Dopamine neurons learn to encode the long-term value of multiple future rewards.

Midbrain dopamine neurons signal reward value, their prediction error, and the salience of events. If they play a critical role in achieving specific distant goals, long-term future rewards should also be encoded as suggested in reinforcement learning theories. Here, we address this experimentally untested issue.

Age-dependent interactive changes in serotonergic and noradrenergic cortical axon terminals in F344 rats.

In the frontal cortex of aging rats, we found an increase in sprouting of the noradrenergic (NA) axons originated from the locus coeruleus (LC). The serotonergic (5-HT) axons originating from the dorsal raphe (DR) share the same cortical area and their age-dependent changes and interactions with NA axons were still unclear. To compare quantitatively the extent of axonal sprouting of DR and LC neurons in the frontal cortex, we extracellularly recorded from both DR and LC neurons in the same animals and antidromically stimulated 32 cortical sites (a pair of stimulating electrodes was moved at 100-mum intervals from 500 to 2000 microm in depth).

Effects of BDNF infusion on the axon terminals of locus coeruleus neurons of aging rats.

Using in vivo electrophysiological techniques and continuous local infusion methods, we examined the effects of brain-derived neurotrophic factor (BDNF) and its specific antibody (anti-BDNF) on the noradrenergic axon terminals of the locus coeruleus (LC) neurons in the frontal cortex of aging rats. Recently, we observed that LC neurons with multiple-threshold antidromic responses (multi-threshold LC neurons) increased critically between 15 and 17 months of age. To examine whether the BDNF is involved in this change occurred in the aging brain, we continuously infused BDNF into the frontal cortex for 14 days.

[Plasticity of central monoaminergic systems during aging].

The locus coeruleus (LC), located within the caudal pontine central gray, is composed of noradrenaline-containing neurons. The axons of these neurons form extensive collateral branches that project widely to many brain sites. The function of the LC is still unclear at present, however, LC neurons are known to exhibit marked axonal regeneration and sprouting in response to brain damage.

Correlated coding of motivation and outcome of decision by dopamine neurons.

We recorded the activity of midbrain dopamine neurons in an instrumental conditioning task in which monkeys made a series of behavioral decisions on the basis of distinct reward expectations. Dopamine neurons responded to the first visual cue that appeared in each trial [conditioned stimulus (CS)] through which monkeys initiated trial for decision while expecting trial-specific reward probability and volume. The magnitude of neuronal responses to the CS was approximately proportional to reward expectations but with considerable discrepancy.

Effects of fasting on thermoregulatory processes and the daily oscillations in rats.

To investigate the mechanism involved in the reduction of body core temperature (T(core)) during fasting in rats, which is selective in the light phase, we measured T(core), surface temperature, and oxygen consumption rate in fed control animals and in fasted animals on day 3 of fasting and day 4 of recovery at an ambient temperature (T(a)) of 23 degrees C by biotelemetry, infrared thermography, and indirect calorimetry, respectively. On the fasting day, 1) T(core) in the light phase decreased (P < 0.05) from the control; however, T(core) in the dark phase was unchanged, 2) tail temperature fell from the control (P < 0.

Brain activation during whole body cooling in humans studied with functional magnetic resonance imaging.

Regional activation of the brain was studied in humans using functional magnetic resonance imaging during whole body cooling that produced thermal comfort/discomfort. Eight normal male subjects lay in a sleeping bag through which air was blown, exposing subjects to cold air (8 degrees C) for 22 min. Each subject scored their degree of thermal comfort and discomfort every min.