John P. Horn

Learn More
Ca(v)1.3 (alpha 1D) L-type Ca(2+) channels have been implicated in substantia nigra (SN) dopamine (DA) neuron pacemaking and vulnerability to Parkinson's disease. These effects may arise from the depolarizing current and cytoplasmic Ca(2+) elevation produced by Ca(v)1.3 channels at subthreshold membrane potentials. However, the assumption that the Ca(2+)(More)
The dynamic-clamp method provides a powerful electrophysiological tool for creating virtual ionic conductances in living cells and studying their influence on membrane potential. Here we describe G-clamp, a new way to implement a dynamic clamp using the real-time version of the Lab-VIEW programming environment together with a Windows host, an embedded(More)
1. Post-ganglionic neurones of the rat superior cervical ganglion were studied in vitro (21-26 degrees C) using single intracellular micro-electrode methods. 2. Three Ca2+-dependent potentials were studied: the shoulder on the normal action potential, the hyperpolarizing afterpotential (h.a.p.), and th Ca2+ spike. 3. Bath-applied noradrenaline reversibly(More)
The strength and number of nicotinic synapses that converge on secretomotor B neurons were assessed in the bullfrog by recording intracellularly from isolated preparations of paravertebral sympathetic ganglia 9 and 10. One input to every B neuron invariably produced a suprathreshold EPSP and was defined as the primary nicotinic synapse. In addition, 93% of(More)
1. The muscarinic inhibitory post-synaptic potential (i.p.s.p.) in sympathetic C neurones has been characterized in an isolated preparation of bullfrog paravertebral chain ganglia. Interactions between the i.p.s.p. and two other synaptic potentials have also been examined. 2. A single presynaptic stimulus to a C cell produces a nicotinic excitatory(More)
Midbrain dopamine neuron activity results from the integration of the responses to metabo- and ionotropic receptors with the postsynaptic excitability of these intrinsic pacemakers. Interestingly, intrinsic pacemaker rate varies greatly between individual dopamine neurons and is subject to short- and long-term regulation. Here responses of substantia nigra(More)
These experiments were designed to characterize the distribution, morphology, and number of spinal preganglionic neurons that selectively innervate the B- and C-type sympathetic neurons in paravertebral ganglia 9 and 10 of the bullfrog. For this purpose, horseradish peroxidase (HRP) was applied to the anterior end of the sectioned sympathetic chain between(More)
1. The cellular organization of the ninth and tenth paravertebral sympathetic ganglia in the bullfrog was studied with intracellular and extracellular recording methods. An isolated preparation was used in which anatomical details of individual cells could be resolved while making physiological measurements. This permitted the characterization of neurones(More)
The predominant form of muscarinic excitation in the forebrain and in sympathetic ganglia arises from m1 receptors coupled to the G(q/11) signal transduction pathway. Functional components of this system have been most completely mapped in frog sympathetic B neurons. Presynaptic stimulation of the B neuron produces a dual-component muscarinic excitatory(More)
Norepinephrine reversibly antagonizes three calcium-dependent potentials recorded from rat postganglionic neurons. Norepinephrine inhibits the development of a shoulder on the aciton potential, the magnitude of the hyperpolarizing afterpotential, and the rate of rise and amplitude of the calcium spike. The action of norepinephrine is antagonized by the(More)