Joost Heeroma | University College London (original) (raw)

Papers by Joost Heeroma

Research paper thumbnail of Tonic GABA A receptor-mediated currents in human brain

European Journal of Neuroscience, 2006

GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition... more GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition. It has been proposed that tonic inhibition plays a critical part in controlling neuronal and network excitability. Although tonic GABA A receptor-mediated currents have been well characterized in rodents, their existence in human tissue has yet to be demonstrated. Here we show that tonic currents can be recorded from human tissue obtained from patients undergoing temporal lobectomies. Tonic GABA A receptor-mediated currents were present in pyramidal cells and interneurons in layer V-VI of temporal neocortex and granule cells in the dentate gyrus. These tonic currents have cell type-specific pharmacologies, opening up the possibility of targeted therapeutics.

Research paper thumbnail of Automatic morphometry of synaptic boutons of cultured cells using granulometric analysis of digital images

Numbers, linear density, and surface area of synaptic boutons can be important parameters in stud... more Numbers, linear density, and surface area of synaptic boutons can be important parameters in studies on synaptic plasticity in cultured neurons. We present a method for automatic identification and morphometry of boutons based on filtering of digital images using granulometric analysis. Cultures of cortical neurons (DIV8 and DIV21) were fixed and marked with fluorescently labeled antibodies for synapsin I (a marker for synaptic boutons) and MAP-2 (a marker for dendrites). Images were acquired on a confocal microscope and automatically processed. Granulometry, a morphological operator sensitive to the geometry and size of objects, was used to construct a filter passing fuzzy fluorescent grains of a certain size. Next, the filter was overlaid with the original image (masking) and the positive pixels were identified by an integral intensity threshold (thresholding). Disjoint grains, representing individual boutons, were reconstructed from the connected pixels above the threshold, numbered and their area was measured. In total, 1498 boutons with a mean diameter of 1.63 ± 0.49 m (S.D.) were measured. Comparisons with manual counts showed that the proposed method was capable of identifying boutons in a systematic manner at the light microscopic level and was a viable alternative to manual bouton counting. (D. Prodanov). number of individual samples to be evaluated. Because of the high variability of the localizations of synapses on dendrites and the clustering of boutons, the stereological assumption of homogeneity of spatial distribution is violated. Therefore, complete dendritic trees are counted. To facilitate counting in cell cultures we developed a reproducible and robust method for automatic identification and morphometry of synaptic boutons. The method was further applied to synaptic boutons marked for synapsin 1 immuno-fluoresecence from microisland cultures of neocortical neurons.

Research paper thumbnail of Characterisation of cortical activity in response to deep brain stimulation of ventral-lateral nucleus: Modelling and experiment

Journal of Neuroscience …, Jan 1, 2009

Research paper thumbnail of The role of regulated secretion in neurite outgrowth, synapse formation and neuronal survival: Munc-18-1 as a spider in the web

Research paper thumbnail of Episodic ataxia type 1 mutations differentially affect neuronal excitability and transmitter release

Disease Models & …, Jan 1, 2009

Research paper thumbnail of Trophic support delays but does not prevent cell‐intrinsic degeneration of neurons deficient for munc18‐1

European Journal …, Jan 1, 2004

The stability of neuronal networks is thought to depend on synaptic transmission which provides a... more The stability of neuronal networks is thought to depend on synaptic transmission which provides activity-dependent maintenance signals for both synapses and neurons. Here, we tested the relationship between presynaptic secretion and neuronal maintenance using munc18-1-null mutant mice as a model. These mutants have a specific defect in secretion from synaptic and large dense-cored vesicles [Verhage et al. (2000), Science, 287, 864-869; Voets et al. (2001), Neuron, 31, 581-591]. Neuronal networks in these mutants develop normally up to synapse formation but eventually degenerate. The proposed relationship between secretion and neuronal maintenance was tested in low-density and organotypic cultures and, in vivo, by conditional cell-specific inactivation of the munc18-1 gene. Dissociated munc18-1-deficient neurons died within 4 days in vitro (DIV). Application of trophic factors, insulin or BDNF delayed degeneration up to 7 DIV. In organotypic cultures, munc18-1-deficient neurons survived until 9 DIV. On glial feeders, these neurons survived up to 10 DIV and 14 DIV when insulin was applied. Co-culturing dissociated mutant neurons with wild-type neurons did not prolong survival beyond 4 DIV, but coculturing mutant slices with wild-type slices prolonged survival up to 19 DIV. Cell-specific deletion of munc18-1 expression in cerebellar Purkinje cells in vivo resulted in the specific loss of these neurons without affecting connected or surrounding neurons. Together, these data allow three conclusions. First, the lack of synaptic activity cannot explain the degeneration in munc18-1-null mutants. Second, trophic support delays but cannot prevent degeneration. Third, a cell-intrinsic yet unknown function of munc18-1 is essential for prolonged survival.

