Sequence conservation analysis and in silico human leukocyte antigen-peptide binding predictions for the Mtb72F and M72 tuberculosis candidate vaccine antigens

Background

Requisites for an efficacious tuberculosis (TB) vaccine are a minimal genomic diversity among infectious Mycobacterium tuberculosis strains for the selected antigen, and the capability to induce robust T-cell responses in the majority of human populations. A tool in the identification of putative T-cell epitopes is in silico prediction of major histocompatibility complex (MHC)-peptide binding. Candidate TB vaccine antigen Mtb72F and its successor M72 are recombinant fusion proteins derived from Mtb32A and Mtb39A (encoded by Rv0125 and Rv1196, respectively). Adjuvanted Mtb72F and M72 candidate vaccines were shown to induce CD4⁺ T-cell responses in European, US, African and Asian populations.

Methods

Sequence conservation of Mtb32A, Mtb39A, Mtb72F and M72 among 46 strains (prevalent Mycobacterium strains causing human TB disease, and H37Ra) was assessed by multiple alignments using ClustalX. For Mtb32A, Mtb39A and Mtb72F, 15-mer human leukocyte antigen (HLA)-class II-binding peptides were predicted for 158 DRB1 alleles prevailing in populations with high TB burden, 6 DRB3/4/5, 8 DQ and 6 DP alleles, using NetMHCII-pan-3.0. Results for 3 DRB1 alleles were compared with previously published allele-matched in vitro binding data. Additional analyses were done for M72. Nonameric MHC class I-binding peptides in Mtb72F were predicted for three alleles representative of class I supertypes A02, A03 and B07, using seven prediction algorithms.

Results

Sequence identity among strains was ≥98 % for each protein. Residue changes in Mtb39A comprised primarily single residue or nucleotide insertions and/or deletions in repeat regions, and were observed in 67 % of strains. For Mtb72F, 156 DRB1, 6 DRB3/4/5, 7 DQ and 5 DP alleles were predicted to contain at least one MHC class II-binding peptide, and class I-binding peptides were predicted for each HLA-A/B allele. Comparison of predicted MHC-II-binding peptides with experimental data indicated that the algorithm’s sensitivity and specificity were variable among alleles.

Conclusions

The sequences from which Mtb72F and M72 are derived are highly conserved among representative Mycobacterium strains. Predicted putative T-cell epitopes in M72 and/or Mtb72F covered a wide array of HLA alleles. In silico binding predictions for class I- and II-binding putative epitopes can be complemented with biochemical verification of HLA binding capacity, processing and immunogenicity of the predicted peptides.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-015-0119-7) contains supplementary material, which is available to authorized users.

Heterologous prime-boost regimens with a recombinant chimpanzee adenoviral vector and adjuvanted F4 protein elicit polyfunctional HIV-1-specific T-Cell responses in macaques

HIV-1-specific CD4+ and CD8+ T lymphocytes are important for HIV-1 replication control. F4/AS01 consists of F4 recombinant fusion protein (containing clade B Gag/p24, Pol/RT, Nef and Gag/p17) formulated in AS01 Adjuvant System, and was shown to induce F4-specific polyfunctional CD4+ T-cell responses in humans. While replication-incompetent recombinant HIV-1/SIV antigen-expressing human adenoviral vectors can elicit high-frequency antigen-specific CD8+ T-cell responses, their use is hampered by widespread pre-existing immunity to human serotypes. Non-human adenovirus serotypes associated with lower prevalence may offer an alternative strategy. We evaluated the immunogenicity of AdC7-GRN ('A'), a recombinant chimpanzee adenovirus type 7 vector expressing clade B Gag, RT and Nef, and F4/AS01 ('P'), when delivered intramuscularly in homologous (PP or AA) and heterologous (AAPP or PPAA) prime-boost regimens, in macaques and mice. Vaccine-induced HIV-1-antigen-specific T cells in peripheral blood (macaques), liver, spleen, and intestinal and genital mucosa (mice) were characterized by intracellular cytokine staining. Vaccine-specific IgG antibodies (macaques) were detected using ELISA. In macaques, only the heterologous prime-boost regimens induced polyfunctional, persistent and balanced CD4+ and CD8+ T-cell responses specific to each HIV-1 vaccine antigen. AdC7-GRN priming increased the polyfunctionality of F4/AS01-induced CD4+ T cells. Approximately 50% of AdC7-GRN-induced memory CD8+ T cells exhibited an effector-memory phenotype. HIV-1-specific antibodies were detected with each regimen. In mice, antigen-specific CD4+ and CD8+ T-cell responses were detected in the mucosal and systemic anatomical compartments assessed. When administered in heterologous prime-boost regimens, AdC7-GRN and F4/AS01 candidate vaccines acted complementarily in inducing potent and persistent peripheral blood HIV-1-specific CD4+ and CD8+ T-cell responses and antibodies in macaques. Besides, adenoviral vector priming modulated the cytokine-expression profile of the protein-induced CD4+ T cells. Each regimen induced HIV-1-specific T-cell responses in systemic/local tissues in mice. This suggests that prime-boost regimens combining adjuvanted protein and low-seroprevalent chimpanzee adenoviral vectors represent an attractive vaccination strategy for clinical evaluation.

