Push‐Pull Perfusion of the Hypothalamus and the Caudate Nucleus in Conscious, Unrestrained Animals^a

Abstract

The present results further confirm the usefulness of the push-pull cannula to study the in vivo activity of several neural systems in conscious, freely moving animals. However, it is evident that the inflammatory reaction to the local injury induced by the cannula may have different consequences in the function of a particular brain area. In the caudate nucleus, the responsiveness of the dopaminergic terminals of the nigrostriatal DA system to local infusion of AMPH was clearly reduced after the first two to three weeks post cannula implant. In contrast, in the hypothalamus of the rat and the rabbit, the spontaneous fluctuating activity of the LHRH pulse generator remained unaffected during a two to three month period when several perfusions could be performed in the same animal. Further studies will be required to establish the reasons for such marked differences in response to injury of these two brain structures. Various neurochemicals can be measured simultaneously from the hypothalamus of conscious rabbits. The present results indicate that NE hypothalamic impulse flow increases during the afternoon whereas the impulse flow of DA (as estimated by DOPAC output) decreases or does not change. In rabbit No. 2, simultaneous measurement of hypothalamic NE release and LHRH release indicates an absence of correlation. In sharp contrast, the simultaneous measurement of prostaglandin E2 release and LHRH release from the hypothalamus of rabbit 2-ER revealed a closer association between these two neuronal events. Apparently the push-pull technique can be used to examine long-term seasonal as well as circadian (extended 24 hr perfusion) spontaneous changes in the activity of the LHRH pulse generator in individual animals. It seems that seasonal changes characterize the function of the rabbit LHRH pulse generator. Lastly, physiological doses of progesterone infused for short times directly into the hypothalamus of female rabbit stimulate the LHRH pulse generator of this species with marked increases in the amplitude of the LHRH signal. In conclusion, the PPP technique coupled to HPLC-EC and RIA procedures to measure localized release of neurotransmitters, metabolites, and neuropeptides simultaneously in the same perfusate samples from discrete brain areas appears to be a powerful technique in furthering our knowledge of the in vivo local neurochemistry of the brain of conscious, freely moving animals.

Coital and Estrogen Signals: A Contrast in the Preovulatory Neuroendocrine Networks of Rabbits and Rhesus Monkeys1

“…In vivo PPP in the rabbit hypothalamus was initiated independently by Ramirez's and our laboratories for measurement of GnRH and catecholamines [17][18][19][20][21], and several reports have described GnRH release in alert, freely moving rabbits [56][57][58]. Estrous rabbits exhibit regular low-amplitude pulses of GnRH, LH, and E 2 [59].…”

“…The ability to monitor GnRH secretion in rodents [16], rabbits [17][18][19][20][21], sheep [22,23], and rhesus monkeys [24,25] has enhanced the understanding of neuroendocrine events controlling ovulation. Several excellent reviews of these findings have appeared [26][27][28][29][30].…”

Neuroendocrine Regulation of GnRH Release in Induced Ovulators

“…Whether progesterone or 20␣-OHP facilitates the postcoital release of LH in the rabbit is still unclear (80,97,179). Infusion of pulses of progesterone directly into the hypothalamus stimulated the release of GnRH in young, intact female rabbits (177). However, no such effect was observed when progesterone was infused continuously (134).…”

“…To date, the rabbit is the only induced ovulating species in which these techniques have been used. Groups headed by Ramirez (177) and Spies (169) showed independently that the in vivo release of GnRH is pulsatile in the rabbit. The pulsatile pattern of tonic GnRH release in the rabbit resembles that seen in spontaneous ovulators such as the rat (131), the monkey (132), and the sheep (130).…”

Peptides in the Brain: Mass Spectrometry–Based Measurement Approaches and Challenges

“…Both microdialysis and push-pull perfusion are exemplary methods for collecting SP release from localized regions (137)(138)(139). These approaches rely on the insertion of a sampling probe into a specific brain region that collects the extracellular peptides.…”