Feeding induced by opiates injected into the paraventricular hypothalamus

Injection of morphine or d-ala-2-met-5-enkephalinamide (DALA) into the paraventricular nucleus of the hypothalamus (PVN) produced a dose dependent increase in feeding in rats. DALA increased feeding within 45 minutes; morphine within 90 minutes. Naloxone injected into the PVN diminished the effect. DALA increased water intake only when food was available, suggesting the primary effect was on feeding. In summary, an enkephalin analogue induced feeding, and an opiate receptor blocker attenuated it; therefore the PVN may contain opiate receptors that facilitate feeding.     

Effects of Feeding and Drinking on Acetylcholine Release in the Nucleus Accumbens, Striatum, and Hippocampus of Freely Behaving Rats

Extracellular levels of acetylcholine (ACh) were measured in the nucleus accumbens (NAC), striatum (STR), and hippocampus (HIPP) using microdialysis in 30-min intervals before, during, and after free-feeding in 20-h food-deprived rats. The effects on ACh in the NAC and STR were also observed in response to water intake in 20-h water-deprived animals. Neostigmine was used in the perfusate to improve ACh recovery. Basal ACh was sensitive to tetrodotoxin and low calcium, and therefore largely neuronal in origin. Feeding caused a 38% increase in extracellular ACh in the NAC and no change in the STR or HIPP. Dopamine was also increased in the NAC (48%) and to a lesser extent in the STR (21%) following feeding. Drinking caused 18-20% increases in ACh release in both the NAC and STR. In a separate experiment, ACh release in the NAC was monitored in 10-min intervals during free-feeding; ACh increased in the interval immediately following maximal food intake. These results suggest a site-specific increase in ACh release following feeding that cannot be solely attributed to the activation associated with this behavior.     

Phencyclidine (PCP) injected in the nucleus accumbens increases extracellular dopamine and serotonin as measured by microdialysis

Phencyclidine (PCP; 20 micrograms in 0.5 microliter) was tested by local brain injection for neurochemical effects in the nucleus accumbens and striatum of rats. Changes in dopamine turnover could not be detected in postmortem tissue assays. In contrast, extracellular levels of dopamine significantly increased as measured by microdialysis in freely moving animals. PCP also increased extracellular levels of serotonin and decreased 3,4-dihydroxyphenylacetic acid (DOPAC), but did not change homovanillic acid (HVA) or 5-hydroxyindoleacetic acid (5HIAA). Microdialysis suggests that PCP acts in some dopamine terminal regions to increase extracellular dopamine and serotonin.