Errors in two particle tracking at close distances.

Tracking single and multiple particles is of great importance for many physical investigations in a variety of different areas. It is essential to find and eliminate sources of systematic errors in the particle position determination (PPD) and to determine the limits of its applicability to a given problem. Particularly when measuring the interactions between colloids at close distances, artifacts in the image taking process pose a great problem. By means of a simulation technique, we investigated the accuracy of the PPD using two-dimensional Gaussian and Gaussian-like fitting functions. For the distance between the two colloidal particles this revealed a systematic overestimation of the inter-particle distance of up to 1.9% of the particle diameter for the Gaussian fitting function. This deviation can be explained by the differences between the intensity distribution of the overlap of the simulated particles and the linear superposition of the Gaussian functions. Modifications of the fitting functions can reduce the systematic error significantly.

Successful treatment of hepatic veno-occlusive disease after myeloablative allogeneic hematopoietic stem cell transplantation by early administration of a short course of methylprednisolone.

Hepatic veno-occlusive disease (VOD) is one of the most common and important regimen-related toxicities observed after hematopoietic stem cell transplantation (HSCT). There are no universally accepted preventative or therapeutic approaches for VOD. We prospectively evaluated the safety and efficacy of a short course of methylprednisolone (MP) in 48 patients undergoing allogeneic HSCT who were diagnosed with hepatic VOD. MP was administered at a dose of 0.5 mg/kg i.v. every 12 h for a total of 14 doses, and then discontinued without taper. Thirty (63%) patients responded with a reduction in total serum bilirubin of 50% or more after 10 days of treatment. In univariate analysis, non-responders had a higher total bilirubin at the start of MP therapy, more weight gain, evidence of fungal infection and platelet refractoriness. High SGPT and early engraftment were significant factors among responders. Twenty-five of the 30 responders survived up to day +100, whereas all but three non-responders died within 100 days post-HSCT, for a probability of survival of 58% among responders and 10% for non-responders. Prospective comparative studies are needed to confirm the observed encouraging outcome of MP therapy for VOD.

Hepatitis B virus reactivation with clinical flare in allogeneic stem cell transplants with chronic graft-versus-host disease.

We conducted a retrospective study with the aim of identifying risk factors and clinical characteristics associated with HBV reactivation and clinical flare after allogeneic stem cell transplantation (aSCT). We reviewed the King Faisal Specialist Hospital and Research Center International Bone Marrow Transplant Registry database from January 1998 to June 2000. Complete serological screening for HBV was available in 128 of 131 patients transplanted during that period. Fifty-four (42%) had evidence of prior infection and recovery from HBV before transplant (hepatitis B core antibody positive, B surface antigen negative). Forty-two were evaluable for HBV reactivation and clinical flare. Six (14%) reactivated with clinical flare as documented by seroconversion and/or positive HBV DNA in the serum with biochemical hepatitis at 5.5, 18, 18, 19, 21 and 23 months post-transplant. Five of fifteen patients with chronic graft-versus-host disease (cGVHD) reactivated with clinical flare in contrast to 1/27 without cGVHD (RR: 9.0, 95% CI: 1.2-70.1 P < 0.02). HBV reactivation with clinical flare occurred during immunosuppressive therapy tapering or withdrawal in all patients. In conclusion, hepatitis B core antibody positive allogeneic stem cell recipients with cGVHD are at significant risk of HBV reactivation with clinical flare.

Monitoring of donor/recipient T-cell engraftment kinetics in myeloablative allogeneic stem cell transplantation using short tandem repeat amplification from cell lysates.

Molecular monitoring of donor/recipient T-cell kinetics early post-transplant can provide clues to the immunological events that govern host-versus-graft reaction (HVGR) and graft versus-host-disease (GVHD). We have previously used fluorescence in situ hybridization (FISH) with X and Y probes to monitor recipient T (R-T) cell clearance early after myeloablative allogeneic stem cell transplantation (ASCT). We demonstrated that impaired clearance of residual host-T-cells in the early days post-transplant was associated with graft rejection, while enhanced clearance could be an indicator of increased donor anti-host alloreactivity and predictive of acute GVHD. Although FISH is the most accurate quantitative molecular tool for the determination of the exact donor/recipient-T-cell numbers at any time points post-transplant, it has the disadvantage of being limited to sex mismatched donor/recipient pairs. Our goal was to develop a molecular approach that, irrespective of gender, would be comparable to FISH in accurately determining host residual T-cell clearance after myeloablative conditioning for ASCT. We have genotyped DNA from cell lysates using polymerase chain reaction (PCR) amplification of short tandem repeats (STR) with fluorescently labeled oligonucleotide primers, and used the Genescan 672 software for accurate quantitative analysis of the amplified alleles. Here, we show that this approach allowed us to achieve in T-cells accurate quantitative analyses of amplified donor/recipient alleles in sex matched patients on days +5, +8 and +12 post-transplant, despite severe leukopenia.