Induction and regulation of T-cell immunity by the novel tuberculosis vaccine M72/AS01 in South African adults

RATIONALE

Tuberculosis (TB) is a major cause of morbidity and mortality worldwide, thus there is an urgent need for novel TB vaccines.

OBJECTIVES

We investigated a novel TB vaccine candidate, M72/AS01, in a phase IIa trial of bacille Calmette-Guérin-vaccinated, HIV-uninfected, and Mycobacterium tuberculosis (Mtb)-infected and -uninfected adults in South Africa.

METHODS

Two doses of M72/AS01 were administered to healthy adults, with and without latent Mtb infection. Participants were monitored for 7 months after the first dose; cytokine production profiles, cell cycling, and regulatory phenotypes of vaccine-induced T cells were measured by flow cytometry.

MEASUREMENTS AND MAIN RESULTS

The vaccine had a clinically acceptable safety profile, and induced robust, long-lived M72-specific T-cell and antibody responses. M72-specific CD4 T cells produced multiple combinations of Th1 cytokines. Analysis of T-cell Ki67 expression showed that most vaccination-induced T cells did not express Th1 cytokines or IL-17; these cytokine-negative Ki67(+) T cells included subsets of CD4 T cells with regulatory phenotypes. PD-1, a negative regulator of activated T cells, was transiently expressed on M72-specific CD4 T cells after vaccination. Specific T-cell subsets were present at significantly higher frequencies after vaccination of Mtb-infected versus -uninfected participants.

CONCLUSIONS

M72/AS01 is clinically well tolerated in Mtb-infected and -uninfected adults, induces high frequencies of multifunctional T cells, and boosts distinct T-cell responses primed by natural Mtb infection. Moreover, these results provide important novel insights into how this immunity may be appropriately regulated after novel TB vaccination of Mtb-infected and -uninfected individuals.

Clinical trial registered with www.clinicaltrials.gov (NCT 00600782).

A randomized, controlled dose-finding Phase II study of the M72/AS01 candidate tuberculosis vaccine in healthy PPD-positive adults

Purpose

In this dose-finding Phase II study (NCT00621322), we evaluated the safety and immunogenicity of different formulations of the candidate tuberculosis vaccine containing the M72 antigen (10/20/40 μg doses) and the liposome-based AS01 Adjuvant System. We aimed to select the lowest-dose combination of M72 and AS01 that was clinically well tolerated with immunogenicity comparable to that of the previously tested M72/AS01_B (40 μg) candidate vaccine.

Methods

Healthy PPD-positive (induration 3–10 mm) adults (18–45 years) in The Philippines were randomized (4:4:4:4:1:1) to receive 2 injections, 1 month apart, of M72/AS01_B (40 μg), M72/AS01_E (10 μg), M72/AS01_E (20 μg), M72/AS02_D (10 μg), M72/Saline (40 μg) or AS01_B alone, and were followed up for 6 months. AS01_E and AS02_D contain half the quantities of the immunostimulants present in AS01_B. AS02_D is an oil-in-water emulsion. Vaccine selection was based on the CD4⁺ T-cell responses at 1 month post vaccination.

Results

All formulations had a clinically acceptable safety profile with no vaccine-related serious adverse events reported. Two vaccinations of each adjuvanted M72 vaccine induced M72-specific CD4⁺ T-cell and humoral responses persisting at 6 months post vaccination. No responses were observed with AS01_B alone. One month post second vaccination, CD4⁺ T-cell responses induced by each of the three M72/AS01 vaccine formulations were of comparable magnitudes, and all were significantly higher than those induced by M72/AS02_D (10 μg) and M72/Saline.

