Iron deficiency alters dopamine uptake and response to L-DOPA injection in Sprague-Dawley rats

Iron deficiency (ID) disrupts brain dopamine (DA) and norepinephrine (NE) metabolism including functioning of monoamine transporters and receptors. We employed caudate microdialysis and no net flux (NNF) in post-weaning rats to determine if ID decreased the extraction fraction ( E _d). Five micromolar quinpirole, a dopamine D₂ receptor agonist, resulted in 80% decrease in extracellular DA and 45% higher E _d in control animals. The D₂ agonist had no effect on E _d in ID animals despite a reduction in basal DA. DAT mRNA levels were reduced by 58% with ID, while DAT protein in ventral midbrain and caudate and membrane associated DAT were also reduced by ID. Carbidopa/ l -DOPA was administered to determine if elevated extracellular DA in ID was due to increased release. The DA response to l -DOPA in ID rats was 50% smaller and delayed, whereas the NE response was threefold higher. The caudate concentration of NE was also elevated in ID. Elevated dopamine-β-hydroxylase activity in ID provides a tentative explanation for the increased NE response to l -DOPA. These experiments provide new evidence that ID results in altered synthesis and functioning of DAT and perhaps suggests some compensatory changes in NE metabolism.     

Effects of pH changes and charge characteristics in the uptake of norepinephrine by synaptosomes of rat brain

The pH dependence of the initial uptake of norepinephrine by rat whole brain synaptosomes was studied short incubation times at 37°C in order to examine the possible involvement of the phenolic OH group. The pH vs. uptake profile exhibits a maximum near pH 8.2 in H₂O medium. When the medium was changed to ²H₂O, the profile showed a shift of maximum corresponding to the pK_a change of the phenolic OH group. The pH vs. uptake profile of tyramine was quite different from that of norepinephrine. These pH effects on uptake were explained as manifestations of the involvement of the phenolic OH group in the process.The amine and phenolic hydroxyl groups in norepinephrine were studied separately by employing two series of compounds structurally related to catecholamines, amphetamine-like and catechol0like, for their inhibitory effects on the uptake. The inhibitions were affected by changes in pH with changes in opposite directions found for the two series indicating the need for a positive charge in the side chain and suggesting an effect of the negative charge on the ring. These charge characteristics agreed with the pH profile observed in uptake. Consequently, the two groups with opposite charge characteristics in norepinephrine both appear to function in the uptake process.     

Modulation of Adherence and Chemotaxis of Macrophages by Norepinephrine. Influence of Ageing

We evaluated thein vitro effect of norepinephrine (NE), over the range of concentrations between 10^-12 M and 10^-3 M, on adherence (to plastic surfaces) and chemotaxis (in a Boyden chamber) of peritoneal macrophages from BALB/c mice of different ages: young (12 weeks), adult (22 weeks), mature (48 weeks) and old (72 weeks). Increased adherence was induced by 10^-12 M of NE in macrophages from young, adult, mature and old mice. Also, 10^-9 M stimulated adherence in old animals, 10^-5 M in mature mice, and 10^-3 M in both young and old mices. With respect to chemotaxis, the low concentration of NE (10^-12 M) was stimulatory only in young and adult animals, higher concentrations (10^-5 M and 10^-7 M) were inhibitory for macrophages from mature and old animals, and the highest concentration of NE (10^-3M) stimulated this capacity of macrophages only in young and mature animals. The conclusion is that while the mobility of macrophages to the focus of infection (i.e. chemotaxis) is stimulated by low concentrations of NE (10^-12, M) only in young-adult animals, this neurotransmitter induces a decline in this capacity in mature and old mice at high concentrations (10^-5 M - 10^-7 M). Also, macrophages from old animals have lost the capacity to respond to pharmacological (10^-3 M) concentrations of NE. The lower capacity of response to NE by macrophages from old animals possibly contributes to immunosenescence.     

