive organisms. Because IgA antibody in bile accounts for much of the specific immune defense of the upper intestinal tract in the rat, the effect of thermal injury on the quantity of IgA protein in bile was examined. Sprague-Dawley rats received a 20% to 30% body surface area burn under anesthesia. Eighteen hours later the common bile duct was cannulated and bile was collected for three hours. Total IgA protein in bile decreased 90% after thermal injury. The bile volume, the concentration of bile protein, and free secretory component did not change significantly. Although blood flow to the liver 18 hours after thermal injury was not changed, there was a significant reduction in total IgA concentration in the circulation; both monomeric (m-IgA) and polymeric IgA (p-IgA) were decreased. This finding may explain, in part, the reduced concentration of IgA protein in bile. Although not examined in this study, decreased local hepatic synthesis and/or transport of p-IgA across the hepatocyte may also contribute to the reduced IgA levels in bile.

Health-care decision making, Part II. Choices for incapacitated patients

The traditional, informal approach to making medical decisions for incapacitated patients is often inappropriate today. Guidelines are needed in two major areas: assessing incapacity and seeking surrogate decision makers. Judicially declared incompetency does not necessarily imply incapacity to make medical choices. Proposed standards for determining incapacity require a multistep evaluation of the patient's abilities to understand, reason, and communicate. When decisions must be made for an incapacitated patient, priority is given to the patient's previously stated preferences. An advance directive--living will or durable power of attorney--simplifies the process. If no advance directive was prepared, a surrogate decision maker may be designated according to applicable state statutes. Standards are still evolving for protecting the autonomy and best interests of vulnerable, incapacitated patients.

Health-care decision making. Part I: Legal and ethical principles

The growing elderly population and the acquired immunodeficiency syndrome (AIDS) epidemic have focused attention on ethical and legal issues surrounding health-care decision making. It is becoming increasingly critical to involve patients in the decisions that affect their care. Legal frameworks are evolving to protect the rights of both "competent" and "incompetent" patients. By writing instructions in advance, patients can increase their control and autonomy over health-care decisions. Physician assistants can facilitate the process by incorporating a patient value history into the chart and explaining legally recognized documents. Living wills generally apply in the context of terminal illness or irreversible coma; however, definitions of terminal conditions, imminent death, or life-sustaining procedures can be problematic. A number of states recognize the health-care durable power of attorney, which establishes a surrogate decision maker to act with specific instructions and limitations should the patient become incompetent or incapacitated.

Ultrastructural and histochemical investigations of Call-Exner bodies in rabbit Graafian follicles

In a histological survey of 19 mammalian species, Call-Exner bodies of conventional size and appearance were found in only 5, namely, human, rhesus monkey, rabbit, guinea-pig and sheep. Rabbit ovaries were used for characterizing these bodies using quantitative histochemistry, lectin binding and electron microscopy. Call-Exner bodies were topographically distinct lacunae of the extracellular space probably containing hyaluronic acid with proteoglycan complexes. The staining characteristics of the antrum and Call-Exner bodies were generally similar. However, in contrast to the antrum, the smaller lacunae contained suspended filaments with a distinctive peripheral membrane upon which a rosette of granulosa cells was resting. The membrane and narrow intercellular clefts probably prevent much exchange of large glycosaminoglycan complexes with the antrum. The origin and significance of Call-Exner bodies require further study, but it is clear that they are associated with secretion rather than with necrosis as sometimes suggested.