Conclusions

The formulation with the lowest antigen and adjuvant dose, M72/AS01_E (10 μg), fulfilled our pre-defined selection criteria and has been selected for further clinical development.

Improved CD4⁺ T cell responses to Mycobacterium tuberculosis in PPD-negative adults by M72/AS01 as compared to the M72/AS02 and Mtb72F/AS02 tuberculosis candidate vaccine formulations: a randomized trial

BACKGROUND

The Bacille Calmette-Guérin (BCG) tuberculosis (TB) vaccine provides incomplete protection, necessitating development of an effective vaccine against TB disease. The Mtb72F/AS02 candidate vaccine was previously shown to be clinically well tolerated and immunogenic in Purified Protein Derivative (PPD)-negative adults. To improve the stability of Mtb72F, a point mutation was introduced into a putative serine protease site to give the final M72 construct. AS01 is an Adjuvant System that can potentially improve both humoral and cellular immune responses compared to the AS02 Adjuvant System or unadjuvanted vaccine. This study evaluated the safety and immunogenicity in Mtb-naïve adults of vaccines containing 40 μg of the M72 antigen with AS02 or AS01 and compared the results with Mtb72F/AS02 vaccine (40 μg dose), M72 in saline (40 μg dose) and AS01 alone.

METHODS

In this Phase I/II observer-blind controlled trial, 110 participants were randomized (4:4:1:1:1) to receive M72/AS01, M72/AS02, Mtb72F/AS02, M72/saline or AS01, following a 0, 1-month schedule. Subjects receiving the adjuvanted M72 vaccines were followed up until 3 years post vaccination. Evaluation of the immune response and safety/reactogenicity was performed.

RESULTS

For all vaccines, solicited adverse events (AEs) were predominantly mild to moderate and transient. No vaccine-related serious AEs occurred and no subject withdrew due to an AE. Immune responses induced by Mtb72F and M72 antigens combined with AS02 were similar. M72/AS01 and M72/AS02 induced robust polyfunctional M72-specific CD4(+) T cell and antibody responses persisting at 3 years, with the highest CD4(+) T cell responses found with M72/AS01.

CONCLUSION

This first clinical study with M72/AS01 and M72/AS02 showed that both vaccines were clinically well tolerated and induced high magnitude and persistent cell-mediated and humoral immune responses. The Mtb72F/AS02 and M72/AS02 vaccines were comparably immunogenic with significantly higher immune responses compared to the M72/saline control. Of the formulations tested, M72/AS01 demonstrated significantly higher vaccine specific Th1 CD4(+) T cell responses supporting its further clinical evaluation.

Identification and characterization of novel recombinant vaccine antigens for immunization against genital Chlamydia trachomatis

Chlamydia trachomatis infection is the most common sexually transmitted bacterial infection worldwide, with over 91 million cases estimated annually. An effective subunit vaccine against Chlamydia may require a multivalent subunit cocktail of antigens in a single formulation for broad coverage of a heterogeneous major histocompatibility complex population. Herein, we describe the identification of novel C. trachomatis antigens by CD4+ and CD8+ T-cell expression cloning, serological expression cloning, and an in silico analysis of the C. trachomatis genome. These antigens elicited human CD4+ T-cell responses, and a subset proved to be immunogenic and protective when administered as immunoprophylactic vaccines against C. trachomatis challenge. Candidate vaccines consisting of the prioritized C. trachomatis antigens adjuvanted in a GlaxoSmithKline proprietary AS01B adjuvant were prioritized based on induction of solid protection against challenge in C57BL/6 and BALB/c mice with C. trachomatis. Some of the vaccines prevented bacterial shedding and colonization of the upper genital tract to varying degrees by mechanisms that may include CD4+ T cells.

Development of an anti-cotinine vaccine to potentiate nicotine-based smoking cessation strategies

Nicotine replacement therapies (NRT) have limited success in smoking cessation. The efficacy of nicotine may be compromised by its main metabolite, cotinine. An anti-cotinine vaccine to remove this antagonism could enhance the efficacy of NRT. We show that cotinine is a weak nicotinic agonist and decreases responses to nicotine, consistent with antagonism through receptor desensitisation. trans-4-Thiol cotinine was coupled to tetanus toxoid, and rats immunised repeatedly. Vaccination raised antibodies specific for cotinine that do not recognise other metabolites or nicotine. Increased serum cotinine concentrations following nicotine administration indicate sequestration of cotinine by antibodies, encouraging further evaluation of this vaccine in behavioural models of nicotine addiction and relapse.

