Metamorphic proteins and how to find them

In the last two decades, our existing notion that most foldable proteins have a unique native state has been challenged by the discovery of metamorphic proteins, which reversibly interconvert between multiple, sometimes highly dissimilar, native states. As the number of known metamorphic proteins increases, several computational and experimental strategies have emerged for gaining insights about their refolding processes and identifying unknown metamorphic proteins amongst the known proteome. In this review, we describe the current advances in biophysically and functionally ascertaining the structural interconversions of metamorphic proteins and how coevolution can be harnessed to identify novel metamorphic proteins from sequence information. We also discuss the challenges and ongoing efforts in using artificial intelligence-based protein structure prediction methods to discover metamorphic proteins and predict their corresponding three-dimensional structures.

Sequence clustering confounds AlphaFold2

Though typically associated with a single folded state, some globular proteins remodel their secondary and/or tertiary structures in response to cellular stimuli. AlphaFold21 (AF2) readily generates one dominant protein structure for these fold-switching (a.k.a. metamorphic) proteins2, but it often fails to predict their alternative experimentally observed structures3,4. Wayment-Steele, et al. steered AF2 to predict alternative structures of a few metamorphic proteins using a method they call AF-cluster5. However, their Paper lacks some essential controls needed to assess AF-cluster's reliability. We find that these controls show AF-cluster to be a poor predictor of metamorphic proteins. First, closer examination of the Paper's results reveals that random sequence sampling outperforms sequence clustering, challenging the claim that AF-cluster works by "deconvolving conflicting sets of couplings." Further, we observe that AF-cluster mistakes some single-folding KaiB homologs for fold switchers, a critical flaw bound to mislead users. Finally, proper error analysis reveals that AF-cluster predicts many correct structures with low confidence and some experimentally unobserved conformations with confidences similar to experimentally observed ones. For these reasons, we suggest using ColabFold6-based random sequence sampling7-augmented by other predictive approaches-as a more accurate and less computationally intense alternative to AF-cluster.

AlphaFold2 has more to learn about protein energy landscapes

Recent work suggests that AlphaFold2 (AF2)-a deep learning-based model that can accurately infer protein structure from sequence-may discern important features of folded protein energy landscapes, defined by the diversity and frequency of different conformations in the folded state. Here, we test the limits of its predictive power on fold-switching proteins, which assume two structures with regions of distinct secondary and/or tertiary structure. Using several implementations of AF2, including two published enhanced sampling approaches, we generated >280,000 models of 93 fold-switching proteins whose experimentally determined conformations were likely in AF2's training set. Combining all models, AF2 predicted fold switching with a modest success rate of ~25%, indicating that it does not readily sample both experimentally characterized conformations of most fold switchers. Further, AF2's confidence metrics selected against models consistent with experimentally determined fold-switching conformations in favor of inconsistent models. Accordingly, these confidence metrics-though suggested to evaluate protein energetics reliably-did not discriminate between low and high energy states of fold-switching proteins. We then evaluated AF2's performance on seven fold-switching proteins outside of its training set, generating >159,000 models in total. Fold switching was accurately predicted in one of seven targets with moderate confidence. Further, AF2 demonstrated no ability to predict alternative conformations of two newly discovered targets without homologs in the set of 93 fold switchers. These results indicate that AF2 has more to learn about the underlying energetics of protein ensembles and highlight the need for further developments of methods that readily predict multiple protein conformations.

SSDraw: Software for generating comparative protein secondary structure diagrams

The program SSDraw generates publication-quality protein secondary structure diagrams from three-dimensional protein structures. To depict relationships between secondary structure and other protein features, diagrams can be colored by conservation score, B-factor, or custom scoring. Diagrams of homologous proteins can be registered according to an input multiple sequence alignment. Linear visualization allows the user to stack registered diagrams, facilitating comparison of secondary structure and other properties among homologous proteins. SSDraw can be used to compare secondary structures of homologous proteins with both conserved and divergent folds. It can also generate one secondary structure diagram from an input protein structure of interest. The source code can be downloaded (https://github.com/ncbi/SSDraw) and run locally for rapid structure generation, while a Google Colab notebook allows easy use.

ColabFold predicts alternative protein structures from single sequences, coevolution unnecessary for AF-cluster

Though typically associated with a single folded state, globular proteins are dynamic and often assume alternative or transient structures important for their functions1,2. Wayment-Steele, et al. steered ColabFold3 to predict alternative structures of several proteins using a method they call AF-cluster4. They propose that AF-cluster "enables ColabFold to sample alternate states of known metamorphic proteins with high confidence" by first clustering multiple sequence alignments (MSAs) in a way that "deconvolves" coevolutionary information specific to different conformations and then using these clusters as input for ColabFold. Contrary to this Coevolution Assumption, clustered MSAs are not needed to make these predictions. Rather, these alternative structures can be predicted from single sequences and/or sequence similarity, indicating that coevolutionary information is unnecessary for predictive success and may not be used at all. These results suggest that AF-cluster's predictive scope is likely limited to sequences with distinct-yet-homologous structures within ColabFold's training set.

SSDraw: software for generating comparative protein secondary structure diagrams

The program SSDraw generates publication-quality protein secondary structure diagrams from three-dimensional protein structures. To depict relationships between secondary structure and other protein features, diagrams can be colored by conservation score, B-factor, or custom scoring. Diagrams of homologous proteins can be registered according to an input multiple sequence alignment. Linear visualization allows the user to stack registered diagrams, facilitating comparison of secondary structure and other properties among homologous proteins. SSDraw can be used to compare secondary structures of homologous proteins with both conserved and divergent folds. It can also generate one secondary structure diagram from an input protein structure of interest. The source code can be downloaded (https://github.com/ethanchen1301/SSDraw) and run locally for rapid structure generation, while a Google Colab notebook allows easy use.

Evolutionary selection of proteins with two folds

Although most globular proteins fold into a single stable structure, an increasing number have been shown to remodel their secondary and tertiary structures in response to cellular stimuli. State-of-the-art algorithms predict that these fold-switching proteins adopt only one stable structure, missing their functionally critical alternative folds. Why these algorithms predict a single fold is unclear, but all of them infer protein structure from coevolved amino acid pairs. Here, we hypothesize that coevolutionary signatures are being missed. Suspecting that single-fold variants could be masking these signatures, we developed an approach, called Alternative Contact Enhancement (ACE), to search both highly diverse protein superfamilies-composed of single-fold and fold-switching variants-and protein subfamilies with more fold-switching variants. ACE successfully revealed coevolution of amino acid pairs uniquely corresponding to both conformations of 56/56 fold-switching proteins from distinct families. Then, we used ACE-derived contacts to (1) predict two experimentally consistent conformations of a candidate protein with unsolved structure and (2) develop a blind prediction pipeline for fold-switching proteins. The discovery of widespread dual-fold coevolution indicates that fold-switching sequences have been preserved by natural selection, implying that their functionalities provide evolutionary advantage and paving the way for predictions of diverse protein structures from single sequences.

Fluid protein fold space and its implications

Fold-switching proteins, which remodel their secondary and tertiary structures in response to cellular stimuli, suggest a new view of protein fold space. For decades, experimental evidence has indicated that protein fold space is discrete: dissimilar folds are encoded by dissimilar amino acid sequences. Challenging this assumption, fold-switching proteins interconnect discrete groups of dissimilar protein folds, making protein fold space fluid. Three recent observations support the concept of fluid fold space: (1) some amino acid sequences interconvert between folds with distinct secondary structures, (2) some naturally occurring sequences have switched folds by stepwise mutation, and (3) fold switching is evolutionarily selected and likely confers advantage. These observations indicate that minor amino acid sequence modifications can transform protein structure and function. Consequently, proteomic structural and functional diversity may be expanded by alternative splicing, small nucleotide polymorphisms, post-translational modifications, and modified translation rates.