Extramedullary myeloid cell tumours localised to the mediastinum: a rare clinicopathological entity with unique karyotypic features.

Extramedullary myeloid cell tumour (EMMT) localised to the mediastinum is a rare manifestation of acute myeloid leukaemia, forming less than 4% of all cases of EMMT. In contrast to other types of EMMT, cytogenetic characteristics of this rare entity are relatively unknown. This report describes a patient with EMMT who had evidence of superior vena cava syndrome and normal peripheral blood counts at diagnosis. The results from an initial biopsy specimen were consistent with a diagnosis of mediastinal large B cell lymphoma. A diagnosis of acute myeloid leukaemia was made three months after initial diagnosis by bone marrow examination. Review of the initial biopsy specimen showed strong positivity for myeloperoxidase, revealing that the patient had been initially misdiagnosed as having large B cell lymphoma. Cytogenetic studies revealed a near triploid and near tetraploid karyotype with structural abnormalities in 12 and three metaphases, respectively. Review of the literature showed that a near tetraploid or triploid karyotype is found in most of the reported cases of mediastinal EMMT. Thus, the presence of a near triploid/tetraploid karyotype and mediastinal EMMT may represent a specific subset of EMMT. The biological relevance of this observation is discussed.

Immunobiology of allogeneic peripheral blood mononuclear cells mobilized with granulocyte-colony stimulating factor.

The use of mobilized peripheral blood (PB) stem cells for autologous transplantation initially generated much enthusiasm because of enhanced engraftment in comparison to marrow stem cells and avoidance of general anesthesia for the donor. Its application to the allogeneic setting seemed inevitable. For obvious ethical reasons, allogeneic donors are mobilized with cytokines only, mainly granulocyte colony-stimulating factor (G-CSF). Results from preliminary studies suggest that in comparison to standard bone marrow transplants, outcomes such as engraftment, host-versus-graft reaction, graft-versus-host disease, graft-versus-leukemia and immunological reconstitution may be different. Surprisingly, G-CSF, previously recognized as a late acting lineage-specific factor for neutrophil production, not only disrupts homeostasis between stem cells and their microenvironment, but also induces significant quantitative and qualitative changes in the accessory cell compartment, affecting lymphocytes, monocytes, natural killer, dendritic, and stromal cells. Furthermore, mobilization of huge numbers of non-professional antigen presenting cells (CD34+ stem cells) amplifies the tolerizing potential of PB stem cell grafts. Thus, G-CSF mobilization provides PB transplants with different immunobiologic properties in comparison to standard bone marrow grafts. Whether these immunobiologic differences will lead to better transplant outcomes remains to be shown through much awaited results of large randomized clinical trials.

The spectrum of Fusarium infection in immunocompromised patients with haematological malignancies and in non-immunocompromised patients: a single institution experience over 10 years.

Fusarium is a newly emerging fungal pathogen associated with significant morbidity and mortality in the immunocompromised host. We have reviewed our hospital's experience with Fusarium between 1985 and 1995. Fusarium species were isolated from 22 specimens, representing 11 patients. Cases were not clustered by time period. The median age of the patients was 36.5 years (range 17-69 years). The sources of the organism were 12 skin lesions from eight patients, seven blood cultures from two patients and one specimen each from a Hickman catheter tip, nail clippings and a bronchoalveolar lavage. Seven of the patients had chemotherapy-induced neutropenia when the Fusarium was isolated. Five of them developed invasive fusarosis during acute leukaemia induction treatment. They remained neutropenic, and none survived. The other two patients recovered from neutropenia and were treated successfully for this infection. The remaining four patients were not neutropenic or immunocompromised. Three grew Fusarium from skin or nail clippings and one from bronchial alveolar lavage (BAL). There was no evidence of invasive disease in any of the four. None of them received antifungal therapy, and they were all alive at last follow-up. We conclude that Fusarium is a newly emerging infection in neutropenic patients. A high index of suspicion, especially for skin lesions, will help in early diagnosis before systemic and visceral dissemination. Excision of the initial focus of infection and antifungal therapy, aided by speedy neutrophil recovery, are likely to protect patients threatened with these fatal infections. Fusarium isolated from non-neutropenic, non-immunosuppressed patients is not significant and does not merit systemic antifungal treatment.