Corollary discharge inhibition and preservation of temporal information in a sensory nucleus of mormyrid electric fish

Knollenorgan electroreceptors in mormyrid fish are concerned with electrocommunication, i.e., with detecting electric organ discharges (EODs) of other electric fish. But knollenorgan electroreceptors are also activated by the fish's own EOD. Potential interference by such self-stimulation is blocked by an inhibitory corollary discharge in the nucleus of the electrosensory lateral line lobe (NELL), the first central relay of the knollenorgan pathway. This study used intracellular recording and staining to examine the mechanism of the corollary inhibition and the specializations in anatomy and physiology that permit the accurate relaying of temporal information about the EODs of other fish. Several events are recorded inside primary knollenorgan afferents in addition to a large orthodromic action potential. The additional events include small orthodromic electronic epsps, postsynaptic action potentials, and a corollary discharge inhibitory postsynaptic potential (ipsp) associated with the EOD motor command. These additional events are also recorded in NELL cells and almost certainly originate there. Electrical coupling between afferents and cells makes it possible to observe the events inside primary afferents. The corollary discharge ipsp in the cell is associated with a conductance increase and inverts rapidly when recorded with chloride-containing electrodes, supporting a hypothesis of GABA mediation. The ipsp lasts longer in cells than in afferents. Each electrotonic excitatory postsynaptic potential (epsp) is probably caused by a single primary afferent, and any one of several epsps in a given cell seems capable of eliciting a postsynaptic spike in that cell. The epsps follow stimulation rates as high as 500/sec with minimal variability. No lateral inhibition is observed in NELL. These and other properties indicate that the knollenorgan pathway is specialized for temporal information rather than spatial or intensity information.

Serotoninergic neurons in the mormyrid brain and their projection to the preelectromotor and primary electrosensory centers: immunohistochemical study

Serotonin-containing neurons in the brain of the weak-electric fish Gnathonemus petersii (mormyridae, teleostei) were studied with the aid of immunohistochemical labeling. Study of the central serotoninergic innervation was focused on the structures subserving the command of the electric organ and the first central relay of the electrosensory system. In the midline raphe nuclei, serotoninergic neurons formed a column that stretched from the ventral caudal medulla to the dorsal midbrain, ending caudal to the cerebellar peduncle. In the dorsal tegmentum, serotoninergic neurons were found bilaterally at the anterior margin of the decussation of the lateral lemniscus. Labeled neurons were also present bilaterally immediately anterior to the cerebellar peduncle and also in the pretectal region. In the hypothalamus, many serotoninergic neurons were in contact with the ventricular wall, and a few were present in the preoptic area. This distribution of serotoninergic cell bodies showed many similarities to that in other fish and higher vertebrates but lacked the lateral spread of the serotoninergic raphe system found in the midbrain tegmentum in mammals. Labeled fibers were found in both the preelectromotor medullary relay nucleus and the electromotor command nucleus. These serotoninergic projections were traced to the posterior raphe. Serotoninergic fibers also formed a dense network in the cortex and in the nucleus of the electrosensory lobe, both of which receive primary input from electroreceptors. These results suggest that serotonin may have a role in the modulation of the intrinsic, rhythmic electromotor command and in the gating of electrosensory input.

Humoral immune responses to XMMCO-791-RTA immunotoxin in colorectal cancer patients

Monoclonal antibody 791 (XMMCO-791) recognizes a colorectal tumour-associated antigen. Antibody 791-ricin A chain immunotoxin (XMMCO-791-RTA) inhibits growth of human tumour xenografts and it is therefore being evaluated for the treatment of colorectal cancer. One of the problems with therapy with mouse monoclonal antibodies is they stimulate humoral responses in patients. However antigens linked to ricin are cytotoxic for B cells and therefore XMMCO-791-RTA may not be immunogenic. The humoral antibody response to murine monoclonal antibody XMMCO-791 (IgG2b) conjugated to the plant toxin, ricin A chain (RTA), was measured in colorectal cancer patients in a phase I clinical trial. All patients produced strong responses to the XMMCO-791 immunoglobulin and to RTA. The predominant response to the antibody was against the idiotypic determinant although anti-subclass and anti-mouse antibodies were also detected. A component of the anti-idiotypic immunoglobulin response in the colorectal cancer patients was directed against the combining site of XMMCO-791. These antibodies inhibited in-vitro binding of XMMCO-791 to target 791 cells and so may be inhibitors of repeated immunotoxin therapy. Immunotoxins do not abrogate the immune response to mouse immunoglobulin in vivo but instead are highly immunogenic.