Priming with an adenovirus 35-circumsporozoite protein (CS) vaccine followed by RTS,S/AS01B boosting significantly improves immunogenicity to Plasmodium falciparum CS compared to that with either malaria vaccine alone

The RTS,S/AS02A protein-based vaccine consistently demonstrates significant protection against infection with Plasmodium falciparum malaria and also against clinical malaria and severe disease in children in areas of endemicity. Here we demonstrate with rhesus macaques that priming with a replication-defective human adenovirus serotype 35 (Ad35) vector encoding circumsporozoite protein (CS) (Ad35.CS), followed by boosting with RTS,S in an improved MPL- and QS21-based adjuvant formulation, AS01B, maintains antibody responses and dramatically increases levels of T cells producing gamma interferon and other Th1 cytokines in response to CS peptides. The increased T-cell responses induced by the combination of Ad35.CS and RTS,S/AS01B are sustained for at least 6 months postvaccination and may translate to improved and more durable protection against P. falciparum infection in humans.

Murine immune responses to liver-stage antigen 1 protein FMP011, a malaria vaccine candidate, delivered with adjuvant AS01B or AS02A

Liver-stage antigen 1 (LSA1) is expressed by Plasmodium falciparum only during the intrahepatic cell stage of the parasite's development. Immunoepidemiological studies in regions where malaria is endemic suggested an association between the level of LSA1-specific humoral and cell-mediated immune responses and susceptibility to clinical malaria. A recombinant LSA1 protein, FMP011, has been manufactured as a preerythrocytic vaccine to induce an immune response that would have the effect of controlling parasitemia and disease in humans. To evaluate the immunogenicity of FMP011, we analyzed the immune response of three inbred strains of mice to antigen immunization using two different adjuvant formulations, AS01B and AS02A. We report here the ability of BALB/c and A/J mice, but not C57BL/6J mice, to mount FMP011-specific humoral (antibody titer) and cellular (gamma interferon [IFN-gamma] production) responses following immunization with FMP011 formulated in AS01B or AS02A. Immunization of BALB/c and A/J mice with FMP011/AS01B induced more antigen-specific IFN-gamma-producing splenocytes than immunization with FMP011/AS02A. A slightly higher titer of antibody was induced using AS02A than AS01B in both strains. C57BL/6J mice did not respond with any detectable FMP011-specific IFN-gamma splenocytes or antibody when immunized with FMP011 in AS01B or AS02A. Intracellular staining of cells isolated from FMP011/AS01B-immunized BALB/c mice indicated that CD4(+) cells, but not CD8(+) cells, were the main IFN-gamma-producing splenocyte. However, inclusion of blocking anti-CD4(+) antibody during the in vitro restimulation ELISpot analysis failed to completely abolish IFN-gamma production, indicating that while CD4(+) T cells were the major source of IFN-gamma, other cell types also were involved.

Life-style vaccines

Multiple immunotherapy approaches are under development to treat various chronic diseases or conditions. Thanks to dramatic technological improvements, the field of vaccinology can now extend from prophylaxis to therapy, and from infectious diseases to dysimmune disorders like cancer or autoimmunity, or even to non-immune related conditions, including neurological or cardiovascular disorders. Life-style vaccines defined as vaccines to manage chronic conditions in healthy individuals can, therefore, also be envisaged. Three examples will be reviewed and discussed here, from both technical and ethical aspects: contraceptive vaccines, vaccines to treat addictions, and anti-dental caries vaccines.

Quais (im)posturas intelectuais? O erro de Darwin

Neste texto busca-se uma teorização do sujeito a partir da psicanálise, do estruturalismo e da noção de pós-modernidade. Os autores propõem-se, aqui, a mostrar como e por que um ocultamento da questão do sujeito incessantemente retorna e conduz às piores derivações ideológicas, diluída que é e em um corpo cujo espírito se vê reduzido a uma função entre outras ou na massa de indivíduos orientados para um fim comum, eventualmente conflitual. E tomam como hipótese “demonstrar que toda disciplina projeta sobre a maneira em que se desenvolve ‘sua’ ciência a epistemologia implícita com a qual freqüentemente se sustenta à sua revela”.