Research paper thumbnail of Automatic morphometry of synaptic boutons of cultured cells using granulometric analysis of digital images

Journal of neuroscience methods, Jan 1, 2006

Numbers, linear density, and surface area of synaptic boutons can be important parameters in stud... more Numbers, linear density, and surface area of synaptic boutons can be important parameters in studies on synaptic plasticity in cultured neurons. We present a method for automatic identification and morphometry of boutons based on filtering of digital images using granulometric analysis. Cultures of cortical neurons (DIV8 and DIV21) were fixed and marked with fluorescently labeled antibodies for synapsin I (a marker for synaptic boutons) and MAP-2 (a marker for dendrites). Images were acquired on a confocal microscope and automatically processed. Granulometry, a morphological operator sensitive to the geometry and size of objects, was used to construct a filter passing fuzzy fluorescent grains of a certain size. Next, the filter was overlaid with the original image (masking) and the positive pixels were identified by an integral intensity threshold (thresholding). Disjoint grains, representing individual boutons, were reconstructed from the connected pixels above the threshold, numbered and their area was measured. In total, 1498 boutons with a mean diameter of 1.63 ± 0.49 m (S.D.) were measured. Comparisons with manual counts showed that the proposed method was capable of identifying boutons in a systematic manner at the light microscopic level and was a viable alternative to manual bouton counting. (D. Prodanov). number of individual samples to be evaluated. Because of the high variability of the localizations of synapses on dendrites and the clustering of boutons, the stereological assumption of homogeneity of spatial distribution is violated. Therefore, complete dendritic trees are counted. To facilitate counting in cell cultures we developed a reproducible and robust method for automatic identification and morphometry of synaptic boutons. The method was further applied to synaptic boutons marked for synapsin 1 immuno-fluoresecence from microisland cultures of neocortical neurons.

Research paper thumbnail of Tonic GABAA receptor‐mediated currents in human brain

European Journal …, Jan 1, 2006

GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition... more GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition. It has been proposed that tonic inhibition plays a critical part in controlling neuronal and network excitability. Although tonic GABA A receptor-mediated currents have been well characterized in rodents, their existence in human tissue has yet to be demonstrated. Here we show that tonic currents can be recorded from human tissue obtained from patients undergoing temporal lobectomies. Tonic GABA A receptor-mediated currents were present in pyramidal cells and interneurons in layer V-VI of temporal neocortex and granule cells in the dentate gyrus. These tonic currents have cell type-specific pharmacologies, opening up the possibility of targeted therapeutics.

Research paper thumbnail of LPS‐induced expression of a novel chemokine receptor (L‐CCR) in mouse glial cells in vitro and in vivo

Research paper thumbnail of Anti-Hebbian long-term potentiation in the hippocampal feedback inhibitory circuit

Science, Jan 1, 2007

Long-term potentiation (LTP), which approximates Hebb's postulate of associative learning, typica... more Long-term potentiation (LTP), which approximates Hebb's postulate of associative learning, typically requires depolarization-dependent glutamate receptors of the NMDA (N-methyl-Daspartate) subtype. However, in some neurons, LTP depends instead on calcium-permeable AMPA-type receptors. This is paradoxical because intracellular polyamines block such receptors during depolarization. We report that LTP at synapses on hippocampal interneurons mediating feedback inhibition is "anti-Hebbian": It is induced by presynaptic activity but prevented by postsynaptic depolarization. Anti-Hebbian LTP may occur in interneurons that are silent during periods of intense pyramidal cell firing, such as sharp waves, and lead to their altered activation during theta activity.