Identification of a covert evolutionary pathway between two protein folds

Although homologous protein sequences are expected to adopt similar structures, some amino acid substitutions can interconvert α-helices and β-sheets. Such fold switching may have occurred over evolutionary history, but supporting evidence has been limited by the: (1) abundance and diversity of sequenced genes, (2) quantity of experimentally determined protein structures, and (3) assumptions underlying the statistical methods used to infer homology. Here, we overcome these barriers by applying multiple statistical methods to a family of ~600,000 bacterial response regulator proteins. We find that their homologous DNA-binding subunits assume divergent structures: helix-turn-helix versus α-helix + β-sheet (winged helix). Phylogenetic analyses, ancestral sequence reconstruction, and AlphaFold2 models indicate that amino acid substitutions facilitated a switch from helix-turn-helix into winged helix. This structural transformation likely expanded DNA-binding specificity. Our approach uncovers an evolutionary pathway between two protein folds and provides a methodology to identify secondary structure switching in other protein families.

Distinguishing features of fold-switching proteins

Though many folded proteins assume one stable structure that performs one function, a small-but-increasing number remodel their secondary and tertiary structures and change their functions in response to cellular stimuli. These fold-switching proteins regulate biological processes and are associated with autoimmune dysfunction, severe acute respiratory syndrome coronavirus-2 infection, and more. Despite their biological importance, it is difficult to computationally predict fold switching. With the aim of advancing computational prediction and experimental characterization of fold switchers, this review discusses several features that distinguish fold-switching proteins from their single-fold and intrinsically disordered counterparts. First, the isolated structures of fold switchers are less stable and more heterogeneous than single folders but more stable and less heterogeneous than intrinsically disordered proteins (IDPs). Second, the sequences of single fold, fold switching, and intrinsically disordered proteins can evolve at distinct rates. Third, proteins from these three classes are best predicted using different computational techniques. Finally, late-breaking results suggest that single folders, fold switchers, and IDPs have distinct patterns of residue-residue coevolution. The review closes by discussing high-throughput and medium-throughput experimental approaches that might be used to identify new fold-switching proteins.

Evolutionary selection of proteins with two folds

Although most globular proteins fold into a single stable structure 1 , an increasing number have been shown to remodel their secondary and tertiary structures in response to cellular stimuli 2 . State-of-the-art algorithms 3-5 predict that these fold-switching proteins assume only one stable structure 6,7 , missing their functionally critical alternative folds. Why these algorithms predict a single fold is unclear, but all of them infer protein structure from coevolved amino acid pairs. Here, we hypothesize that coevolutionary signatures are being missed. Suspecting that over-represented single-fold sequences may be masking these signatures, we developed an approach to search both highly diverse protein superfamilies-composed of single-fold and fold-switching variants-and protein subfamilies with more fold-switching variants. This approach successfully revealed coevolution of amino acid pairs uniquely corresponding to both conformations of 56/58 fold-switching proteins from distinct families. Then, using a set of coevolved amino acid pairs predicted by our approach, we successfully biased AlphaFold2 5 to predict two experimentally consistent conformations of a candidate protein with unsolved structure. The discovery of widespread dual-fold coevolution indicates that fold-switching sequences have been preserved by natural selection, implying that their functionalities provide evolutionary advantage and paving the way for predictions of diverse protein structures from single sequences.

Measuring Ostracism-Induced Changes in Consumption of Palatable Food: Feasibility of a Novel Behavioral Task

Purpose

Ostracism is a highly aversive interpersonal experience. Previous research suggests that it can increase consumption of highly palatable food in some individuals, but decrease it in others. Thus, we developed the Cyberball-Milkshake Task (CMT), to facilitate research investigating individual differences in ostracism's effects on consumption of highly palatable food. We present data on feasibility for the CMT in a sample of young adult women.

Materials and Methods

Participants were 22 women, 18-30 years old, reporting very low or very high levels of emotional eating at screening. Participants performed the CMT, which consisted of 12 trials. Each trial included: playing a round of Cyberball (a computerized game of catch with fictitious "other participants" programmed to either include or exclude the participant); viewing a chocolate image; and then consuming a participant-determined amount of milkshake. Participants subsequently played an additional inclusion and exclusion round of Cyberball, each immediately followed by questionnaires assessing current mood and recent Cyberball experience.

Results

Cyberball exclusion (vs. inclusion) was associated with large, significant increases in reported ostracism and threats to self-esteem; exclusion's effects on affect were in the expected direction (e.g., increased negative affect), but generally small and non-significant. Milkshake intake was measurable for 95% of participants, on 96% of trials. Intake decreased quadratically across trials, with a steep negative slope for low trial numbers that decreased to the point of being flat for the highest trial numbers.

Discussion

The CMT is a generally feasible approach to investigating ostracism's effects on consumption of highly palatable food. The feasibility (and validity) of the CMT may benefit from modification (e.g., fewer trials and longer rounds of Cyberball). Future research should examine whether performance on a modified version of the CMT predicts real-world behavior in a larger sample.

A high-throughput predictive method for sequence-similar fold switchers

Although most experimentally characterized proteins with similar sequences assume the same folds and perform similar functions, an increasing number of exceptions is emerging. One class of exceptions comprises sequence-similar fold switchers, whose secondary structures shift from α-helix <-> β-sheet through a small number of mutations, a sequence insertion, or a deletion. Predictive methods for identifying sequence-similar fold switchers are desirable because some are associated with disease and/or can perform different functions in cells. Here, we use homology-based secondary structure predictions to identify sequence-similar fold switchers from their amino acid sequences alone. To do this, we predicted the secondary structures of sequence-similar fold switchers using three different homology-based secondary structure predictors: PSIPRED, JPred4, and SPIDER3. We found that α-helix <-> β-strand prediction discrepancies from JPred4 discriminated between the different conformations of sequence-similar fold switchers with high statistical significance (P < 1.8*10-19 ). Thus, we used these discrepancies as a classifier and found that they can often robustly discriminate between sequence-similar fold switchers and sequence-similar proteins that maintain the same folds (Matthews Correlation Coefficient of 0.82). We found that JPred4 is a more robust predictor of sequence-similar fold switchers because of (a) the curated sequence database it uses to produce multiple sequence alignments and (b) its use of sequence profiles based on Hidden Markov Models. Our results indicate that inconsistencies between JPred4 secondary structure predictions can be used to identify some sequence-similar fold switchers from their sequences alone. Thus, the negative information from inconsistent secondary structure predictions can potentially be leveraged to identify sequence-similar fold switchers from the broad base of genomic sequences.

A sequence-based method for predicting extant fold switchers that undergo α-helix ↔ β-strand transitions

Extant fold‐switching proteins remodel their secondary structures and change their functions in response to cellular stimuli, regulating biological processes and affecting human health. Despite their biological importance, these proteins remain understudied. Predictive methods are needed to expedite the process of discovering and characterizing more of these shapeshifting proteins. Most previous approaches require a solved structure or all‐atom simulations, greatly constraining their use. Here, we propose a high‐throughput sequence‐based method for predicting extant fold switchers that transition from α‐helix in one conformation to β‐strand in the other. This method leverages two previous observations: (a) α‐helix ↔ β‐strand prediction discrepancies from JPred4 are a robust predictor of fold switching, and (b) the fold‐switching regions (FSRs) of some extant fold switchers have different secondary structure propensities when expressed by themselves (isolated FSRs) than when expressed within the context of their parent protein (contextualized FSRs). Combining these two observations, we ran JPred4 on 99‐fold‐switching proteins and found strong correspondence between predicted and experimentally observed α‐helix ↔ β‐strand discrepancies. To test the overall robustness of this finding, we randomly selected regions of proteins not expected to switch folds (single‐fold proteins) and found significantly fewer predicted α‐helix ↔ β‐strand discrepancies. Combining these discrepancies with the overall percentage of predicted secondary structure, we developed a classifier to identify extant fold switchers (Matthews correlation coefficient of .71). Although this classifier had a high false‐negative rate (7/17), its false‐positive rate was very low (2/136), suggesting that it can be used to predict a subset of extant fold switchers from a multitude of available genomic sequences.

