A telemetry system for single neuronal discharge recording from behaving monkey

Telemetry system for reliable recording of action potentials from freely moving rats

Recording single cells from alert rats currently requires a cable to connect brain electrodes to the acquisition system. If no cable were necessary, a variety of interesting experiments would become possible, and the design of other experiments would be simplified. To eliminate the need for a cable we have developed a one-channel radiotelemetry system that is easily carried by a rat. This system transmits a signal that is reliable, highly accurate and can be detected over distances of > or = 20 m. The mobile part of the system has three components: (1) a headstage with built-in amplifiers that plugs into the connector for the electrode array on the rat's head; the headstage also incorporates a light-emitting diode (LED) used to track the rat's position; (2) a backpack that contains the transmitter and batteries (2 N cells); the backpack also provides additional amplification of the single cell signals; and (3) a short cable that connects the headstage to the backpack; the cable supplies power to the headstage amplifiers and the LED, and carries the physiological signals from the headstage to the backpack. By using a differential amplifier and recording between two brain microelectrodes the system can transmit action potential activity from two nearly independent sources. In a future improvement, two transmitters with different frequencies would be used telemeter signals from four microelectrodes simultaneously.

Single neuron activity in the rat lateral hypothalamus during 2-deoxy-D-glucose induced and natural feeding behavior

Single neuron activity in the lateral hypothalamic area (LHA) was recorded extracellularly in freely moving rats. Intra-third-cerebroventricular injection of 2-deoxy-D-glucose (2-DG) increased the activity in 38% of 69 neurons and decreased it in 19%. The remaining 43% of the neurons were not affected. Of the neurons excited, 50% showed definite inhibition of activity after long-lasting excitation. In 58% of the 69 neurons, the following changes in neuronal activity were observed during spontaneous feeding. Most of the tonic type neurons, which increased activity throughout the period of a meal, were excited by 2-DG, while the phasic type, which showed an abrupt increase in activity just before eating followed by a decrease, tended to be inhibited by 2-DG. Although injection of 2-DG induced feeding for a brief period in 61 cases (88%), the total food intake during 24 h was reduced significantly below normal. These findings indicate that 2-DG both excites and inhibits LHA neurons and induces facilitation followed by inhibition of feeding behavior.

A computerized control system for a bar-press feeding task initiated by monkey vocalization

Computerized control of a bar-press feeding task initiated by a monkey's vocalization was designed to study the motivational roles of brain regions in feeding behavior. In this paradigm, the monkey was required to vocalize in order to initiate the task and then press the bar 30 times to obtain the reward. A microcomputer was used to sense the vocalization and to control the task. Using this system, changes in single neuron activity in the orbitofrontal cortex and the lateral hypothalamic area preceding the time of the vocalization were observed. The entire system including interface and control program is described.

Neuronal activity in the medial orbitofrontal cortex of the behaving monkey: modulation by glucose and satiety

To investigate neuronal responses to interoceptive information, single neuron activity of the orbitofrontal cortex (OBF) of the behaving monkey was recorded during glucose injection, natural feeding and an operant bar press feeding task. Intravenous glucose injection had almost no effect on rates of spontaneous firing, but tended to attenuate neuronal responses during the bar press and reward periods. In about half of the neurons tested, the spontaneous firing rate changed for a relatively long period after the animal ate to satiety. The results suggest that blood glucose concentration is a modulatory factor in neuronal processing for feeding, but other interoceptive information generated by satiety strongly affects the activity of OBF neurons.

Monkey orbitofrontal neuron activity during emotional and feeding behaviors

Long term, single neuron activity was recorded in the monkey orbitofrontal cortex (OBF) through chronic platinum-iridium microwire electrodes. Tonic as well as phasic changes in neuronal activity occurred upon presentation of palatable (food) and aversive stimuli during bar pressing for food. Lesions in this region are known to induce changes in emotional behavior. Therefore, the results suggest that the OBF neurons are involved in processing emotion.

Responses of lateral hypothalamic neurons to simulative hypogravic condition induced by body suspension

In unanesthetized rats, neuronal activity in the lateral hypothalamic area was recorded during horizontal and head-down tilt suspension. When the rat was raised in the horizontally suspended position, 21 of 44 neurons changed activity as follows: immediate increase (7/21, Type I), immediate decrease (3/21, Type II), and gradual decrease (11/21, Type III). When the rat was raised with a head-down tilt position, the responses were suppressed in about half of the neurons tested. These results showed that the LHA neurons altered their activity in response to low G simulation induced by body suspension. Possible signals which induce the changes in the LHA neuronal activity, and an involvement of the LHA in the autonomic reflexes under hypogravic condition are discussed.