Research paper thumbnail of Hebbian LTP in feed-forward inhibitory interneurons and the temporal fidelity of input discrimination

Nat Neurosci, Jan 1, 2005

Cortical information processing requires a delicate balance of excitatory and inhibitory signalin... more Cortical information processing requires a delicate balance of excitatory and inhibitory signaling. How is this balance preserved during hippocampal memory encoding, which involves NMDA receptor-dependent long term potentiation (LTP)? This form of LTP occurs at synapses between pyramidal neurons but has not been detected in feed-forward inhibitory interneurons. We show that paired pre-and postsynaptic activity evokes pathway-specific LTP in half of rat stratum radiatum interneurons if cytoplasmic integrity is preserved. LTP occurs in aspiny feed-forward interneurons and propagates to pyramidal neurons as an enhancement of disynaptic inhibition. We also show that when LTP is restricted to synapses on pyramidal neurons, the temporal fidelity of synaptic integration and action potential generation in pyramidal cells is compromised. However, when LTP also occurs at synapses on feed-forward interneurons, temporal fidelity is preserved. We propose that Hebbian LTP at synapses driving disynaptic inhibition is necessary to maintain information processing without degradation during memory encoding.

Research paper thumbnail of Synaptic assembly of the brain in the absence of neurotransmitter secretion

Science, Jan 1, 2000

The user has requested enhancement of the downloaded file. a sublethal dose for this strain of L.... more The user has requested enhancement of the downloaded file. a sublethal dose for this strain of L. monocytogenes, were injected intravenously. The titer of viable bacteria in the inoculum and in organ homogenates was determined by plating 10-fold serial dilutions on trypticase soy agar plates. Eta-1 Ϫ/Ϫ mice contained liver-associated Listeria-infected cysts that were apparent 4 to 5 days after infection. Plates were incubated at 37°C, and the numbers of CFU were counted after 24 hours. 24. Spleen cells (4 ϫ 10 6 /ml) from four to five C57BL/ 6 ϫ 129 Eta-1 ϩ/ϩ or four to five C57BL/6 ϫ 129 Eta-1 Ϫ/Ϫ mice that had been intravenously inoculated 5 days earlier with 10 3 CFU were stimulated with heat-killed L. monocytogenes (2 ϫ 10 8 CFU/ml) 96 hours before IFN-␥ measurement by an OptEIA ELISA kit (PharMingen). 5 mM GRGDS peptide but not GRADS peptide (29) to cultures of peritoneal macrophages (38) resulted in an 80% reduction of the IL-12 response after LPS stimulation. 29. Single-letter abbreviations for the amino acid residues are as follows:

Research paper thumbnail of Tonic GABA A receptor-mediated currents in human brain

European Journal of Neuroscience, 2006

GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition... more GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition. It has been proposed that tonic inhibition plays a critical part in controlling neuronal and network excitability. Although tonic GABA A receptor-mediated currents have been well characterized in rodents, their existence in human tissue has yet to be demonstrated. Here we show that tonic currents can be recorded from human tissue obtained from patients undergoing temporal lobectomies. Tonic GABA A receptor-mediated currents were present in pyramidal cells and interneurons in layer V-VI of temporal neocortex and granule cells in the dentate gyrus. These tonic currents have cell type-specific pharmacologies, opening up the possibility of targeted therapeutics.

Research paper thumbnail of Automatic morphometry of synaptic boutons of cultured cells using granulometric analysis of digital images

Numbers, linear density, and surface area of synaptic boutons can be important parameters in stud... more Numbers, linear density, and surface area of synaptic boutons can be important parameters in studies on synaptic plasticity in cultured neurons. We present a method for automatic identification and morphometry of boutons based on filtering of digital images using granulometric analysis. Cultures of cortical neurons (DIV8 and DIV21) were fixed and marked with fluorescently labeled antibodies for synapsin I (a marker for synaptic boutons) and MAP-2 (a marker for dendrites). Images were acquired on a confocal microscope and automatically processed. Granulometry, a morphological operator sensitive to the geometry and size of objects, was used to construct a filter passing fuzzy fluorescent grains of a certain size. Next, the filter was overlaid with the original image (masking) and the positive pixels were identified by an integral intensity threshold (thresholding). Disjoint grains, representing individual boutons, were reconstructed from the connected pixels above the threshold, numbered and their area was measured. In total, 1498 boutons with a mean diameter of 1.63 ± 0.49 m (S.D.) were measured. Comparisons with manual counts showed that the proposed method was capable of identifying boutons in a systematic manner at the light microscopic level and was a viable alternative to manual bouton counting. (D. Prodanov). number of individual samples to be evaluated. Because of the high variability of the localizations of synapses on dendrites and the clustering of boutons, the stereological assumption of homogeneity of spatial distribution is violated. Therefore, complete dendritic trees are counted. To facilitate counting in cell cultures we developed a reproducible and robust method for automatic identification and morphometry of synaptic boutons. The method was further applied to synaptic boutons marked for synapsin 1 immuno-fluoresecence from microisland cultures of neocortical neurons.