Predictable fold switching by the SARS-CoV-2 protein ORF9b

Extant fold-switching proteins remodel their secondary structures and change their functions in response to environmental stimuli. These shapeshifting proteins regulate biological processes and are associated with a number of diseases, including tuberculosis, cancer, Alzheimer's, and autoimmune disorders. Thus, predictive methods are needed to identify more fold-switching proteins, especially since all naturally occurring instances have been discovered by chance. In response to this need, two high-throughput predictive methods have recently been developed. Here we test them on ORF9b, a newly discovered fold switcher and potential therapeutic target from the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Promisingly, both methods correctly indicate that ORF9b switches folds. We then tested the same two methods on ORF9b1, the ORF9b homolog from SARS-CoV-1. Again, both methods predict that ORF9b1 switches folds, a finding consistent with experimental binding studies. Together, these results (a) demonstrate that protein fold switching can be predicted using high-throughput computational approaches and (b) suggest that fold switching might be a general characteristic of ORF9b homologs.

Functional and Regulatory Roles of Fold-Switching Proteins

Fold-switching proteins respond to cellular stimuli by remodeling their secondary structures and changing their functions. Whereas several previous reviews have focused on various structural, physical-chemical, and evolutionary aspects of this newly emerging class of proteins, this minireview focuses on how fold switching modulates protein function and regulates biological processes. It first compares and contrasts fold switchers with other known types of proteins. Second, it presents examples of how various proteins can change their functions through fold switching. Third, it demonstrates that fold switchers can regulate biological processes by discussing two proteins, RfaH and KaiB, whose dramatic secondary structure remodeling events directly affect gene expression and a circadian clock, respectively. Finally, this minireview discusses how the field of protein fold switching might advance.

Inaccurate secondary structure predictions often indicate protein fold switching

Although most proteins conform to the classical one‐structure/one‐function paradigm, an increasing number of proteins with dual structures and functions have been discovered. In response to cellular stimuli, such proteins undergo structural changes sufficiently dramatic to remodel even their secondary structures and domain organization. This “fold‐switching” capability fosters protein multi‐functionality, enabling cells to establish tight control over various biochemical processes. Accurate predictions of fold‐switching proteins could both suggest underlying mechanisms for uncharacterized biological processes and reveal potential drug targets. Recently, we developed a prediction method for fold‐switching proteins using structure‐based thermodynamic calculations and discrepancies between predicted and experimentally determined protein secondary structure (Porter and Looger, Proc Natl Acad Sci U S A 2018; 115:5968–5973). Here we seek to leverage the negative information found in these secondary structure prediction discrepancies. To do this, we quantified secondary structure prediction accuracies of 192 known fold‐switching regions (FSRs) within solved protein structures found in the Protein Data Bank (PDB). We find that the secondary structure prediction accuracies for these FSRs vary widely. Inaccurate secondary structure predictions are strongly associated with fold‐switching proteins compared to equally long segments of non‐fold‐switching proteins selected at random. These inaccurate predictions are enriched in helix‐to‐strand and strand‐to‐coil discrepancies. Finally, we find that most proteins with inaccurate secondary structure predictions are underrepresented in the PDB compared with their alternatively folded cognates, suggesting that unequal representation of fold‐switching conformers within the PDB could be an important cause of inaccurate secondary structure predictions. These results demonstrate that inconsistent secondary structure predictions can serve as a useful preliminary marker of fold switching.

Amino acid signatures of HLA Class-I and II molecules are strongly associated with SLE susceptibility and autoantibody production in Eastern Asians

Human leukocyte antigen (HLA) is a key genetic factor conferring risk of systemic lupus erythematosus (SLE), but precise independent localization of HLA effects is extremely challenging. As a result, the contribution of specific HLA alleles and amino-acid residues to the overall risk of SLE and to risk of specific autoantibodies are far from completely understood. Here, we dissected (a) overall SLE association signals across HLA, (b) HLA-peptide interaction, and (c) residue-autoantibody association. Classical alleles, SNPs, and amino-acid residues of eight HLA genes were imputed across 4,915 SLE cases and 13,513 controls from Eastern Asia. We performed association followed by conditional analysis across HLA, assessing both overall SLE risk and risk of autoantibody production. DR15 alleles HLA-DRB1*15:01 (P = 1.4x10^-27, odds ratio (OR) = 1.57) and HLA-DQB1*06:02 (P = 7.4x10^-23, OR = 1.55) formed the most significant haplotype (OR = 2.33). Conditioned protein-residue signals were stronger than allele signals and mapped predominantly to HLA-DRB1 residue 13 (P = 2.2x10^-75) and its proxy position 11 (P = 1.1x10^-67), followed by HLA-DRB1-37 (P = 4.5x10^-24). After conditioning on HLA-DRB1, novel associations at HLA-A-70 (P = 1.4x10^-8), HLA-DPB1-35 (P = 9.0x10^-16), HLA-DQB1-37 (P = 2.7x10^-14), and HLA-B-9 (P = 6.5x10^-15) emerged. Together, these seven residues increased the proportion of explained heritability due to HLA to 2.6%. Risk residues for both overall disease and hallmark autoantibodies (i.e., nRNP: DRB1-11, P = 2.0x10^-14; DRB1-13, P = 2.9x10^-13; DRB1-30, P = 3.9x10^-14) localized to the peptide-binding groove of HLA-DRB1. Enrichment for specific amino-acid characteristics in the peptide-binding groove correlated with overall SLE risk and with autoantibody presence. Risk residues were in primarily negatively charged side-chains, in contrast with rheumatoid arthritis. We identified novel SLE signals in HLA Class I loci (HLA-A, HLA-B), and localized primary Class II signals to five residues in HLA-DRB1, HLA-DPB1, and HLA-DQB1. These findings provide insights about the mechanisms by which the risk residues interact with each other to produce autoantibodies and are involved in SLE pathophysiology.

The Human leukocyte antigen (HLA) region is a key genetic factor conferring risk of systemic lupus erythematosus (SLE). In spite of multiple SLE association signals identified in the HLA region, only amino-acid residues within HLA-DRB1 have been specifically described previously. In this study, we performed an imputation-based analysis on individuals with East Asian ancestry, and characterized SLE risk within the HLA region for all involved independent genes (HLA-DRB1, HLA-DPB1, HLA-DQB1, HLA-A, and HLA-B). Furthermore, we identified a characteristic SLE risk residue signature as well as a pattern of specific nRNP and Ro/La autoantibody residues located in the peptide-binding grooves, suggesting their key involvement in autoantibody production.

