In vivo electrophysiology of central nervous system terminal autoreceptors

Transcranial electric stimulation entrains cortical neuronal populations in rats

Low intensity electric fields have been suggested to affect the ongoing neuronal activity in vitro and in human studies. However, the physiological mechanism of how weak electrical fields affect and interact with intact brain activity is not well understood. We performed in vivo extracellular and intracellular recordings from the neocortex and hippocampus of anesthetized rats and extracellular recordings in behaving rats. Electric fields were generated by sinusoid patterns at slow frequency (0.8, 1.25 or 1.7 Hz) via electrodes placed on the surface of the skull or the dura. Transcranial electric stimulation (TES) reliably entrained neurons in widespread cortical areas, including the hippocampus. The percentage of TES phase-locked neurons increased with stimulus intensity and depended on the behavioral state of the animal. TES-induced voltage gradient, as low as 1 mV/mm at the recording sites, was sufficient to phase-bias neuronal spiking. Intracellular recordings showed that both spiking and subthreshold activity were under the combined influence of TES forced fields and network activity. We suggest that TES in chronic preparations may be used for experimental and therapeutic control of brain activity.

D2-Like dopamine autoreceptor activation reduces quantal size in PC12 cells

D2-like dopamine autoreceptors regulate dopamine release and are implicated in important actions of antipsychotic drugs and rewarding behaviors. To directly observe the effects of D2 autoreceptors on exocytic neurotransmitter release, we measured quantal release of dopamine from pheochromocytoma PC12 cells that express D2 and D4 autoreceptors. High potassium-evoked secretion in PC12 cells produced a unimodal population of quantal sizes. We found that exposures to the D2-like agonist quinpirole that inhibited tyrosine hydroxylase activity by approximately 50% also reduced quantal size by approximately 50%. The reduced quantal size was blocked by the D2 antagonist sulpiride and reversed by L-DOPA. Quinpirole also decreased the frequency of stimulation-evoked quantal release. Together, these findings indicate effects on quantal neurotransmission by D2-like dopamine autoreceptors previously distinguished as synthesis-modulating autoreceptors that regulate tyrosine hydroxylase activity versus impulse-regulating autoreceptors that modulate membrane potential. The results also provide an initial demonstration of a receptor-mediated mechanism that alters quantal size.

Atlas of the neurons that express mRNA for the long form of the prolactin receptor in the forebrain of the female rat

Prolactin has a variety of important physiological effects on peripheral tissue and on the brain. The behavioral effects of prolactin include the induction of maternal behavior and increased food intake. Prolactin acts via its cognate receptors which have two forms, a short and a long form. The long form of the receptor is predominant in the preoptic area-hypothalamus and is positioned to support maternal behavior since this form is regulated across pregnancy and lactation (Nagano and Kelly [1994] J. Biol. Chem. 269:13337-13345; Sugiyama et al. [1994] J. Endocrinol. 141:325-333). By using in situ hybridization with [33P] labelled cRNA probe specific for the long form of the receptor mRNA(L-PRL mRNA) we have mapped, in brains from 2- and 21-day-old pregnant females, the neuroanatomical distribution of neurons expressing the long form of the receptor. Many neurons with high expression of L-PRL mRNA were located in the anteroventral periventricular nucleus, the medial preoptic area (MPO), specific subdivisions of the paraventricular and supraoptic nuclei, and in the arcuate and ventromedial nuclei. Labelled neurons were also found in limbic system structures such as the bed nucleus of stria terminalis (BST) and the medial nucleus of the amygdala, in a few thalamic nuclei, and in the central gray. All cells throughout the choroid plexus expressed high levels of L-PRL mRNA. The levels of L-PRL mRNA were higher in females on day 21 of pregnancy in the MPO and in the choroid plexus, than in females on day 2 of pregnancy; levels in the ventromedial nucleus of the hypothalamus (VMH) were unchanged across pregnancy. The neuroanatomical distribution of neurons expressing L-PRL mRNA may have special relevance for the mediation of maternal behavior, lactation, sexual behavior, and feeding.