Biomedical subjects

B Roerig

Publications and source records attributed to B Roerig.

6 recordsLinked to original sources

PubMed2002

Relationships of local inhibitory and excitatory circuits to orientation preference maps in ferret visual cortex.

The contribution and precise role of intracortical circuits in generating orientation tuned responses in visual cortical neurons is still controversial. To address this question, the relationship between excitatory and inhibitory synaptic connections and orientation maps in ferret striate cortex was investigated by combining in vivo optical imaging and in vitro scanning laser photostimulation. Excitatory and inhibitory inputs to pyramidal cells originated preferentially from regions with similar orientation preference. Prominent cross-orientation inhibition was not observed, arguing against cross-orientation models of orientation selectivity. The tuning of inhibitory inputs was significantly broader in both layer 2/3 and layer 5/6 pyramidal neurons compared to the tuning of excitatory inputs. Local excitatory inputs were more prominent in the 0-20 degrees tuning difference range between pre- and postsynaptic cells than inhibitory inputs, whereas inhibition dominated in the 20-40 degrees tuning difference range. These differences in tuning of excitatory and inhibitory inputs onto individual cells are consistent with the predictions of recurrent models of orientation selectivity.

Animals↗

PubMed2001

Direction selectivity of excitatory and inhibitory neurons in ferret visual cortex.

Direction selectivity is a characteristic feature of neurons in the visual cortex of higher mammals. Excitatory and inhibitory cortical neurons receive different patterns of synaptic connections resulting in different receptive field properties. We have analyzed the direction tuning of excitatory and inhibitory neurons of ferret visual cortex using single unit recordings. Direction tuning was constant among neurons in a vertical column. The majority (> 80%) of excitatory (regular spiking) neurons were direction tuned or direction biased. Fast spiking (inhibitory) neurons were orientation, but only weakly or not direction tuned. This indicates that excitatory and inhibitory neurons have different functions in visual processing and their different integration in thalamocortical and intracortical circuits results in a diversification of receptive field properties.

Action Potentials↗

PubMed2000

Neurotransmitters and gap junctions in developing neural circuits.

A growing body of evidence suggests that highly correlated, spontaneous neural activity plays an important role in shaping connections in the developing nervous system prior to the maturation of sensory afferents. In this article we discuss the mechanisms involved in the generation and the regulation of spontaneous activity patterns in the developing retina and the developing neocortex. Spontaneous activity in the developing retina propagates across the ganglion cell layer as waves of action potentials and drives rhythmic increases in intracellular calcium in retinal neurons. Retinal waves are mediated by a combination of chemical synaptic transmission and gap junctions, and the circuitry responsible for generating retinal waves changes with age and between species. In the developing cortex, spontaneous calcium elevations propagate across clusters of cortical neurons called domains. Cortical domains are generated by a regenerative mechanism involving second messenger diffusion through gap junctions and subsequent calcium release from internal stores. The neocortical gap junction system is regulated by glutamate-triggered second messenger systems as well as neuromodulatory transmitters, suggesting extensive interactions between synaptic transmission and information flow through gap junctions. The interaction between gap junctions and chemical synaptic transmission observed in these developing networks represent a powerful mechanism by which activity across large groups of neurons can be correlated.

Animals↗

PubMed1999

Organization of intracortical circuits in relation to direction preference maps in ferret visual cortex.

Neurons in the primary visual cortex are selective for the direction of movement of a visual stimulus. Like other stimulus features, direction preference is mapped on the cortical surface in a systematic manner. Intracortical synaptic circuits, in particular inhibitory connections, have been implicated in the emergence of direction selectivity. Whether intracortical inhibition specifically suppresses responses to the nonpreferred direction or has a nonspecific "thresholding" effect is still controversial. To address these questions we investigated the relationship between patterns of intracortical synaptic connections and direction domains in ferret primary visual cortex (area 17) using a combined in vivo-in vitro approach. Excitatory synaptic inputs were iso-direction-tuned. The majority of local inhibitory inputs were also iso-direction-tuned. However, approximately 40% of inhibitory connections originated in regions preferring the opposite direction. These findings indicate that specific inhibitory interactions between cortical regions of opposite direction preference may contribute to the emergence and sharpening of direction selectivity.

Animals↗

PubMed1997

Modulation of intrinsic circuits by serotonin 5-HT3 receptors in developing ferret visual cortex.

Serotonergic projections are widespread in the developing neocortex, but their functions are obscure. The effects of 5-HT3 receptor agonists on cortical circuit response properties were studied in slices of ferret primary visual cortex using high-speed optical imaging of voltage-sensitive dye signals and whole-cell patch-clamp recording. Activation of the 5-HT3 receptor decreased the amplitude and lateral extent of excitation throughout postnatal development. This effect peaks after eye opening, which indicates a function for serotonergic modulation of circuit responses during the period of refinement of cortical connections. Whole-cell patch-clamp recordings from single neurons revealed that synaptic responses evoked by white matter stimulation were reduced by 5-HT3 receptor agonists, whereas the frequency of spontaneous GABAergic synaptic currents was enhanced dramatically. This indicates that the modulation of spontaneous synaptic activity by fast-acting serotonin receptors is reflected in an inhibition of the circuit response, in line with the notion of background synaptic activity altering the spatiotemporal integration properties of cortical cells by changing their membrane potential and their electrotonic structure. These mechanisms may regulate the response properties of intrinsic circuits in both the adult and developing neocortex.

2-Amino-5-phosphonovalerate↗

PubMed1997

Fast synaptic signaling by nicotinic acetylcholine and serotonin 5-HT3 receptors in developing visual cortex.

Cholinergic and serotonergic fiber systems invade the developing visual cortex several weeks before eye opening; both transmitters have been implicated in plasticity of neocortical circuits. These transmitters have been presumed to act predominantly through second messenger-coupled receptors, because fast cholinergic or serotonergic neurotransmission has never been observed in neocortex. However, acetylcholine and serotonin also act on ligand-gated ion channels; the nicotinic acetylcholine receptor and the serotonin 5-HT3 receptor, respectively. Here, using whole-cell patch-clamp techniques in developing ferret visual cortex, we pharmacologically isolated fast, spontaneous, and evoked cholinergic and serotonergic synaptic events in pyramidal cells and interneurons of all cortical layers. The number of cells receiving such inputs increased with the ingrowth of thalamic afferents, and the frequencies of the spontaneous events increased at eye opening. Thus, both acetylcholine and serotonin can mediate fast synaptic transmission in the visual cortex; the early onset of these mechanisms suggests a role during initial stages of circuit formation and during subsequent experience-dependent remodeling of cortical connections.

Acetylcholine↗