Subdomain interactions foster the design of two protein pairs with ∼80% sequence identity but different folds

Metamorphic proteins, including proteins with high levels of sequence identity but different folds, are exceptions to the long-standing rule-of-thumb that proteins with as little as 30% sequence identity adopt the same fold. Which topologies can be bridged by these highly identical sequences remains an open question. Here we bridge two 3-α-helix bundle proteins with two radically different folds. Using a straightforward approach, we engineered the sequences of one subdomain within maltose binding protein (MBP, α/β/α-sandwich) and another within outer surface protein A (OspA, β-sheet) to have high sequence identity (80 and 77%, respectively) with engineered variants of protein G (GA, 3-α-helix bundle). Circular dichroism and nuclear magnetic resonance spectra of all engineered variants demonstrate that they maintain their native conformations despite substantial sequence modification. Furthermore, the MBP variant (80% identical to GA) remained active. Thermodynamic analysis of numerous GA and MBP variants suggests that the key to our approach involved stabilizing the modified MBP and OspA subdomains via external interactions with neighboring substructures, indicating that subdomain interactions can stabilize alternative folds over a broad range of sequence variation. These findings suggest that it is possible to bridge one fold with many other topologies, which has implications for protein folding, evolution, and misfolding diseases.

Counting peptide-water hydrogen bonds in unfolded proteins

It is often assumed that the peptide backbone forms a substantial number of additional hydrogen bonds when a protein unfolds. We challenge that assumption in this article. Early surveys of hydrogen bonding in proteins of known structure typically found that most, but not all, backbone polar groups are satisfied, either by intramolecular partners or by water. When the protein is folded, these groups form approximately two hydrogen bonds per peptide unit, one donor or acceptor for each carbonyl oxygen or amide hydrogen, respectively. But when unfolded, the backbone chain is often believed to form three hydrogen bonds per peptide unit, one partner for each oxygen lone pair or amide hydrogen. This assumption is based on the properties of small model compounds, like N-methylacetamide, or simply accepted as self-evident fact. If valid, a chain of N residues would have approximately 2N backbone hydrogen bonds when folded but 3N backbone hydrogen bonds when unfolded, a sufficient difference to overshadow any uncertainties involved in calculating these per-residue averages. Here, we use exhaustive conformational sampling to monitor the number of H-bonds in a statistically adequate population of blocked polyalanyl-six-mers as the solvent quality ranges from good to poor. Solvent quality is represented by a scalar parameter used to Boltzmann-weight the population energy. Recent experimental studies show that a repeating (Gly-Ser) polypeptide undergoes a denaturant-induced expansion accompanied by breaking intramolecular peptide H-bonds. Results from our simulations augment this experimental finding by showing that the number of H-bonds is approximately conserved during such expansion⇋compaction transitions.

Phase I trial of outpatient weekly docetaxel, carboplatin and concurrent thoracic radiation therapy for stage III unresectable non-small-cell lung cancer: a Vanderbilt cancer center affiliate network (VCCAN) trial

PURPOSE

Docetaxel, an active agent for non-small cell lung cancer (NSCLC), has demonstrated activity as a radiosensitizer in numerous pre-clinical studies. We conducted a phase I trial to determine the maximum-tolerated dose (MTD) and dose-limiting toxicities (DLT) of weekly Docetaxel, Carboplatin with concurrent thoracic radiation therapy (TRT) in patients with unresectable stage III NSCLC.

PATIENTS AND METHODS

In this phase I clinical trial, Docetaxel was administered weekly as a 1-h intravenous infusion for 6 weeks with a starting dose of 20 mg/m(2). Docetaxel doses were escalated by 10 mg/m(2) increments in successive cohorts of three patients. DLT was defined as grade >or=3 nonhematologic and hematologic toxicity according to RTOG toxicity criteria. Once the DLT of Docetaxel alone was reached, weekly Carboplatin (AUC 2) was added at a DLT-2 dose of Docetaxel (two dose levels below that of dose limiting toxicity). Docetaxel doses were again escalated at 10 mg/m(2) increments in successive cohorts of three new patients to define further DLT and MTD of Docetaxel/Carboplatin with TRT. TRT was administered to the primary tumor and regional lymph nodes (40 Gy) followed by a boost to the tumor (20 Gy).

RESULTS

Fifteen patients were entered onto this study with Docetaxel alone through three dose escalations (from 20 to 40 mg/m(2) weekly). The DLT of weekly Docetaxel/TRT was esophagitis and the MTD was 30 mg/m(2) per week for 6 weeks. Nine more patients were added with the Docetaxel/Carboplatin/TRT regimen. The DLT of weekly Docetaxel/Carboplatin with TRT was esophagitis and the MTD of Docetaxel was 20 mg/m(2) per week with weekly Carboplatin (AUC 2). There were 2 complete responses and 13 partial responses in 25 evaluable patients (RR 60%).

CONCLUSIONS

This combination regimen has activity with manageable toxicity in patients with stage III NSCLC. A phase II study is planned to define activity.

Characteristics of GABAergic neurons and their synaptic relationships with intrinsic axons in the cat motor cortex

The intrinsic circuitry of the motor cortex comprises a complex network of connections whose synaptic relationships are poorly understood. This study was designed to determine the characteristics of subsets of GABAergic neurons containing the calcium-binding proteins parvalbumin (PV) and calbindin (CB), and their relationships with intrinsic axons in motor cortex. Immunohistochemically identified PV-containing neuronal profiles were more evenly distributed across cortical laminae (38% in II-III, 32% inV, 30% in VI) and more numerous (2.1/1) than CB-containing neuronal profiles (71% in II-III, 17% in V, 12% in VI). Relationships between neurons and axons intrinsic to motor cortex were visualized with fluorescent markers using the laser scanning confocal microscope. Similar percentages of PV (43%) and CB-immunoreactive (IR) (40%) neurons formed sparsely distributed appositions (1-5/neuron) with anterogradely labeled axons. The mean distances of such appositions from the somata were significantly different for the two groups (PV, mean = 22 microm, range = 1.6-93 microm; CB, mean = 32 microm, range = 6.2-132 microm). PV-IR neurons had a lower ratio of axosomatic/axodendritic appositions (1/99) compared with CB-IR neurons (14/86). Ultrastructural studies confirmed these findings. Fifty-seven percent of CB-IR neurons and 38% of PV-IR neurons formed synapses with intrinsic axons. Both populations received sparse input (1-6 synapses/neuron). Nearly all appositions between labeled terminals and postsynaptic profiles formed one synapse. Postsynaptic dendrites of PV-IR neurons (mean = 1.4 microm diameter) were larger than those of CB-IR neurons (mean = 1.1 microm), indicating more proximal synapses. Distinct input patterns of intrinsic axons to the two populations of neurons suggest unique roles in cortical processing.

A phase II study of paclitaxel, carboplatin, and hyperfractionated radiation therapy for locally advanced inoperable non-small-cell lung cancer (a Vanderbilt Cancer Center Affiliate Network Study)

PURPOSE

We conducted a prospective phase II study to determine the response rate, toxicity, and survival rate of concurrent weekly paclitaxel, carboplatin, and hyperfractionated radiation therapy (paclitaxel/carboplatin/HFX RT) followed by 2 cycles of paclitaxel and carboplatin for locally advanced unresectable non-small cell lung cancer (NSCLC). The weekly paclitaxel and carboplatin regimen was designed to optimize the radiosensitizing properties of paclitaxel during the concurrent phase of treatment.

METHODS AND MATERIALS

Forty-three patients with unresectable stage IIIA and IIIB NSCLC from the Vanderbilt Cancer Center and Affiliate Network (VCCAN) institutions were entered onto the study from June 1996 until May 1997. Weekly intravenous (IV) paclitaxel (50 mg/m(2)/l-hour) and weekly carboplatin (AUC 2) plus concurrent hyperfractionated chest RT (1.2 Gy/BID/69.6 Gy) were delivered for 6 weeks followed by 2 cycles of paclitaxel (200 mg/m(2)) and carboplatin (AUC 6).

