Issue with shooting projectiles in the direction of the arrow keys

I'm trying to make a small shooter "Binding of Isaac" kind of game and I'm attempting to use the arrow keys to shoot a projectile object. My issue is that I can shoot LEFT and RIGHT perfectly fine but no force is added for the Z axis when shooting UP and DOWN.

 if (Input.GetKey (KeyCode.RightArrow) && Time.time > nextFire) {
             //Instantiate (prefab, new Vector3 (playerBody.transform.position.x + 1f, 0.5f, playerBody.transform.position.z), playerBody.rotation);
             GameObject projectile = Instantiate (prefab, new Vector3 (playerBody.transform.position.x + 1f, 0.5f, playerBody.transform.position.z), playerBody.rotation);
             projectile.GetComponent<Rigidbody> ().AddForce (new Vector3(1000, 0));
             nextFire = Time.time + fireRate;
         }
 
         if (Input.GetKey (KeyCode.LeftArrow) && Time.time > nextFire) {
             GameObject projectile = Instantiate (prefab, new Vector3 (playerBody.transform.position.x - 1f, 0.5f, playerBody.transform.position.z), playerBody.rotation);
             projectile.GetComponent<Rigidbody> ().AddForce (new Vector3(-1000, 0));
             nextFire = Time.time + fireRate;
         }
 
         if (Input.GetKey (KeyCode.UpArrow) && Time.time > nextFire) {
             Instantiate (prefab, new Vector3 (playerBody.transform.position.x, 0.5f, playerBody.transform.position.z + 1f), playerBody.rotation);
             GameObject projectile = Instantiate (prefab, new Vector3 (playerBody.transform.position.x, 0.5f, playerBody.transform.position.z + 1f), playerBody.rotation);
             projectile.GetComponent<Rigidbody> ().AddForce (new Vector3(0, 0, 1000));
             nextFire = Time.time + fireRate;
         }
 
         if (Input.GetKey (KeyCode.DownArrow) && Time.time > nextFire) {
             GameObject projectile = Instantiate (prefab, new Vector3 (playerBody.transform.position.x, 0.5f, playerBody.transform.position.z - 1f), playerBody.rotation);
             projectile.GetComponent<Rigidbody> ().AddForce (new Vector3(0, 0, -1000));
             nextFire = Time.time + fireRate;
         }

I really don't see where the issue lies. Any ideas?

EDIT: I just realised that I froze the projectiles Z axis movement instead of Y which is what I had originally intended). The AddForce was working fine.