Dendritic cells fused with mastocytoma cells elicit therapeutic antitumor immunity

Characterization of the spontaneous immune response that frequently occurs in tumor-bearing animals, as well as immunization using dendritic cells pulsed with tumor antigens, suggests that a limiting factor of the tumor-specific immune response may be a defect in the co-stimulatory signal that is required for optimal activation of T cells. In this work, we describe a new approach to improve the antigen-presenting capacity of tumor cells, which does not require a source of purified tumor-associated antigen. We fused P815 mastocytoma cells with bone marrow-derived dendritic cells. We obtained one hybrid that displayed the phenotypic and functional properties of dendritic cells and expressed mRNA coding for the tumor-associated antigen P815 A/B. Injections of irradiated hybrid cells prevented the growth of preimplanted mastocytoma and induced long-lasting tumor resistance.

Dendritic cells fused with mastocytoma cells elicit therapeutic antitumor immunity

Characterization of the spontaneous immune response that frequently occurs in tumor-bearing animals, as well as immunization using dendritic cells pulsed with tumor antigens, suggests that a limiting factor of the tumor-specific immune response may be a defect in the co-stimulatory signal that is required for optimal activation of T cells. In this work, we describe a new approach to improve the antigen-presenting capacity of tumor cells, which does not require a source of purified tumor-associated antigen. We fused P815 mastocytoma cells with bone marrow-derived dendritic cells. We obtained one hybrid that displayed the phenotypic and functional properties of dendritic cells and expressed mRNA coding for the tumor-associated antigen P815 A/B. Injections of irradiated hybrid cells prevented the growth of preimplanted mastocytoma and induced long-lasting tumor resistance.

The immune response induced in vivo by dendritic cells is dependent on B7-1 or B7-2, but the inhibition of both signals does not lead to tolerance

Dendritic cells (DC) can be used as physiological adjuvant in vivo. Indeed, a single injection of DC, pulsed in vitro with antigen, induces activation of specific T and B lymphocytes in syngeneic mice. The unique capacity of DC to sensitize naive T lymphocytes correlates with elevated expression of MHC antigens as well as co-stimulatory molecules. The aim of this work was to evaluate the functional role of the individual CD28 ligands in the induction of primary humoral and cellular responses, and to characterize the nature of the immune response induced in the presence of selected co-stimulatory molecules. Our data show that the primary response is strictly B7 dependent, and that B7-1 and B7-2 mediate overlapping co-stimulatory functions, as either molecule alone is sufficient to initiate an immune reaction. Inhibition of B7-1 and B7-2, however, does not lead to tolerance as predicted by the two-signal hypothesis. Rather, recognition of antigen in the absence of B7 appears as a null event, since subsequent immunogenic stimulation results in a primary response. Blockade of B7-2 co-stimulatory molecules significantly inhibits antigen-specific IgG1 but not IgG2a production, suggesting that B7-2 may direct the development of Th2 cells. These data emphasize the critical role of the CD28/B7 pathway in the induction of the immune response by DC, which appear to be the initiating antigen-presenting cells in situ.

Effect of muscimol microinjections into the prepositus hypoglossi and the medial vestibular nuclei on cat eye movements

1. For horizontal eye movements, previous observations led to the hypothesis that the legendary neural integrator necessary for correct gaze holding, adequate vestibuloocular reflex (VOR), and optokinetic nystagmus, was located in the region of the complex formed by the nucleus prepositus hypoglossi (NPH) and the medial vestibular nucleus (MVN). 2. The aim of the present study was to test the respective contributions of the NPH, of the rostral part of the MVN, which contains most second-order vestibular neurons, and of the central part of the MVN to the horizontal integrator. 3. An injection of muscimol was used to inactivate each of these three zones in the cat's brain. Muscimol is a gamma-aminobutyric acid (GABA) agonist. By binding to GABAA receptors, it induces a hyperpolarization of the neurons that nullifies their activity. Muscimol was injected into the brain stem of the alert cat through a micropipette by an air pressure system. 4. The search coil technique was used to record spontaneous eye movements and the VOR induced by rotating a turntable at a constant velocity. VOR was analyzed by a new method: transient analysis of vestibular nystagmus. 5. A unilateral injection of muscimol into the NPH induced a bilateral gaze-holding failure: saccades were followed by a centripetal postsaccadic drift. A vestibular imbalance was also present but it was moderate and variable. The VOR responses were distorted drastically. Through transient analysis of vestibular nystagmus, that distortion was revealed to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator. The responses to a rotation either toward the injected side or in the opposite direction were asymmetrical. The direction of that asymmetry was variable. 6. A unilateral injection of muscimol into the rostral part of the MVN caused a vestibular imbalance: in complete darkness, a nystagmus appeared, whose linear slow phases were directed toward the side of injection. 7. A unilateral injection of muscimol into the central part of the MVN induced a syndrome where a severe bilateral gaze-holding failure was combined with a vestibular imbalance. In the light, saccades were followed by a bilateral centripetal postsaccadic drift. In complete darkness, a nystagmus was observed, whose curved slow phases were directed towards the side of injection. The VOR responses were distorted drastically. Here again, that distortion was revealed by our analysis to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of the vestibular commissure in gaze-holding in the cat: a pharmacological evaluation