RESULTS

Forty-two patients were evaluable for response and toxicities. Three patients achieved a complete response (7.2%) and 30 patients achieved a partial response (71.4%), for an overall response rate of 78.6% [95% C.I. (66.2%-91.0%)]. The 1- and 2-year overall and progression-free survival rates of all 43 patients were 61.6% and 35% respectively, with a median survival time of 14.3 months. The median follow-up time was 14 months. Esophagitis was the principal toxicity. Grade 3 or 4 esophagitis occurred in 11 patients (26%). There was an incidence of 7% grade 3 and 9.5% grade 4 pulmonary toxicities.

CONCLUSIONS

Weekly paclitaxel, carboplatin, plus concurrent hyperfractionated RT is a well-tolerated outpatient regimen. The response rate from this regimen is encouraging and appears to be at least equivalent to the more toxic chemoradiation trials. These findings warrant further clinical evaluation of weekly paclitaxel/carboplatin/HFX RT in a phase III study.

A Phase I Trial of Outpatient Weekly Docetaxel and Concurrent Radiation Therapy for Stage III Unresectable Non–Small-Cell Lung Cancer: A Vanderbuilt Cancer Center Affiliate Network (VCCAN) Trial

Docetaxel has demonstrated activity as a radiosensitizer in numerous preclinical studies, probably due to its role as a cell cycle synchronizer for the G2/M radiosensitive phase of the cell cycle. We conducted a phase I trial to determine the maximum-tolerated dose (MTD) and dose-limiting toxicities (DLT) of docetaxel with concurrent thoracic radiation therapy (TRT) to patients with unresectable stage III non small-cell lung cancer (NSCLC). Fifteen patients were entered into this study. Docetaxel was administered as a 1-hour intravenous (I.V.) infusion, repeated every week for 6 weeks with starting dose of 20 mg/m2. Doses were escalated in 10 mg/m2 increments in successive cohorts of three new patients, if tolerated. Unacceptable toxicity was defined as grade = 3 nonhematologic or hematologic toxicity according to Eastern Cooperative Oncology Group (ECOG) toxicity criteria. TRT was administered to the primary tumor and regional lymph nodes (40 Gy) followed by a boost to the tumor (20 Gy). At the first dose level (20 mg/m2/week), one patient developed grade 4 hyperglycemia and accrual was expanded to five patients. At the second level (30 mg/m2/week), two out of six patients developed grade 3 esophagitis. At the third level (40 mg/m2/week), two out of four patients developed grade 3 esophagitis and one patient developed grade 3 pulmonary toxicity. The weekly docetaxel MTD with concurrent radiation therapy (RT) was found to be 30 mg/m2. The DLT was esophagitis and pulmonary toxicity. Other toxicities encountered included skin reaction, nausea and vomiting, as well as diarrhea. Additionally, there were no treatment-related mortalities or late-occurring toxicities. Esophagitis was the principal DLT of concurrent weekly docetaxel and thoracic radiation in the outpatient setting. The MTD of concurrent weekly docetaxel with TRT is 30 mg/m2 weekly for 6 weeks. This study is still open to accrual with weekly docetaxel and TRT in locally advanced NSCLC patients.

Dopamine affects parvalbumin expression during cortical development in vitro

This study was undertaken to determine how dopamine influences cortical development. It focused on morphogenesis of GABAergic neurons that contained the calcium-binding protein parvalbumin (PV). Organotypic slices of frontoparietal cortex were taken from neonatal rats, cultured with or without dopamine, harvested daily (4-30 d), and immunostained for parvalbumin. Expression of parvalbumin occurred in the same regional and laminar sequence as in vivo. Expression in cingulate and entorhinal preceded that in lateral frontoparietal cortices. Laminar expression progressed from layer V to VI and finally II-IV. Somal labeling preceded fiber labeling by 2 d. Dopamine accelerated PV expression. In treated slices, a dense band of PV-immunoreactive neurons appeared in layer V at 7 d in vitro (DIV), and in all layers of frontoparietal cortex at 14 DIV, whereas in control slices such labeling did not appear until 14 and 21 DIV, respectively. The laminar distribution and dendritic branching of PV-immunoreactive neurons were quantified. More labeled neurons were in the superficial layers, and their dendritic arborizations were significantly increased by dopamine. Treatment with a D1 receptor agonist had little effect, whereas a D2 agonist mimicked dopamine's effects. Likewise, the D2 but not the D1 antagonist blocked dopamine-induced changes, indicating that they were mediated primarily by D2 receptors. Parvalbumin expression was accelerated by dopaminergic reinnervation of cortical slices that were cocultured with mesencephalic slices. Coapplication of the glutamate NMDA receptor antagonist MK801 or AP5 blocked dopamine-induced increases in dendritic branching, suggesting that changes were mediated partly by interaction with glutamate to alter cortical excitability.

Preliminary analysis of a phase II study of paclitaxel, carboplatin, and hyperfractionated radiation therapy for locally advanced inoperable non-small cell lung cancer

We conducted a prospective phase II study to determine the response rate, toxicity profile, and survival rate among patients with locally advanced unresectable non-small cell lung cancer receiving concurrent weekly paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ), carboplatin, and hyperfractionated radiation therapy followed by two cycles of adjuvant paclitaxel and carboplatin. The weekly paclitaxel/carboplatin regimen was designed to optimize the radiosensitizing properties of paclitaxel during the concurrent phase of treatment. Thirty-two patients with unresectable stage IIIA and IIIB non-small cell lung cancer from Vanderbilt Cancer Center Affiliate Network institutions entered the study from June 1996 until February 1997. Weekly intravenous paclitaxel (50 mg/m2 over 1 hour) and weekly carboplatin (area under the concentration-time curve of 2) plus concurrent hyperfractionated chest radiotherapy (1.2 Gy twice daily [69.6 Gy total]) delivered for 6 weeks were followed by two cycles of paclitaxel (200 mg/m2) and carboplatin (area under the concentration-time curve of 6). Among 22 patients evaluable for response, one (4.5%) achieved a complete response and 16 (72.7%) achieved partial response, for an overall response rate of 77%. Among 23 patients evaluable for toxicity, esophagitis was the principal finding: grade 3 or 4 esophagitis occurred in eight patients (35%). Grade 3 and 4 pulmonary toxicities each occurred in 26% of patients. Thus, weekly paclitaxel/carboplatin plus concurrent hyperfractionated radiotherapy is a well-tolerated outpatient regimen with an encouraging response rate that is at least equivalent to more toxic chemoradiation regimens. These findings indicate that further clinical evaluation of weekly paclitaxel/carboplatin/hyperfractionated radiotherapy is warranted in phase III trials.