KCl stimulation increases norepinephrine transporter function in PC12 cells

The norepinephrine transporter (NET) plays a pivotal role in terminating noradrenergic signaling and conserving norepinephrine (NE) through the process of re-uptake. Recent evidence suggests a close association between NE release and regulation of NET function. The present study evaluated the relationship between release and uptake, and the cellular mechanisms that govern these processes. KCl stimulation of PC12 cells robustly increased [3H]NE uptake via the NET and simultaneously increased [3H]NE release. KCl-stimulated increases in uptake and release were dependent on Ca2+. Treatment of cells with phorbol-12-myristate-13-acetate (PMA) or okadaic acid decreased [3H]NE uptake but did not block KCl-stimulated increases in [3H]NE uptake. In contrast, PMA increased [3H]NE release and augmented KCl-stimulated release, while okadaic acid had no effects on release. Inhibition of Ca2+-activated signaling cascades with KN93 (a Ca2+ calmodulin-dependent kinase inhibitor), or ML7 and ML9 (myosin light chain kinase inhibitors), reduced [3H]NE uptake and blocked KCl-stimulated increases in uptake. In contrast, KN93, ML7 and ML9 had no effect on KCl-stimulated [3H]NE release. KCl-stimulated increases in [3H]NE uptake were independent of transporter trafficking to the plasma membrane. While increases in both NE release and uptake mediated by KCl stimulation require Ca2+, different intracellular mechanisms mediate these two events.     

Dual phases of functional change in norepinephrine transporter in cultured bovine adrenal medullary cells by long-term treatment with clozapine

The effects of long-term treatment with clozapine, a prototype of atypical antipsychotic drugs, on the functional activity, synthesis and mRNA of norepinephrine (NE) transporter were examined in bovine adrenal medullary cells in culture. Treatment of cells with clozapine at 0.1-3.0 microM concentrations produced dual phases of changes in [(3)H]NE uptake, i.e. the first phase showed a decrease in [(3)H]NE uptake at 2-48 h, and the following phase showed an increase in uptake at 72-168 h. Treatment with clozapine for 6 h decreased V(max) to 40% of the control without changing the K(m) value for [(3)H]NE uptake. However, treatment with clozapine for 96 h increased V(max) by 56% over the control without a change in K(m). Scatchard plot analysis of [(3)H]desipramine (DMI) binding to membranes isolated from cells treated with clozapine for 6 h revealed a decrease in B(max) without any change in K(d); in contrast, treatment with clozapine for 96 h caused an increase in B(max) without any change in K(d). Both actinomycin D and cycloheximide, which are inhibitors of protein synthesis, suppressed the clozapine (96 h)-induced increase in [(3)H]NE uptake. Treatment of cells with clozapine for 12-96 h increased the level of NE transporter mRNA in a concentration-dependent manner (0.3-3.0 microM). These findings suggest that treatment of cells with clozapine results in the down-regulation and subsequent up-regulation of NE transporter. The latter change may be caused by the synthesis of new proteins of NE transporter via an increase in its mRNA.     

Angiotensin-(1-7) through Mas receptor up-regulates neuronal norepinephrine transporter via Akt and Erk1/2-dependent pathways

As angiotensin (Ang) (1-7) decreases norepinephrine (NE) content in the synaptic cleft, we investigated the effect of Ang-(1-7) on NE neuronal uptake in spontaneously hypertensive rats. [(3)H]-NE neuronal uptake was measured in isolated hypothalami. NE transporter (NET) expression was evaluated in hypothalamic neuronal cultures by western-blot. Ang-(1-7) lacked an acute effect on neuronal NE uptake. Conversely, Ang-(1-7) caused an increase in NET expression after 3 h incubation (40 ± 7%), which was blocked by the Mas receptor antagonist, a PI3-kinase inhibitor or a MEK1/2 inhibitor suggesting the involvement of Mas receptor and the PI3-kinase/Akt and MEK1/2-ERK1/2 pathways in the Ang-(1-7)-stimulated NET expression. Ang-(1-7) through Mas receptors stimulated Akt and ERK1/2 activities in spontaneously hypertensive rat neurons. Cycloheximide attenuated Ang-(1-7) stimulation of NET expression suggesting that Ang-(1-7) stimulates NET synthesis. In fact, Ang-(1-7) increased NET mRNA levels. Thus, we evaluated the long-term effect of Ang-(1-7) on neuronal NE uptake after 3 h incubation. Under this condition, Ang-(1-7) increased neuronal NE uptake by 60 ± 14% which was blocked by cycloheximide and the Mas receptor antagonist. Neuronal NE uptake and NET expression were decreased after 3 h incubation with an anti-Ang-(1-7) antibody. Ang-(1-7) induces a chronic stimulatory effect on NET expression. In this way, Ang-(1-7) may regulate a pre-synaptic mechanism in maintaining appropriate synaptic NE levels during hypertensive conditions.     

