PubMed Health⌕ Search

Biomedical subjects

L A Kukstas

Publications and source records attributed to L A Kukstas.

6 recordsLinked to original sources
PubMed1998

Opponent processes and anxiety: toward a neurophysiological formulation.

As a general philosophical framework, the author presents a theoretical position according to which 'opposition' is at the heart of the workings of the living being and the very origins of life. He then deals with 'opposing processes' and neural mechanisms which appear to underlie them. The theory rests on the premise that a great number of our actions are derived from our emotions, and that the coupling of pleasure/suffering controls the expression of our desires. Developed in the 1970s, this theory is founded on the observation of dependence phenomena (addictions), but its value extends far beyond drugs, to all types of human conduct, including sexuality, play, alimentary behaviours, etc. Inconsistent with classical theories, it subordinates the act to an affective state. The author finally examines the phenomenon of anxiety in the light of these considerations.

Animals↗
PubMed1991

Different expression of the two dopaminergic D2 receptors, D2415 and D2444, in two types of lactotroph each characterised by their response to dopamine, and modification of expression by sex steroids.

Dopamine inhibits prolactin liberation acting via the D2 type receptor. Two different electrophysiological responses to dopamine have been shown to characterise two types of lactotroph isolated from the lactating female rat. It is now known that differential splicing of the pre-messenger RNA coding for the D2 receptor leads to the production of two D2 subtypes, D2(415) and D2(444). These subtypes differ in the region which is believed to be responsible for the binding of G proteins, and could thus lead to the activation of different intracellular second messenger systems. Here we show that the pre-messenger RNA for the D2 receptor is differentially spliced in such a way that the ratio D2(415)/D2(444) is significantly different (2.91 +/- 0.6 vs 1.29 +/- 0.14) between two populations of lactotrophs, each enriched in cells showing one type of response to DA. We further show that the ratio D2(415)/D2(444) can be changed by treatment of prolactin cells in primary culture with progesterone or testosterone. Estrogen did not change the ratio, but diminished the total amount of D2 cDNA. Regulation of differential splicing by sex steroids could provide a mechanism for modifying lactotroph responsiveness to DA in different physiological situations.

Animals↗
PubMed1990

Evidence for a relationship between lactotroph heterogeneity and physiological context.

Two lactotroph subpopulations differing in their functional properties have previously been isolated from lactating female rats. It was found that adult female rats at proestrus similarly yield two subpopulations of lactotrophs, whereas those from adult female rats at metestrus show different properties and in males only one functional population is found. As the period of lactation and proestrus are characterised by high circulating estrogen levels, estrogen is considered to modify lactotroph properties in the female, and as the functional differences concern the lactotroph responsiveness to TRH, it is supposed that lactotroph heterogeneity provides a means for particular secretory patterns during lactation and at proestrus.

Animals↗
PubMed1990

Plateau potentials recorded from lactating rat enriched lactotroph cells are triggered by thyrotropin releasing hormone and shortened by dopamine.

Enrichment of dispersed pituitary cells from normal lactating rats on a continuous BSA gradient permitted the isolation of two prolactin cell populations--light and heavy. Hormone release studies indicated that spontaneous prolactin (PRL) release of the heavy fraction cells was particularly sensitive to TRH stimulation (mean of 450%) and that this effect of TRH was totally inhibited by Ca2+ channel blockers (Co2+, Cd2+, Ni2+ and Mn2+). For this reason, the electrophysiological response to TRH was investigated on heavy fraction cells. Experiments performed on 264 cells after 4-12 days in culture showed that these cells could be divided into two groups. The first group, called high resting potential (HRP) cells, constituted 73% of the total and was characterized by a mean resting potential of -60 mV and a mean input membrane resistance of 700 M omega, and these cells displayed plateau potentials, which were triggered by application of brief (2 s), large (1 nA) depolarizing or hyperpolarizing current steps. The plateaux were characterized by a sustained depolarization at a potential near -20 mV and they were concomitant with an increase of the membrane conductance. The repolarization consisted of a slight, gradual hyperpolarization followed by a rapid return to the resting potential. The second group of cells (the remaining 27%; called low resting potential or LRP cells) was characterized by a mean resting potential of -45 mV and a mean input membrane resistance of 250 M omega. These cells were excitable, 30% of them displaying spontaneous activity but never showing plateaux. Electrophysiological experiments showed that the majority of the HRP cells (99%) responded to TRH but were insensitive to dopamine (DA) ejections (up to 10(-6) M) at resting potential. Ejection of TRH onto HRP cells induced a slow depolarization (10-15 mV) concomitant with a decrease of the membrane resistance. This led the cell membrane potential to a critical value (approximately -50 mV), at which the plateau response was triggered. The plateau lasted for about 10 s from potentials greater than -100 mV, and could reach 10 min from holding potentials close to the resting potential. The amplitude of the plateau varied according to the holding potential and the reversal potential was found to be -20 mV. Local application of tetraethylammonium chloride (TEA, 30 mM) only slightly affected the amplitude of the plateaux but they were shortened or totally blocked by Co2+, Cd2+ and Ni2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