Microinjection of thyrotropin-releasing hormone analogue into the central nucleus of the amygdala stimulates gastric contractility in rats

Efferent projections of thyrotropin-releasing hormone-synthesizing neurons residing in the anterior parvocellular subdivision of the hypothalamic paraventricular nucleus

The anterior parvocellular subdivision of the PVN (aPVN) contains nonhypophysiotropic thyrotropin-releasing hormone (TRH) neurons that are densely innervated by feeding-related neuronal groups of the hypothalamic arcuate nucleus. To determine how these TRH neurons are integrated within the brain, the major projection fields of this cell group were studied by anterograde and retrograde tract-tracing methods. Projection sites were identified by injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHAL) into the aPVN, and subsequent double immunofluorescent staining was used to visualize axons containing both PHAL and pro-TRH. To distinguish between the projection sites of TRH neurons residing in the aPVN and the closely situated perifornical area, the retrograde tracer cholera toxin B subunit (CTB) was injected into regions where PHAL/pro-TRH-containing axons were densely accumulated. TRH neurons in the aPVN were found to project to the hypothalamic arcuate, dorsomedial and ventral premammillary nuclei, medial preoptic region, tuber cinereum area, paraventricular thalamic nucleus, bed nucleus of the stria terminalis, lateral septal nucleus, and central amygdaloid nucleus. Projection fields of perifornical TRH neurons were in partial overlap with those of the aPVN TRH cells. In addition, these neurons also innervated the hypothalamic ventromedial nucleus, the medial amygdaloid nucleus, and the amygdalohippocampal area. The data suggest that, through its efferent connections, aPVN TRH neurons may be involved in the regulation of energy homeostasis coordinately with effects on behavior, locomotor activity, and thermogenesis. In addition, the major differences in the projection fields of aPVN and perifornical TRH neurons suggest that these two TRH-synthesizing neuronal groups are functionally different.

Intracerebroventricular calcitonin prevents stress-induced gastric dysfunction

BACKGROUND

Restraint stress produces gastric hypercontractility and acidity leading to stress ulceration. Intracerebroventricular (ICV) salmon calcitonin (sCT) decreases restraint injury and acidity, but its effects on restraint-induced hypercontractility are unknown.

METHODS

Using stereotactic guidance, ICV catheters were placed into the lateral ventricle of adult male rats and calibrated gastric strain gauge transducers were implanted 5 days prior to restraint stress. sCT rats (n = 8) were pretreated with 5 microg of calcitonin ICV (10 microl volume), while controls (n = 10) received 10 microl of ICV saline prior to restraint for 2 h at 20 degrees C followed by 2 h at 4 degrees C. Gastric motility data were collected with AT-CODAS and analyzed with ADVANCED CODAS. Gastric volume, pH, and lesions were recorded following the stress.

RESULTS

ICV calcitonin prevented gastric mucosal injury in all animals (0% vs 100%, P <.01) and elevated pH slightly (2.5 +/-.3 vs 1.6 +/-.1, P <.05). Stress caused the force of contractions to increase from 0.35 +/-.1 to 1.38 +/-.4 g in controls (P <.01), while treated animal's force fell from.42 +/-.1 to 0.2 +/-.05 g (P <.01 vs control). Stress did not affect contractions/min (3.4 +.6 vs 3.5 +.3), but sCT increased frequency (2.5 +.4 to 5.0 +.2, P <.01). Stress prolonged contraction duration (11.5 + 1 to 16.5 + 1.7 s, P <.01), but stress's effect was prevented by sCT (11.0 +.5 to 11.2 +.3, P <.01 vs control).

CONCLUSIONS

Pretreatment with 5 microg central sCT prevents the increased amplitude and duration of gastric contractions produced by restraint stress for 2 h, in association with gastroprotection.

The amygdala: vigilance and emotion

Here we provide a review of the animal and human literature concerning the role of the amygdala in fear conditioning, considering its potential influence over autonomic and hormonal changes, motor behavior and attentional processes. A stimulus that predicts an aversive outcome will change neural transmission in the amygdala to produce the somatic, autonomic and endocrine signs of fear, as well as increased attention to that stimulus. It is now clear that the amygdala is also involved in learning about positively valenced stimuli as well as spatial and motor learning and this review strives to integrate this additional information. A review of available studies examining the human amygdala covers both lesion and electrical stimulation studies as well as the most recent functional neuroimaging studies. Where appropriate, we attempt to integrate basic information on normal amygdala function with our current understanding of psychiatric disorders, including pathological anxiety.