In vivo and in vitro sugar transport in frog intestine

In the frog intestine, both in vitro and in vivo, experiments were carried out in order to increase knowledge of the mechanism of sugar exit across the basolateral membrane of the enterocyte. The frog intestine was chosen because it lacks crypt cells and, consequently, any external fluid circuit mechanism during sugar transport can be avoided. Therefore, the sugar concentration in the absorbate collected on the serosal side is likely to be similar to that present underneath the basolateral membrane of the enterocyte. Under this condition, cell and absorbate sugar concentrations are similar; yet there is a concomitant net transintestinal sugar transport. Moreover, in in vivo experiments a net transintestinal sugar transport takes place even against a concentration difference. These results suggest that sugar exit across the basolateral membrane is not simply due to a chemically facilitated diffusion.     

Amygdala Reward Neurons Form and Store Fear Extinction Memory

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Characterization of K+ Channels in the Basolateral Membrane of Rat Tracheal Epithelia

To study K⁺ channels in the basolateral membrane of chloride-secreting epithelia, rat tracheal epithelial monolayers were cultured on permeable filters and mounted into an Ussing chamber system. The mucosal membrane was permeabilized with nystatin (180 μg/ml) in the symmetrical high K⁺ (145 mm) Ringer solution. During measurement of the macroscopic K⁺ conductance properties of the basolateral membrane under a transepithelial voltage clamp, we detected at least two types of K⁺ currents: one is an inwardly rectifying K⁺ current and the other is a slowly activating outwardly rectifying K⁺ current. The inwardly rectifying K⁺ current is inhibited by Ba²⁺. The slowly activating K⁺ current was potentiated by cAMP and inhibited by clofilium, phorbol 12-myristae 13-acetate (PMA) and lowering temperature. This is consistent with the biophysical characteristics of I _SK channel. RT-PCR analysis revealed the presence of I _SK cDNA in the rat trachea epithelia. Although 0.1 mm Ba²⁺ only had minimal affect on short-circuit current (I _sc) induced by cAMP in intact epithelia, 0.1 mm clofilium strongly inhibited it. These results indicate that I _SK might be important for maintaining cAMP-induced chloride secretion in the rat trachea epithelia. Received: 1 March 1996/Revised: 5 August 1996     

Diurnal variation of corticotropin-releasing factor binding sites in the rat brain and pituitary

Summary 1. Corticotropin-releasing factor (CRF) is thought to be involved in the regulation of the diurnal activity of the hypothalamus-pituitary-adrenal (HPA) axis and to act as a neurotransmitter in the brain. To date it is unknown whether the binding sites of the central CRF system are subject to diurnal variations. 2. We measured the number of CRF binding sites over the course of a complete 24-hr light-dark cycle in the pituitary, amygdala, bed nucleus of the stria terminalis (BNST), cingulate cortex, visceral cortex, paraventricular nucleus of the hypothalamus, hippocampus, and locus ceruleus of rats byin vitro receptor autoradiography with iodinated ovine CRF. A 24-hr time course was also established for plasma CRF and corticosterone. 3. The diurnal pattern of plasma CRF does not correlate with the pattern of plasma corticosterone. Within the brain, CRF binding in the basolateral nucleus of the amygdala showed a U-shaped curve with maximum levels in the morning and a wide hallow between 1500 and 0100. A biphasic profile with a small depression in the afternoon and a more pronounced depression in the second half of the activity period is characteristic for the other brain areas and the pituitary. The profile for the pituitary correlates with those for the BNST and the area of the locus ceruleus. Furthermore, the diurnal pattern of CRF binding sites in the BNST correlates with that of the hippocampus, and the daytime pattern of the visceral cortex is similar to that of both the hippocampus and the BNST. 4. Since the CRF-binding profiles in the brain and the pituitary clearly differ from the profiles of both plasma CRF and corticosterone, one may assume that the diurnal pattern of central CRF binding sites is not directly coupled to the activity of the HPA axis.     

c-fos expression in the amygdala:In vivo antisense modulation and role in anxiety

Summary 1. The amygdaloid complex is a key structure in mechanisms of fear and anxiety. Expression of the immediate-early gene c-fos has been reported in the central nucleus of the amygdala following various stressors, but the functional role of this phenomenon has remained unknown.2. c-fos expression was observed in the central nucleus when rats were subjected to a pharmacologically validated animal model of anxiety, the Vogel conflict test, but not after mere exposure to the test apparatus. Bilateral amygdala injection of a 15-mer phosphorothioate c-fos antisense oligodeoxynucleotide prior to testing blocked conflict-induced c-fos expression and had behavioral effects similar to those of established antianxiety drugs.3. Separate experiments determined that antisense treatment did not affect conflict behavior by acting on shock thresholds or drinking motivation.4. These findings provide evidence that neuronal activation and c-fos induction in the amygdala may be of importance for mechanisms of fear and anxiety.     