Recent theoretical studies have proposed that the vestibular commissure is a major component of the horizontal gaze-holding system. In order to test this hypothesis, we injected either bicuculline, a GABA receptor antagonist, or strychnine, a glycine receptor antagonist, into the medial vestibular nucleus of alert cats. The intervestibular connection is indeed inhibitory and mediated by GABA and glycine. As neither bicuculline nor strychnine caused serious deficit of the gaze-holding system, we conclude that the vestibular commissure is not essential for gaze-holding.

NMDA receptors are involved in temporal integration in the oculomotor system of the cat

Spontaneous eye movements were recorded before and after a microinjection (0.1-0.2 microliter) of either APV (an NMDA receptor antagonist) or NBQX (a non-NMDA receptor antagonist) into the nucleus prepositus hypoglossi (NPH) of the alert cat. A unilateral injection of APV caused bilateral failure of the horizontal gaze-holding system: in the light, each saccade was followed by a post-saccadic drift. A unilateral injection of NBQX caused no sign of gaze-holding failure; in the light, spontaneous eye movements were unaffected; in complete darkness, a nystagmus with linear slow phases directed towards the injected side was observed. We conclude that NMDA receptors of the NPH neurones are involved in the gaze-holding system.

Involvement of the N-methyl-D-aspartate receptors of the vestibular nucleus in the gaze-holding system of the cat

Eye movements were recorded in alert cats after injections into one of the medial vestibular nuclei (MVN) either of a N-methyl-D-aspartate (NMDA) antagonist or of a non-NMDA antagonist. A gaze-holding failure was caused by the NMDA antagonist when it was injected into the central part of the MVN but not when it was injected into the rostral part of that nucleus. By contrast, injections of the non-NMDA-receptor antagonist into the MVN did not cause any sign of gaze-holding failure. We conclude that the NMDA receptors located in the central part of the MVN are involved in the gaze-holding system.

Differential effect of injections of kainic acid into the prepositus and the vestibular nuclei of the cat

1. In order adequately to control eye movements, oculomotoneurones have to be supplied with both an eye-velocity signal and an eye-position signal. However, all the command signals of the oculomotor system are velocity signals. Nowadays, there is general agreement about the existence of a brainstem network that would convert velocity command-signals into an eye-position signal. This circuit, because of its function, is called the oculomotor neural integrator. The most obvious symptom of its eventual failure is a gaze-holding deficit: in this case, saccades are followed by a centripetal post-saccadic drift. Although the oculomotor neural integrator is central in oculomotor theory, its precise location is still a matter for debate. 2. Previously, microinjections of kainic acid (KA) into the region of the nucleus prepositus hypoglossi (NPH) and of the medial vestibular nucleus (MVN) were found to induce a horizontal gaze-holding failure both in the cat and in the monkey. However, the relatively large volumes (1-3 microliters) and concentrations (2-4 micrograms microliters-1) used in these injections made it difficult to know if the observed deficit was due to a disturbance of the NPH or of the nearby MVN. These considerations led us to inject very small amounts of kainic acid (50 nl, 0.1 microgram microliter-1) either into the rostral part of the MVN or into different sites along the NPH of the cat. 3. The search coil technique was used to record (1) spontaneous eye movements (2) the vestibulo-ocular reflex (VOR) induced by a constant-velocity rotation (50 deg s-1 for 40 s) and the optokinetic nystagmus (OKN) elicited by rotating an optokinetic drum at 30 deg s-1 for 40 s. 4. In each injection experiment, the location of the abducens nucleus of the alert cat was mapped out by recording the antidromic field potentials evoked by the stimulation of the abducens nerve. Two micropipettes were then glued together in such a way that when the tip of the recording micropipette was in the centre of the abducens nucleus the tip of the injection micropipette was in a target area. The twin pipettes were then lowered in the brainstem until the recording micropipette reached the centre of the abducens nucleus. Kainic acid was then injected into the brainstem of the alert cat through the injection micropipette by an air pressure system. 5. Carried out according to such a protocol, KA injections into the NPH or the rostral part of the MVN consistently led to specific eye-movement changes.(ABSTRACT TRUNCATED AT 400 WORDS)

