Regional changes in brain 14C-2-deoxyglucose uptake after feeding-inducing intrahypothalamic norepinephrine injections

Changes in serotonin and norepinephrine uptake sites after chronic cocaine: pre- vs. post-withdrawal effects

Although acute cocaine is a strong reuptake inhibitor at dopamine (DA), norepinephrine (NE) and serotonin (5-HT) synapses, the effects of chronic cocaine on 5-HT and NE transporters have received less attention than its effects on DA transporters. In the present study, quantitative autoradiography was used to map effects of chronic cocaine exposure on the binding of [3H]nisoxetine and [3H]cyanoimipramine to NE and 5-HT transporters, respectively. Female Wistar rats were given increasing concentrations of cocaine in the drinking water for 4 weeks (mean dose during the final two weeks: approximately 25 mg/kg body weight) and sacrificed either on the 30th day of cocaine administration or at one of two time points after withdrawal (4 days or 30 days). In animals sacrificed while on cocaine. [3H]cyanoimipramine binding was significantly elevated in the infralimbic cortex (+13%, P < 0.05), n. accumbens (+16%, P < 0.05, P < 0.05), lateral septal n. (+21%, P < 0.05), pedunculopontine n. (+16%, P < 0.05), and vestibular n. (+19%, P < 0.05). These changes were no longer observed when brains were examined either 4 days or 30 days after cessation of cocaine. In animals sacrificed while on cocaine, [3H]nisoxetine binding was decreased in the bed n. of the stria terminalis (-18%, P < 0.05), the lateral parabrachial area (-35%, P < 0.05) and the inferior olive (-26%, P < 0.05). In animals sacrificed 4 days after cessation of cocaine, these effects were no longer apparent, except for a 16% reduction in the inferior olive (P < 0.05). In this 4-day withdrawal group, a significant increase in [3H]nisoxetine binding was seen in the paraventricular n. of the hypothalamus (PVN, +33%, P < 0.05). This PVN change was still seen in the group sacrificed 30 days after cessation of cocaine (+44%, P < 0.02). Binding of [3H]WIN 35,428 to dopamine transporters was unaltered in this group. Taken together, these observations indicate that chronic cocaine has different effects on brain 5-HT and NE transporters, both while the animals are on cocaine and after withdrawal. They support the notion that increased 5-HT uptake in limbic forebrain may play a role in behavioral/psychiatric effects of chronic cocaine. They are also consistent with previous indications that chronic cocaine does not induce degeneration of nerve terminals in noradrenergic or serotonergic neurons. The persistent increase in [3H]nisoxetine binding in the paraventricular hypothalamus suggests the possibility of neuroendocrine changes after withdrawal from chronic cocaine use.

Effects of intracisternal vs. intrahypothalamic 5,7-DHT on feeding elicited by hypothalamic infusion of NE

A variety of evidence has led to suggestions that brain serotonin (5-HT) and norepinephrine (NE) interact within the medial hypothalamus to control food intake. To test the possibility that chronic decrements in 5-HT might enhance NE-induced feeding, adult male rats were prepared with permanently indwelling cannulae aimed at the paraventricular nucleus (PVN), then received either intracisternal (IC) or PVN injections of the 5-HT neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT) vs. its vehicle, 1% ascorbic acid. Over a 4-week period, IC-5,7-DHT rats showed no signs of enhanced daily feeding or drinking. However, in 40-min intake tests, feeding but not drinking was enhanced by injecting 20 nmol NE into the PVN commencing 2 weeks after neurotoxin treatment. Terminal monoamine assays confirmed that IC-5,7-DHT produced large (80-90%) depletions of brain regional 5-HT. A functional index of 5-HT terminal damage was also implied by the impaired short-term feeding responses IC-5,7-DHT rats showed to the systemic administration of the 5-HT1A agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) when tested between 3 and 4 weeks after IC treatment. Over a comparable 4-week period, PVN-5,7-DHT rats also showed no tendencies to overeat or overdrink on a daily basis. However, in contrast to IC-5,7-DHT rats, they also showed no differences in their feeding or drinking responses to NE injections into the PVN. This was so despite reliable depletions of 5-HT in the hypothalamus (-28%) and hippocampus (-71%). These results support earlier work showing that neither widespread nor localized hypothalamic damage to brain 5-HT neurons produce chronic overeating. However, the data suggest that phasic enhancements of PVN NE activity may trigger enhanced feeding when there is widespread damage to brain 5-HT neurons, although the PVN does not appear to be the brain site mediating this effect.

Serotonin-depleting midbrain lesions do not prevent ovariectomy-induced weight gain

Past research has shown that subdiaphragmatic vagotomy and midbrain raphe lesions are each effective in impeding the development of hypothalamic obesity while neither affects the development of genetic obesity in Zucker rats. To further test the parallels that may exist between these two manipulations on another putative obesity model, we studied the effects of midbrain raphe lesions on the development of ovariectomy-induced weight gain, previously shown to be unaffected by vagotomy. Ten adult female rats received thermal lesions of the dorsal and median raphe nuclei (RAPHE) while 7 served as sham controls (SHAM). Following a 26-day recovery period during which body weight, food intake and water intake were periodically monitored, bilateral ovariectomy (OVX) was performed on 7 RAPHEs and 4 SHAMs, with laparotomy (LAP) being performed on 3 RAPHEs and 3 SHAMs. Body weights and intake variables were monitored for an additional 58 days, then animals were sacrificed for brain histological and biochemical assessments. RAPHEs weighed less despite eating and drinking more than SHAMs throughout this study. Nevertheless, OVX rats gained more weight regardless of lesion (mean +/- SEM weight gain = 73.9 +/- 5.5 g for RAPHE + OVX and 67.0 +/- 6.6 g for SHAM + OVX vs. 30.7 +/- 3.0 g for RAPHE + LAP and 39.7 +/- 5.5 g for SHAM + LAP). This occurred without reliable changes in the food or water intakes of either OVX subgroup. Histology confirmed that RAPHE lesions were largely localized to the dorsal and median raphe nuclei, as planned.(ABSTRACT TRUNCATED AT 250 WORDS)