Regulation of the neuronal norepinephrine transporter by endothelin-1 and -3 in the rat anterior and posterior hypothalamus

We previously reported that endothelin-1 and endothelin-3 modulate norepinephrine neuronal release and tyrosine hydroxylase activity and expression in the hypothalamus. In the present study we sought to establish the role of endothelin-1 and -3 in the regulation of norepinephrine uptake in the anterior and posterior hypothalamus. Results showed that in the anterior hypothalamus endothelin-3 increased neuronal norepinephrine uptake whereas endothelin-1 decreased it. Conversely, in the posterior hypothalamic region both endothelins diminished the neuronal uptake of the amine. Endothelins response was concentration dependent and maintained at all studied times. Endothelins also modified the kinetic and internalization of the NE neuronal transporter. In the anterior hypothalamic region endothelin-3 increased the V_max and the B_max whereas endothelin-1 decreased them. However, in the posterior hypothalamic region both endothelins diminished the V_max as well as B_max. Neither endothelin-1 nor endothelin-3 modified neuronal norepinephrine transporter K_d in the studied hypothalamic regions. These findings support that in the posterior hypothalamic region both endothelins diminished neuronal norepinephrine transporter activity by reducing the amine transporter expression on the plasmatic membrane. Conversely, in the anterior hypothalamic region endothelin-3 enhanced neuronal norepinephrine transporter activity by increasing the expression of the transporter on the presynaptic membrane, whereas endothelin-1 induced the opposite effect. Present results permit us to conclude that both endothelins play an important role in the regulation of norepinephrine neurotransmission at the presynaptic nerve endings in the hypothalamus.     

Insulin receptors in the brain: Structural and physiological characterization

The present study was conducted to characterize insulin receptors and to determine the effects of insulin in synaptosomes prepared from adult rat brains. Binding of¹²⁵I-insulin to synaptosome insulin receptors was highly specific and time dependent: equilibrium binding was obtained within 60 minutes, and a t_1/2 of dissociation of 26 minutes. Cross-linking of¹²⁵I-insulin to its receptor followed by SDS-PAGE demonstrated that the apparent molecular weight of the alpha subunit of the receptor was 122,000 compared with 134,000 for the liver insulin receptor. In addition, insulin stimulated the dose-dependent phosphorylation of exogenous tyrosine containing substrate and a 95,000 MW plasma membrane associated protein, in a lectin-purified insulin receptor preparation. The membrane associated protein was determined to be the subunit of the insulin receptor. Incubation of synaptosomes with insulin caused a dose-dependent inhibition of specific sodium-sensitive [³H]norepinephrine uptake. Insulin inhibition of [³H]norepinephrine uptake was mediated by a decrease in active uptake sites without any effects in theK _m, and was specific for insulin since related and unrelated peptides influenced the uptake in proportion to their structural similarity with insulin. These observations indicate that synaptosomes prepared from the adult rat brain possess specific insulin receptors and insulin has inhibitory effects on norepinephrine uptake in the preparation.     

Hormonal and Neurotransmitter Regulation of Ca++ Influx Through Voltage-Dependent Slow Channels in Cardiac Muscle Membrane

The voltage-and time-dependent slow channels in the myocardial cell membrane are the major pathway by which Ca⁺⁺ ions enter the cell during excitation for initiation and regulation of the force of contraction of cardiac muscle. These slow channels behave kinetically as if their gates open, close, and recover more slowly than those of the fast Na⁺ channels; in addition, the slow channel gates operate over a less negative (more depolarized) voltage range. Tatrodotoxin does not block the slow channels, whereas the calcium antagonistic drugs, Mn⁺⁺, Co⁺⁺, and La⁺⁺⁺ ions do. The slow channels have some special properties, including their functional dependence on metabolic energy, their selective blockade by acidosis, and their regulation by cyclic AMP level. Because of their regulation by cyclic AMP, it is proposed that either the slow channel protein or an associated regulatory protein must be phosphorylated in order for the channel to be made available for voltage activation during excitation. That is, the dephosphorylated channel would be electrically silent.

The requirement for phosphorylation allows the extrinsic control of the slow channels and Ca⁺⁺ influx by neurotransmitters, hormones, and autacoids that affect the cyclic nucleotide levels.     

Endocrine responses during exercise-heat stress: effects of prior isotonic and hypotonic intravenous rehydration

Exercise following exercise-induced dehydration (EID) has been shown to elevate concentrations of plasma norepinephrine (NE) and hypothalamic-pituitary-adrenal axis hormones. However, it is not known how intravenous (i.v.) rehydration (Rh) with isotonic (ISO) or hypotonic (HYPO) saline affects these hormone concentrations. It was hypothesized that HYPO, versus ISO, would lead to lower plasma NE and cortisol concentrations ([CORT]) during subsequent exercise following EID due to a decrease in plasma sodium concentration [Na⁺]. Eight non-heat acclimated men completed three experimental treatments (counterbalanced design) immediately following EID (33°C) to −4% body mass loss. The Rh treatments were i.v. 0.9% NaCl (ISO, 25 ml · kg⁻¹), i.v. 0.45% NaCl (HYPO, 25 ml · kg⁻¹), and no fluid (NF). After Rh and rest (2 h total), the subjects walked at 53–54 percent of maximal O₂ uptake for 45 min at 36°C. After Rh, the following observations were made before/during exercise: percentage change in plasma volume (PV) was lower in NF compared to ISO and HYPO but similar between ISO and HYPO; Δ[Na⁺] was similar between ISO and NF and higher in ISO compared to HYPO; Δ plasma NE was higher in NF compared to ISO and HYPO, but similar between ISO and HYPO; Δ plasma [CORT] was higher in NF compared to ISO and HYPO and higher in ISO compared to HYPO; rectal temperature was higher in NF compared to ISO and HYPO. These data would suggest that sympathetic nervous activity and [CORT] during exercise, subsequent to EID and Rh, was affected by lower PV (probably through cardiopulmonary baroreflexes) as well as core temperature. Furthermore, [CORT] was affected by Δ[Na⁺] after Rh through an unknown mechanism. Accepted: 16 July 1997     

Automated surface area measurement of cultured cardiac myocytes

An automated method for rapidly measuring surface area of individual cardiac myocytes was used as an index of myocyte growth. Hearts from 2- to 4-day-old rats were digested by overnight incubation in cold trypsin solution. Enriched suspensions of myocytes were plated at 2×10⁵ cells/well in 12-well-culture plates. Cells were grown in M199 supplemented with 1%, 10% serum or 10% serum plus 10^–7 M norepinephrine. On days 1–4 after plating, cells were fixed in Bouin's Solution and stained with Weigert's Iron Hematoxylin and Biebrich Scarlet-Acid Fuchsin. An inverted microscope, video camera and monitor were coupled to a video image processor (Image Technology Corp.). The enhanced image of stained heart cells was digitized, and perimeter, length, width and area of each selected cell were calculated. One hundred randomly selected cells were measured in each of eight wells from each treatment-day group. Areas of individual myocytes varied widely in culture dishes and the distribition was skewed toward larger cells. The standard deviation increased in proportion to an increase in mean cell area. A logarithmic transformation of the data normalized the data and yielded a more homogeneous variance. The geometric mean area of heart cells supplemented with 1% serum increased only slightly, but significantly, during four days in culture. Geometric mean area of cells supplemented with 10% serum increased nearly four-fold. Supplementing cells with norepinephrine (10^–7 M) in addition to 10% serum did not induce a further increase in cell size. This technique has the potential to rapidly and objectively monitor heart cell growth following pharmacological or toxicological treatments.     

Molecular cloning and structural analysis of human norepinephrine transporter gene（NETHG）

A cDNA molecule encoding a major part of the human Norepinephrine transporter(hNET) was synthesized by means of Polymerase Chain Reaction(PCR) technique and used as a probe for selecting the human genomic NET gene.A positive clone harbouring the whole gene was obtained from a human lymphocyte genomic library through utilizing the “genomic walking” technique.The clone,designated as phNET,harbours a DNA fragment of about 59 kd in length inserted into BamH I site in cosmid pWE15.The genomic clone contains 14 exons encoding all amino acid residues in the protein.A single exon encodes a distinct transmembrane domain,except for transmembrane domain 10 and 11,which are encoded by part of two exons respectively,and exon 12,which encodes part of domain 11 and all of domain 12.These results imply that there is a close relationship between exon splicing of a gene and structureal domains of the protein,as is the case for the human γ－aminobutyric acid transporter(hGAT) and a number of other membrane proteins.     

Nonlinear propagation of agonist-induced cytoplasmic calcium waves in single astrocytes

In astrocytes in primary culture, activation of neurotransmitter receptors results in intracellular calcium signals that propagate as waves across the cell. Similar agonist-induced calcium waves have been observed in astrocytes in organotypic cultures in response to synaptic activation. By using primary cultured astrocytes grown on glass coverslips, in conjunction with fluorescence microscopy we have analyzed agonist-induced Ca²⁺ wave initiation and propagation in individual cells. Both norepinephrine and glutamate elicited Ca²⁺ signals which were initiated focally and discretely in one region of the cell, from where the signals spread as waves along the entire length of the cell. Analysis of the wave propagation and the waveform revealed that the propagation was nonlinear with one or more focal loci in the cytoplasm where the wave was regeneratively amplified. These individual loci appear as discrete focal areas 7–15 μm in diameter and having intrinsic oscillatory properties that differ from each other. The wave initiation locus and the different amplification loci remained invariant in space during the course of the experiment and supported an identical spatiotemporal pattern of signalling in any given cell in response to multiple agonist applications and when stimulated with different agonists which are coupled via InsP₃. Cytoplasmic Ca²⁺ concentration at rest was consistently higher (17 ± 4nM, mean ± S.E.M.) in the wave initiation locus compared with the rest of the cytoplam. The nonlinear propagation results from significant changes in signal rise times, amplitudes, and wave velocity in cellular regions of active loci. Analysis of serial slices across the cell revealed that the rise times and amplitudes of local signals were as much as three- to fourfold higher in the loci of amplification. A phenomenon of hierarchy in local amplitudes of the signal in the amplification loci was observed with the wave initiation locus having the smallest and the most distal locus having largest amplitude. By this mechanism locally very high concentrations of Ca²⁺ are achieved in strategic locations in the cell in response to receptor activation. While the average wave velocity calculated over the length of the cell was 10–15 μm/s, in the active loci rates as high as 40 μm/s were measured. Wave velocity was fivefold lower in regions of the cell separating active loci. The differences in the intrinsic oscillatory periods give rise to local Ca²⁺ waves that show the properties of collision and annihilation. It is hypothesized that the wave front provokes regenerative Ca²⁺ release from specialized areas in the cell where the endoplasmic reticulum is endowed with higher density of InsP₃ receptor channels. Thus wave propagation is achieved by a process of diffusion and regenerative Ca²⁺ release in multiple cellular loci provoked by the advancing wave front; in this way, wave propagation is nonlinear and saltatory. Regenerative Ca²⁺ wave propagation from distal atrocytic processes to the cell body and neighboring cells is likely to provide an important signalling mechanism in the nervous system. 1994 John Wiley & Sons, Inc.     

The proportion of tetrahydrobiopterin deficiency and PAH gene deficiency variants among cases with hyperphenyalaninemia in Western Iran

BACKGROUND:

Defects either in phenylalanine hydroxylase (PheOH) or in the production and recycling of its cofactor (tetrahydrobiopterin [BH4]) are the causes of primary hyperphenylalaninemia (HPA). The aim of our study was to investigate the current status of different variants of HPA Kurdish patients in Kermanshah province, Iran.

MATERIALS AND METHODS:

From 33 cases enrolled in our study, 32 were identified as HPA patients. Reassessing of pre-treatment phenylalanine concentrations and the analysis of urinary pterins was done by high-performance liquid chromatography method.

RESULTS:

A total of 30 patients showed PAH deficiency and two patients were diagnosed with BH4 deficiency (BH4/HPA ratio = 6.25%). Both of these two BH4-deficient patients were assigned to severe variant of dihydropteridine reductase (DHPR) deficiency. More than 75% of patients with PAH deficiency classified as classic phenylketonuria (PKU) according their levels of pre-treatment phenylalanine concentrations.

CONCLUSION:

Based on the performed study, we think that the frequency of milder forms of PKU is higher than those was estimated before and/or our findings here. Furthermore, the frequency of DHPR deficiency seems to be relatively high in our province. Since the clinical symptoms of DHPR deficiency are confusingly similar to that of classic PKU and its prognosis are much worse than classical PKU and cannot be solely treated with the PKU regime, our pilot study support that it is crucial to set up screening for BH4 deficiency, along with PAH deficiency, among all HPA patients diagnosed with HPA.     

内皮素对大鼠肠系膜微血管的作用

应用显微电视录象技术可观察到内皮素(ET)对戊巴比妥钠麻醉的 Wistar 大鼠的肠系膜微血管有收缩作用,血液流速减慢,甚至产生微循环障碍,这个作用相当持久,并呈剂量依赖关系。ET 的这个作用远高于去甲肾上腺素。这些结果提示,ET 作为强烈的微血管收缩剂,在微循环紊乱疾病的发病学中可能具有重要意义。     

Fasting and hypothalamic catecholamines in goldfish

Hypothalamic catecholamines and their metabolites have been studied after 7 days starvation and starvation plus 1 day refeeding in goldfish Carassius auratus. A reduction of norepinephrine (NE) and dopamine (DA) content (21 and 28%, respectively) together with an increase (53%) of NE turnover, without significant modifications of DA turnover was observed following 7 days starvation. These data indicate that NE and DA are involved in the hypothalamic response to fasting in fish. Different mechanisms can be suggested, that is, an activation of noradrenergic system and a decrease of dopaminergic system by fasting. NE would stimulate food intake, whereas DA would inhibit it.     

Circadian Characteristics of Urinary Epinephrine and Norepinephrine from Healthy Young Women in Japan and USA

Clinically healthy diurnally active young adult women were studied during the same season (March) at the Universities of Kyushu (Fukuoka City, Japan) and of Minnesota (Minneapolis, USA), under comparable conditions, except that the habitual diets were not changed. The subjects (20 Japanese and 16 Americans of mixed Caucasian background) were studied over a single 24-hr span. Urine was collected at 4-hr intervals. A circadian rhythm in total urinary norepinephrine excretion showed similar characteristics in Japanese and Americans. In epinephrine excretion, the Japanese women showed a statistically significantly higher amplitude with higher peak values, but no statistically significant difference in the rhythm-adjusted mean. This intergroup difference is strictly time dependent; it does not come to the fore in urine samples covering the nocturnal rest span of the subjects.     

Increased resting energy expenditure after 40 minutes of aerobic but not resistance exercise

Objective: Resting energy expenditure (REE) is increased 24 hours after high‐intensity aerobic exercise lasting 60 minutes, whereas results have been inconsistent after resistance training and aerobic exercise of shorter duration. The objective of the study was to compare the effects of 40 minutes of high‐intensity aerobic vs. resistance exercise on REE 19 to 67 hours after exercise. Research Methods and Procedures: REE was compared 19, 43, and 67 hours after 40 minutes of aerobic training (AT; 80% maximum heart rate) or resistance training (RT; 10 repetitions at 80% maximum strength, two sets and eight exercises). Twenty‐three black and 22 white women were randomly assigned to AT, RT, or no training (controls). Exercisers trained 25 weeks. REE was measured after a 12‐hour fast. Results: There was a significant time × group interaction for REE when adjusted for fat‐free mass and fat mass, with post hoc tests revealing that the 50‐kcal difference between 19 and 43 hours (1310 ± 196 to 1260 ± 161 kcal) and the 34‐kcal difference between 19 and 67 hours (1310 ± 196 to 1276 ± 168 kcal) were significant for AT. No other differences were found, including RT (19 hours, 1256 ± 160; 43 hours, 1251 ± 160; 67 hours, 1268 ± 188 kcal). Urine norepinephrine increased with training only in AT. After adjusting for fat‐free mass, REE Δ between 19 and both 43 and 67 hours was significantly related to urine norepinephrine (r = 0.76, p < 0.01 and 0.68, p < 0.03, respectively). Discussion: Consistent with findings on longer duration AT, these results show that 40 minutes of AT elevates REE for 19 hours in trained black and white women. This elevation did not occur with 40 minutes of RT. Results suggest that differences are, in part, due to increased sympathetic tone.     

Response of soybean genotypes to boron,zinc and manganese deficiency in tissue culture

The effect of boron (B), zinc (Zn), and manganese (Mn) deficiency in the medium on eight soybean genotypes was evaluated using friable callus after a 21 day growth period. Of the three micronutrients evaluated, Zn and B deficiencies had the greatest effect on callus weight, while Mn had only a slight effect. Despite this, significant differences in callus weight reduction of the eight genotypes tested were observed on the three different media. These results indicate that genotypic variation for response to B, Zn, and Mn deficiency is present in soybean at the cellular level. If the resistant genotypes identified in this study are also resistant at the whole plant level, then they could be used in soils which are deficient in the above micronutrients.