Mycobacterium tuberculosis infection in allogeneic bone marrow transplantation patients.

Bone marrow transplant (BMT) recipients are prone to bacterial, viral and fungal infections. Mycobacterium tuberculosis infection can occur in these patients, but the incidence is lower than that of other infections. This report describes four patients with Mycobacterium tuberculosis infection identified from 641 adult patients who received a BMT over a 12-year period (prevalence 0.6%). The pre-transplant diagnosis was AML in two patients and CML in the other two. Pre-transplant conditioning consisted of BU/CY in three patients and CY/TBI in one. Graft-versus-host disease (GVHD) prophylaxis was MTX/CsA in three patients and T cell depletion of the graft in one patient. Sites of infection were lung (two), spine (one) and central nervous system (one). Onset of infection ranged from 120 days to 20 months post BMT. Two patients had co-existing CMV infection. One patient had graft failure. The two patients who received anti-tuberculous (TB) therapy recovered from the infection. Although the incidence of tuberculosis in BMT patients is not as high as in patients with solid organ transplants, late diagnosis due to the slow growth of the bacterium can lead to delay in instituting anti-TB therapy. A high index of suspicion should be maintained, particularly in endemic areas.

Two different schedules for integrating filgrastim as adjuvant therapy in the treatment of patients with advanced stage Hodgkin's lymphoma receiving MOPP/ABV hybrid chemotherapy.

PURPOSE: Management of advanced-stage Hodgkin's disease with a MOPP/ABV hybrid regimen (mechlorethamine, vincristine, procarbazine, prednisone, Adriamycin, bleomycin and vinblastine) has yielded a high complete response rate (75-85%). However, myelosuppression can limit delivery of treatment. Filgrastim has been shown to reduce chemotherapy-related neutropenia and allow for on-time administration of planned doses of chemotherapeutic agents. The objective of this study was to find the best way to integrate filgrastim with the MOPP/ABV hybrid regimen. METHODS: Enrolled in this study were 24 patients (aged 18-52 years) with newly diagnosed, histologically documented Hodgkin's disease. In schedule I, patients received filgrastim (5 microg/kg s.c. daily) beginning on day 9, 24 h after administration of ABV. In schedule II, patients received filgrastim concomitantly with procarbazine on days 2-7 (starting 24 h after day-1 MOPP administration and stopping 24 h before ABV administration) as well as after ABV beginning on day 9. Filgrastim after ABV administration was administered until two consecutive ANC readings of 10 x 10(9)/l were achieved. RESULTS: All patients were able to complete all six cycles of therapy. There was a trend to fewer dose reductions in schedule II (0.76%) as compared to schedule I (4.2%) with a P-value of 0.077 (chi-squared test). Specifically, 11.6% of MOPP courses and 5.5% of ABV courses were dose-reduced in schedule I versus 1.7% and 1.4%, respectively, in schedule II. CONCLUSION: In conclusion, filgrastim was effective in supporting the delivery of the MOPP/ABV chemotherapy. Concomitant administration of filgrastim with procarbazine (days 2-7) appears to be safe and allows the maximum dose intensity of this therapy.

A phase I trial of standard and cyclophosphamide dose-escalated CHOP with granulocyte colony stimulating factor in elderly patients with non-Hodgkin's lymphoma.