Morphological Characterization of a Cortico-cortical relay in the cat sensorimotor cortex

One feature of the cerebral cortex circuitry is the complex network of fibers which links its different functional regions. Our knowledge of the specific relationships between neurons which form these pathways is limited. The cortico-cortical connections between primary somatosensory cortex (SI) and primary motor cortext (MI) were the focus of the study. The aims were twofold: first, to identify characteristics of inter-areal cortico-cortical connections; and second, to determine if pathways exist which support the notion that peripheral signals are integrated in the somatosensory cortext before being relayed to the motor cortex. Neurons in area 2 of SI, which projected to the motor cortex were identified. The morphological characteristics of these neurons and the pattern of input that they received from the area 3a were determined. The fluorescent retrograde tracer, fast blue, was injected into the electrophysiologically defined forepaw representation of motor cortex and the anterograde tracer, dextran-tetramethylrhodamine (DR), was injected into the somatotopically matched region of area 3a. Labeled neurons in area 2 which were located in a field of labeled axons arising from area 3a were identified in fixed tissue sections. Some of these labeled cells were impaled with a Lucifer yellow (LY)-filled micropipette and were intracellulary labeled by iontophoretic injection of LY Cells in area 2 that projected to the motor cortex were located primarily in layers II-III. They were all classified as pyramidal neurons and were morphologically similar. Their apical dendrites for the most part did not extend beyond layer II. Their apical tufts exhibited 2-4 branches within layers II-III, while basal dendrites exhibited more numerous tertiary basal dendritic branches. Light microscopic (LM) examination revealed the presence of appositions between LY-filled profiles and DR-labeled axons. Appositions were observed between swellings along DR-labeled axons and dendritic shafts or spines of 1 degrees, 2 degrees and 3 degrees branches of apical and 1 degrees and 2 degrees branches of basal dendrites. The appositions were primarily on proximal segments of labeled dendritic shafts. Fewer appositions with distal dendrites were observed and some of these were with dendritic spines. No appositions with the somata were observed. Only one or two appositions were observed for individual cells. The pattern of cortico-cortical synaptic input arising from area 3a onto this population of cells was predicted from these LM findings. An ultrastructural analysis was performed to confirm the existence of contacts and the predicted pattern of connectivity. Neurons in area 2 which projected to the motor cortex, and area 3a axons which projected to area 2, were identified with electron dense retrograde and anterograde tracers respectively. Labeled neurons located in a field of labeled axons were examined throughout a sequential series of ultrathin sections. Electron microscopic analysis revealed a similar pattern, but with a slightly higher density of synaptic input (1-8 contacts per target cell) than that predicted from the LM studies. These results revealed a specific density and pattern of coritco-cortical input onto an identified population of cortico-cortical projection neurons. Individual target cells received only sparse input from a functionally different but somatotopically related region of the cortex. The pattern of input onto cells was unexpected in that most axons contacted the shafts of proximal dendrites. This aspect of the connection may exemplify a unique feature of the cortical circuit which helps to define its functional role. The significance of these results in defining cortical function is that the particular cortical circuit described may provide an anatomical substrate for the modulation of motor cortex activity by integrated signals from the sensory cortex. The synaptic relationships of neurons in this pathway may be characteristic of i

Oral dolasetron mesylate in patients receiving moderately emetogenic platinum-containing chemotherapy. Oral Dolasetron Dose Response Study Group

PURPOSE

This double-blind, dose-response study was conducted to assess the safety and efficacy of four oral doses of dolasetron mesylate for preventing acute emesis in cancer patients receiving their first course of moderately emetogenic platinum-containing chemotherapy.

PATIENTS AND METHODS

Patients were randomized to receive a single oral dose of 25, 50, 100, or 200 mg dolasetron 30 minutes before receiving IV carboplatin (275-400 mg/m2)- or cisplatin (20-50 mg/m2)-containing chemotherapy, then monitored for nausea and vomiting for 24 hours.

RESULTS

Three hundred seven cancer patients from 32 sites completed the study. There was a statistically significant dose response across the four doses for complete response (no emetic episodes or rescue medication): 44.7%, 71.3%, 73.2%, and 82.5% for the 25, 50, 100, or 200 mg doses of dolasetron, respectively. Patients' nausea severity and patient satisfaction visual analogue scale scores also showed a statistically significant trend with dose. All doses of dolasetron were well tolerated. The most common adverse events were headache (17.6%) and dizziness (2.0%).

DISCUSSION

This study demonstrates the safety and antiemetic efficacy of oral dolasetron mesylate in patients receiving moderately emetogenic platinum-containing chemotherapy with the highest antiemetic activity observed at 200 mg.

Somatosensory input onto pyramidal tract neurons in rodent motor cortex

This study was performed to determine whether pyramidal tract neurons (PTNs), the output cells of the motor cortex, are targets of direct input from the somatosensory cortex (SI). PTNs were identified by light microscope (LM) and electron microscope (EM) retrograde tract tracing techniques. For LM analysis, they were intracellularly filled to exhibit their full dendritic arbor. Axons originating from the electrophysiologically identified forelimb representation of SI were labeled by LM and EM anterograde tract tracing techniques. LM analysis of dual-labeled tissue showed that PTNs were situated to receive direct input from SI. The distribution and density of this input was predicted from the findings. EM analysis confirmed that PTNs receive direct input from SI. The input is sparse and not all PTNs appear to receive input. SI terminals do not appear to target specific segments of PTN dendrites. This corticocortical pathway may provide MI with the short latency sensory feedback which is needed to produce coordinated voluntary movements.

Paclitaxel and 5-fluorouracil in metastatic breast cancer: the US experience

Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) is an effective drug in the treatment of metastatic breast cancer (MBC). In the salvage setting, 5-fluorouracil (5-FU) and folinic acid have proved to be effective against MBC as well. Recent preclinical data suggest that paclitaxel plus 5-FU has additive cytotoxicity. Given these observations, we initiated a phase II trial in which 38 women with MBC have been treated with a combination of all three drugs. All patients are currently evaluable for toxicity and 34 are evaluable for response. All women had histologically proven and assessable disease. Patients with prior exposure to paclitaxel were ineligible. Patient characteristics include a median age of 51 years (age range, 31 to 73 years) and a median performance status of 1 (range, 0 to 2). Thirty-three patients have received prior chemotherapy, of whom 23 had adjuvant chemotherapy only. Fifty-eight percent of the patients (22 of 38) had received prior doxorubicin or mitoxantrone; four patients had only hormonal therapy. Four patients had bone-only disease, and three patients had lymphangitic spread or cytologically positive pleural effusion as the only evaluable disease. Treatment consisted of paclitaxel 175 mg/m2 over 3 hours (day 1 only), followed by folinic acid 300 mg over 1 hour, followed by 5-FU 350 mg/m2 on days 1 to 3. Patients received standard paclitaxel premedications. To date, 175 cycles have been administered (median cycle length, 29 days; median number of cycles per patient, five). Toxicities included grade 3/4 infections in nine cycles (5%), grade 3/4 mucositis in three cycles, grade 3/4 nausea/vomiting in three cycles, grade 1 paresthesias in 12 patients (32%), alopecia 100%, and 17 cycles (10%) associated with dose reduction. Based on Cancer and Leukemia Group B toxicity criteria, arthralgia/myalgias were modest and graded mild (32 cycles), moderate (nine cycles), or severe (two cycles). There were two major hypersensitivity reactions, prompting removal of those patients from further protocol treatment. Four patients are unassessable for response due to hypersensitivity reactions (two) and unevaluable disease (two). Among the 34 patients evaluable for response, there were three complete responses, 18 partial responses, one minor response, nine stable disease, and three progressive disease (response rate, 62%). Responses were seen in patients who had received prior doxorubicin or mitoxantrone (11 of 22 patients) and in anthracycline/naive patients (10 of 16 patients). Responses were observed in all metastatic sites: soft tissue, viscera, and bone. Paclitaxel/5-FU/folinic acid appears to be an effective and well-tolerated outpatient regimen for women with MBC, even after failure of anthracycline-containing therapy.

