Intracellular staining of physiologically identified neurons and axons in the somatosensory thalamus of the cat

Neurons and axons responding to somesthetic stimulation in the thalamic ventrobasal complex (VB) were characterized electrophysiologically by intracellular recording and then individually injected with horseradish peroxidase. Two types of thalamocortical relay neuron were identified, primarily on the basis of dendritic morphology and axon diameter. Types with cutaneous or deep receptive fields were found in each class. Neither type had collateral axons in VB but each gave branches to the thalamic reticular nucleus (RTN). Small putative interneurons in VB and RTN neurons with somatosensory receptive fields were also injected. The RTN neurons had profusely branched widely ramifying axons in VB and adjoining nuclei. Injected medial lemniscal axons in VB had a range of receptive field properties and conduction velocities and ended in elongated anteroposterior domains with one or more dense concentrations of terminal boutons of varying size and with varying numbers of boutons.

Control of cardiovascular function by electrical stimulation within the medullary raphe region of the cat

An investigation was made of the effect on cardiovascular function of electrical stimulation within the midline medullary region of the anesthetized cat. Stimuli consisted of low-intensity trains of pulses. Stimulation sites were defined histologically and in some experiments, detailed stimulus maps were obtained for the effect of electrical stimulation on mean arterial blood pressure (MABP). In other experiments, measurements were made of changes produced by electrical stimulation on heart rate, cardiac output, cardiac contractility, and total peripheral resistance. Comparisons were made between the effect of stimulation at sites on the midline and sites to 1.5 mm more lateral. At midline sites, electrical stimulation most often produced a depression of the MABP. Effective depressor sites were located preferentially in two regions along the anteroposterior axis of the brain stem. At more lateral sites, electrical stimulation elevated the MABP. At most sites, changes in MABP occurred concomitantly with changes in total peripheral resistance while cardiac output was unchanged. Sites where electrical stimulation directly altered heart rate and cardiac contractility had a different distribution within the medulla compared with sites where stimulation changed the MABP.