The purpose of this study was to assess the safety and feasibility of using standard and escalated doses of cyclophosphamide with doxorubicin, vincristine and prednisone (CHOP) plus granulocyte colony stimulating factor (G-CSF) to treat elderly patients who have advanced stage intermediate grade lymphoma. Consenting patients age > or = 65 years who had an acceptable performance status and adequate cardiac, renal and liver function were eligible for this Phase I study. G-CSF, 5 ug per kg, was given daily with each cycle from day 2 until neutrophil recovery of > or = 10 x 10(9)/L. Ten patients received standard CHOP; sequential cohorts of 5 patients were then to be given CHOP with cyclophosphamide doses of 900, 1050, 1200, and 1350 mg/m2. If 2 patients had dose limiting toxicity, cohorts were expanded to 10 patients; if 3 patients within a cohort had dose limiting toxicity, the previous dose level was considered the maximum tolerated dose of cyclophosphamide. Secondary outcomes were average relative received dose intensity, response, progression-free and overall survival, toxicity, hospitalizations and transfusions. Eight patients (80%) completed 6 cycles of standard CHOP plus G-CSF. Therapy was stopped prematurely in 2 patients due to pneumonia (1) and disease progression (1). Six of 11 patients (55%) given CHOP with cyclophosphamide 900 mg/m2 (CHOP-900) completed treatment. Therapy was stopped in 5 patients due to a toxic death from infection (1), cumulative fatigue (3), and pneumonitis (1). Further dose escalations were not attempted due to the inability to complete 6 treatment cycles in 45% of CHOP-900 cases. The received dose intensities of cyclophosphamide relative to standard CHOP measured over the actual time on therapy were 96% with standard CHOP and 115% with CHOP-900. At 3 years, progression free survival is 40% with standard CHOP and 82% with CHOP-900; overall survivals are 40% and 91% respectively. Neutropenia of < 1.0 x 10(9)/L occurred in 47% of treatment cycles with standard CHOP and in 77% with CHOP-900. In both groups, the mean duration of neutropenia was < 2 days. From these studies we conclude that, standard CHOP with G-CSF can be safely given to elderly patients. Escalating the dose of cyclophos

Quantitative assessment of hematopoietic chimerism after allogeneic bone marrow transplantation has predictive value for the occurrence of irreversible graft failure and graft-vs.-host disease.

Primary graft failure, secondary to either host-vs.-graft reaction or delayed engraftment, and graft-vs.-host disease (GVHD) are among the most difficult clinical problems to manage in the field of allogeneic bone marrow transplantation (BMT). Early diagnosis of both conditions would greatly improve their outcome. Using fluorescence in situ hybridization (FISH) with an X- and Y-probe mixture, we sequentially monitored chimerism of neutrophils and lymphoid cells from day 1 to 100 in 28 consecutive recipients of sex-mismatched unmanipulated bone marrow grafts. The objective was to quantitatively assess the evolution of chimerism during this crucial time interval and to determine whether chimerism patterns would be predictive of engraftment and GVHD. In recipients with primary graft failure (n=7), the presence of donor-type neutrophils and NK cells as well as the predominance of donor-type T cells distinguished patients who responded to G-CSF (n=5) from nonresponders (n=2). Furthermore, the clearance of host CD3+CD56- cells during days 5-10 posttransplantation was significantly hastened in patients who subsequently developed acute (delta=80%) or chronic (delta=81%) GVHD compared with patients without GVHD (delta=17%). Thus, our data suggest that molecular monitoring of the fate of host/donor hematopoietic cells in the early posttransplantation period could be useful in differentiating patients with delayed engraftment from those with irreversible rejection and in predicting the occurrence of GVHD as soon as day 10. This investigational approach may provide an appropriate basis on which to select adequate treatment for primary graft failure and high-risk candidates that could benefit from novel preemptive therapies for GVHD.

Lymphoma cell burden in progenitor cell grafts measured by competitive polymerase chain reaction: less than one log difference between bone marrow and peripheral blood sources.

A controversy persists in autologous transplantation as to which source of progenitor cells, bone marrow (BM) or peripheral blood (PB), contains the lowest number of contaminating lymphoma cells, and how mobilization procedures affect these numbers. To accurately measure the number of non-Hodgkin's lymphoma (NHL) cells harboring the bcl-2/immunoglobulin H (IgH) rearrangement in progenitor cell grafts, we developed a nested quantitative competitive polymerase chain reaction assay (QC-PCR). DNA from lymph nodes of four patients with NHL were cloned into the pSK(+) vectors to generate four internal controls (ICs) (two with major breakpoint region [MBR] and two with minor cluster region [mcr] rearrangements). The kinetics of amplification of ICs paralleled those of bcl-2/IgH rearranged genomic DNA. When used in a QC-PCR assay, these ICs were accurate at a 0.2-log level and provided reproducible results, as shown by low intrarun and interrun variability. An excellent correlation between predicted and observed lymphoma cell content (r = .99) was observed over a range of at least 5 logs of rearranged cells. This approach was used to measure involvement by NHL cells at the time of progenitor cell harvest in 37 autologous transplant patients. The number of bcl-2/IgH rearranged cells in BM, PB, and mobilized PB (mPB) was found to vary from 1 to 1.1 x 10(5) per million cells. The number of lymphoma cells present in BM was significantly higher than in PB (P = .0001), with a median difference in lymphoma cell content between BM and PB of 0.48 log of cells (range, -0.7 to 5 logs). In contrast, we found no difference in the concentration of bcl-2/IgH rearranged cells present in BM versus PB progenitor cells mobilized with cyclophosphamide and granulocyte colony-stimulating factor (G-CSF) (mPB) (P = .57). In conclusion, the QC-PCR assay described in this study could measure accurately and reproducibly the number of bcl-2/IgH rearranged cells among normal cells. Differences in levels of contamination by lymphoma cells between BM and PB were of less than one log (10-fold), and no differences in lymphoma cell concentrations were observed between BM and mobilized PB. As more cells are usually infused with mPB than with BM grafts, mPB progenitor cell grafts may actually be associated with higher levels of contamination by lymphoma cells. Furthermore, this QC-PCR assay should provide an important tool to assess the prognostic impact of lymphoma cell burden both in progenitor cell grafts and in vivo.

Thymic and extrathymic differentiation and expansion of T lymphocytes following bone marrow transplantation in irradiated recipients.

Thymic function is severely impaired in most marrow transplant recipients. To evaluate the impact of thymic hypoplasia on T cell reconstitution following marrow transplantation, we compared the phenotype and function of T lymphocytes in thymectomized recipients with those of euthymic hosts. Irradiated C57BL/6 mice (Thy1.2+, Ly5.1+) received 10(7) T cell-depleted B6.Ly5.2 bone marrow cells (Thy1.2+, Ly5.2+), with or without 3 x 10(5) B6.PL lymph node cells (Thy1.1+, Ly5.1+) as a source of T lymphocytes. Multiparameter flow cytometry analysis showed that in euthymic mice (group 1), T cell reconstitution was carried out by donor hematopoietic stem cells that differentiated in the host's thymus, whereas the production of chimeric T cells in athymic recipients depended on the presence or absence of T cells in the graft. When T lymphocytes were present in the graft (group 2), their progeny constituted the vast majority of splenic T cells on day 100 posttransplant. When the graft did not contain T lymphocytes (group 3), T cell reconstitution resulted from extrathymic maturation of donor hematopoietic progenitors; T cells differentiating along this pathway expressed lower levels of T cell receptor and a large proportion of the CD8+ subset expressed CD8alpha alpha homodimers. The T cell receptor Vbeta profile of all chimeras was similar to that of normal C57BL/6 mice. Compared with T cells found in euthymic recipients, those in mice from groups 2 and 3 were less abundant (particularly with respect to the CD4+ subset), displayed the CD44/CD45 phenotype of activated memory cells, and expressed high levels of IL-2 receptor beta chain. These results show that both the presence or absence of the thymus and the composition of the grafted inoculum determine the source and extent of posttransplant T cell reconstitution. Because they determine the nature of the differentiation pathway taken during T cell development in the host, these two factors can exert a critical influence on the appearance of graft vs. host disease and the level of host immunocompetence.

Neurotoxicology and amino acid intake during development: the case of threonine.

The development of the central nervous system is highly dependent on an adequate supply of nutrients. In particular, protein and amino acid availability is of major concern during gestation and in early postnatal life. Numerous data have been published on some amino acids directly involved in brain functions as neurotransmitters or indirectly as precursors of neurotransmitters, but scant information is available on the possible consequences of hyperthreoninemia, a phenomenon repeatedly noted in clinical reports. The results of neurochemical and behavioral studies in the developing rat suggest that despite numerous possible effects of threonine on brain constituents, moderate hyperthreoninemia does not impair markedly the development of the central nervous system.

A centrifugally controlled circuit in the avian retina and its possible role in visual attention switching.

The isthmo-optic nucleus (ION) is the main source of efferents to the retina in birds. Isthmo-optic neurons project in topographical order on amacrine cells in the ventral parts of the retina, and a subclass of these known as proprioretinal neurons project onto the dorsal retina. We propose that, through the intermediary of the amacrine target cells, activity in the isthmo-optic pathway excites ganglion cells locally in the ventral retina but inhibits those in dorsal regions. This circuit would thereby mediate centrifugally controlled switches in attention between the dorsal retina, involved in feeding, and the more ventral parts, involved in scanning for predators. This hypothesis accounts for a wide range of disparate data from behavior, comparative anatomy, endocrinology, hodology, and neurophysiology.