Research paper thumbnail of Characterisation of cortical activity in response to deep brain stimulation of ventral-lateral nucleus: Modelling and experiment

Journal of Neuroscience …, Jan 1, 2009

Research paper thumbnail of The role of regulated secretion in neurite outgrowth, synapse formation and neuronal survival: Munc-18-1 as a spider in the web

Research paper thumbnail of Episodic ataxia type 1 mutations differentially affect neuronal excitability and transmitter release

Disease Models & …, Jan 1, 2009

Research paper thumbnail of Trophic support delays but does not prevent cell‐intrinsic degeneration of neurons deficient for munc18‐1

European Journal …, Jan 1, 2004

The stability of neuronal networks is thought to depend on synaptic transmission which provides a... more The stability of neuronal networks is thought to depend on synaptic transmission which provides activity-dependent maintenance signals for both synapses and neurons. Here, we tested the relationship between presynaptic secretion and neuronal maintenance using munc18-1-null mutant mice as a model. These mutants have a specific defect in secretion from synaptic and large dense-cored vesicles [Verhage et al. (2000), Science, 287, 864-869; Voets et al. (2001), Neuron, 31, 581-591]. Neuronal networks in these mutants develop normally up to synapse formation but eventually degenerate. The proposed relationship between secretion and neuronal maintenance was tested in low-density and organotypic cultures and, in vivo, by conditional cell-specific inactivation of the munc18-1 gene. Dissociated munc18-1-deficient neurons died within 4 days in vitro (DIV). Application of trophic factors, insulin or BDNF delayed degeneration up to 7 DIV. In organotypic cultures, munc18-1-deficient neurons survived until 9 DIV. On glial feeders, these neurons survived up to 10 DIV and 14 DIV when insulin was applied. Co-culturing dissociated mutant neurons with wild-type neurons did not prolong survival beyond 4 DIV, but coculturing mutant slices with wild-type slices prolonged survival up to 19 DIV. Cell-specific deletion of munc18-1 expression in cerebellar Purkinje cells in vivo resulted in the specific loss of these neurons without affecting connected or surrounding neurons. Together, these data allow three conclusions. First, the lack of synaptic activity cannot explain the degeneration in munc18-1-null mutants. Second, trophic support delays but cannot prevent degeneration. Third, a cell-intrinsic yet unknown function of munc18-1 is essential for prolonged survival.

Research paper thumbnail of Automatic morphometry of synaptic boutons of cultured cells using granulometric analysis of digital images

Journal of neuroscience methods, Jan 1, 2006

Numbers, linear density, and surface area of synaptic boutons can be important parameters in stud... more Numbers, linear density, and surface area of synaptic boutons can be important parameters in studies on synaptic plasticity in cultured neurons. We present a method for automatic identification and morphometry of boutons based on filtering of digital images using granulometric analysis. Cultures of cortical neurons (DIV8 and DIV21) were fixed and marked with fluorescently labeled antibodies for synapsin I (a marker for synaptic boutons) and MAP-2 (a marker for dendrites). Images were acquired on a confocal microscope and automatically processed. Granulometry, a morphological operator sensitive to the geometry and size of objects, was used to construct a filter passing fuzzy fluorescent grains of a certain size. Next, the filter was overlaid with the original image (masking) and the positive pixels were identified by an integral intensity threshold (thresholding). Disjoint grains, representing individual boutons, were reconstructed from the connected pixels above the threshold, numbered and their area was measured. In total, 1498 boutons with a mean diameter of 1.63 ± 0.49 m (S.D.) were measured. Comparisons with manual counts showed that the proposed method was capable of identifying boutons in a systematic manner at the light microscopic level and was a viable alternative to manual bouton counting. (D. Prodanov). number of individual samples to be evaluated. Because of the high variability of the localizations of synapses on dendrites and the clustering of boutons, the stereological assumption of homogeneity of spatial distribution is violated. Therefore, complete dendritic trees are counted. To facilitate counting in cell cultures we developed a reproducible and robust method for automatic identification and morphometry of synaptic boutons. The method was further applied to synaptic boutons marked for synapsin 1 immuno-fluoresecence from microisland cultures of neocortical neurons.