Vibrissal motor cortex in the rat: connections with the barrel field

The flow of information in the sensorimotor cortex may determine how somatic information modulates motor cortex neuronal activity during voluntary movement. Electrophysiological recordings and neuroanatomical tracing techniques were used to study the connections between the primary somatosensory cortex (SI) and the vibrissal representation of the primary motor cortex (MI) in rodents. Intracortical microstimulation (ICMS) was applied to the vibrissal region of the motor cortex to identify a site from which stimulation evoked movements of the vibrissae. Movements of only a single whisker were evoked by applying low-intensity stimulating current to particular locations within MI. A single injection of either horseradish peroxidase (HRP) or biocytin was made at the stimulus site in each animal, to retrogradely label cells in the somatosensory cortex. Receptive field (RF) responses were recorded from neurons in the barrel cortex to identify the sensory cortex representation of the same whisker that responded to ICMS. The site at which neurons responded predominately to manual stimulation of this particular vibrissa was marked by a small electrolytic lesion. The projection from the somatosensory cortex to the identified whisker representation in the motor cortex was determined by mapping the location of labeled neurons in tissue sections processed for either HRP or biocytin. The relationship of the labeled cells in SI to the barrel structures was determined from adjacent sections that were stained for cytochrome oxidase. In all cases, the barrel column associated with the relevant whisker contained labeled cells. Surrounding barrels also contained labeled cells, although fewer in number. Very few labeled cells were found in non-contiguous barrels. These results show that the SI to MI projection is somatotopically arranged, such that the sensory cortex representation of a whisker is morphologically connected to the motor cortex representation of the same whisker. Thus, sensory information is relayed to MI from the relevant whisker region in SI. Adjacent whisker regions also appear to relay somatic input, but presumably to a lesser degree. A second group of animals received single small injections of the anterograde tracer, Phaseolus vulgaris leucoagglutinin, to an electrophysiologically identified whisker representation in the sensory cortex. A single narrow column of labeled fibers was found in the motor cortex following such injections. Thus, the sensory cortex appears to relay somatic information from the vibrissae to restricted regions of the motor cortex in a somatotopically organized manner. Furthermore, the stimulus-evoked whisker movements suggest that certain features of the output map of the motor cortex are discretely organized.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of localized inactivation of somatosensory cortex, area 2, on the cat motor cortex

Direct corticocortical afferents to the primary motor cortex (MI) originate in area 2 and area 3a of the primary somatosensory cortex (SI). The functional and morphological characteristics of the two pathways indicate that they relay different sensory signals to MI. The role of area 2 in relaying peripheral information to the cat MI was studied using electrophysiological techniques. Neurons that responded to stimulation of peripheral receptive fields on the contralateral forepaw were identified in MI by extracellular recordings. In area 2 of SI, neurons with the same receptive field modality and location as those in MI were also identified. Field potentials to electrical stimulation of the peripheral receptive field were recorded at the somatotopically matched sites in both MI and SI. Neuronal activity at the recording site in area 2 was blocked by injection of lidocaine, a local anesthetic. Changes in MI and area 2 responses were monitored before and after inactivation of area 2. Neuronal activity near the injection site was abolished, and evoked potentials (EPs) in area 2 were considerably diminished immediately following the injection. In MI, spontaneous activity levels were altered at some sites, but overall these changes were not significant. MI EPs recorded in response to peripheral stimulation were altered, and various patterns of change were noted in the early and late phases of the EPs. Changes often occurred in only one phase of the response. In some EPs, both early and late phases changed, but the direction and magnitude of change in one phase were not always linked to such changes in the other phase. Both increases and decreases in the amplitude and the area of each phase were observed. The morphological characteristics of the projection were reviewed and related to the findings in the study. It is proposed that inherent features of the pathway may account for the variable patterns of change that were observed.

The effects of localized inactivation of somatosensory cortex, area 3a, on area 2 in cats

In cats and primates, area 3a of the somatosensory cortex is the primary recipient of proprioceptive input (Phillips et al., 1971). Neurons in area 3a project to area 2 (Pons and Kaas, 1986; Porter, 1991), where somatic input relayed from the cortex and the thalamus may be integrated (Iwamura and Tanaka, 1978a,c). The goal of the present study was to determine the effects of area 3a input on neuronal activity in area 2 of cats. Extracellular recording techniques were used to identify neurons in area 2 that responded to deep stimulation of the contralateral forepaw. Neurons in area 3a that responded to the same receptive field modality and location as those in area 2 were also isolated. Single-unit or multiunit responses and evoked potentials to electrical stimulation of the shared peripheral receptive field and spontaneous activity were recorded from areas 2 and 3a. Lidocaine, a local anesthetic, was injected at the area 3a recording site to block neuronal activity. Spontaneous activity and receptive fields were abolished and evoked potentials were considerably diminished at the injection site, immediately after lidocaine was administered. Changes in unit responses, spontaneous activity, and evoked potentials in area 2 were monitored following inactivation of the somatotopically "matched" site in area 3a. Unit activity was recorded at 15 matched sites. In area 2, changes in unit responses to the peripheral stimulation and/or in spontaneous activity were observed at most of the recording sites following inactivation of area 3a. Spontaneous activity rates changed at 63% of the sites (mean change = 85%). Unit responses to the peripheral stimulation changed at 57% of the recording sites (mean change = 47%). The remaining sites in area 2 did not show lidocaine-induced changes. These sites may not have been connected with the matched sites in area 3a. Spontaneous activity and unit responses were not always similarly altered at a given site; sometimes one increased while the other decreased. Decreases in unit responses and spontaneous activity following inactivation of area 3a input were the predominant effects, indicating that area 3a has a facilitatory effect on neuronal activity observed in some regions of area 2. However, increases in neuronal activity at some sites indicated that the effects of area 3a input on area 2 are nonuniform. Evoked potentials were recorded at 19 matched sites, before and after injection of lidocaine. Evoked potentials also changed at some area 2 recording sites following area 3a inactivation.(ABSTRACT TRUNCATED AT 400 WORDS)

Patterns of projections from area 2 of the sensory cortex to area 3a and to the motor cortex in cats

Peripheral information reaches the motor cortex partly through corticocortical pathways that arise from two functional subdivisions, area 2 and area 3a, of the sensory cortex. These sensory areas are synaptically linked with one another. The patterns of connectivity and the different submodality input that each area receives suggest that they send different efferent signals to the motor cortex. The projections from area 2 to area 3a and to the motor cortex were studied with retrogradely transported fluorescent tracers. The pattern and distribution of neuronal labeling in area 2 was determined following injections of different tracers into the forelimb regions of area 3a and the motor cortex. The results showed that the projections from area 2 to the two target regions were topographically and somatotopically related. Multiple clusters of motor cortex projection neurons were found in area 2, and these clusters overlapped extensively with clusters of area 3a projection neurons. Although cells labeled with one of the dyes were often in close proximity to cells labeled with the other dye, no double-labeled cells were found. Two different laminar patterns were seen for the two populations of neurons. The projection to area 3a originated from cells located in layers II-III and layers V-VI. The projection to the motor cortex originated from cells spread throughout layers II-IV, but predominantly in layer III. Differences in laminar arrangement of the two populations of cells suggest a directional flow of information processing in the sensorimotor cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Patterns of connectivity in the cat sensory-motor cortex: a light and electron microscope analysis of the projection arising from area 3a

Through its complex network of interconnections, each of the functionally specialized subdivisions in the cat primary somatosensory cortex may provide the motor cortex with different input and thus play a unique role in motor behavior. Areas 2 and 3a receive separate peripheral information. Cells in both regions project directly to the cat motor cortex but are thought to target different populations of neurons. In this study the morphology and distribution patterns of the area 3a projection to the motor cortex were compared to previous findings on the projection from area 2. Also, details of the projection from area 3a to area 2 were studied. Injections of Phaseolus vulgaris leucoagglutinin were made into area 3a and fixed brain tissue was processed for immunohistochemical staining of this anterograde tracer. Tissue was examined with the light microscope to determine the patterns of the 3a projections to area 2 and motor cortex, area 4. Axons arising from cells in area 3a terminated in multiple column-like clusters in both motor cortex and area 2. The small number of cells labeled at the injection sites suggested that multiple foci of the 3a fibers are formed by collateral axonal branches of the same neurons. The topography of the projection from area 3a to the motor cortex was more clearly defined than that from area 3a to area 2. Electron microscope analysis determined the laminar distribution and types of synapses formed between area 3a efferents and their target neurons. A high proportion of synapses was found in layer III in both target regions. However, unlike in area 4, labeled terminals were sparse in laminae I and II of area 2. Axospinous synapses were slightly more numerous than axodendritic synapses, but both were distributed similarly throughout the thickness of the cortex. In area 2 the axospinous synapses accounted for 63% of synapses and in area 4 for 57% of synapses. No axosomatic synapses were detected.

Light and electron microscopic evidence for a GABAergic projection from the caudal basal forebrain to the thalamic reticular nucleus in rats

Neurons in the magnocellular nucleus of the caudal basal forebrain extend an axonal projection which arborizes within the reticular nucleus of the thalamus. The present study addresses the ultrastructure and neurochemistry of this projection in rats. Many labeled terminals are apparent within the thalamic reticular nucleus following Phaseolus vulgaris leucoagglutinin injections into the caudal basal nucleus; anterogradely labeled axon terminals most commonly contact both somata and dendrites of reticular nucleus neurons with symmetric membrane specializations. Thus, the majority of the labeled terminals examined contrast with choline acetyltransferase positive terminals which have been previously identified as contacting dendrites and forming asymmetric synapses within this nucleus. Many of the neurons within the caudal basal nucleus which are retrogradely labeled following tracer injections into the thalamic reticular nucleus are gamma-aminobutyric acid (GABA) immunoreactive. In addition, following injections of Phaseolus vulgaris leucoagglutinin or fluoro-ruby into the caudal basal forebrain, some of the labeled axonal swellings and boutons within the thalamic reticular nucleus also contain glutamic acid decarboxylase. These results indicate that a significant component of the projection is GABAergic. These anatomical observations suggest that the projection from the caudal basal nucleus onto the thalamic reticular nucleus could facilitate the relay of information through the dorsal thalamus by inhibiting reticular nucleus neurons, and thus, in turn, disinhibiting thalamic relay neurons.

Morphological and physiological identification of neurons in the cat motor cortex which receive direct input from the somatic sensory cortex

The population of neurons in the cat motor cortex which receives monosynaptic input from a specific functional region of the somatic sensory cortex was identified with the techniques of intracellular recording and staining with HRP. Both pyramidal and nonpyramidal cells located in the superficial layers of the pericruciate cortex responded to stimulation of the sensory cortex with short latency, excitatory postsynaptic potentials. More than half of the labeled cells were classified as pyramidal cells and the remainder as sparsely spinous or aspinous nonpyramidal cells. The characteristics of the EPSP's of the 2 groups of cells, ie. latency, time from beginning to peak and amplitude were found to vary only slightly. The results suggest that input from the sensory cortex impinges upon neurons which may in turn have an excitatory or inhibitory effect on cortico-fugal neurons in the motor cortex.

Organization and synaptic relationships of the projection from the primary sensory to the primary motor cortex in the cat

It is known from previous studies that fibers originating from cells in area 2 of the cat primary somatosensory cortex project topographically to area 4 of the motor cortex and that they terminate preferentially in the caudal region of the cruciate sulcus. We examined this pathway to determine more precisely the distribution pattern of fibers and the laminar arrangement of axon terminals in the motor cortex. The recently developed technique of PHA-L staining enabled us to label anterogradely the axons that form this projection. Iontophoretic injections of PHA-L were made into the rostral bank of the ansate sulcus (area 2). After 7 days the cats were perfused and the tissue was processed immunohistochemically to stain the PHA-L filled fibers. Light microscopic examination revealed that a small cluster of cells in the sensory cortex gave rise to multiple foci of labeled axons in area 4. The labeled fibers formed columnlike arrays, which were located for the most part in the posterior bank of the cruciate sulcus and were separated by irregular intervals of cortex devoid of labeled fibers. Clusters of labeled fibers were also found in the anterior region of the cruciate sulcus in some of the animals. The dimensions of the labeled areas and the small number of cells that gave rise to each group of fibers suggested that axonal branches of cells within the injection site formed the multiple foci. Variations in the immunohistochemical staining enabled us to study the laminar distribution of sensory cortex axon terminals with the electron microscope. Whereas some PHA-L labeled terminals were found in the deep cortical layers, the majority (82%) were spread throughout layers I-III. Differences in the laminar distribution of sensory cortex afferents that formed axodendritic or axospinous synapses were noted. Synapses formed with dendritic shafts were relatively sparse (28%) and were confined to the superficial layers. Some of the more numerous axospinous synapses, which accounted for 72% of identified synapses, were found in layers V and VI, although most were in layers I-III. The distribution pattern of terminals showed little variation between columns in different areas of the motor cortex, including that in the anterior cruciate region. The pattern of termination of the sensory to motor cortex projection is discussed in relation to the physiological characteristics of this pathway.

The physiological identification of pyramidal tract neurons within transplants in the rostral cortex taken from the occipital cortex during development

Axons from neurons in the occipital cortex transiently extend to the pyramidal tract (PT) during the early postnatal development of rats. Normally, these axons are eliminated by the end of the third postnatal week. However, if a portion of fetal occipital cortex is transplanted to the parietofrontal region in newborn hosts then some neurons in the transplant will extend pyramidal tract axons and maintain them. Intracortical microstimulation and electrophysiological recording techniques were used to identify the physiological characteristics of the transplanted pyramidal tract cells and to determine if motor effects could be elicited from the occipital transplant. Microstimulation of the transplant did not reliably evoke movement but the low density and disarray of PT cells within the transplant might account for this. Recording from within the transplant revealed that the overall cell activity was depressed. We were able to identify neurons within the transplant which responded antidromically to stimulation of the pyramidal tract, indicating that their axons have the capacity to conduct impulses and are therefore likely to have developed some viable connections. The functional significance of such projections remains uncertain.

Long-lasting potentiation of synaptic potentials in the motor cortex produced by stimulation of the sensory cortex in the cat: a basis of motor learning

A long-lasting increase in the efficiency of synaptic transmission in the central nervous system has been thought to be one of the bases of learning and memory. To explore the possibility that the motor cortex (area 4 gamma) itself is involved in motor learning, the existence of long-term potentiation (LTP) was examined by recording excitatory postsynaptic potentials (EPSPs) from motor cortical neurons. Short tetanic intracortical microstimulation (ICMS) of the somatic sensory cortex produced a marked potentiation of the EPSPs in a small group of motor cortical neurons. The results raised the possibility that the input from the sensory cortex participates in motor learning and retention of the learned motor skills.

Acute nonlymphocytic leukemia after treatment of small cell lung cancer

From 1977 to 1982, 377 patients with small cell lung cancer were treated at Vanderbilt University Medical Center. All patients received combination chemotherapy consisting of cyclophosphamide, doxorubicin, and vincristine (CAV) with or without methotrexate, etoposide, and/or hexamethylmelamine. Thoracic and/or prophylactic cranial irradiation was administered to 159 (42 percent) and 192 (51 percent) patients, respectively. Acute nonlymphocytic leukemia was observed in two patients at 22 and 81 months from the start of therapy. The relative risk of leukemia was 154 (95 percent confidence limit, 38 to 293). A Kaplan-Meier estimate of the cumulative probability of leukemia was 1.9 +/- 1.4 percent seven years after the start of treatment. The relative risk of leukemia is significantly increased in this group of patients (p less than 0.0001). Acute nonlymphocytic leukemia is a long-term complication of small cell lung cancer therapy.