Acute and chronic heroin dependence in mice: contribution of opioid and excitatory amino acid receptors

Abstract

Opioid and excitatory amino acid receptors contribute to morphine dependence, but there are no studies of their role in heroin dependence. Thus, mice injected with acute or chronic heroin doses in the present study were pretreated with one of the following selective antagonists: 7-benzylidenenaltrexone (BNTX), naltriben (NTB), nor-binaltorphimine (nor-BNI; delta1, delta2, and kappa opioid receptors, respectively), MK-801, or LY293558 (NMDA and AMPA excitatory amino acid receptors, respectively). Naloxone-precipitated withdrawal jumping frequency, shown here to be a reliable index of heroin dependence magnitude, was reduced by BNTX or NTB in mice injected with both acute and chronic heroin doses. In contrast, nor-BNI did not alter jumping frequencies in mice injected with an acute heroin dose but significantly increased them in mice receiving chronic heroin injections. Continuous MK-801 or LY293558 infusion, but not injection, reduced jumping frequencies during withdrawal from acute heroin treatment. Their delivery by injection was nonetheless effective against chronic heroin dependence, suggesting mechanisms not simply attributable to NMDA or AMPA blockade. These data indicate that whereas delta1, delta2, NMDA, and AMPA receptors enable acute and chronic heroin dependence, kappa receptor activity limits the dependence liability of chronic heroin. With the exception of delta1 receptors, the apparent role of these receptors to heroin dependence is consistent with their contribution to morphine dependence, indicating that there is substantial physiological commonality underlying dependence to both heroin and morphine. The ability of kappa receptor blockade to differentially alter acute and chronic dependence supports previous assertions from studies with other opioids that acute and chronic opioid dependence are, at least in part, mechanistically distinct. Elucidating the substrates contributing to heroin dependence, and identifying their similarities and differences with those of other opioids such as morphine, may yield effective treatment strategies to the problem of heroin dependency.

Figure 1

Time-response study of naloxone precipitated withdrawal from acute and chronic heroin treatment. ACUTE (top figure): mice were injected with a single heroin dose (50 mg/kg). CHRONIC (bottom figure): mice were injected t.i.d. for three days with escalating heroin doses (10, 20, and 40 mg/kg on treatment Days 1, 2, and 3, respectively) and a final 40 mg/kg heroin dose on Day 4. Withdrawal was precipitated by injecting naloxone (50 mg/kg) at various intervals after heroin treatment was completed. Control mice were subject to the identical acute or chronic heroin treatment protocols but received saline injections in place of either heroin or naloxone and tested at the heroin-naloxone interval yielding maximal frequencies. Significant differences from control values (* P <0.05; ** P <0.01) are indicated.

Figure 2

Dose-response relationship between acute and chronic heroin doses and jumping frequency. ACUTE (top figure): Mice received a single injection of various heroin doses followed 2 h later by naloxone. CHRONIC (bottom figure): Mice were injected t.i.d. for three days with escalating heroin doses (5, 10, and 20 or 10, 20, and 40 mg/kg on treatment Days 1, 2, and 3, respectively) and a final single heroin dose (40 mg/kg) on Day 4. Withdrawal was precipitated by injecting naloxone (50 mg/kg). Heroin control mice in both treatment paradigms were injected with saline instead of naloxone after injecting the heroin dose eliciting the greatest jumping frequency. Significant differences from control group (**P <0.01) and all other non-control groups (+) are indicated.

Figure 3

Dose-response relationship between naloxone doses after heroin treatment and jumping frequency. ACUTE (top figure): mice were injected with a single heroin dose (50 mg/kg). CHRONIC (bottom figure): mice were injected t.i.d. for three days with escalating heroin doses (5, 10, and 20 mg/kg on treatment Days 1, 2, and 3, respectively) and a final 40 mg/kg heroin dose on Day 4. Naloxone doses were injected 2 and 1 h after acute and chronic heroin treatment, respectively. Naloxone control mice in both treatment paradigms were injected with saline instead of heroin followed by an injection of the naloxone dose eliciting the greatest jumping frequency. Significant differences from control group (*P <0.05; ** P <0.01) and the lower preceding dose (+) are indicated.

Figure 4

Effect of opioid and excitatory amino acid receptor blockade on withdrawal jumping after acute and chronic heroin treatment. ACUTE (left figure): mice were injected with a single heroin dose (50 mg/kg). CHRONIC (right figure): mice were injected t.i.d. for three days with escalating heroin doses (10, 20, and 40 mg/kg on treatment Days 1, 2, and 3, respectively) and a final 40 mg/kg heroin dose on Day 4. All mice were also injected with one of the following antagonists: BNTX, NTB, nor-BNI (δ₁, δ₂, and κ opioid receptor antagonists, respectively), MK-801 and LY293558 (NMDA and AMPA receptor antagonists, respectively: see text for antagonist doses and injection schedule). MK-801 and LY293558 were also delivered by continuous infusion during acute heroin treatment. Withdrawal was precipitated by naloxone (50 mg/kg) injection 2 and 1 h after completing acute and chronic heroin treatment, respectively. Control mice in both treatment paradigms were injected with saline instead of antagonist. Significant differences from control group are indicated (*P <0.05).

Figure 5

Effect of δ₁ opioid receptor blockade on withdrawal jumping after acute and chronic morphine treatment. Mice subject to acute morphine treatment (left) were injected with a single morphine dose (50 mg/kg) whereas those subject to chronic morphine treatment (right) were injected t.i.d. for three days with escalating morphine doses (10, 20, and 40 mg/kg on treatment Days 1, 2, and 3, respectively) and a final 40 mg/kg morphine dose on Day 4. All mice were also injected with the δ₁ opioid receptor antagonist BNTX (0.5 mg/kg) 30 min prior to every morphine injection. Withdrawal was precipitated by naloxone (50 mg/kg) injection 3 h after completing acute and chronic morphine treatment. Antagonist control mice in both treatment paradigms were injected with saline instead of BNTX. There were no significant differences between saline and BNTX treated groups (P >0.05).