Facilitated Transport of Lactate by Rat Jejunal Enterocyte

L-lactate transport mechanism across rat jejunal enterocyte was investigated using isolated membrane vesicles. In basolateral membrane vesicles l-lactate uptake is stimulated by an inwardly directed H⁺ gradient; the effect of the pH difference is drastically reduced by FCCP, pCMBS and phloretin, while furosemide is ineffective. The pH gradient effect is strongly temperature dependent. The initial rate of the proton gradient-induced lactate uptake is saturable with respect to external lactate with a K _m of 39.2 ± 4.8 mm and a J _max of 8.9 ± 0.7 nmoles mg protein⁻¹ sec⁻¹. A very small conductive pathway for l-lactate is present in basolateral membranes. In brush border membrane vesicles both Na⁺ and H⁺ gradients exert a small stimulatory effect on lactate uptake. We conclude that rat jejunal basolateral membrane contains a H⁺-lactate cotransporter, whereas in the apical membrane both H⁺-lactate and Na⁺-lactate cotransporters are present, even if they exhibit a low transport rate. Received: 22 October 1996/Revised: 11 March 1997     

Synaptology of three peptidergic neuron types in the central nucleus of the rat amygdala

The synaptology of neurotensin (NT)-, somatostatin (SS)- and vasoactive intestinal polypeptide (VIP)-immunoreactive neurons was studied in the central nucleus of the rat amygdala (CNA). Three types of axon terminals formed synaptic contacts with peptide-immunoreactive neurons in the CNA: Type A terminals containing many round or oval vesicles; Type B terminals containing many pleomorphic vesicles; and Type C terminals containing fewer, pleomorphic vesicles. Peptide-immunoreactive terminals were type A. All three types of terminals formed symmetrical axosomatic and asymmetrical axodendritic contacts. However, type B and peptide-immunoreactive terminals frequently formed symmetrical axodendritic synaptic contacts. VIP-immunoreactive terminals also formed asymmetrical axodendritic contacts. SS- and NT-immunoreactive terminals commonly formed symmetrical contacts on SS- and NT-immunoreactive cell bodies, respectively. VIP-immunoreactive axon terminals were postsynaptic to nonreactive terminals. Type B terminals appeared more frequently on VIP neurons than on NT or SS neurons.     

Neural steroid sensitivity and aggression: comparing individuals of two songbird subspecies

Hormones coordinate the expression of complex phenotypes and thus may play important roles in evolutionary processes. When populations diverge in hormone‐mediated phenotypes, differences may arise via changes in circulating hormones, sensitivity to hormones or both. Determining the relative importance of signal and sensitivity requires consideration of both inter‐ and intrapopulation variation in hormone levels, hormone sensitivity and phenotype, but such studies are rare, particularly among closely related taxa. We compared males of two subspecies of the dark‐eyed junco (Junco hyemalis) for territorial aggression and associations among behaviour, circulating testosterone (T), and gene expression of androgen receptor (AR), aromatase (AROM) and oestrogen receptor α in three behaviourally relevant brain regions. Thus, we examined the degree to which evolution may shape behaviour via changes in plasma T as compared with key sex steroid binding/converting molecules. We found that the white‐winged junco (J. h. aikeni) was more aggressive than the smaller, less ornamented Carolina junco (J. h. carolinensis). The subspecies did not differ in circulating testosterone, but did differ significantly in the abundance of AR and AROM mRNA in key areas of the brain. Within populations, both gene expression and circulating T co‐varied significantly with individual differences in aggression. Notably, the differences identified between populations were opposite to those predicted by the patterns among individuals within populations. These findings suggest that hormone–phenotype relationships may evolve via multiple pathways, and that changes that have occurred over evolutionary time do not necessarily reflect standing physiological variation on which current evolutionary processes may act.