L.J. Forman

The response to analgesia testing is affected by gonadal steroids in the rat.

The effect of gonadal steroids on the response to analgesia testing was determined in castrated male and female rats and castrated male and female rats treated with testosterone propionate (TP) and estradiol benzoate (EB), respectively. The time to respond to a noxious somatic stimulus in the form of heat was assessed using the tail withdrawal test (tail withdrawal from hot water) and hot plate test (the time to paw lick or jump). In male rats, castration resulted in a significant reduction of the reaction time for tail withdrawal. This effect was reversed by treatment with TP. The time to paw lick or jump in male rats was also diminished by castration. Treatment with TP resulted in a partial reversal of the effect of castration on this response. In castrated female rats, the time required for tail withdrawal was decreased by castration and increased by treatment with EB. The reaction time to the hot plate in female rats was diminished by castration and further reduced by EB administration. These data indicate that gonadal steroids influence the response to a noxious heat stimulus in male and female rats and that the effect may vary according to sex and the way in which the stimulus is applied.

A potential vaccine for cocaine abuse prophylaxis.

Presently, there are estimated to be 1.5 to 2.0 million individuals infected with HIV-1 in the U.S. and about 12 million worldwide. In the U.S. over 90% of reported cases of AIDS occurred among two subgroups, homosexual males and intravenous substance abusers (IVSAs). Currently, there is no anti-cocaine addiction medication available. In order to explore vaccination as an alternative means for protection against cocaine addition, we immunized inbred male Fisher rats with either cocaine emulsification in complete Freund adjuvant (CFA) or with cocaine conjugated with keyhole limpet hemocyanin (KLH), as carrier plus CFA. Animals were initially immunized with 0.1 mg/animal of cocaine or cocaine-KLH. Animals were given a booster with the corresponding agents after 4 weeks. Ten animals/group were used. Controls received normal saline at the time of immunizations. These animals were injected, intraperitoneally, with 25 mg/kg of cocaine, and were examined for the analgesic effect of cocaine by the hot plate method. The average analgesic effect of cocaine was significantly reduced (p greater than 0.03) in animals immunized with cocaine-KLH (13.77 s) as compared to saline controls (21.6 s). Fifty percent of the animals (5/10) in the cocaine-KLH group and 33% of the animals (3/9) in the cocaine immunized group appeared completely resistant to the effect of cocaine on the central nervous system (CNS). We also have determined the levels of cocaine-specific antibodies produced by each animal by an ELISA method. Degree of protection from cocaine seems to correlate well with the amount of anti-cocaine antibodies produced by each animal (-0.61).(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine influences beta-endorphin levels and release.

Immunoreactive beta-endorphin (IR-BE) was measured in the plasma, anterior pituitary (AP), neurointermediate lobe of the pituitary (NIL) and hypothalamus of male rats treated chronically (once daily for ten days) with cocaine. Cocaine produced a consistent elevation in the concentration of IR-BE in the plasma, the AP and the NIL at doses of 2.5 - 20 mg/kg/ip. The release of IR-BE from the AP and the NIL was determined in vitro and was found to be increased by treatment with cocaine. Chronic administration of cocaine did not affect the concentration of IR-BE in the hypothalamus. Chromatographic analysis revealed that cocaine produced a slight decrease in the amount of beta-endorphin relative to beta-lipotropin in the AP. Beta-endorphin was the major form of IR-BE released by the AP and the sole constituent and secretory product of the NIL. These data indicate that chronic administration of cocaine stimulates the endogenous opiate system, elevating the levels of IR-BE in the pituitary and promoting beta-endorphin release.

NMDA receptor antagonism produces antinociception which is partially mediated by brain opioids and dopamine

Inhibition of nitric oxide synthase (NOS) activity results in opioid-mediated supraspinal analgesia in the rat, as indicated by increased reaction time in the hot plate test. It is documented that a relationship exists between NMDA receptor activation and the activity of NOS. The present investigation sought to determine if inactivation of the NMDA receptor produced antinociception of supraspinal origin, as was observed in response to inhibition of NOS, and if this response was mediated by brain opioids, by activation of receptors for the neurotransmitter, dopamine, or both. Administration of MK-801, a non-competitive antagonist of the NMDA receptor, produced significant antinociception as measured by reaction time in the hot plate test of analgesia. Antinociception resulting from treatment with MK-801 appeared to be mediated by brain opioids, as indicated by the ability of the opioid antagonist, naloxone, to partially reverse the effect of MK-801 administration. This analgesic response was also partially diminished by administration of the dopamine D1 receptor antagonist, SCH 23390 and the dopamine D2 receptor antagonist, sulpiride. The analgesia resulting from NMDA receptor antagonism was found to be only partially attributable to dopamine and brain opioids, since co-administration of naloxone and SCH 23390 or naloxone and sulpiride, were unable to completely reverse the antinociceptive response to MK-801. The present findings suggest that inhibition of NMDA receptor activity produces supraspinal analgesia. Furthermore, it appears that antinociception induced by blockade of the NMDA receptor results, at least in part, from activation of endogenous brain opioids and stimulation of D1 and D2 subtypes of the dopamine receptor.

Pituitary growth hormone and hypothalamic somatostatin in young female rats versus old constant estrous female rats.

Pituitary content and concentration of growth hormone was significantly reduced, and hypothalamic somatostatin content significantly increased, in old constant estrous as compared to young female rats. Increased levels of somatostatin may contribute to the decrease in pituitary growth hormone levels in these animals.