Gaze holding defect induced by injections of ketamine in the cat brainstem

The signal responsible for horizontal gaze holding is known to be generated, at least in part, by the prepositus hypoglossi (PH) nucleus, whereas that responsible for vertical gaze holding is known to be generated by the interstitial nucleus of Cajal (INC). An intramuscular injection of ketamine was recently demonstrated to induce a gaze holding failure. The aim of the present study was to analyse if ketamine produced this effect by acting, at least in part, on the PH nucleus. We found that a unilateral injection of a small amount of ketamine in the PH nucleus could cause either bilateral horizontal gaze holding failure or a vertical gaze holding failure or both an horizontal and a vertical gaze holding failure.

Effects of Ketamine on Ocular Movements of the Cat

We studied the effects of ketamine, an antagonist of the N-methyl-D-aspartate receptors, on (1) the spontaneous saccades, (2) the vestibulo-ocular reflex (VOR), and (3) the optokinetic nystagmus (OKN) in 8 cats. Ketamine was given intramuscularly at four dosages (1, 2, 8, and 16 mg/kg). Eye movements were measured using the magnetic field-search coil technique. Ketamine did not prevent the occurrence of saccades, but each of them was followed by a centripetal postsaccadic drift. The time-constant of the drift induced by ketamine was 1.0 s when the given dosage was 1 mg/kg and 0.35 s when the given dosage was 16 mg/kg. Post-saccadic drift caused by a low dosage of ketamine may reflect only a mismatch between the pulse and the step commands that create saccades. The highest used dosages of ketamine aggravated the post-saccadic drift probably by disturbing the oculomotor neural integrator. To elicit the horizontal VOR, the head was submitted either to sinusoidal rotations (± 20∘; 0.05 to 1 Hz) or to a rotation at a constant velocity (100∘/s during 40 s). In darkness, the VOR step gain was reduced by ketamine in a dosage-dependent manner. VOR phase lead at 0.10 Hz oscillation in darkness increased from 4.0∘ ± 2.4∘ to 51.6∘ ± 7.5∘ after administration of ketamine at 16 mg/kg. This suggests that ketamine, at least at higher dosages, induces a failure of the neural integrator. Chemical blockade of the vestibular commissure by ketamine may also be responsible for the reduction of the VOR gain. Horizontal OKN was tested using a step stimulus (30∘/s during 40 s). When ketamine was given at 1 mg/kg, the average steady-state gain of the OKN diminished from 0.6 ± 0.2 to 0.3 ± 0.1. After administration of ketamine at 2 mg/kg, the OKN was abolished. The sensitivity of OKN to ketamine is explained at least partly by the fact that ketamine acts against the visual pathways in the retina, in the geniculate nucleus, and in the visual cortex. The time course of the optokinetic afternystagmus (OKAN) and that of the decrease of the perrotatory and postrotatory VOR were not reduced by ketamine administered at 1 or 2 mg/kg. This shows that ketamine does not affect the velocity-storage mechanism at these dosages.

Ketamine induces failure of the oculomotor neural integrator in the cat

We studied the effect of intramuscular injection of low dose of ketamine (1 mg/kg) on the spontaneous ocular movements of the cat. Ketamine is a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptors, which is used as an anesthetic agent in human surgery. We found that ketamine administration caused a failure of gaze holding: each saccade was followed by a centripetal post-saccadic drift. This defect was selective: the dynamics of the saccades was not altered (the amplitude/maximum velocity relationship was unaffected by ketamine at the dose of 1 mg/kg). We postulated that the observed effect was due to the fact that NMDA receptors were implicated in the network of the oculomotor neural integrator that converted activity related to the saccade (pulse signal) into activity responsible for gaze holding (step signal).