Sequential analysis of early hematopoietic reconstitution following allogeneic bone marrow transplantation with fluorescence in situ hybridization (FISH).

Using in situ hybridization with an X and Y chromosome probe mixture, we have sequentially studied peripheral blood samples from 10 patients (four males/six females) in an HLA-matched allogeneic setting in order to monitor the kinetics of early hematopoietic reconstitution. Interphase cells from smears consisting of purified granulocytic and lymphocytic populations respectively were studied in three patients at 24, 48, 72 and 96 h post-transplant. This period was arbitrarily defined as the immediate post-transplant period. These three patients plus seven others were studied sequentially at days 5, 10, 15, 20, 25 and 50 post-transplant, defined as the intermediate post-transplant period. The X and Y probes were indirectly labelled with rhodamine and fluoresceine isothiocyanate, respectively. Donor neutrophils were detected as early as 24 h post marrow infusion followed by a significant expansion at 48 h. At 96 h post-transplant, the median percentage of donor neutrophils was > 90%. In the immediate post-transplant period, most of the lymphocytes were of recipient origin. However, we have documented a significant expansion in donor lymphocytes, starting at day 5 post-transplant in most patients. Almost complete chimerism for the myeloid and lymphoid lineages was established at days 10 and 25 post-transplant, respectively. All patients engrafted normally according to standard clinical criteria. Follow-up data for those surviving > or = 100 days (eight patients), showed persistence of this pattern of hematopoietic reconstitution in all but one patient. Molecular monitoring of early engraftment has enabled us to unravel a distinct biphasic pattern of myeloid and lymphoid engraftment.

Phenotypic and functional characterization of peripheral blood and bone marrow natural killer cells prior to autologous transplantation.

NK cells can exert potent anti-leukemia activity after either autologous or allogeneic BMT. However, in autologous blood or marrow transplant patients, NK cell number and/or function could be reduced, and also may vary according to the sampling site. In order to evaluate the hypothesis that blood or marrow grafts from autologous transplant patients exhibit impaired NK cell activity that could contribute to disease recurrence, we evaluated the immunologic characteristics of NK cells in the bone marrow (BM) and peripheral blood (PB) from 27 patients undergoing autologous BMT, and also from 20 normal donors. We measured baseline and interleukin-2 (IL-2)-activated NK cell cytotoxicity, as well as expression of IL-2 receptors (IL-2R) (alpha-chain (p55) and beta-chain (p75)), and adhesion molecules. The cytotoxic activity of PB NK cells was significantly lower in autologous transplant patients than in normal donors (P < 0.0005) and this difference was not mitigated following IL-2 activation. In contrast, BM from autologous patients showed normal NK cell cytotoxicity, but contained higher numbers of NK cells (P < 0.025), with more intense CD56 expression (P < 0.05). Expression of p75 was lower on BM than on PB NK cells in both patients and normal donors. In addition, induction of p55 by IL-2 was abrogated in autologous PB NK cells. Therefore, depending on the site of harvest and the nature of donor cells (pre-BMT vs normal), our results show significant differences in NK cell number, function, and IL-2 receptor expression. This may affect relapse rates following autologous transplants performed with either PB or BM grafts.

Effect of threonine on the behavioural development of the rat.

Rats received different levels of threonine (Thr), one, 1.7 and four times the normal dietary intake, from conception to adulthood. The mothers were fed the experimental diets before and during pregnancy. Their offspring received a daily oral load of Thr or placebo until weaning. Thereafter, the juveniles were fed the same diet as their mothers. Morphologic development, ingestive behaviour, homing, and locomotion were observed before weaning. Exploration and spontaneous alternation were studied thereafter. Animals exposed during gestation to 1.7 times the normal Thr intake consumed more food during the test of independent ingestion. Grooming showed inconsistent variations between days 12 and 29 in pups fed 1.7 times the normal Thr intake. Rats performed equally well on the other behavioural tasks independently of the dietary treatment. We conclude that Thr intake as much as four times higher than the levels found in normal diets does not impair the behavioural ontogenesis of the rat.