Multiunit Spiking Activity Research Articles

Changes in multiunit spike activity in the rat preoptic area induced by stimulating the midbrain

Differential effects of electrochemical stimulation of the midbrain raphe and dorsal tegmentum on multiple unit activity in the medial preoptic area were observed in proestrous female rats. Stimulation of the median raphe nucleus induced a marked increase in activity (spikes per minute). This increase was not found in unstimulated sham-treated rats or after a control lesion at the same site. Dorsal tegmental stimulation had the opposite effect, i.e., a marked tendency to decreased activity after stimulation, an effect not reproduced by a control lesion of similar size without iron deposition. It is suggested that the changes observed may be related to the effects on luteinizing hormone release and ovulation induced by the same stimulation parameters.

Effects of Intraventricular Catecholamines on Luteinizing Hormone Release in Ovariectomized-Steroid-Primed Rats

The effects of intraventricular norepinephrine (NE) and dopamine (DA) were studied in the awake, freely behaving rat. In long-term ovariectomized, estrogen-progesterone-primed (OVE E2-P) animals, blood samples were taken via indwelling intra-atrial catheters before and after intraventricular infusion of either pH-adjusted saline, NE )5 mug, 15 mug, 20 mug), or DA (4 mug, 15 mug), and plasma LH was measured by radioimmunoassay. Under urethane anesthesia, records were made of the effects of intraventricular saline and NE on the electrical activity of the arcuate nucleus in the form of multi-unit spike activity. In unanesthetized animals, intraventricular NE caused marked changes in behavior. The typical response consisted of three phases: generalized activation (5-7 min), feeding (5-15 min), and sleep 1-2 h). DA exerted similar behavioral effects but without the marked sleep phase characteristic of the NE response. The effects of the catecholamines on LH output were significant increases in plasma LH levels for all NE doses tested (5 mug, p less than .025; 15 mug, p less than .05; 20 mug, p less than .005), while DA had no effect. The dynamics of the LH response to NEwere similar at all dosage levels, and the increase caused by 20 mug NE was found to be essentially equal to that induced by a quick intravenous infusion of 1.25 ng LHRH. Arcuate nucleus multi-unit spike activity (MUSA) showed a clear response to intraventricular NE at a dosage capable of stimulating the release of LH. In every case, the initial effect was a decrease in spike activity. These results, considered in relation to previous findings, suggest that NE may be stimulatory to neurons secreting LH-releasing hormone (LHRH). The decrease in arcuate nucleus MUSA in response to NE implies that certain elements of this nucleus are inhibited during LH release, perhaps the dopaminergic tuberoinfundibular neurons.

Differential effects of intraventricular luteinizing hormone releasing hormone (LH-RH) and norepinephrine on electrical activity of the arcuate nucleus in the proestrous rat.

Effects of intraventricular infusions of LH-RH and norepinephrine (NE) on the electrical activity of the arcuate nucleus were investigated in normally cycling proestrous rats. Under urethane anesthesia, recordings were made of amplitude-discriminated multiple unit spike activity and integated multiunit activity (MUA) in parallel with cortical EEG. Control infusions of saline (2 microliter, isotonic, pH 5.5) were ineffectual, but LH-RH (0.5 microgram) induced a significant increase in both multiunit spike activity and integrated MUA. While the response appeared to be continuous, statistical analysis revealed 2 phases: a quick rise which persisted for approximately 5 min, followed 15 min later by a longer-lasting elevation in activity. The onset of the 2nd increase corresponded with the attainment of peak values of pituitary LH output. Subsequent treatment with 20 microgram NE, on the other hand, resulted in a marked depression of activity. The fact that NE depresses arcuate neuronal activity at dose levels which cause the release of LH and that LH-RH increases activity within the same population of neurons, while possibly mediating an 'ultrashort-loop' negative feedback effect, suggest that this responsive component of the arcuate nucleus, perphaps the tuberoinfundibular dopaminergic system of neurons, is inhibitory to LH release.

Electrical Responses of the Olfactory Epithelium of Atlantic Salmon (Salmo salar)

Multiunit spike activity was recorded from the olfactory mucosa of Atlantic salmon (Salmo salar) using metal-filled glass microelectrodes. A number of simple and complex solutions were tested for stimulatory effectiveness. Amino acids as a class of compounds were highly stimulatory; little or no response was obtained to a variety of simple sugars, n-aliphatic acids, alcohols, or amino-substituted alcohols. An increase in asynchronous spike activity was evoked by low concentrations of amino acids and oscillatory activity was evoked by higher concentrations of amino acids. Brief treatment of the epithelium with dilute solutions of HgCl2 blocked the chemosensitivity of the receptors.