Demonstration by in situ hybridization of the proopiomelanocortin gene in the rat heart

A biotinylated oligonucleotide probe was used to demonstrate the presence in the heart of the portion of the proopiomelanocortin messenger RNA which contains the sequence for beta-endorphin. The probe indicated the presence of beta-endorphin messenger RNA in cardiac tissue and specifically in the cardiac muscle cell. The probe also confirmed the well-documented presence of messenger RNA for beta-endorphin in the anterior and neurointermediate lobes of the pituitary. These findings indicate that in addition to the pituitary, beta-endorphin is produced in situ in the heart.

Administration of gonadal steroids to neonatal rats affects beta-endorphin levels in the adult

Administration of gonadal steroids to neonatal rats has a profound effect on the function of the neuroendocrine system in the adult animal. Considering that gonadal steroids modulate hypothalamic and pituitary levels of beta-endorphin (BE) in adult male and female rats, the effects of neonatal gonadal steroid treatment on BE levels in the adult animal were investigated. Neonatal male rats were administered testosterone and neonatal female rats were treated with estrogen. Matched control littermates received vehicle. All animals were sacrificed at 90 days of age. Neonatal gonadal steroid treatment did not affect the level of immunoreactive beta-endorphin (IR-BE) in the anterior pituitary (AP) of male rats but did result in a significant increase in IR-BE in the AP of female rats. Neonatal administration of gonadal steroids produced a significant decrease in IR-BE in the neurointermediate lobe of the pituitary (NIL) of both male and female rats, with the magnitude of the decrease being greater in the NIL of the female rats. IR-BE levels in the hypothalamus of male or female rats were not altered by the treatments. Column chromatography indicated that the increase in IR-BE in the AP represented a proportional increase in BE and beta-lipotropin, while the reduction in IR-BE in the NIL of the treated rats represented a reduction in BE. These findings suggest that gonadal steroids may influence the development of the neurotransmitter systems which regulate BE levels in the adult pituitary, the development of the biosynthetic mechanisms of the adult pituitary, or both.

Characterization of β-endorphin- and α-MSH-related peptides in rat heart

Abstract POMC-derived peptides and mRNA have been identified in heart tissue, although POMC processing has not been fully characterized. In the present study, we found that β-lipotropin and ACTH were localized in rat heart, although they were almost entirely converted to β-endorphin- and α-MSH-related peptides. Ion exchange HPLC analysis revealed that β-endorphin(1–31) was further processed to α-N- acetyl -β- endorphin (1–31) , which comprised 35.9 ± 0.1% of total immunoreactivity, and smaller amounts of β-endorphin(1–27), β-endorphin(1–26), and their α-N- acetylated derivatives. The predominant α-MSH immunoreactive peptides coeluted with α-MSH and N,O- diacetyl -α- MSH by reverse-phase HPLC, although small amounts of ACTH(1–13)-NH 2 were also present. Thus, multiple forms of β-endorphin and α-MSH are localized in rat heart. β-Endorphin(1–31) is a minor constituent, however, indicating that nonopioid β-endorphin peptides predominate.

The effects of immobilization stress on beta-endorphin levels are modulated by testosterone

Immunoreactive beta-endorphin (IR-BE) levels were determined in the anterior pituitary (AP), neurointermediate lobe of the pituitary (NIL) and the hypothalamus of castrated male rats and castrated male rats treated with testosterone proprionate (TP), subsequent to exposure to acute (once for 45 min) or chronic (45 min each day for 15 consecutive days) immobilization stress. Acute stress resulted in a reduction in the concentration of IR-BE in the AP of castrated male rats, which was potentiated by TP. The concentration of IR-BE in the NIL was elevated by acute stress in castrated male rats and was not affected by acute stress in castrated male rats administered TP. Exposure to chronic immobilization stress elevated the concentration of IR-BE in the AP of castrated animals and not animals treated with TP. The concentration of IR-BE in the NIL of castrated animals was not altered by chronic immobilization. Chronic stress did result in a significant rise in the level of IR-BE in the NIL of castrated male rats given TP. Hypothlamic IR-BE levels in castrated male rats were reduced by TP and were not influenced by acute or chronic stress. Chromatographic analysis indicated that acute and chronic stress promoted the accumulation of beta-lipotropin rather than beta-endorphin in the AP. This effect was attenuated by TP. Beta-endorphin was the only form of immunoreactivity detected in the NIL and hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotransmitters and estrogen interact to affect beta-endorphin levels in castrated female rats

The possibility of an interaction between neurotransmitter systems and estrogen in affecting levels of immunoreactive beta-endorphin (IR-BE) in the anterior pituitary (AP), the neurointermediate lobe of the pituitary (NIL) and the hypothalamus was investigated in ovariectomized (OVX) female rats. Chronic administration of the dopamine antagonist, haloperidol (HALO), had no effect on IR-BE levels in the AP. By contrast, the content of IR-BE in the NIL was increased and the content of IR-BE in the hypothalamus was decreased by HALO. Chronic treatment with estradiol benzoate (EB) produced a decrease in IR-BE in all three tissues. The effect of EB on IR-BE levels in the AP and NIL was reversed by administration of HALO, while EB and HALO appeared to act independently on the hypothalamus. Gel chromatography indicated that alterations in IR-BE in the AP corresponded to similar changes in beta-endorphin (BE) and beta-lipotropin (LPH) and that BE alone comprised the immunoreactivity detected in the NIL and hypothalamus regardless of treatment. Chronic treatment with the alpha-adrenergic agonist, clonidine (CLON), increased, whereas treatment with EB decreased, IR-BE levels in the AP, NIL and hypothalamus. EB attenuated the effect of CLON on IR-BE levels in the AP and hypothalamus. Chronic treatment with CLON appeared to promote the formation of BE in the AP, whereas the proportions of BE and LPH were similar in the AP of controls and animals treated with EB or EB and CLON. BE alone was detected in the NIL and hypothalamus of treated and control animals.(ABSTRACT TRUNCATED AT 250 WORDS)