Research paper thumbnail of Tonic GABAA receptor‐mediated currents in human brain

European Journal …, Jan 1, 2006

GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition... more GABA A receptors can mediate both phasic (synaptic) and tonic (extrasynaptic) forms of inhibition. It has been proposed that tonic inhibition plays a critical part in controlling neuronal and network excitability. Although tonic GABA A receptor-mediated currents have been well characterized in rodents, their existence in human tissue has yet to be demonstrated. Here we show that tonic currents can be recorded from human tissue obtained from patients undergoing temporal lobectomies. Tonic GABA A receptor-mediated currents were present in pyramidal cells and interneurons in layer V-VI of temporal neocortex and granule cells in the dentate gyrus. These tonic currents have cell type-specific pharmacologies, opening up the possibility of targeted therapeutics.

Research paper thumbnail of LPS‐induced expression of a novel chemokine receptor (L‐CCR) in mouse glial cells in vitro and in vivo

Research paper thumbnail of Anti-Hebbian long-term potentiation in the hippocampal feedback inhibitory circuit

Science, Jan 1, 2007

Long-term potentiation (LTP), which approximates Hebb's postulate of associative learning, typica... more Long-term potentiation (LTP), which approximates Hebb's postulate of associative learning, typically requires depolarization-dependent glutamate receptors of the NMDA (N-methyl-Daspartate) subtype. However, in some neurons, LTP depends instead on calcium-permeable AMPA-type receptors. This is paradoxical because intracellular polyamines block such receptors during depolarization. We report that LTP at synapses on hippocampal interneurons mediating feedback inhibition is "anti-Hebbian": It is induced by presynaptic activity but prevented by postsynaptic depolarization. Anti-Hebbian LTP may occur in interneurons that are silent during periods of intense pyramidal cell firing, such as sharp waves, and lead to their altered activation during theta activity.

Research paper thumbnail of Hebbian LTP in feed-forward inhibitory interneurons and the temporal fidelity of input discrimination

Nat Neurosci, Jan 1, 2005

Cortical information processing requires a delicate balance of excitatory and inhibitory signalin... more Cortical information processing requires a delicate balance of excitatory and inhibitory signaling. How is this balance preserved during hippocampal memory encoding, which involves NMDA receptor-dependent long term potentiation (LTP)? This form of LTP occurs at synapses between pyramidal neurons but has not been detected in feed-forward inhibitory interneurons. We show that paired pre-and postsynaptic activity evokes pathway-specific LTP in half of rat stratum radiatum interneurons if cytoplasmic integrity is preserved. LTP occurs in aspiny feed-forward interneurons and propagates to pyramidal neurons as an enhancement of disynaptic inhibition. We also show that when LTP is restricted to synapses on pyramidal neurons, the temporal fidelity of synaptic integration and action potential generation in pyramidal cells is compromised. However, when LTP also occurs at synapses on feed-forward interneurons, temporal fidelity is preserved. We propose that Hebbian LTP at synapses driving disynaptic inhibition is necessary to maintain information processing without degradation during memory encoding.

Research paper thumbnail of Synaptic assembly of the brain in the absence of neurotransmitter secretion

Science, Jan 1, 2000

The user has requested enhancement of the downloaded file. a sublethal dose for this strain of L.... more The user has requested enhancement of the downloaded file. a sublethal dose for this strain of L. monocytogenes, were injected intravenously. The titer of viable bacteria in the inoculum and in organ homogenates was determined by plating 10-fold serial dilutions on trypticase soy agar plates. Eta-1 Ϫ/Ϫ mice contained liver-associated Listeria-infected cysts that were apparent 4 to 5 days after infection. Plates were incubated at 37°C, and the numbers of CFU were counted after 24 hours. 24. Spleen cells (4 ϫ 10 6 /ml) from four to five C57BL/ 6 ϫ 129 Eta-1 ϩ/ϩ or four to five C57BL/6 ϫ 129 Eta-1 Ϫ/Ϫ mice that had been intravenously inoculated 5 days earlier with 10 3 CFU were stimulated with heat-killed L. monocytogenes (2 ϫ 10 8 CFU/ml) 96 hours before IFN-␥ measurement by an OptEIA ELISA kit (PharMingen). 5 mM GRGDS peptide but not GRADS peptide (29) to cultures of peritoneal macrophages (38) resulted in an 80% reduction of the IL-12 response after LPS stimulation. 29. Single-letter abbreviations for the amino acid residues are as follows: